Role of quaternary ammonium salts as new additives in the enantioselective organocatalytic β-benzylation of enals.

We report herein the efficiency of quaternary ammonium salts as co-catalysts in organocatalytic Michael reactions involving iminium activation of α,β-unsaturated aldehydes. The enantioselective formal benzylation of these substrates has been optimized and used to rationalize the role of the ammonium salts in these processes.

An organocatalytic approach to enantiomerically enriched α-arylcyclohexenones and cyclohexanones.

The presence of a p-nitrophenyl group converts acetone into an excellent and versatile nucleophile in organocatalytic processes, able to react with α,β-unsaturated aldehydes affording β-substituted α-arylcyclohexenones via a Michael reaction/aldol reaction/dehydration sequence, which occurs in good yields, ee up to 96% and complete diastereoselectivity. The resulting compounds are excellent synthons for the diastereoselective preparation of a variety of synthetically useful polysubstituted cyclohexanones and derivatives.

Enantioselective organocatalytic formal allylation of α-branched aldehydes.

Heteroarylvinyl sulfone 1 has been successfully used as a new sulfonyl Michael acceptor in aminocatalytic reactions with branched aldehydes. Subsequent one-pot Julia-Kocienski olefination allows the challenging preparation of enantiomerically pure α-allylated aldehydes bearing C-α quaternary carbons.

Nitrophenylacetonitriles as versatile nucleophiles in enantioselective organocatalytic conjugate additions.

Arylacetonitriles are able to participate in organocatalytic Michael additions to alpha,beta-unsaturated aldehydes by incorporating a nitro group at the phenyl ring, which acts as a temporary activating group in a remote position and allows further transformations. The sequential protocol Michael addition/NaBH(4) reduction/lactonization allows the synthesis of diastereomerically pure disubstituted lactones in high yield and optical purity.

Enantioselective organocatalytic approach to the synthesis of alpha,alpha-disubstituted cyanosulfones.

Optically pure cyano tert-alkyl sulfones have been obtained by organocatalytic enantioselective Michael addition of alpha-substituted cyanosulfones to vinyl ketones using cinchona alkaloids as catalysts. The best results were obtained for p-trifluorophenylsulfones by using VIII as catalyst in toluene at -40 degrees C. Reactions proved to be applicable for a variety of alpha,beta-unsaturated ketones, affording alpha,alpha-disubstituted cyanosulfones in excellent yields with er's up to 90:10.