Lewis acid-mediated reactions of alkyl azides with alpha,beta-unsaturated ketones

[reaction: see text] Alkyl azides react with saturated ketones upon treatment with Lewis acids to afford ring-expansion products through the azido-Schmidt reaction, but this reaction does not proceed when alpha,beta-unsaturated ketones are used. In this study, alkyl azides were reacted with enones in the presence of Lewis acids to give enaminones (vinylogous amides), which formally involve a ring contraction reaction. The mechanism and scope of this reaction is discussed.     

Asymmetric Lewis acid-catalyzed Diels-Alder reactions of alpha,beta-unsaturated ketones and alpha,beta-unsaturated acid chlorides

[reaction: see text] Conformational analysis, van der Waals attractions, and transition structure calculations are combined to design an asymmetric Lewis acid-catalyzed Diels-Alder reaction for simple acyclic alpha,beta-unsaturated ketones and alpha,beta-unsaturated acid chlorides, giving up to 83 and 92% ee, respectively. The two-point-binding chiral recognition mechanism, Lewis acid-Lewis base coordination with boron and a van der Waals attraction with the naphthyl group, uses the inherent enone unit of simple alpha,beta-unsaturated carbonyl compounds, ending the need for auxiliary oxygen binding sites on the dienophile.     

Asymmetric tandem Michael-aldol reactions between 3-cinnamoyloxazolidine-2-thiones and aldehydes

Reactions between chiral 3-cinnamoyl-4-methyl-5-phenyl-1,3-oxazolidine-2-thiones and aromatic aldehydes in the presence of BF3Et2O diastereoselectively produced tricyclic compounds incorporating a bridgehead carbon bound to four heteroatoms in high yields. Four stereocenters were induced during the reaction. The tricyclic products were transformed into propane-1,3-diols bearing three consecutive stereocenters by acid hydrolysis, S-methylation, and reductive removal of the chiral auxiliary.     

Diastereoselective intermolecular cobalt-catalyzed reductive aldol reactions of alpha,beta-unsaturated amides with ketones

Under cobalt catalysis, diethylzinc mediates the conjugate reduction of alpha,beta-unsaturated amides to produce ethylzinc enolates that react with ketones in situ to produce tertiary alcohol-containing aldol products with up to >19:1 diastereoselectivity.     

Anionic four-electron donor-based palladacycles as catalysts for addition reactions of arylboronic acids with alpha,beta-unsaturated ketones, aldehydes, and alpha-ketoesters

Anionic four-electron donor-based palladacycle-catalyzed 1,4-additions of arylboronic acids with alpha,beta-unsaturated ketones and 1,2-additions of arylboronic acids with aldehydes and alpha-ketoesters are described. Our study demonstrated that palladacycles were highly efficient, practical catalysts for these addition reactions. The work described here not only opened a new paradigm for the application of palladacycles, but may also pave the road for other metalacycles as practically useful catalysts for such addition reactions including asymmetric ones. [reaction: see text].     

Selective synthesis of alpha,beta-unsaturated ketones by dibutyltin dimethoxide-catalyzed condensation of aldehydes with alkenyl trichloroacetates

Various alpha,beta-unsaturated ketones were stereoselectively synthesized in high yields up to 94% by a condensation reaction between alkenyl trichloroacetates and aldehydes using dibutyltin dimethoxide as a catalyst in the presence of methanol. This process is superior to the classical Claisen-Schmidt condensation with respect to mildness of the base catalyst and product selectivity.     

A novel pyrrolidine imide catalyzed direct formation of alpha,beta-unsaturated ketones from unmodified ketones and aldehydes

A method for direct, stereoselective preparation of (E)-alpha,beta-unsaturated ketones from ketones and aldehydes, promoted by a novel pyrrolidine imide organocatalyst, has been developed in moderate to high yields. Unlike the Claisen-Schmidt condensation and Lewis acid catalyzed tandem aldol-dehydration processes, this method provides mild reaction conditions to access alpha,beta-unsaturated ketones from simple, unmodified ketones. [reaction: see text]     

Facile epoxidation of alpha,beta-unsaturated ketones with cyclohexylidenebishydroperoxide

Cyclohexylidenebishydroperoxide was successfully used as the oxygen source for the oxidation of α,β-unsaturated ketones for the first time. The corresponding epoxides were obtained in excellent yields under the Weitz-Scheffer reaction conditions.     

Highly stereoselective three-component reactions of phenylselenomagnesium bromide,acetylenic sulfones,and saturated aldehydes/ketones or alpha,beta-unsaturated enals or enones

beta-Phenylseleno-alpha-tolylsulfonyl-substituted alkenes were synthesized via the three-component conjugate-nucleophilic addition of acetylenic sulfones, phenylselenomagnesium bromide, and carbonyl compounds, such as aldehydes, aliphatic ketones, or alpha,beta-unsaturated enals or enones. The reaction is highly regio- and stereoselective with moderate to good yields. Functionalized allylic alcohols were obtained in the case of aldehydes and aliphatic ketones. In the case of alpha,beta-unsaturated enones, functionalized allylic alcohols or functionalized gamma,delta-unsaturated ketones were obtained, depending on the structures of the ketones.     

Catalytic enantioselective peroxidation of alpha,beta-unsaturated ketones

Despite the potential of chiral peroxides as biologically interesting or even clinically important compounds, no catalytic enantioselective peroxidation has been reported. With a chiral catalyst not only to induce enantioselectivity but also to convert a well established epoxidation pathway into a peroxidation pathway, the first efficient catalytic peroxidation has been successfully developed. Employing readily available alpha,beta-unsaturated ketones and hydroperoxides and an easily accessible cinchona alkaloid catalyst, this novel reaction will open new possibilities in the asymmetric synthesis of chiral peroxides. Under different conditions a highly enantioselective epoxidation with the same starting materials, reagents, and catalyst has was also established.     

Organocatalytic enantioselective domino Michael-aldol condensation of 5-oxoalkanal and alpha,beta-unsaturated aldehydes. Efficient assembly of densely functionalized cyclohexenes

Organocatalytic Michael reaction of glutaraldehyde and 3-arylpropenal followed by the subsequent intramolecular aldol condensation provided 2-arylcyclohex-3-ene-1,3-dicarbaldehydes. Reactions with the 5-oxohexanal variant afforded the highly functionalized cyclohexenedicarbaldehydes in high diastereoselectivity and high enantioselectivity (>99% ee). Structure of the adduct 3j was confirmed unambiguously by X-ray analysis.     

Ruthenium-Lewis acid catalyzed asymmetric Diels-Alder reactions between dienes and alpha,beta-unsaturated ketones

The complex [Ru(Cp)(R,R-BIPHOP-F)(acetone)][SbF(6)], (R,R)-1 a, was used as catalyst for asymmetric Diels-Alder reactions between dienes (cyclopentadiene, methylcyclopentadiene, isoprene, 2,3-dimethylbutadiene) and alpha,beta-unsaturated ketones (methyl vinyl ketone (MVK), ethyl vinyl ketone, divinyl ketone, alpha-bromovinyl methyl ketone and alpha-chlorovinyl methyl ketone). The cycloaddition products were obtained in yields of 50-90 % and with enantioselectivities up to 96 % ee. Ethyl vinyl ketone, divinyl ketone and the halogenated vinyl ketones worked best and their reactions with acyclic dienes consistently provided products with >90 % ee. alpha-Chlorovinyl methyl ketone performed better than alpha-bromovinyl methyl ketone. The reaction also provided a [4.3.1]bicyclic ring system in 95 % ee through an intramolecular cycloaddition reaction. Crystal structure determinations of [Ru(Cp)((S,S)-BIPHOP-F)(mvk)][SbF(6)], (S,S)-1 b, and [Ru(Cp)((R,R)-Me(4)BIPHOP-F)(acrolein)][SbF(6)], (R,R)-2 b, provided the basis for a rationalization of the asymmetric induction.