Regio- and stereoselective reactions of a rhodanine derivative with optically active 2-methyl- and 2-phenyloxirane

Abstract

The reaction of a rhodanine derivative (=( Z)-5-benzylidene-3-phenyl-2-thioxo-1,3-thiazolidin-4-one; 1 ) with ( S)-2-methyloxirane ( 2 ) in the presence of SiO 2 in dry CH 2Cl 2 for 10 days led to two diastereoisomeric spirocyclic 1,3-oxathiolanes 3 and 4 with the Me group at C(2) (Scheme 2). The analogous reaction of 1 with ( R)-2-phenyloxirane ( 5 ) afforded also two diastereoisomeric spirocyclic 1,3-oxathiolanes 6 and 7 bearing the Ph group at C(3) (Scheme 3). The structures of 3 , 4 , 6 , and 7 were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that oxiranes react selectively with the thiocarbonyl group (CS) in 1 . Furthermore, the nucleophilic attack of the thiocarbonyl S-atom at the SiO 2-activated oxirane ring proceeds with high regio- and stereoselectivity via an S N2-type mechanism.