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The present paper employs supported ruthenium nanoparticles alongside catalytic quantities of the radical initiator, which are proven to be capable of cyclooctene oxidation with green conditions, in the absence of solvent, with air as the main oxidant and without sacrificial reductant. The paper examines the effects of a range of radical initiators and how the products are distributed over time. Furthermore, the paper addresses the reaction pathways to the epoxides and allylic alcohol, the latter being the primary by-product, whilst also analysing the impact of the technique of synthesis, reaction time, and various supports. Catalyst activity can be markedly improved by adopting a sol-immobilization technique to synthesise the catalysts, with retention of selectivity to the epoxide.

Titanosilicates with extra-large pores or cages are expected to effectively release the diffusion constraints suffered by the bulky substrates in the hydrogen peroxide-involved liquid-phase selecti...

The recently synthesized 9-borataphenanthrene anion (1) shows a reactivity in its central ring that resembles both a cycloalkene and an aromatic ring. Computational studies using the magnetic approach support these results. However, due to the limitations that the use of a single criterion can offer, a complete analysis was performed using multiple aromaticity criteria including magnetic, geometric, electron delocalization, reactivity and orbital localization in order to elucidate the nature of the six-membered rings in 1. Our results show that the outer rings in 1 exhibit an aromatic character similar to benzene, while the central ring is better described as an (cyclo)alkene. Additionally, it is shown that assessments using various criteria allow a complete understanding of aromaticity in polycyclic systems.

The intermolecular interactions in cycloalkene-water adducts were computationally characterized, thus demonstrating that the primary O-H...pi(C=C) hydrogen bond is dominated by the electrostatic interaction. A deeper investigation by means of a joint rotational spectroscopy/state-of-the-art quantum chemistry approach also led to the determination of an accurate semi-experimental equilibrium structure for the cyclopentene adduct.

An efficient synthetic method of seven- and six-membered cycloalkenes through the generation of strained cycloalkynes and following carbomagnesiation is described. Further bond formations of the resulting cycloalkenylmagnesium intermediates with a wide variety of electrophiles enabled us to prepare diverse cycloalkene derivatives including benzoxepine analogs having a fully substituted alkene structure.

The reaction mechanism of the hydroxycarbonylation of cyclohexene with formic acid to form cyclohexanecarboxylic acid using organorhodium complexes was investigated both experimentally and computationally. It was found that excess CH3I and PPh3 promote this reaction. The active catalyst species was determined to be a five-coordinated rhodium hydride 16-electron complex derived from a mononuclear rhodium 16-electron complex (Vaska-type complex). PPh3 and CH3I played the following roles: i) to promote the formation of the Vaska-type Rh complex from Rh2Cl2(CO)4 (1), ii) to aid the elimination of the PPh3 ligand from the Vaska-type complex by stabilizing the free energy of formation of a mononuclear three-coordinated rhodium 14-electron complex through the formation of phosphonium iodide ([Ph3P(CH3)]I), and iii) to generate the active rhodium hydride species.

A bromo-capped metal-metal bonded diruthenium(i,i) complex Ru2(CO)4(PIN)2Br2 (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene) generates bromine with N-bromosuccinimide (NBS) at room temperature. Cycloalkene and stilbene are readily brominated by stoichiometric reactions with 1 and NBS. An analysis of the dibrominated products suggests the formation of cyclic bromonium intermediates indicating in situ Br2 generation. Complex 2, an iodide analogue of 1, is also synthesized. The reaction of 2 with N-iodosuccinimide releases I2, which is confirmed by the starch-iodine test. The catalytic utility of 1 is examined for the bromination of phenol. Catalyst 1, in combination with NBS and base, exhibits regioselectivity towards monobrominated products. Furthermore, efficient olefin aziridination is demonstrated utilizing catalyst 1 in the presence of NBS, K2CO3 and TsNH2.

Titanium-containing zeolitic catalysts show high activity and selectivity in numerous environmentally-friendly oxidation reactions. However, the small micropores show severe restrictions for the oxidation of large organic reactants. Here, Ti-SFN zeolite with 14-ring extra-large-pores (6.2 × 8.5 A) was firstly synthesized by a chemical vapor deposition method and proved to have superior catalytic performance for bulker molecular oxidation using hydrogen peroxide as an oxidant compared to 10-ring TS-1 and 14-ring Ti-CIT-5 zeolites.

International audience; Dicarboxylic acids constitute one of the most important oxygenated intermediates in the chemical industry providing a wide range of daily products: fibers, pharmaceuticals, cosmetics, lubricants, pesticides and plasticizers. A major part of their large-scale production relies on the oxidative cleavage processes of unsaturated acids and cyclic olefins but suffers from severe drawbacks such as the use of harmful compounds, the need of specific set-ups to produce oxidants, expensive catalysts and energy-consuming conditions. In the context of the development of sustainable oxidation reactions, hydrogen peroxide has attracted growing interest thanks to its multiple benefits to replace conventional oxidants: low toxicity, no need of energetic conditions to perform catalytic oxidation and generation of benign H2O as a by-product. The present review aims at bringing a critical view on the development of catalytic systems for the H2O2-mediated oxidative cleavage of cycloalkenes toward green chemistry criteria. Different transition metal-based catalysts investigated for the reaction will be discussed with a special emphasis on tungsten. Next, the performance of different heterogeneous and homogeneous W-based systems on the oxidative cleavage of various cycloolefins will be presented. More specifically, their relevance towards sustainable oxidation will be assessed by studying key reaction features: solvent, H2O2 amount, reaction time and catalyst synthesis, recoverability and activity. The main challenges regarding the oxidative cleavage of medium-sized cycloalkenes with W–H2O2 systems will also be exposed. Finally, the potential of ultrasound as an unconventional activation method will be pointed out to overcome the limits encountered with the conventional thermal heating leading to even more environmentally-friendly cycloalkene oxidative cleavage.

Iron(III)-catalyzed carbonyl-olefin ring-closing metathesis employs reactivity not typically observed in Lewis acid-catalyzed reactions. In converting a ketone with a pendant olefin into a cycloalkene and a simple carbonyl byproduct, the reaction requires the Lewis acid catalyst to differentiate between the carbonyl of the substrate and that of the byproduct. It is necessary to determine how this solution interaction imparts the desired reactivity to best employ this method. Herein, we report detailed kinetic, spectroscopic, and colligative measurements applied toward the identification of the solution structures of the active Fe(III) and Ga(III) carbonyl-olefin metathesis catalysts. These data are consistent with formation of Lewis acid-carbonyl pairs for both metal systems under stoichiometric conditions. However, they diverge in the presence of higher equivalents of carbonyl, with Fe(III) forming highly ligated complexes, and no observed change for Ga(III). These findings are consistent with the resting state identity of the Fe(III) metathesis catalyst changing over the course of the reaction.

Development of a novel synthetic method for medium-sized trans-cycloalkenes (TCAs) is described. Functionalized TCAs are readily prepared from simple cycloalkanones in a few steps, namely, enol silyl ether formation, [2+2] cycloaddition, and domino 4π electrocyclic ring opening/alkylation (conjugate addition). The first example of central-to-planar chirality transfer from enantiomerically enriched cyclobutenes to TCAs is also described.

Bi-functional zeolite catalyst, incorporated with both organic groups and transition metal ions, has been firstly one-step synthesized by dry gel conversion method, which is characterized by powder XRD, solid-state 27Al, 29Si, 13C MAS NMR, FT-IR, Raman, UV–vis, X-ray photoelectron spectroscopy, and so on. Notably, the SiO/SiI ratio in the synthesis gel has important influence on the coordination state and distribution of cobalt species in the hybrid zeolite. Low SiO/SiI ratio has accelerated the formation of hybrid zeolite with tetrahedral framework cobalt while high SiO/SiI ratio has accelerated the additional assembly of hybrid zeolite with octahedral extra-framework cobalt. In the catalytic epoxidation of bulky cycloalkenes with air, hybrid zeolite with both tetrahedral framework cobalt and octahedral extra-framework cobalt shows the most excellent catalytic performance and TON value, compared with pure inorganic zeolite, hybrid zeolites with only tetrahedral framework cobalt species, and hybrid zeolites with Co species introduced by ion-exchange or wet impregnation methods, which is ascribed to the synergistic roles of organic groups and cobalt species. On one hand, the highly exposed octahedral extra-framework cobalt species act as an efficient supplement of tetrahedral framework cobalt, and the interactions of accessible catalytic active sites with bulky cycloalkene molecules have been strengthened greatly. On the other hand, mercaptopropyl groups are beneficial for the formation of stable heterogeneous catalyst with lipophilic surface through anchoring the extra-framework cobalt species and modifying the surface of the zeolite, which accelerate the epoxidation reaction efficiently.

Nazarov cyclization is an important and versatile method for the synthesis of five-membered carbocycles, and extensive studies have been conducted to optimize the reaction. Among recent studies, several trends are recognized. One is the combination of different reactions with Nazarov cyclization in a one-pot reaction system which enables the preparation of unique cyclization products. The second is the use of a transition-metal catalyst, though Lewis or Brønsted acids have generally been used for the reaction. The third is the realization of the asymmetric Nazarov cyclization. The fourth is the base-catalyzed Nazarov cyclization. Furthermore, several useful protocols for realizing Nazarov cyclization have also been developed. The recent progress on Nazarov cyclizations is summarized in Section 2. Section 3 is our chronicle in this field. We focused on the use of iron as the catalyst in Nazarov cyclizations and ionic liquids as solvents: Nazarov cyclization of thiophene derivatives using FeCl3 as the catalyst was accomplished and we succeeded in demonstrating the first example of an iron-catalyzed asymmetric Nazarov reaction. We next established Nazarov cyclization of pyrrole or indole derivatives using Fe(ClO4 )3 ·Al2 O3 as the catalyst with high trans selectivities in excellent yields. Since the cyclized product was reacted with a vinyl ketone in the presence of the same iron salt, the system allowed realization of the sequential type of Nazarov/Michael reaction of pyrrole derivatives. Furthermore, we demonstrated the recyclable use of the iron catalyst and obtained the desired Nazarov/Michael reaction products in good yields for five repetitions of the reactions without any addition of the catalyst using an ionic liquid, [bmim][NTf2 ], as the solvent. We expect that the iron-catalyzed Nazarov cyclization, in particular, in an ionic liquid solvent might become a useful method to synthesize functional molecules that include cycloalkene moieties.

Gold-catalyzed imination/Mannich reaction cascades on readily available 3-en-1-ynamides enable the diastereoselective synthesis of 1,5-iminoamino compounds in a one-pot operation. The reactions work well with diversified 3-en-1-ynamides, aldehydes and anilines with good to excellent diastereoselectivities. Our control experiments indicate gold-catalyzed aminations of 3-en-1-ynamides to yield α-imino allylgold intermediates that react subsequently with iminiums to implement the Mannich reactions stereoselectively. The reactions proceed with anti-selectivity for those 3-en-1-ynamides bearing acyclic alkenes whereas syn-selectivity is seen for their cycloalkene-based analogues. An open-transition state can satisfactorily rationalize these observed stereoselectivities based on an antiperiplanar conformation.

Sugar enol ethers undergo efficient coupling at C-2 with unactivated cycloalkenes under a low Pd loading affording allylic substitution products. High diastereoselectivity was observed at the allylic centre with sterically hindered substrates. Generation of a π-allyl complex by the Pd(II) catalyst via cleavage of the allylic C–H bond of the cycloalkene may be responsible for the formation of sp2–sp3 coupling products.

Renewable terpene biomass has attracting interest for producing high energy density fuel, particularly cycloalkane in the range of jet fuels. In this contribution, catalytic conversion of menthol to p-menthane was systematically investigated. Noble metals (Pt, Pd and Ru) supported on a Lewis-Bronsted acidic oxide (Nb2O5) were explored, considering the effects of reaction temperature and the balance between acid and metal sites. Catalysts kinetics were quite distinct, and Pd-based catalyst rendered the most active one. Yields of p-menthane of around 90% were determined over Pt and Pd catalysts, while it was only ~70% on Ru/Nb2O5, on which the formation of p-menthene was also observed. These results evidenced that the reaction proceeds as a cascade reaction at which acid-catalyzed menthol dehydration and metal-catalyzed cycloalkene hydrogenation lead to the aimed cycloalkane. Reaction temperature and the balance between acid and metal sites were shown to be the key aspects affecting catalyst performance.

Transition metal-mediated catalysis routinely enables substrates of multiple π-systems to be efficiently coupled with various carbon nucleophiles along with simultaneous ring formation. This transformation, however, remains unexplored in connection with pericyclic processes. Reported here is a protocol for cycloalkene synthesis based on the merger of rhodium catalysis and a retro-ene reaction. The approach allows alkyne-tethered hydrazones and organoboronic acids to undergo a cascade of addition–cyclization–rearrangement reactions to provide cycloalkene products. The process is initiated by the rhodium-catalyzed addition–cyclization and completed with the allylic diazene rearrangement. The reaction can also be rendered asymmetric by using chiral diene ligands for the rhodium catalyst, whereby enantioselective addition to the C═N bond establishes the C—N stereocenter whose chirality is transferred to an allylic C—H center via suprafacial rearrangement.

Recently, our group successfully developed two new polymerization methodologies for monomers containing two cycloalkene moieties. These polymerization methods yielded well-defined polymers via a combination of ring-opening and ring-closing metathesis (cascade polymerization) or ring-opening, ring-closing, and cross-metathesis (multiple olefin metathesis polymerization (MOMP)) using a second monomer. However, cascade polymerization had some limitations such as low polymerization efficiency (maximum turnover number (TON) of 250) and narrow monomer scope. Furthermore, one-shot MOMP also showed a very narrow monomer scope because of certain undesired side reactions. To overcome these problems, we designed various new monomers containing cyclopentene and even more challenging ring-strain-free cyclohexene moieties, so that polymerization would produce a thermodynamically favored six-membered-ring backbone repeat unit. With this enhanced driving force for polymerization, these new monomers successfully underwent cascade polymerization with a high polymerization efficiency, leading to a maximum TON of 1940 and maximum number-average molecular weight ( M

This work first reports high-efficiency epoxidation of large cycloalkenes (carbon number ≥ 7) with tert-butyl hydroperoxide (TBHP) over single-/double-/multi-unit-cell nanosheet-constructed hierarchical zeolite, which is synthesized by one-step hydrothermal crystallization using piperidine as the structure-directing agent of the microporous structure. The excellent catalytic property of the material is ascribed to its unique structural characteristic. Plenty of surface titanols or silanols on the surface of MWW nanosheets are beneficial for the formation of transition-state intermediates; a large number of intercrystalline mesopores in the shell of the material not only facilitate the formation of the intermediate for TBHP but also have nearly no hindrance for the diffusion and mass transfer of bulky cycloalkene to the above intermediates; the 12-MR side cups penetrating into the crystals from the external surface are exposed as much as possible to the reaction system because of the single-/double-/multi-unit-cell MWW nanosheet, serving as the primary reaction space for the epoxidation of bulky cyclic alkene and oxidants and providing enough space for the transition state of Ti-OOtBu and bulky cycloalkane. Moreover, an efficient calcination-free catalytic reaction-regeneration method is developed to overcome the challenge for the recyclability of microporous Ti-zeolite in the catalytic epoxidation of bulky cycloalkenes.

Carbon nitride nanosheets decorated with WO 3 nanorods (WO 3 /g-C 3 N 4 ) were fabricated via ultrasonic-assisted dispersion and conventional incipient wetness impregnation method. It is found that ultrasonic promoted the formation of g-C 3 N 4 nanosheets efficiently. The promotion effect in the structural evolution and catalytic performance for the rod-like structure of WO 3 caused by g-C 3 N 4 nanosheets were well studied. For the first time, the novel WO 3 /g-C 3 N 4 nanocomposites were used as efficient catalysts in the green process of dialdehydes from the selective oxidation of cycloalkene oxides using H 2 O 2 as a clean oxidant, owing to the high dispersion of active sites and the strong interaction between cycloalkene oxides and the NH or NH 2 groups on the surface of g-C 3 N 4 sheets. Here, C 3 N 4 nanosheets are considered as the catalyst support and co-catalyst as well. The novel nanocomposites are very stable and can be reused for five times without obvious loss of catalytic activity.

Novel aryl-substituted alicyclic β-amino acid derivatives were synthesized through substrate-determined palladium-catalysed cross-coupling of aryl iodides with five- or six-membered cycloalkene β-amino esters. The arylations were investigated with different catalysts, solvents, bases and aryl halides, and with some cyclohexene 2-aminocarboxylate isomers. The stereochemistry and the position of the ring olefinic bond of the starting 2-aminocycloalkanecarboxylate influenced the coupling reaction, and predetermined the structure of the arylated product.

A direct Pd-catalyzed C=H functionalization of benzoquinone (BQ) can be controlled to give either mono- or disubstituted BQ, including the installation of two different groups in a one-pot procedure. BQ can now be directly functionalized with aryl, heteroaryl, cycloalkyl, and cycloalkene groups and, moreover, the reaction is conducted in environmentally benign water or acetone as solvents.

Catalytic oxidation of cyclohexene and its methyl and vinyl derivatives with air oxygen in the presence of Co- and Mo-Co-modified microstructured carbon materials has been studied. Regardless of structure of the parent cycloalkene, cobalt-containing samples at 40–50°C are highly selective towards formation of corresponding hydroperoxides, whereas molybdenum-cobalt containing samples are selective towards cycloalkenes epoxidation. The ratio of epoxide to unsaturated alcohol strongly depends on the structure of the starting substrate.

Enantioselective α-deprotonation–rearrangement of cis-cyclooctene oxide 1 using organolithiums in the presence of (–)-sparteine 4 or (–)-α-isosparteine 5 gives the (–)-alcohol 2 in good yields and ees. The use of C2-symmetric bisoxazolines (–)-6a–d as ligands allows access to the (+)-alcohol 2. (–)-α-Isosparteine 5 functions as an efficient asymmetric ligand catalyst in the rearrangement of 1. The α-deprotonation process can be extended to other cycloalkene-derived achiral epoxides 7, 9, 11, 15 and 19. Lithium amide-induced transformations of rigid bicycloalkene-derived epoxides (25, 34 and 42) are described, providing insight into the rearrangement mechanisms which operate following α-lithiation in such systems. The enantioselective α-deprotonation–rearrangement of bicycloalkene-derived epoxides (25, 29 and 42) to ketones (28, 33 and 44 respectively) is described.

Nazarov cyclization is an important and versatile method for the synthesis of five-membered carbocycles, and extensive studies have been conducted to optimize the reaction. Among recent studies, several trends are recognized. One is the combination of different reactions with Nazarov cyclization in a one-pot reaction system which enables the preparation of unique cyclization products. The second is the use of a transition-metal catalyst, though Lewis or Bronsted acids have generally been used for the reaction. The third is the realization of the asymmetric Nazarov cyclization. The fourth is the base-catalyzed Nazarov cyclization. Furthermore, several useful protocols for realizing Nazarov cyclization have also been developed. The recent progress on Nazarov cyclizations is summarized in Section 2. Section 3 is our chronicle in this field. We focused on the use of iron as the catalyst in Nazarov cyclizations and ionic liquids as solvents: Nazarov cyclization of thiophene derivatives using FeCl3 as the catalyst was accomplished and we succeeded in demonstrating the first example of an iron-catalyzed asymmetric Nazarov reaction. We next established Nazarov cyclization of pyrrole or indole derivatives using Fe(ClO4 )3 ·Al2 O3 as the catalyst with high trans selectivities in excellent yields. Since the cyclized product was reacted with a vinyl ketone in the presence of the same iron salt, the system allowed realization of the sequential type of Nazarov/Michael reaction of pyrrole derivatives. Furthermore, we demonstrated the recyclable use of the iron catalyst and obtained the desired Nazarov/Michael reaction products in good yields for five repetitions of the reactions without any addition of the catalyst using an ionic liquid, [bmim][NTf2 ], as the solvent. We expect that the iron-catalyzed Nazarov cyclization, in particular, in an ionic liquid solvent might become a useful method to synthesize functional molecules that include cycloalkene moieties.

Mechanistic details of the ring-opening metathesis polymerization of 3-substituted-Z-cyclooctenes (3RCOEs) catalyzed by the second-generation Grubbs’ catalyst were systematically studied at the M06-2X/SDD|6-311+G(2df,p)//M06-L/SDD|6-31G(d) level of theory to elucidate factors contributing to observed regioselectivities. All possible conformational isomers for Z-cyclooctene (4 total) and 3-methyl-Z-cyclooctene (16 total) were taken into account. The potential energy surfaces for both the initiation and the propagation steps were calculated including all stereochemically distinct approaches of the cycloalkene to the active catalyst. In contrast to the situation with smaller cycloalkenes, the rate-limiting step for the polymerization of Z-cyclooctenes was determined to be the breakdown of the metallacyclobutane intermediate. This change is attributed to increased repulsive interactions between the growing polymer chain and the mesityl groups of the N-heterocyclic carbene ligand when the effective cone angle ...

N-hydroxyphthalimide (NHPI) and copper chloride (CuCl2) were first utilized for aerobic oxidation of αisophorone (α-IP) to ketoisophorone (KIP) and the effects of co-catalysts, temperature, reaction time, solvent, amount of CuCl2 and pressure of oxygen were investigated extensively. NHPI/CuCl2 turned out to be highly efficient to this oxidation with up to 91.3% conversion and 81.0% selectivity under mild conditions. And various hydrocarbons including benzylic compounds, cycloalkene and its derivatives were also oxidized smoothly under optimized conditions. Moreover, the possible reaction mechanism was proposed and verified by FT-IR spectra.

The kinetics of the catalytic hydrodeoxygenation of phenol and substituted phenols has systematically been investigated on the dual-functional catalyst system Pd/C and H(3)PO(4) in order to better understand the elementary steps of the overall reaction. The reaction proceeds via stepwise hydrogenation of the aromatic ring, transformation of the cyclic enol to the corresponding ketone, hydrogenation of the cycloalkanone to the cycloalkanol and its subsequent dehydration as well as the hydrogenation of the formed cycloalkene. The presence of dual catalytic functions is indispensible for the overall hydrodeoxygenation. The dehydration reaction is significantly slower than the hydrogenation reaction and the keto/enol transformation, requiring a significantly larger concentration of Bronsted acid sites compared to the available metal sites for hydrogenation. (C) 2011 Published by Elsevier Inc.

Four bis(tetrahydroisoquinoline) N,N′-dioxides were used as catalysts for the epoxide ring opening with tetrachlorosilane under various conditions. A strong solvent effect on asymmetric induction was observed for each of the used catalysts. The highest achieved asymmetric induction for the opening of meso-stilbene oxide was 69% ee. Regarding the cycloalkene oxides, 56% ee was obtained in the reaction with cyclooctene oxide.

Rh(PPh 3 ) 3 Cl was immobilized on a (OEt) 3 Si(CH 2 ) 3 PPh 2 modified MCM-41 to form a stable hydrogenation catalyst. The morphology of the catalyst was characterized by X-ray absorption spectroscopy. The EXAFS results indicates that the immobilized Rh catalyst has an average Rh–O s (O s is a surface oxygen) and Rh–Si bond distances of 2.01 A and 3.15 A, respectively, suggesting that monomeric Rh complex bonds to the MCM-41 surface. However, the structure of the immobilized Rh complex is not retained after hydrogenation of cyclohexene at 75 °C under 150 psi of H 2 . After the reaction, the presence of Rh–Rh contribution with average bond distance of 2.68 A and coordination number of 1.3 and the missing contribution with bond distance of 3.85 A suggest that the reaction induces the coalescence of Rh complex to form dimeric Rh species. However, formation of trace amount of Rh metal clusters cannot be ruled out because rather small characteristic peak for the missing Rh–Rh shell may be covered by noise.

Pt-Ni bimetallic catalysts and their corresponding monometallic catalysts supported on γ-Al2O3 were prepared by incipient wetness impregnation and characterized by CO chemisorption. Their low-temperature activity for the hydrogenation and dehydrogenation of 1,3-cyclohexadiene (1,3-CHD) was tested at 308 K in a batch reactor using Fourier transform infrared spectroscopy. The Pt-Ni/γ-Al2O3 bimetallic catalyst showed higher activity than either Pt/γ-Al2O3 or Ni/γ-Al2O3. We correlated the experimental results with density functional theory calculations of the binding energy for 1,3-CHD on the corresponding model surfaces. The correlation confirmed that bimetallic surfaces with weaker cycloalkene binding energies generally showed higher hydrogenation activity.

The Pd(0) complex 1 that bears the Trost ligand 2 undergoes a facile redox reaction with 1,4-biscarbonates 5b-d and rac-22 under formation of the diamidato-Pd(II) complex 7 and the corresponding 1,3-cycloalkadienes 8b-d. The redox deactivation of complex 1 was the dominating pathway in the reaction of 5b-d with HCO(3)(-) at room temperature. However, at 0 degrees C the six-membered biscarbonate 5b, catalytic amounts of complex 1, and HCO(3)(-) mainly reacted in an allylic alkylation, which led to a highly selective desymmetrization of the substrate and gave alcohol 6b with > or = 99% ee in 66% yield. An increase of the catalyst loading in the reaction of 5b with 1 and HCO(3)(-) afforded the bicyclic carbonate 12b (96% ee, 92%). Formation of carbonate 12b involves two consecutive inter- and intramolecular substitution reactions of the pi-allyl-Pd(II) complexes 16b and 18b, respectively, with O-nucleophiles and presumably proceeds through the hydrogen carbonate 17b as key intermediate. The intermediate formation of 17b is also indicated by the conversion of alcohol rac-6b to carbonate 12b upon treatment with HCO(3)(-) and 1. The Pd(0)-catalyzed desymmetrization of 5b with formation of 12b and its hydrolysis allow an efficient enantioselective synthesis of diol 13b. The reaction of the seven-membered biscarbonate 5c with ent-1 and HCO(3)(-) afforded carbonate ent-12c (99% ee, 39%). The Pd(0) complex 1 is stable in solution and suffers no intramolecular redox reaction with formation of complex 7 and dihydrogen as recently claimed for the similar Pd(0) complex 9. Instead, complex 1 is rapidly oxidized by dioxygen to give the stable Pd(II) complex 7. Thus, formation of the Pd(II) complex 10 from 9 was most likely due to an oxidation by dioxygen. Oxidative workup (air) of the reaction mixture stemming from the desymmetrization of 5c catalyzed by 1 gave the Pd(II) complex 7 in high yield besides carbonate 12c.

The immobilization of molybdenum (Mo) compounds on poly(4-vinylpyridine) (P4VP) microspheres for catalytic epoxidation was reported. P4VP-supported Mo compounds were highly efficient and selective for the epoxidation of cis-cyclooctene using hydrogen peroxide (H2O2) as oxygen source. When ethanol was used as solvents, outstanding catalytic activity and selectivity were observed for Mo-containing catalysts in the epoxidation of cis-cyclooctene. A completely green epoxidation system based on H2O2 and cleaner solvent has been achieved, and the heterogenized Mo catalyst can be recovered for five times without loss of its activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 558–562, 2010

Alkaline-earth chloride was used as an effective promoter for the aerobic oxidation of hydrocarbons catalyzed by N-hydroxyphthalimide (NHPI). Various hydrocarbons including benzylic compounds, cycloalkene, and cycloalkane can be easily oxygenated with molecular oxygen catalyzed by the alkaline-earth chloride/NHPI system. Ultraviolet-visible (UV-vis) spectroscopy and Fourier transform infrared (FT-IR) spectroscopy were employed to investigate the essential of the promotion effect of alkaline-earth chloride. The results revealed that alkaline-earth chloride facilitated the generation of the active species phthalimide-N-oxyl (PINO) radical which further catalyzed the oxidation of hydrocarbons. (C) 2009 Elsevier B.V. All rights reserved.

Unsubstituted and tertiary-butyl substituted salicylaldimine complexes of Cu(II) and Co(II) immobilized on silica supports (MCM-41, SBA-15 and Davisil 710) were tested as catalysts for cyclohexene oxidation using hydrogen peroxide as an oxidant under an oxygen atmosphere. The effect of the nature of the salicylaldimine ligand and the type of support were investigated. Allylic species were isolated as the major products with cyclohexene–epoxide produced as a by-product in only some instances. Product selectivity was found to be greatly influenced by the nature of the support material.

A multitasking C-silylation strategy using the readily available compound 26 as a surrogate for cinnamic acid represents the key design element of a total synthesis of all known members of the ipomoeassin family of resin glyosides. This protecting group maneuver allows the unsaturated acids decorating the glucose subunit of the targets to be attached at an early phase of the synthesis, prevents their participation in the ruthenium-catalyzed ring-closing metathesis (RCM) used to form the macrocyclic ring, and protects them against reduction during the hydrogenation of the resulting cycloalkene over Wilkinson's catalyst. As the C-silyl group can be concomitantly removed with the O-TBS substituent using tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) in acetonitrile, no separate protecting group manipulations were necessary in the final stages, thus contributing to a favorable overall "economy of steps". In addition to the naturally occurring ipomoeassins, a small set of synthetic analogues has also been prepared by "diverted total synthesis". The cytotoxicity of these compounds was assayed with two different cancer cell lines. The recorded data confirm previous findings that the acylation- and oxygenation pattern of these amphiphilic glycoconjugates is highly correlated with their biological activity profile. Ipomoeassin F turned out to be the most promising member of the series, showing IC(50) values in the low nanomolar range.

Tridentate Schiff base ligands derived from aromatic aldehydes and benzhydrazide, and their iron complexes [Fe(L1)(HL1)] 1, [Fe(HL1)Cl2(CH3OH)]·(CH3OH) 2 and [Fe(HL2)Cl2(H2O)] 3 have been prepared and characterized (H2L1 = (E)-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide, H2L2 = (E)-N′-(5-bromo-2-hydroxybenzylidene)benzohydrazide). The crystal structure of 2 has been determined. The electrochemical properties of these complexes have been investigated by cyclic voltammetric technique in acetonitrile solutions. Electrochemical studies have revealed quasi-reversibility for these compounds. The catalytic potential of these complexes has been tested for the oxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxidant. The effects of the molar ratio of oxidant to substrate, the temperature, the co-catalyst concentration and the solvent have been studied. Excellent selectivities have been obtained for the epoxidation of cyclohexene, cyclooctene, norbornene, cis- and trans-stilbene.

Selective cis -dihydroxylation of various olefins has been carried out using molybdenum acetylide complex CpMo(CO) 3 (C CPh) ( 1 ) as catalyst and hydrogen peroxide as an efficient and environmentally benign oxidant. In case of cyclohexene, very high conversion (95%) and selectivity (86%) for cis -dihydroxylated product has been achieved using H 2 O 2 as an oxidant and t -butanol as a solvent. cis -Dihydroxylation of other substrates like styrene, α-methyl styrene, limonene and cyclopentene has also been carried out with very high selectivity for diol. The catalyst and intermediate species have been characterized using FT-IR, UV–vis spectral analysis and XPS studies as well as cyclic voltametric studies. These studies suggest that molybdenum oxo–peroxo complex is the catalytically active species. The intermediate blue complex when characterized by ESI MS suggested the formation of dimeric molybdenum complex and XPS and cyclic voltametric studies confirm the presence of mixed valence Mo(V) and Mo(VI) in the reaction intermediate. Based on the characterization results possible mechanism for dihydroxylation is proposed. Interestingly, even though the catalyst is homogeneous; it could be recovered quantitatively by extraction in aqueous phase and recycled five times without any appreciable loss in cyclohexene conversion and selectivity for cis -1,2-cyclohexanediol.

In the presence of a catalytic amount of Bi(OTf)3·4H2O and under microwave irradiation, neat mixtures of epoxides and amines afforded smoothly the corresponding 2-amino alcohols. A wide variety of aliphatic amines were reacted with cycloalkene oxide, styrene oxide, and stilbene oxide. The reaction proceeded rapidly and afforded the 2-amino alcohols in high up to quantitative yields. All products could be obtained without aqueous work-up by simple filtration.

Metal complexes of poly(2-N,N-dimethylaminoethyl) methacrylate were prepared by complex-forming with aqueous solutions of salts of FeSO4.2H2O; CoCl2.6H2O; CuCl2.2H2O; VOSO4.5H2O; Na2MoO4.2H2O and Na2WO4.2H2O. The catalytic activity of the complexes was studied in the oxidation of cyclohexene as a model reaction. The activities of the complexes synthesized towards the reaction of cyclohexene epoxidation can be arranged by the following order: PDMAEM-MoO2 2+> PDMAEM-VO2+ > PDMAEM-WO2 2+> PDMAEM-Co2+ > PDMAEM-Fe3+> PDMAEM-Cu2+. The complexes catalyzing the homolytic decomposition of tert-butylhydroperoxide increased the maximum yield of 2-cyclohexene-1-ol and 2-cyclohexene-1-on. The yield of cyclohexene oxide and 2-cyclohexene-1-ol were 58% and 13%, respectively.

As a prelude to commissioning a reactive distillation column (RDC) for the continuous epoxidation of cyclohexene using t -butylhydroperoxide and a heterogeneous polymer-supported Mo(VI) catalyst, the long-term stability of three candidate polymer-supported Mo catalysts has been evaluated. The polymer catalysts are a polybenzimidazole-supported species, PBI.Mo , and two poly(styrene-divinylbenzene) resin-based species, Ps.AMP.Mo1 and 2 , prepared in-house by amination of vinyl benzyl chloride-containing resins using 2-aminomethyl pyridine, followed by loading with Mo. The stability of each polymer catalyst was assessed by recycling a sample 10 times in small batch reactions using conditions that will form the basis of the continuous process. At the same time the loss of Mo from each support has been investigated by isolating any residue from reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions. This is a powerful technique for identifying unambiguously loss of catalytically active Mo from the support and is not dependent on Mo analytical procedures. All three polymer catalysts are highly active and selective in 10 consecutive reactions but the supernatant solutions also contain catalytically active Mo residues. In the case of PBI.Mo and Ps.AMP.Mo2 the contribution to catalysis from homogeneous Mo species lost from the supports is all but eliminated after aging through 10 cycles, but in the case of Ps.AMP.Mo1 the contribution from leached Mo species remains significant even after similar aging. The major factor determining this differential behaviour seems to be the mole ratio of polymer-bound ligand to Mo which must be significantly above unity to provide long-term retention of Mo.

The synthesis and characterisation of three dimeric cis-dioxomolybdenum(VI) complexes involving Schiff-base ligands is described. Ligands were obtained by condensation of salicylaldehyde with aromatic nitrogen–nitrogen linkers (4,4′-diaminodiphenylmethane; 4,4′-diaminodiphenylether; 4,4′-diaminodiphenylsulfone). [MoO2(acac)2] reacted with the prepared ligands; bis[(N,O-salicylidene)-4,4′-diaminodiphenyl]methane, H2L1; bis[(N,O-salicylidene)-4,4-diaminodiphenyl]ether, H2L2; bis[(N,O-salicylidene)-4,4′-diaminodiphenyl]sulfone, H2L3; forming six-coordinated cis-dioxoMo(VI) complexes; [MoO2L1–3]2. The yellow colored, non-electrolytic and diamagnetic compounds were characterized by elemental analyses and spectroscopic techniques (IR, 1H NMR and UV–vis). These complexes show good catalytic activity and selectivity in the epoxidation of cyclohexene with t-butylhydroperoxide (TBHP), especially for complex [MoO2L3]2, which could give a nearly 88% of epoxidation conversion and 94% of selectivity. Introduction of the electron-withdrawing group to the aromatic nitrogen–nitrogen linkers of complex strongly increases the effectiveness of a catalyst. The addition of single-wall carbon nanotubes (SWNT) can enhance the activity of the Mo complexes and the selectivity toward epoxide. It is also better for the recycling of the Mo complex, the catalytic activity and the selectivity toward which still held at a high level after four times using.

The synthesis of copolymers functionalized with phosphonate groups, incorporation of them into ordered meso-macroporous silica, characterization and evaluation of the obtained materials as catalysts in oxidation of cyclohexene are presented. The catalysts obtained are very active and selective in epoxidation of cyclohexene using hydrogen peroxide as an environmentally friendly oxidant.

Catalytic epoxidation of cycloalkenes to corresponding epoxides using molecular oxygen was carried out in presence of cobalt(II) exchanged zeolite X based catalysts. Effect of temperature (353–418 K) and pressure (30–150 psi) was studied to obtain the optimum conditions for the reaction. The best results were obtained at 60 psi pressure and 373 K using NaCoX96 catalyst with cycloalkene conversion and epoxide selectivity for cyclohexene, cycloheptene and cis-cyclooctene were obtained in the range 26–47 and 48–100% respectively. Alkali and alkaline earth cationic promoters were introduced into the zeolite catalyst in order to study the effect of basicity of the catalyst on the cycloalkene conversion and epoxide selectivity. Cobalt(II) exchanged zeolites X, NaCoX96, seems to be efficient heterogeneous catalysts for the epoxidation reactions using molecular oxygen. The catalyst was observed to be recyclable as conversion and selectivity were retained even after four catalytic reaction cycles.

Mn(III) and Mo(IV)-Salen complexes homogeneous and immobilized on a silica surface have been tested in the catalytic epoxidation of cyclooctene and cyclohexene with tert-butylhydroperoxide (TBHP) and hydrogen peroxide (HP) as an oxidant. The effects of reaction conditions on the epoxide yield as well as the epoxidation rate with different catalysts have been established. The catalytic decomposition of TBHP by manganese and molybdenum-Salen complexes has been studied. The peptide immobilized Salen complexes were compared in catalytic activity with ester bound ones. The immobilized catalysts show stable catalytic activity in manifold reuses. The Mo-Salen complexes homogeneous as well as immobilized exhibited high catalytic activity for the epoxidation of cyclooctene, whereas Mn-Salen complex systems cause additionally non-productive decomposition of hydroperoxide.

Commercially available zinc perchlorate hexahydrate [Zn(ClO 4 ) 2 ·6H 2 O] was found to be highly effective catalyst for opening of epoxide ring by thiols under solvent-free condition at room temperature for efficient synthesis of 2-hydroxysulfides. The catalytic activity of various group I/II metal perchlorates followed the order Zn(ClO 4 ) 2 ·6H 2 O ≫ Mg(ClO 4 ) 2 ·6H 2 O > Ba(ClO 4 ) 2 ·6H 2 O ⋙ LiClO 4 . The Zn(ClO 4 ) 2 ·6H 2 O-catalysed reaction of epoxides derived from cyclic and acyclic olefines with thiols afforded β-hydroxysulfides in high yields. Reaction with cycloalkene oxides led to stereoselective formation of the trans -2-hydroxysulfides. Excellent regioselectivity was observed for unsymmetrical epoxides. In case of styrene oxide, the hydroxysulfide from nucleophilic attack at the benzylic carbon of the epoxide was the major product. Preferential nucleophilic attack by thiophenol took place at sterically less hindered position of the epoxide ring of unsymmetrical non-styrenoid alkene oxides. Epichlorohydrin exemplified a case of chemo- and regioselective reaction with no detectable (GC–MS) side product formation by direct displacement of the chlorine atom. The methodology was extended for an efficient synthesis of the key intermediate of diltiazem.

A novel Ti–O–Ti bonding complex constructed in the monomeric, mono-lacunary α-Keggin polyoxotungstate, [{Ti(OH2)(ox)}2(μ-O)(α-PW11O39)]5− (1) can act as a precatalyst for the epoxidation of cyclooctene, cyclohexene, and 1-octene with aqueous H2O2 at 25 °C in a homogeneous system. The catalytic activities of complex 1 were considerably higher than those of dimeric mono-, di-, and tri-titanium(IV)-substituted Keggin polyoxotungstates [(α-PTiW11O39)2O]8− (2), [(α-1,2-PW10Ti2O38)2O2]10− (3), and [(α-1,2,3-PTi3W9O37)2O3]12− (4).

Cyclohexene and tetralin can be oxidized to a slight extent by N 2 O in the presence of quaternary ammonium salt promoters under mild experimental conditions. In non-polar solutions, the higher yields of the oxidations of cyclohexene and tetralin are influenced by the donor–acceptor properties of the solvents. The changes in the IR spectrum of N 2 O lend further support to the assumption that ion-pair interactions between the solvated oxidant and the onium salts result in an enhanced rate of O-transfer from the oxidant. Onium-decavanadate ion-pair complexes are more effective promoters than simple onium salts.