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Abstract: Functionalization of the indole benzene ring was achieved by using an organocatalytic enantioselective Friedel–Crafts alkylation/lactonization reaction of hydroxyindoles with a variety of substituted methyleneoxindoles. This reaction was applicable to indoles substituted with the hydroxy group at different positions of the benzene ring, and the corresponding pyrrolodihydrocoumarins were obtained in moderate to high yields (37–99%) with high stereoselectivities (up to 99% ee and >20:1 dr) in most cases. A scale‐up reaction and derivatization of the representative products were also carried out to investigate the usefulness of this protocol. [ABSTRACT FROM AUTHOR]

This work highlights the use of 3-vinyl-1,2,4-triazines as original thia-Michael acceptors and inverse electron demanding Diels-Alder platforms en route to new 7,8-dihydro-5 H-thiopyrano[4,3- b]pyridines. The required but rather unstable propargylthiol nucleophiles were successfully generated in-situ upon an innovative DBU-catalyzed methanolysis event of the corresponding propargyl thioacetate derivatives. [ABSTRACT FROM AUTHOR]

The first catalytic asymmetric [3+3] cycloaddition of azomethine ylides with C3-substituted 2-indolylmethanols has been established, leading to diastereo- and enantioselective construction of a tetrahydropyrimido[1,6-a]indole framework (up to 91% yield, >95:5 dr, 98:2 er). This reaction also represents a new type of catalytic enantioselective [3+3] cycloaddition using azomethine ylides. [ABSTRACT FROM AUTHOR]

Recently, organic catalysis has become a powerful alternative to the use of more traditional metal-based catalysts. In this study, 4-dimethylaminopyridine (DMAP), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were applied to mediate the ring-opening graft polymerization (ROGP) of p-dioxanone (PDO) with xylan-based hemicelluloses in ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). Excellent control of the molar ratio of the catalyst to anhydroxylose units (AXU) in xylan was found for a good tuning of the weight percent gain (WPG) of xylan-graft-poly(p-dioxanone) (xylan-g-PPDO) copolymers. As a result, the maximum WPG of xylan-g-PPDO copolymers was 431.07% (DMAP/AXU of 2/1), 316.72% (DBU/AXU of 0.2/1), and 323.15% (TBD/AXU of 0.2/1), respectively. The structure of xylan-g-PPDO copolymers was characterized with FT-IR and NMR. The thermal properties of copolymers were investigated using thermogravimetric analysis (TGA/DTG) and differential scanning calorimetry (DSC), and a significant difference was observed regarding the transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc). [ABSTRACT FROM AUTHOR]

Multi-step processes catalysed by several catalysts working concurrently have been developed in nature, thus improving reaction efficiency. The quest for novel and improved catalytic systems has led to the development of biocatalytic and later to organocatalytic procedures as very valuable tools in asymmetric synthesis while using mild reaction conditions in the absence of metal catalysts. As a timeless challenge, chemists are facing the need for process designs in which different sorts of catalysts can operate successfully in a one-pot concurrent fashion. Likewise, such designs bring about the best of each catalyst and, in certain cases, enable us to improve problematic issues, such as reactivity, selectivity, solubility, inhibition, etc. Specifically, to combine these two types of catalysts in one-pot, achieving high yields and selectivity, is a fascinating aspect of catalysis. This review covers representative advances in this field, in particular those in which biocatalysts and organocatalysts are employed either in sequential reactions or in simultaneous processes. [ABSTRACT FROM AUTHOR]

It is a challenging issue to achieve efficient aerobic oxidation desulfurization (AODS) under mild conditions. Inspired by respiratory chain system, a metal-free biomimetic system was developed in this paper with a functionalized ternary deep eutectic solvent (DES) containing N-hydroxyphthalimide (NHPI), p -toluene sulfonic acid (p -TsOH), and polyethylene glycol (PEG) for deep oxidative desulfurization. It was found that the NHPI/5PEG4000/ p -TsOH system exhibited an outstanding desulfurization activity, and the removal of dibenzothiophene (DBT) reached 100% within 5 h at 80 οC. Significantly, it is the first attempt to use a DES as an extraction agent, reaction medium, catalyst, and electron transfer mediator (ETM) simultaneously. Mechanistic studies revealed that NHPI demonstrated a dual function: namely, producing the PINO radical to initiate the reaction, and acting as an ETM in biomimetic systems to promote the activation of oxygen molecules, thereby finely improving the AODS performance of the acidic DESs. These findings regarding the aforementioned biomimetic oxygen activation mechanism of the NHPI-based ternary DES for AODS provide a novel insight into the construction of biomimetic system in the future. [Display omitted] • A metal-free biomimetic system was developed with a ternary DES for AODS. • The NHPI/5PEG4000/p-TsOH system exhibited an outstanding AODS activity. • The removal of DBT could reach 100% under quite mild conditions. • The DES was used as an extractant, reaction medium, catalyst, and ETM simultaneously. [ABSTRACT FROM AUTHOR]

The efficient sulfinate-catalyzed intermolecular addition reaction of α-substituted allenyl sulfones and allenoates with Michael acceptors is highlighted. The sequence proceeds under mild conditions to provide a scalable and efficient access to versatile functionalized alkynes, displaying a quaternary stereocentre at the propargylic position. This work enriches the diversity of Lewis base organocatalysts in the field of allene chemistry, in addition to the well-established phosphine and amine catalysts. [ABSTRACT FROM AUTHOR]

A rotor-stator homogenizer was found to be an effective mixing tool that accelerated solid-liquid phase-transfer reactions. In the asymmetric alkylation under phase-transfer conditions using the homogenizer, a considerably high turnover frequency was observed. [ABSTRACT FROM AUTHOR]

Catalyzed by a Cinchona-based thiourea, the [3+2] cycloadditions of barbiturate-based olefins with 3-isothiocyanatooxindoles proceeded readily, and furnished dispirobarbiturates in excellent chemical yields with excellent diastereo- and enantioselectivities. The absolute configuration of dispirobarbiturates was firmly confirmed by an X-ray single crystal structure analysis. A reaction mechanism was proposed to account for the enantioselective formation of dispirobarbiturates. [ABSTRACT FROM AUTHOR]

A highly enantioselective [3+2] cyclization of 3-vinylindoles with isatin-derived 3-indolylmethanols has been established in the presence of chiral phosphoric acid, which constructed the enantioenriched cyclopenta[ b]indole scaffold linking a 3-vinylindole moiety in generally good yields, considerable diastereoselectivities and high enantioselectivities (up to 93%, >95:5 dr, >99.5:0.5 er). More importantly, this reaction utilized N-protected 3-vinylindoles as competent reactants, which confronted the challenge in realizing a successful monoactivation mode of chiral phosphoric acid to vinyliminium in 3-indolylmethanol-involved enantioselective transformations. Besides, this protocol also settled the challenge in realizing a highly enantioselective [3+2] cyclization of 3-vinylindoles with 3-indolylmethanols, which would serve as a useful strategy for constructing an enantioenriched cyclopenta[ b]indole scaffold linking a 3-vinylindole moiety. [ABSTRACT FROM AUTHOR]

The first example of enantioselective nitronate protonation following Michael addition of a carbon nucleophile to an α,β,β-trisubstituted nitroalkene is reported. An N-sulfinylurea catalyst was employed to catalyze the addition of a variety of 3-substituted pyrazol-5-one nucleophiles to trisubstituted nitroalkenes incorporating an oxetane or azetidine ring at the β-position. The nitroalkane-pyrazolone adducts were obtained with good yield and enantioselectivity. Furthermore, the Michael addition products can be reduced to the corresponding enantioenriched amines with minimal loss of enantiomeric purity. [ABSTRACT FROM AUTHOR]

Monoacylation of long-chain linear diols often encounters difficulties associated with unavoidable overacylation affording the diacylate. However, several C1- and C2-symmetrical pyrrolidinopyridine (PPY) catalysts were found to effectively promote the chemoselective monoacylation of 1,5-pentanediol. The effects of catalyst structure on the performance for the monoacylation were investigated. The amide carbonyl group(s) in the pyrrolidine ring in both C1- and C2-symmetrical catalysts was(were) suggested to play the key role in selective monoacylation. On the other hand, the indolyl NH group in the amide side chain of the catalysts was found to be critically important for further increasing the chemoselectivity of monoacylation only when the catalyst has a C2-symmetrical structure. The effects of the catalyst structure on the chemoselective monoacylation were elucidated by DFT calculations, and the origin of the precise molecular recognition for 1,5-pentanediol by the catalysts and transition state (TS) stabilization effects by these functionalities were disclosed. [ABSTRACT FROM AUTHOR]

Organocatalyzed highly stereoselective 1,4-thia-Michael addition of mercaptans to linear 2,4-dienones and 2-en-4-ynones was developed using Cinchona alkaloid-based squaramides. Application of only 0.5-1 mol % loading afforded products in up to 98:2 e.r. and above 99:1 after a single recrystallization. The adducts of allyl mercaptan can be conveniently further transformed to new chiral 2-substituted 2,5-dihydrothiophenes by ring-closing metathesis. [ABSTRACT FROM AUTHOR]

An environmentally friendly oxidative cleavage of tetrahydrofuran-2-methanols to the corresponding γ-lactones using a catalytic amount of 2-iodo- N-isopropylbenzamide has been developed. The reaction of various tetrahydrofuran-2-methanols with the catalyst in the presence of Oxone® (2 KHSO5⋅KHSO4⋅K2SO4) as a co-oxidant in DMF at room temperature successfully affords the corresponding lactones in good to high yields, and recovery of the catalyst is readily accomplished using a reductive work-up. This method is notable because it enables the transformation of tetrahydrofuran-2-methanols to γ-lactones under mild conditions without the use of any toxic heavy metals. [ABSTRACT FROM AUTHOR]

An environmentally friendly oxidative cleavage of tetrahydrofuran-2-methanols to the corresponding γ-lactones using a catalytic amount of 2-iodo- N-isopropylbenzamide has been developed. The reaction of various tetrahydrofuran-2-methanols with the catalyst in the presence of Oxone® (2 KHSO5⋅KHSO4⋅K2SO4) as a co-oxidant in DMF at room temperature successfully affords the corresponding lactones in good to high yields, and recovery of the catalyst is readily accomplished using a reductive work-up. This method is notable because it enables the transformation of tetrahydrofuran-2-methanols to γ-lactones under mild conditions without the use of any toxic heavy metals. [ABSTRACT FROM AUTHOR]

A cost-effective, operationally simple and eco-compatible protocol for the one-pot synthesis of photochromic pyrans by the reaction of propargyl alcohols as well as propargyl ethers with differently substituted phenols under ambient atmosphere in aqueous medium has been developed using β-cyclodextrin hydrate as an efficient, recyclable and stable catalyst. This is the first report where β-cyclodextrin hydrate acted as a catalyst for an organic transformation but β-cyclodextrin alone failed. [ABSTRACT FROM AUTHOR]

We previously reported a bifunctional organic catalyst that promotes highly efficient enantioselective halolactonizations of a broad array of olefinic acids. As part of that work, we demonstrated the desymmetrization of a prochiral substrate through a catalytic enantioselective halolactonization, and we report herein the application of one such desymmetrization process to the syntheses of F-ring subunit synthons of (+)-kibdelone C. [ABSTRACT FROM AUTHOR]

Catalytic enantioselective oxaziridination is one of the challenging reactions in the oxidation of organic molecules. In this article, a series of novel chiral thiourea moleculars were synthesized from natural cinchona alkaloids and primary amines. By using these molecules as organocatalysts and m -chloroperoxybenzoicacid ( m -CPBA) as the oxidant, a methodology on highly enantioselective epoxidation of aldimines has been developed. Several optically active oxaziridines have been constructed in good yields (up to 95%) and moderate to excellent enantioselectivities (up to 99% ee). A plausible transition state was also proposed. [ABSTRACT FROM AUTHOR]

This mini-reviewis intended to serve as a concise introduction to polymerizations that are catalysed byN-heterocyclic carbenes. The content is structured according to accessiblemonomerfunctionalities and type ofpolymerization. Both major achievements as well as the latest developments in this rapidly evolving field are presented. A broad range of different types of monomers is covered in this way, including among others lactones, epoxides, anhydrides, acrylates, siloxanes and lactams. Special emphasis is put on mechanistic understanding and structure-activity relationships. [ABSTRACT FROM AUTHOR]

An efficient methodology for introducing a β-alkoxy acrylate unit onto the indolic C-2 position of 3-substituted indoles has been realized by oxidative radical alkylation of indoles with a xanthate bearing dialkyl acetal functionality and subsequent elimination of alcohol by treatment with 1,8-diazabicyclo[ 5.4.0]undec-7-ene (DBU). The indole-dienes thus prepared are quite stable and can be stored at room temperature for several months without obvious deterioration. Next, the indole-dienes were successfully applied in an asymmetric cascade reaction with propargyl aldehyde catalyzed by MacMillan's imidazolidinone and trichloroacetic acid (TCA), affording tetracyclic spiroindolines or tricyclic hydrocarbazoles in good to excellent yields with excellent ees. The practicality of this cascade was demonstrated by a gram scale preparation of a tetracyclic spiroindoline product with as low as 1 mol% catalyst loading and further elaboration of this spiroindoline compound into valuable intermediates for alkaloid synthesis. [ABSTRACT FROM AUTHOR]

The first catalytic asymmetric dearomatization of 3-methyl-2-vinylindoles has been established by using quinone monoimides as suitable electrophiles in the presence of chiral phosphoric acid, which afforded chiral indole derivatives bearing a quaternary stereogenic center in a chemospecific and highly enantioselective fashion (up to 81% yield, >99% ee). The success of this reaction was enabled by the reactivity switch of 3-methyl-2-vinylindoles, which has not been reported before. This reaction also represents the first catalytic asymmetric arylative dearomatization of vinylindoles, which will help confront the challenges in catalytic asymmetric arylative dearomatization and dearomatization of vinylindoles. [ABSTRACT FROM AUTHOR]

A series of new water-compatible “spiropyrrolidine triazole” catalysts was designed and synthesized. The asymmetric Michael addition of nitromethane and α,β-unsaturated aldehydes in an aqueous system was investigated to evaluate these new catalysts, and the resulting adducts were obtained with excellent enantioselectivity (up to 95.5% ee) and moderate to good yield (63–88%). [ABSTRACT FROM AUTHOR]

An amine-catalyzed, one-pot synthesis of thioesters directly from carboxylic acids, thioureas, and Michael acceptors is described. This process was further improved by use of 1-[2-(methylamino)ethyl]-3-phenylthiourea ( 4) as the catalyst. Aromatic and aliphatic carboxylic acids with functional groups are compatible with this process, and both α,β-unsaturated esters and ketones can be the Michael acceptors for this reaction. The progress of this reaction was monitored by 1H NMR, and a reaction mechanism is proposed. [ABSTRACT FROM AUTHOR]

An organocatalytic metal-free strategy has been established for the synthesis of pharmaceutically relevant meta-indolylanilines in generally excellent yields (up to 99 %). This strategy took advantage of the reaction of indoles and quinone imine ketals (QIKs) in the presence of racemic phosphoric acid, which proceeded via a 1,4-addition/alcohol elimination reaction sequence. The control experiment demonstrated that the dual hydrogen-bonding activation mode of the catalyst to the substrates played a crucial role in the reaction. This protocol provides a metal-free and step-economical approach to meta-anilines bearing either 3-indolyl or 2-indolyl moiety, which is of high value for the synthesis of compounds with potential bioactivities. [ABSTRACT FROM AUTHOR]

The N-heterocyclic carbene (NHC)-catalyzed oxidative amidation of aromatic aldehydes with amines in the presence of N-bromosuccinimide (NBS) as an oxidant has been developed for the synthesis of amides. This amidation strategy is tolerant to both the electronic and the steric nature of the aryl aldehydes employed. The present methodology was extended to chiral amino acid derivatives to generate the corresponding amides in good yields and excellent ee values (>98%). [ABSTRACT FROM AUTHOR]

Previous studies of the C(3)-hydrogen/deuterium of the triazolium ion conjugate acids of triazolyl N-heterocyclic carbenes revealed a change of mechanism under acidic conditions with N1-protonation to a dicationic salt. Interestingly, the data suggested an increase in p KaN1 in the presence of a N-pentafluorophenyl substituent relative to other N-aryl substituents with hydrogens or methyl substituents rather than fluorines at the ortho-positions. To probe the presence of an apparent donor effect of a N-pentafluorophenyl substituent, which differs from the more common electron withdrawing effect of this group, we have studied the analogous deuterium of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N-aryl ring. These include triazolium salts with N-2,4,6-tribromophenyl 11, N-2,6-dichlorophenyl 12, N-2-pyridyl 13 and N-2-pyrimidinyl 14 substituents. The log kex - p D profiles for 11, 12 and 14 were found to show similar trends at lower p Ds as for the previously studied N-pentafluorophenyl triazolium salt, hence supporting the presence an apparent donor effect on p KaN1. Surprisingly, the log kex - p D profile for N-pyridyl salt 13 uniquely showed at lower p Ds. We propose herein that this data is best explained by invoking an general base role for the N-(2-pyridyl) substituent in conjunction with N1-protonation on the triazolium ring. Finally, the second order rate constants for deuteroxide ion catalysed C(3)-H/D exchange ( kDO, M−1 s−1), which could be obtained from data at p Ds >1.5, were used to provide estimates of C(3)-carbon acid p KaC3 values for the four triazolium salts 11, 12, 13, 14. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recent progress in asymmetric organocatalysis has led to the development of several asymmetric transformations that employ various substrates. Among these, cyanoacetates have emerged as excellent nucleophiles in conjugate addition, alkylation, Mannich and α-heterofunctionalization reactions. In this review we discuss the enantioselective functionalization of 2-cyanoacetates through organocatalytic reactions. [ABSTRACT FROM AUTHOR]

Reactions among minerals and organic compounds in hydrothermal systems are critical components of the Earth's deep carbon cycle, provide energy for the deep biosphere, and may have implications for the origins of life. However, there is limited information as to how specific minerals influence the reactivity of organic compounds. Here we demonstrate mineral catalysis of the most fundamental component of an organic reaction: the breaking and making of a covalent bond. In the absence of mineral, hydrothermal reaction of cis- and trans-1,2-dimethylcyclohexane is extremely slow and generates many products. In the presence of sphalerite (ZnS), however, the reaction rate increases dramatically and one major product is formed: the corresponding stereoisomer. Isotope studies show that the sphalerite acts as a highly specific heterogeneous catalyst for activation of a single carbon-hydrogen bond in the dimethylcyclohexanes. [ABSTRACT FROM AUTHOR]

The N-heterocyclic carbene/Brønsted base cascade catalysis in the reaction of 3-(2-formylphenoxy)propenoates with N-Boc-arylimines has been studied. Both multifunctional benzofuran-3-ones and benzopyran-4-ones (flavone derivatives) were selectively synthesized in good yields simply by regulating the loading of the base catalyst. [ABSTRACT FROM AUTHOR]

The first catalytic asymmetric construction of the biologically important dibenzo[1,4]diazepine scaffold has been established via SPINOL-derived chiral phosphoric acid-catalyzed three-component reactions of aldehydes, 1,2-phenylenediamines and cyclohexane-1,3-diones, which afforded structurally complex and diverse dibenzo[1,4]diazepines in high yields and good enantioselectivities (up to 98% yield, 92:8 er). This transformation also represents the first catalytic asymmetric version of this three-component reaction and provides an easy access to structurally rigid seven-membered chiral heterocycles. [ABSTRACT FROM AUTHOR]

An asymmetric organocatalytic tandem reaction comprising cyclization/transfer hydrogenation has been established in a compatible and synergistic way, leading to the step-economical synthesis of enantioenriched tetrahydroquinoxalines and dihydroquinoxalinones from readily accessible materials in excellent enantioselectivity of up to >99% ee. This protocol of a one-operation tandem reaction combines the merits of both tandem reactions and asymmetric organocatalysis, providing an efficient strategy for concisely and enantioselectively synthesizing nitrogen heterocycles with biological relevance. [ABSTRACT FROM AUTHOR]

A series of substituted alloxazinium perchlorates has been prepared and tested as catalysts for the oxidation of sulfides to sulfoxides with hydrogen peroxide. The logarithms of the observed rate constants of thioanisole oxidation correlate with the Hammett σ constants of the substituents on the alloxazinium catalysts, as well as with their reduction potentials E0′ and their p KR+ values, representing the alloxazinium salt/pseudobase equilibrium. The stronger the electron-withdrawing substituent, the more efficient is the alloxazinium catalyst. The alloxazinium salts with a cyano or trifluoromethyl group in position 8 proved to be the most efficient, operating at room temperature at small loadings, down to 0.1 mol%, achieving turnover number values of up to 640 and acceleration by a factor of 350 relative to the non-catalyzed oxidation. The 8-cyanoalloxazinium perchlorate was evaluated as the best catalyst; however, due to its relatively good accessibility, the 8-(trifluoromethyl)alloxazinium perchlorate seems to be the catalyst of choice for sulfoxidations with hydrogen peroxide. It was successfully tested for the sulfoxidation of a series of aliphatic and aromatic sulfides on a preparative scale. It produced the corresponding sulfoxides in quantitative conversions and with high isolated yields (87-98%). No over-oxidation to sulfone was ever observed. [ABSTRACT FROM AUTHOR]

Meldrum's acid has turned out to be a useful ketene equivalent when faced to nitrone dipoles to form various isoxazolidin-5-one derivatives under very mild Brønsted base organocatalytic conditions. The first asymmetric version of this original domino anionic formal [3+2] cycloaddition-decarboxylation reaction was demonstrated by means of quinine-based organocatalysts. [ABSTRACT FROM AUTHOR]

Homogeneous catalysis employing carbon dioxide (CO2) as a carbon-based renewable feedstock has been and continues to be a flourishing area of research, providing new and improved synthetic methodologies towards a range of organic products. Since CO2 is inexpensive, non-toxic and available in virtually unlimited amounts, the progress in CO2 catalysis is of widespread academic, industrial and societal interest. This interest is sparked by the demanding necessity to provide viable alternatives for fossil fuel-derived organic precursors and their post-modification. Whereas most of the advances have been made in the area of CO2 conversion focusing on simple organic structures, the more challenging and gratifying stereoselective syntheses have only recently become a subject of increasing attention. This review therefore aims at presenting a concise overview of the most recent achievements in the field of stereoselective transformations where CO2 is used as a key reagent. As such, it should empower the synthetic community with a starting point for expansion of the toolbox leading to a greater variety of value-added organic matter based on CO2. [ABSTRACT FROM AUTHOR]

The first catalytic asymmetric 1,3-dipolar cycloadditions of alkynes with isatin-derived azomethine ylides have been established in the presence of chiral phosphoric acid, affording synthetically and pharmaceutically important spiro[indoline-3,2′-pyrroles] with quaternary stereogenic centers in high yields and excellent enantioselectivities (up to 99% yield, >99% ee). This protocol not only represents the first enantioselective 1,3-dipolar cycloadditions of alkynes with ketone-derived azomethine ylides, but also provides the first example of an enantioselective construction of spiro-oxindole-based 2,5-dihydropyrrole scaffold. [ABSTRACT FROM AUTHOR]

Abstract: Aliphatic polyesters from three macrolactones (pentadecalactone, globalide and ambrettolide) were synthesized by organic acid catalyzed polymerization in bulk and in an aqueous miniemulsion. Two different mechanism of polymerization take place depending on the polymerization media. Relatively high molecular weight polyesters (Mn aprox. 10,000g/mol) were obtained in bulk following a ring opening polymerization mechanism. Interestingly, relatively fast polymerizations were observed which depended in the acid pK a (triflic acid>benzene sulphonic acids>diphenyl phosphate). On the other hand, a condensation mechanism is observed in water miniemulsion leading to oligoesters of aprox. 2000g/mol. This molecular weight limitation prevented these latexes to be suitable for most applications. Interestingly, it is demonstrated that the introduction of unsaturated macrolactones in these aqueous latexes allows subsequent cross-linking leading to cured polyester films. [Copyright &y& Elsevier]

The first catalytic asymmetric five-component tandem reactions of β-keto esters, aromatic aldehydes and anilines have been established in the presence of a chiral phosphoric acid, affording densely functionalized tetrahydropyridines with concomitant generation of five σ bonds and two stereogenic centers in high diastereo- and enantioselectivities (up to >99:1 dr, 95:5 er). In addition, the first isolation and preparation of a diene species as the key intermediate of the reaction has been successfully realized, leading to the formation of the desired tetrahydropyridine via further condensation with in situ generated imine, which supported the proposed tandem [4+2] reaction pathway to some extent. This protocol not only represents the first enantioselective example of this five-component tandem reaction, but also provides an unprecedented access to enantioenriched tetrahydropyridines with structural diversity, which holds great potential in medicinal chemistry. [ABSTRACT FROM AUTHOR]

The spirocyclic pyrazolones are an important class of molecular structures with significant biological and pharmaceutical activities. Herein, we demonstrate that the combination of a Cinchona-based chiral primary amine and an ortho-fluorobenzoic acid is an efficient catalyst system for the double Michael addition of arylidenepyrazolones with α,β-unsaturated ketones, providing chiral unsymmetrical 6,10-diaryl-substituted spiro[cyclohexanone-pyrazolone] derivatives in high yields (up to 98%) with good diastereoselectivities and excellent enantioselectivities (up to 88:12 dr, 99% ee). [ABSTRACT FROM AUTHOR]

Synthetic applications of cyclobutanones other than ring expansion and fragmentation reactions are rare. Herein, highly efficient diastereo- and enantioselective organocatalytic Michael additions of 2-substituted cyclobutanone derivatives to nitroalkenes are reported allowing the stereocontrolled creation of 'all-carbon' quaternary centers. The approach relies on both the use of Brønsted base/hydrogen-bond donor bifunctional organocatalysts, and importantly, the specific stabilization and activation of cyclobutanone with a secondary amide moiety. The reaction was found to nicely accommodate a broad scope of substrates, allowing the control of up to three contiguous stereogenic centers. This work has opened new synthetic opportunities. [ABSTRACT FROM AUTHOR]

The production of chemical building blocks and polymer precursors from biorenewable and sustainable resources is an attractive method to bypass traditional fossil fuel derived materials. Accordingly, we report the organocatalytic recycling of postconsumer polylactide (PLA) into value-added small molecules. This strategy, using the highly active transesterification catalyst triazabicyclodecene, is shown to completely depolymerize PLA in the presence of various alcohols into valuable lactate esters. Using previously used PLA packaging material, the depolymerization is complete in minutes at room temperature and fully retains the stereochemistry of the lactate species. Further, the modularity and utility of this methodology with respect to polyester substrate is detailed by using a variety of functional alcohols to depolymerize both PLA and polyglycolide, with the corresponding ester small-molecules being used to make new polymeric materials. The opportunities to transform waste streams into value-added chemicals and new materials through simple and versatile chemistry hold significant potential to extend the lifecycle of renewable chemical feedstocks. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 [ABSTRACT FROM AUTHOR]

An organocatalytic asymmetric vinylogous Michael addition of dicyanoolefins to vinylogous imine intermediates generated in situ from arenesulfonylalkylindoles has been developed. This protocol provides an easy and convenient approach to C-3 alkyl-substituted indole derivatives with high yields (up to 93%), diastereomeric ratios (up to 99:1 dr) and enantioselectivities (up to 99% ee). The resulting adducts can be also readily converted to pyrazolo derivatives or α-alkylation products of ketones without any decrease of the diastereoselectivities and enantioselectivities. [ABSTRACT FROM AUTHOR]

The asymmetric addition of malonates to in situ generated N-formylimines of aromatic aldehydes was achieved under phase-transfer catalysis using Cinchona alkaloids-derived quaternary ammonium salts. The resulting β-formamidomalonates have been efficiently converted into β-aryl-β-isocyano esters. Their utility in the multicomponent Ugi reaction with chiral cyclic imines has been demonstrated. [ABSTRACT FROM AUTHOR]

A series of new modular bifunctional chiral thiourea organocatalysts were synthesized from natural Cinchona alkaloids and amino acids, and their performance in the aza-Henry reaction of nitroalkanes to imines, the Michael addition of acetylacetone to nitroolefins and the Michael addition of acetone to nitroolefins was investigated. Under the mild conditions, the important building blocks β-nitro amines and γ-nitro carbonyl compounds could be obtained in good yields (up to 95%) with excellent enantioselectivities (up to 99% ee) and diastereoselectivity (up to 17:1). [ABSTRACT FROM AUTHOR]