Divergent synthesis of new naphtho-fused 2-aminoindolines and naphthoxindoles based on straightforward construction of phenanthrene

An environmentally friendly, highly atom-economical and operationally simple approach toward the synthesis of naphtho-fused 2-aminoindolines and naphthoxindoles starting from biaryl aldehydes and secondary amines has been developed. This notable methodology integrates consecutive intramolecular Mannich-type cyclization triggered by the dearomatization of indole with subsequent aromatization via β-elimination and then amination or oxidation at the C2-position of the indole nucleus. The secondary amine-controlled divergent protocol together with an easy product isolation process provides a practical route for the first time to access naphtho-fused 2-substituted indoline.