Highly Diastereoselective Synthesis of Polycyclic Indolines through Formal [4+2] Propargylic Cycloaddition of Indoles with Ethynyl Benzoxazinanones

A formal [4+2] propargylic annulation of indoles and pyrrole with ethynyl benzoxazinanones was described. This protocol provides a concise synthesis of tetrahydro-5H-indolo[2,3-b]quinolines and tetrahydro-3H-pyrrolo[3,2-b]quinoline, the core structures of alkaloid frameworks, featuring excellent yields, high diastereoselectivity, mild conditions and wide substrate scope.