Vinylene Carbonate as an Ethylene Equivalent for the Synthesis of 1,2-Bis(indolyl)ethenes and Benzo[α]carbazoles

An unprecedented strategy for synthesizing 1,2-bis(indolyl)ethenes and benzo[α]carbazoles is described herein. Mechanistically, an acetal intermediate, derived from vinylene carbonate and HFIP, is involved in electrophilic substitution to free (NH)-indoles, generating indolyl-3-acetaldehydes. Subsequent electrophilic condensation between these indolyl-3-acetaldehydes and additional indoles or C2-aryl rings affords (E)-1,2-bis(indolyl)ethenes and benzo[α]carbazoles, respectively.