The reactions of benzothiazole 1 with dimethyl acety- lenedicarboxylate (DMAD) have been studied by various groups of workers during the last 12 years, but only recent- ly have the structures of the various products been unam- biguously assigned by Ogura and his colleagues.2 At least three products can be obtained, depending on the nature of the solvent used; thus, 2 and 3 are formed in 5 and 8% yield, respectively, when methanol is employed, whereas 4 is ...
