The Diels-Alder product, dimethyl 5-methyl-4a-methyl-1-methylthiothiopyrano[4,3-b] indole-3,4-dicarboxylate (2b), which was obtained by the reaction of methyl 1,2-dimethylindole-3 -dithiocarboxylate (1b) with DMAD (dimethyl acetylenedicarboxylate), was easily converted to a 1,5-dimethyl-2,3-bis(methoxycarbonyl)indolo[2,3-b]thiopyrylium perchlorate (5) as the key intermediate for the thiopyrylocyanine and merocyanine dyes. Compounds (5 and 6) were allowed to react with aromatic aldehydes and some electrophilic reagents to yield cyanine and merocyanine dyes (8a-c, 10-12) in good yields.