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

The reaction of a rhodanine derivative (=(Z)-5-benzylidene-3-phenyl-2-thioxo-1,3-thiazolidin-4-one; ) with (S)-2-methyloxirane () in the presence of SiO2 in dry CH2Cl2 for 10 days led to two diastereoisomeric spirocyclic 1,3-oxathiolanes and with the Me group at C(2) (Scheme 2). The analogous reaction of with (R)-2-phenyloxirane () afforded also two diastereoisomeric spirocyclic 1,3-oxathiolanes and bearing the Ph group at C(3) (Scheme 3). The structures of , , , and were confirmed by X-ray crystallography (Figs. 1 and 2). These results show that oxiranes react selectively with the thiocarbonyl group (CS) in . Furthermore, the nucleophilic attack of the thiocarbonyl S-atom at the SiO2-activated oxirane ring proceeds with high regio- and stereoselectivity via an SN2-type mechanism.