An unprecedented strategy for synthesizing 1,2-bis(indolyl)ethenes and benzoαcarbazoles 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 benzoαcarbazoles, respectively.
Hyun et al. (Wed,) studied this question.