P III -Mediated intramolecular cyclopropanation and metal-free synthesis of cyclopropane-fused heterocycles

A P(NMe 2 ) 3 -mediated reductive intramolecular cyclopropanation is developed for the first time, which provides facile access to a wide variety of cyclopropane-fused heterocycles including chromanes, tetrahydroquinolines, lactones, and lactams. Catalytic hydrogenative ring-expansion of the cyclopropane-fused heterocycles is also elaborated, leading to various structurally important medium-sized heterocycles.