Formation of a novel thiopyranoindole ring system

The novel thiopyran[2,3,4-c,d]indole ring system (e.g. 3 ) has been prepared from a substituted indole by intramolecular cyclisation of a t-BuS group onto an allyl substituent. The reaction occurs in high yield under the influence of protic acids, Lewis acids or electrophiles (Br 2, I 2, Hg(OAc) 2) The intramolecular S-alkylation/dealkylation of 3-t-butylthio-4-allylindoles provides a facile route to the novel thiopyrano[2,3,4-c,d]indole nucleus.