De Novo Gold-Catalyzed one-pot Synthesis of Azepino[1,2-a]indoles

The development of efficient and sustainable catalytic processes for the concomitant synthesis and functionalization of indolyl cores is becoming an hot topic in organic chemistry with particular interest in target-oriented synthesis. The combined use of tailor-designed chemical precursors and functional group-tolerant catalytic additives are mandatory requirements in this direction. Despite growing attention, direct and selective methodologies in this segment are still sporadic. With this communication we describe an unprecedented De novo synthesis of functionalized azepino-indoles from readily available propargylic alcohols via gold-catalyzed cascade sequence involving hydroamination of C-C triple bonds and subsequent trapping of vinyl-gold intermediates by the preinstalled keto-group. Cationic carbene gold(I) complexes (i.e. AuIPrOTf) proved particular competence in the titled transformation. Straightforwardly accessible substrates leading to high chemoselectivity, good yields and water as the only stoichiometric by-products are some of the main advantageous features of the reaction sequence. A mechanistic rationale for the final outcome is finally documented.