The new synthesis of pyrrole-fused dibenzo[b,f][1,4]oxazepine/thiazepines by the pseudo-Joullie-Ugi reaction via an unexpected route with high chemoselectivity

A novel and unexpected route for synthesizing pyrrole-fused dibenzoxazepines/thiazepines has been designed based on a modified Ugi reaction of cyclic imines with isocyanides and acetylenedicarboxylates under catalyst-free conditions. Mechanism investigation indicates that this process is carried out through the production of zwitterion species (Huisgen's 1,4-dipole), which is a key intermediate in the chemoselectivity of products. This Huisgen's 1,4-dipole is trapped in situ with isocyanides and a variety of pyrrole-fused dibenzoxazepines/thiazepines are synthesized in a simple one-pot operation with high yields and chemoselectivity. This strategy opens a new route in Ugi reactions (pseudo-Joullie-Ugi reaction) for the synthesis of pyrrole-fused heterocycles as special pharmaceutical scaffolds.