β-ethylenic sulfoxides, which in turn can be used as asymmetric dienophiles or Michael acceptors.1 The first enantioselective synthesis of a 1-oxo 2-phosphonothiolane 2 had already been achieved via the [2,3]-sigmatropicrearrangement of the carbanion derived from di(-)-menthyl (allylsulfanyl)methanephosphonate.2 We now describe more direct and general ways to prepare nonracemic sulfoxides of the same
The Michael addition of selected sulfur and nitrogen nucleophiles to a chiral non-racemic 2-phosphono2,3-didehydrothiolane S-oxide is fully diastereoselective. The enantiomeric excesses of the adducts obtained could be determined by P-31 NMR spectroscopy using (R)-(+)-tert-butyl(phenyl)phosphinothioic acid as a chiral solvating agent. The addition of thiophenol was monitored by P-31 NMR spectroscopy which made it possible to observe the formation and evolution of the kinetic and thermodynamic adducts in the reaction mixture. The structures of both enantiomeric thiophenol adducts have been determined by X-ray analysis. (C) 2009 Elsevier Ltd. All rights reserved.
Asymmetric synthesis of α-sulfinylphosphonates in the thiolane series
A series of enantiomerically enriched 2-phosphonothiolane sulfoxides were obtained by diastereoselective S-oxidation combined with kineticresolutionusing a chiraloxaziridine. Enantioselective oxidation of the corresponding 2-phosphono-2,3-didehydrothiolanes with the same oxidizing agent led to the corresponding sulfoxides with ee up to 98%.