Selective Synthesis of Acenaphtho[1,2-b]indole Derivatives via Tandem Regioselective Aza-Ene Addition/N-Cyclization/SN1 Type Reaction

A concise and efficient synthesis of acenaphtho[1,2-b]indoles with different substitution patterns from a [3+2] condensation of enaminones with acenaphthoquinone has been developed. During the first pathway, products 3 were synthesized in the presence of Et3N, while a second reaction in the presence of p-toluenesulfonic acid leads to compounds 5 via intramolecular cyclization and highly regioselective S(N)1-type reaction with alcohols under solvent-free conditions. Both procedures give excellent yields and are highly eco-benign, are convenient one-pot operations, are highly regioselectivity, and use environmentally friendly solvent systems or operate under solvent-free conditions. This method offers an alternative to regioselective construction of biologically meaningful polycyclic indoles.