STRUCTURE AND REACTIVITY OF ISOANNULLATED HETEROCYCLIC-SYSTEMS WITH 4N-PI AND (4N+2)-PI ELECTRONS .18. BENZO[C]THIOPHENES WITH SYMMETRICAL STRUCTURE - MODIFIED AND OPTIMIZED PREPARATION BY THE S-OXIDE ROUTE

Benzo[c]thiophenes (15) with symmetric structure have been prepared efficiently from 1,3-dihydrobenzo[c]thiophene 2-oxides (9) by reaction with aluminium oxide, by O-acylation with trifluoroacetic anhydride, or O-alkylation with methyl trifluoromethanesulfonate. The aromatization of the S-oxides 9 is achieved by O-functionalization, subsequent elimination, and consecutive deprotonation.