Diastereoselective sulfonate-directed carbonyl reduction of γ-keto-sulfonates

Quaternary Ammonium Salts Interact with Enolates and Sulfonates via Formation of Multiple +N-C-H Hydrogen Bonding Interactions

We report herein sharp physical evidence, i.e., single-crystal X-ray diffraction and 1H-NMR spectral data, confirming that quaternary ammonium species interact with anions via a set of directional ion–dipole cooperative +N-C-H unusual H-bonding interactions and not via pure non-directional ionic electrostatic interactions. This finding, which has been often invoked by calculations, is herein substantiated by the preparation of two model compounds and an analysis of their X-ray crystal structures in the solid state and 1H-NMR spectra in solution. These observations are particularly pertinent for the rational design of novel catalyses and catalysts and providing guidance to an understanding of these species in solution and during asymmetric enantioselective catalysis.

First enantioselective synthesis of gingesulfonic acids and unequivocal determination of their absolute stereochemistry

Herein we report the first organocatalysed enantioselective synthesis of gingesulfonic acids and shogasulfonic acids via a mild and convenient aminothiourea-catalysed conjugate addition of bisulfite to the olefin moiety of α,β-unsaturated carbonyls-a technology previously reported by us. A series of optically active naturally occurring sulfonic acids are prepared in their natural and unnatural configurations, and their absolute configurations are unequivocally confirmed by single crystal X-ray diffractometry.