A Catalytic Diastereoselective Formal [5+2] Cycloaddition Approach to Azepino[1,2‐<i>a</i>]indoles: Putative Donor–Acceptor Cyclobutanes as Reactive Intermediates

Abstract

A catalytic formal [5+2] cycloaddition approach to the diastereoselective synthesis of azepino[1,2-a]indoles is reported. The reaction presumably proceeds through a Lewis acid catalyzed formal [2+2] cycloaddition of an alkene with an N-indolyl alkylidene β-amide ester to form a donor-acceptor cyclobutane intermediate, which subsequently undergoes an intramolecular ring-opening cyclization. Azepine products are formed in up to 92% yield with high degrees of diastereoselectivity (up to 34:1 d.r.).