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Dicyanoalkenes are versatile reagents in organic synthesis and they have been extensively used in a wide variety of organic transformations. However, their reactivity towards fluorinated imines remained almost unnoticed. The divergent reactivity of fluorinated conjugated sulfinyl imines with dicyanoalkenes is described herein. On the one hand, when tert‐butyl sulfinyl imines were employed, a cycloaromatization cascade process took place preferentially, rendering valuable trifluoromethyl arenes. On the other hand, the reaction with p‐tolyl sulfinyl imines mainly led to a complex tetracyclic skeleton, involving an azetidinimine rearrangement of a reaction intermediate. Finally, when 1‐indanone‐derived dicyanoalkenes were employed, the aromatization process was interrupted, rendering a new family of diene derivatives. Theoretical calculations were performed in order to shed light on the mechanistic outcome of this transformation. [ABSTRACT FROM AUTHOR]

The Cp*Co(III) C−H allylation of (hetero)arenes with allyl aryl ethers has been developed using an amide as directing group (24 examples). DFT calculations have shed light on the mechanistic course and reactivity pattern, showing that strong electron releasing groups favour the reaction by reducing the activation barrier of the rate‐determining C−H activation step. However, the steric strain can increase the energy of the migratory insertion step to the point of completely preventing the reaction, as in the case of the 3,5‐dimethylbenzamide. The obtained allylated compounds have been transformed into a variety of interesting heterocyclic and carbocyclic structures, such as isoquinolones and isochromanones. [ABSTRACT FROM AUTHOR]

From an (R)‐(+)‐pulegone‐derived building block that incorporates the stereo‐defined tertiary carbon bearing a methyl group, as found in the targeted sesquiterpenoid, a four‐step synthesis of (−)‐4‐epi‐presilphiperfolan‐8‐α‐ol was achieved. The key processes involved are a ring‐closing metathesis leading to a bridged alkene‐tethered ketone and its subsequent FeIII‐mediated metal‐hydride atom transfer (MHAT) transannular cyclization. This synthetic method, implying an irreversible addition of a carbon‐centered radical upon a ketone by means of a hydrogen atom transfer upon the alkoxy radical intermediate, was also applied in the synthesis of trans‐fused hydrindanols structurally related to botrydial compounds. [ABSTRACT FROM AUTHOR]

In this paper, we present an unprecedented and general umpolung protocol that allows the functionalization of silyl enol ethers and of 1,3‐dicarbonyl compounds with a large range of heteroatom nucleophiles, including carboxylic acids, alcohols, primary and secondary amines, azide, thiols, and also anionic carbamates derived from CO2. The scope of the reaction also extends to carbon‐based nucleophiles. The reaction relies on the use of 1‐bromo‐3,3‐dimethyl‐1,3‐dihydro‐1λ3[d][1,2]iodaoxole, which provides a key α‐brominated carbonyl intermediate. The reaction mechanism has been studied experimentally and by DFT, and we propose formation of an unusual enolonium intermediate with a halogen‐bonded bromide. [ABSTRACT FROM AUTHOR]

A catalytic method to synthesize a broad array of cyclometalated (C^N)gold(III) complexes is reported here. An unprecedented Rh‐to‐AuIII transmetalation allows the facile transfer of (C^N) ligands between these two metals in a redox‐neutral process. The reaction employs commercially available precursors and proceeds under mild and environmentally benign conditions. Both experimental and computational studies support a multistep transmetalation from rhodium to gold as the underlying mechanism for these transformations. This process involves first, a rate‐determining transfer of the C ligand followed by the subsequent incorporation of the N donor to form the monocyclometalated (C^N)gold(III) species. [ABSTRACT FROM AUTHOR]

Herein, we report a catalytic system based on the earth‐abundant manganese for the ketone, amine, alkyne (KA2) reaction. The efficiency of manganese manifests at relatively high temperatures, combined with sustainable reaction conditions, and provides a tool for accessing propargylamines from structurally diverse starting materials, including synthetically relevant and bioactive molecules. Our efforts were also aimed at shedding light on the catalytic mode of action of manganese in this transformation, in order to explain its temperature‐related behavior. The use of computational methods reveals mechanistic aspects of this reaction indicating important points regarding the reactivity of both manganese and ketones. [ABSTRACT FROM AUTHOR]

An efficient and straightforward organocatalytic method for the direct, multicomponent carboxylation of terminal alkynes with CO2 and organochlorides, towards propargylic esters, is reported for the first time. 1,3‐Di‐tert‐butyl‐1H‐imidazol‐3‐ium chloride, a simple, widely‐available, stable, and cost‐efficient N‐heterocyclic carbene (NHC) precursor salt was used as the (pre)catalyst. A wide range of phenylacetylenes, bearing electron‐withdrawing or electron‐donating substituents, react with allyl‐chlorides, benzyl chlorides, or 2‐chloroacetates, providing the corresponding propargylic esters in low to excellent yields. DFT calculations on the mechanism of this transformation indicate that the reaction is initiated with the formation of an NHC‐carboxylate, by addition of the carbene to a molecule of CO2. Then, the nucleophilic addition of this species to the corresponding chlorides has been computed to be the rate limiting step of the process. [ABSTRACT FROM AUTHOR]

A catalyst‐driven one‐pot reaction sequence is developed for the enantio‐ and diastereoselective synthesis of tetrasubstituted cyclohexenes from simple unsaturated ketones or thioesters. The method involves a tertiary amine/squaramide‐catalyzed α‐selective addition of transiently generated trienolates to nitroolefins, subsequent base‐catalyzed double bond isomerization, and an intramolecular (vinylogous) 1,6‐addition reaction, a rare key carbocyclization step that proceeded with essentially perfect stereocontrol. [ABSTRACT FROM AUTHOR]

In this study, the unique capacity of bifunctional Brønsted bases to generate α‐branched ketone dienolates and control both site‐ and stereoselectivity of their addition reactions to representative classes of carbon electrophiles (i.e. vinyl sulfones, nitroolefins, formaldehyde) is documented. We demonstrate that by using selected chiral tertiary amine/squaramide catalysts, the reactions of β,γ‐unsaturated cycloalkanones proceed through the dienolate Cα almost exclusively and provide all‐carbon quaternary cyclic ketone adducts in good yields with very high enantioselectivities. A minor amount (<5 %) of γ‐addition is observed when nitroolefins are used as electrophiles. The parent acyclic ketone dienolates proved to be less reactive under these conditions, and thus still constitute a challenging class of substrates. Quantum chemical calculations correctly predict these differences in reactivity and explain the observed site‐specificity and enantioselectivity. [ABSTRACT FROM AUTHOR]

A completely regioselective and highly stereoselective palladium‐catalyzed intramolecular hydroarylation of arenesulfonyl ynamines to benzothiazoles was developed. The presence of an electron‐withdrawing group on the triple bond of the sulfonyl ynamine was crucial for the success of the reaction and our mechanistic studies suggest an alkyne‐directed 5‐exo‐dig cyclization pathway. The products easily underwent photoinduced rearrangement to 3‐amino‐1‐benzothiophene‐1,1‐diones (up to 35 % yields after two steps). A completely regioselective and highly stereoselective palladium‐catalyzed intramolecular hydroarylation of arenesulfonyl ynamines to benzothiazoles was developed. Our mechanistic studies suggest an alkyne‐directed 5‐exo‐dig cyclization pathway of the process. The products easily underwent photoinduced rearrangement to 3‐amino‐1‐benzothiophene‐1,1‐diones (up to 35 % yields after two steps). [ABSTRACT FROM AUTHOR]

Abstract: A range of functionalized heteroaromatic boronic acid derivatives are readily accessed by a diboration/6π‐electrocyclization sequence. This study revealed the surprising observation that there is a direct relationship between oxime ether stereochemistry and reactivity towards electrocyclization. Specifically, E‐oxime ethers are found to be significantly more reactive than their Z‐counterparts (stereochemistry relative to azatriene scaffold). In contrast, the configuration at the azatriene alkene terminus has little impact on reaction rates. Computational analysis offers a rationale for this observation; a Nlone pair→C=C π* orbital interaction lowers the energy of the transition state in the electrocyclization of E‐oxime ethers. Finally, unreactive Z‐oxime ethers can be converted to the corresponding heterocyclic products by a photolytically promoted E→Z isomerization and electrocyclization sequence. [ABSTRACT FROM AUTHOR]

The first stable gold(III) formate and experimental evidence for its β-hydride elimination are described. A catalytic dehydrogenation of formic acid together with mechanistic studies shed light on potential pathways operating in fundamental gold-catalyzed transformations. [ABSTRACT FROM AUTHOR]

Cationic pyridiniophosphine ligands have been synthetized in an attempt to develop a deep eutectic solvents (DESs) compatible catalytic systems. These ligands, in combination with PdCl2, have been successfully applied to different palladium-catalyzed cross coupling reactions, such as Suzuki-Miyaura, Sonogashira, or Heck couplings. While traditional palladium ligands in DES medium failed to reproduce the results obtained in VOC solvents, these cationic phosphines improved the catalytic activity of palladium as no other traditional ligand could in such a polar medium. In addition, the recyclability of these processes was studied, allowing us to reuse both, catalyst and solvent up to 5 times in Suzuki and Sonogashira reactions without a significant drop in the catalytic activity. Regarding the structure of the Pd catalysts, titration, NMR, and DFT studies have clearly demonstrated the coordination properties of the DES-compatible cationic phosphine ligands. [ABSTRACT FROM AUTHOR]

Ten borylated bipyridines (BOBIPYs) have been synthesized and selected structural modifications have been made that allow useful structure-optical property relationships to be gathered. These systems have been further investigated using DFT calculations and spectroscopic measurements, showing blue to green fluorescence with quantum yields up to 41 %. They allow full mapping of the structure to determine where selected functionalities can be implemented, to tune the optical properties or to incorporate linking groups. The best derivative was thus functionalised with an alkyne linker, which would enable further applications through click chemistry and in this optic, the stability of the fluorophores has been evaluated. [ABSTRACT FROM AUTHOR]

The gold(I)-catalyzed tandem rearrangement/Nazarov reaction of propargylic ester derivatives is a useful strategy for the synthesis of cyclopenta-fused N-heterocyclic structures present in many natural compounds. Readily available lactams are converted into enol phosphates and triflates and coupled to propargyl alcohols under Sonogashira conditions. After acetylation, the gold-catalyzed rearrangement of the enynyl acetates readily occurs when using 3-5 mol-% of a gold(I) catalyst. The rearrangement generates a divinyl cation which undergoes a 4π electrocyclization (Nazarov reaction) leading to the target compound in good to excellent yield. This process has been studied in details both experimentally and computationally to understand the influence of both the reaction conditions and substrate structural features on the reaction rate and regioselectivity, as well as the torquoselectivity in the ring closure step. A series of examples illustrates at the end the scope of the reaction. [ABSTRACT FROM AUTHOR]

The gold(I)-catalysed reaction of N-Boc-protected 6-alkynyl- 3,4-dihydro-2H-pyridines, which gives synthetically useful vinylogous amides (β-enaminones), has been studied in detail, in order to optimize the reaction conditions, enlarge the scope and gain insight into the mechanism and the structural features that selectively favour the 6-endo-dig oxyauration of the triple bond. Experimental studies and DFT calculations demonstrate that the 6-endo-dig approach is exclusive with substituted alkynes, whereas with terminal alkynes the 5- exo-dig cyclization prevails, despite the large angle (120°) at C-6. The same selectivity was observed with N-Cbz-protected 2-alkynylpiperidines. With these compounds, β-amino ketones are obtained as a consequence of the 6-endo-dig attack onto a substituted triple bond. Sedamine alkaloids are easily obtained by this approach. [ABSTRACT FROM AUTHOR]

Chiral L-prolinamides 2 containing the (R,R)- and (S,S)-transcyclohexane-1,2-diamine scaffold and a 2-pyrimidinyl unit are synthesized and used as general organocatalysts for intermolecular and intramolecular aldol reactions with 1,6-hexanedioic acid as a co-catalyst under solvent-free conditions. The intermolecular reaction between ketone--aldehyde and aldehyde--aldehyde must be performed under wet conditions with catalyst (S,S)-2b at 10 °C, which affords anti-aldols with high regio-, diastereo-, and enantioselectivities. For the Hajos--Parrish--Eder--Sauer--Wiechert reaction, both diastereomers of catalyst 2 give similar results at room temperature in the absence of water to give the corresponding Wieland--Miescher ketone and derivatives. Both types of reactions were scaled up to 1 g, and the organocatalysts were recovered by extractive workup and reused without any appreciable loss in activity. DFT calculations support the stereochemical results of the intermolecular process and the bifunctional role played by the organocatalyst by providing a computational comparison of the H-bonding networks occurring with catalysts 2a and 2b. [ABSTRACT FROM AUTHOR]

A simple change in the polarity of the solvent allows both enantiomers of substituted succinimides to be obtained in the enantioselective conjugate addition reaction of aldehydes, mainly α,α-disubstituted, to maleimides catalysed by chiral carbamate-monoprotected trans-cyclohexane-1,2-diamines. Using a single enantiomer of the organocatalyst, both enantiomers of the resulting Michael adducts are obtained in high yields by simply changing the reaction solvent from aqueous DMF (up to 84 % ee) to chloroform (up to 86 % ee). Theoretical calculations are used to explain this uncommon reversal of the enantioselectivity; two transition state orientations of different polarities are differently favoured in polar or nonpolar solvents. [ABSTRACT FROM AUTHOR]

The monoguanylation of (1 S,2 S)- and (1 R,2 R)-cyclohexane-1,2-diamine affords chiral primary amine-guanidines that are used as chiral organocatalysts in the enantioselective Michael addition of aldehydes, particularly α,α-disubstituted aldehydes, to maleimides. The reaction is carried out in the presence of imidazole, as an additive, in aqueous N, N-dimethylformamide, as the solvent, and affords the corresponding enantioenriched succinimides in high or quantitative yields with enantioselectivities up to 96 % ee. Theoretical calculations (DFT and M06-2X) suggest a different hydrogen-bonding coordination pattern between the maleimide (C=O) and the catalyst (NH groups) is responsible for the enantioinduction switch that is observed when the reaction is carried out using primary amine-guanidines versus primary amine-thioureas as the organocatalysts. [ABSTRACT FROM AUTHOR]

A wide variety of chiral succinimides have been prepared in high yields and enantioselectivities by asymmetric conjugate addition of 1,3-dicarbonyl compounds to maleimides under very mild reaction conditions using a bifunctional benzimidazole-derived organocatalyst. Computational and NMR studies support the hydrogen-bonding activation role of the catalyst and the origin of the stereoselectivity of the process. [ABSTRACT FROM AUTHOR]

New chiral cis-dioxidomolybdenum compounds [MoO2(acac)(RN,O)] [R = Bn ( 1), pic ( 2)] and [{MoO2(acac)}2{μ-(O,N,N,O)}] ( 3) have been synthesized by treating [MoO2(acac)2] withthe corresponding enantiomerically pure alcohol-iminocompounds derived from (+)-α-pinene modification, (RN,OH) (R = Bn, pic) and (HO,N,N,OH), respectively. Compound [MoO2Cl2(O,N,N,O)] ( 4) has also been prepared. All the compounds were fully characterized both in solution and in the solid state, including by single-crystal X-ray diffraction analysis of enantiomerically pure 3. DFT studies support the stereoselectivity of the synthesis of compound 3. Catalytic olefin epoxidation studies were performed with cis-cyclooctene, ( R)-limonene, and trans-β-methylstyrene by using derivatives 1- 4 as catalyst precursors and tert-butyl hydroperoxide (TBHP) or H2O2 as oxidant. All the catalytic systems showed high chemoselectivity irrespective of the terminal oxidant used. The molybdenum compounds exhibited medium to high catalytic activity at mild reaction temperatures, but no substantial optical induction was observed. This study represents the first use of chiral monoacetylacetonato- cis-dioxidomolybdenum compounds as homogeneous olefin epoxidation catalysts. [ABSTRACT FROM AUTHOR]