A Simple, Serendipitous Synthesis of Heterohexahelicenes

Abstract

Oxidation of benzo[1,2‐b:3,4‐b′:5,6‐b′′]trithiophene (1) with MCPBA at room temperature gives the corresponding monosulfone 3. This material readily undergoes a Diels–Alder dimerization with extrusion of SO2 to form the dihydroheterohelicene 5. This, in turn, is easily converted into the heterohelicene 6 in a one‐pot NBS bromination and elimination. In a similar manner, oxidation of phenanthro[9,10‐b]thiophene (12) gives the dihydroheterohelicene 13, and bromination/elimination forms the corresponding heterohelicene 8. The X‐ray structures of compounds 5, 6, and 13 are reported, as well as computational studies that illuminate the unusual regiochemical outcome of the dimerization reactions.