Heterofulvalenes. II. Synthesis and Reaction of 2,3 : 7,8-Dibenzo-1,4-dithia-6-azafulvalene

Article abstract of DOI:10.1246/bcsj.53.1661

Reaction of 2-isopentyloxy-1,3-benzodithiole with indole in acetic acid gave a 93percent yield of 3-(1,3-benzodithiol-2-yl)indole (4a) which was converted to 2-(3-indolyl)-1,3-benzodithiolylium tetrafluoroborate (5a) in a 77percent yield by treatment with trityl tetrafluoroborate. 5a was also prepared by reaction of indole with 2 molar amounts of 1,3-benzodithiolylium tetrafluoroborate.Treatment of 5a with triethylamine afforded the title compound 6a in 93percent yield. 6a was protonated, methylated, and benzoylated at its 6-position by tetrafluoroboric acid, methyl iodide, and benzoylchloride, respectively.Reaction of 6a with dimethyl acetylenedicarboxylate gave a 1,6-dipolar intermediate which was trapped as an adduct with ethanol. 6a was smoothly reduced by sodium borohydride to give its 5,6-dihydro derivative.