alpha-Oxothioaldehyde S-oxides 4a-f can be generated under very mild c
onditions from the corresponding sulfinyl compounds 3a-f, which in tur
n are obtained by m-chloroperoxybenzoic acid (MCPBA) oxidation of alph
a-oxothiophthalimides 2a-f. The reactive sulfine intermediates can be
trapped as electron-poor dienophiles as well as electron-poor dienes w
ith formation of dihydrothiopyran S-oxides 5a-e or 1,4-oxathiin S-oxid
es 6a-f, respectively. (C) 1997 Published by Elsevier Science Ltd.