Cleavage of the C=N bond in carbodiimides via release of high ring strain: A new strategy for the selective synthesis of 2-aminoaryl alkynyl imines

Abstract

A novel pattern of the cleavage and reorganization of C=N bond in the multicomponent reaction (MCR) of terminal alkynes or haloalkynes, carbodiimides, and benzynes is achieved for the first time to construct efficiently 2-aminoaryl alkynyl imines. The selective formation and ring-opening of the azetine intermediate with the high ring strain is essential for this reaction. Further transformation of 2-aminoaryl alkynyl imines via the Cu-catalyzed cycloisomerization is explored to provide steroselectively the bi-, tri-, and tetracyclic fused pyrrolines. A novel pattern in the cleavage and reorganization of the C=N bond in the multicomponent reaction of terminal alkynes or haloalkynes, carbodiimides, and benzynes is achieved for the first time to construct efficiently 2-aminoaryl alkynyl imines. The selective formation and ring-opening of the azetine intermediate with high ring strain is essential for this reaction (see scheme; Tf=trifluoromethanesulfonyl, TMS=trimethylsilyl). Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.