1,3-Benzodithiolylium Salts. Synthesis and Reactions with Nucleophilic Reagents

Various salts of 1,3-benzodithiolylium ion were prepared in excellent yields on treatment of 2-alkoxy- and 2-alkylthio-1,3-benzodithioles with acids in acetic anhydride. The reactions of 1,3-benzodithiolylium tetrafluoroborate (1a) with a wide variety of nucleophilic reagents (alcohols, water, thiols, hydrogen sulfide, primary, secondary, and tertiary amines, ammonia, N,N-dimethylformamide, electron-rich aromatic compounds, active methylene compounds, tropilidene, and sodium borohydride) were studied. In all cases examined, 1a reacted with nucleophilic reagents at the 2-position to give the corresponding 1,3-benzodithioles in good yields, excepting the reactions with tertiary amines and N,N-dimethylformamide which resulted in the formation of dibenzotetrathiafulvalene. Salt 1a was also prepared from 1,3-benzodithiole and trityl tetrafluoroborate.