Developments of Asymmetric Synthesis Mediated by Chiral Sulfur Reagents

Abstract

Our work on the thio-Claisen rearrangement mediated by an adjacent sulfinyl group is reviewed. The substrates could easily be prepared on a large scale from diacetone-D-glucose. The rearrangement was effected with a diastereoselectivity of 95:5, in favor of the (S,S) or the (R,R) isomer. An approach to natural bis(lactones) was investigated, using a halolactonization reaction and a second [3,3] sigmatropic shift, again mediated by the sulfinyl group. The second part deals with the catalytic enantioselective benzylidenation of aldehydes, mediated by chiral sulfur ylides. We have introduced simple C ₂ symmetric thiolanes for that purpose. The procedure is very practical and enantiomeric excesses up to 96% have been reported for the model of stilbene oxide. A series of ferrocenyl sulfides with planar chirality has also been investigated, leading to unexpected diastereoselectivities and enantiomeric excesses up to 94%.

keywords:

• Chiral sulfur ylides;
• epoxides;
• ferrocenes;
• sulfoxides;
• thio-Claisen rearrangement

Acknowledgments

Our developments have been made possible by a group of dedicated and enthusiastic chemists at Caen. The thio-Claisen studies were started by Carole Alayrac and Stéphanie Nowaczyk; applications were achieved by Virginie Blot and Vincent Reboul. The sulfur ylide adventure started with Karine Julienne, and has continued mainly with Jacques Zanardi, Stéphanie Minière, Jean-François Brière, and Marion Davoust. Thanks also to Bianca Bonini, Mariafrancesca Fochi, Juan Carlos Carretero, and Ramon Gómez Arrayás for their kind and efficient collaboration. We gratefully acknowledge the “PunchOrga” Network (Pôle Universitaire Normand de Chimie Organique), the “Ministère de la Recherche et des Nouvelles Technologies,” CNRS (Centre National de la Recherche Scientifique), the “Région Basse-Normandie,” and the European Union (FEDER funding) for financial support.