Asymmetric thia-Diels-Alder reactions involving new dithioesters bearing a chiral auxiliary are described, with diastereoselectivities up to 78%. Double-stereodifferentiating experiments employing chiral substrates in the presence of a chiral Lewis acid catalyst have been also carried out and, in this case, a diastereomeric excess of 90% was reached. The absolute stereochemistry of cycloadducts resulting from dithiooxalates and carbonyloxazolidinone dithioesters was assigned based on an X-ray structure and chemical correlation. In order to rationalize the sense of the chiral induction, stereochemical models for Cu(II)/bis(oxazoline)/dithioester complexes are proposed. (C) 2012 Elsevier Ltd. All rights reserved.
The First Asymmetric Synthesis of α-Sulfanylphosphonates
[reaction: see text] Diastereoselectivity of up to 88% was achieved for the synthesis of an alpha-mercapto gamma-unsaturated phosphonate using the readily available chiral dimenthylphosphonyl ester group and a carbanionic [2,3]-sigmatropic rearrangement. Absolute configuration of the newly formed chiral center of this nonracemic thiol was determined, and the corresponding phosphono thiolane and thiolane