Unusual 1,2-aryl migration in Pd(ii)-catalyzed aza-Wacker-type cyclization of 2-alkenylanilines

Inspired by the Hegedus aza-Wacker indole synthesis, we were intrigued with the fate of the aminopalladation intermediate if syn β-hydrogen is made inaccessible or unavailable. In contrast to our previously reported β-carbon elimination, cyclization of a variety of 2-alkenylaniline substrates under electrophilic palladium conditions unexpectedly afforded C3-substituted indoles. This unusual 1,2-migratory process was found to be operative across a variety of substrates with predictable migratory aptitude. A mechanistic proposal was put forward to rationalize the observed substrate dependence, and this unexpected finding could provide an opportunity for other related processes.