Palladium-catalyzed cyclization reactions of 2-vinylthiiranes with heterocumulenes. Regioselective and enantioselective formation of thiazolidine, oxathiolane, and dithiolane derivatives

The first palladium-catalyzed ring-expansion reaction of 2-vinylthiiranes w ith heterocumulenes to form sulfur-containing five-membered-ring heterocycl es is described. This regioselective reaction requires 5 mol % of Pd-2(dba) (3). CHCl3 and 10 mol % of bidendate phosphine ligand (dppp, BINAP), at 50- 80 degreesC, in THF. The reaction of 2-vinylthiiranes with carbodiimides, i socyanates, and ketenimines affords 1,3-thiazolidine derivatives, whereas t he reaction with diphenylketene or isothiocyanates results in the formation of 1,3-oxathiolane or 1,3-dithiolane compounds in good to excellent isolat ed yields and in up to 78% ee.