[4+2+1] Domino cyclization in water for chemo- and regioselective synthesis of spiro-substituted benzo[b]furo[3,4-e][1,4]diazepine derivatives

Abstract

New regio- and chemoselective [4+2+1] domino cyclization consisting of the formation of two spiro rings and five σ bonds has been developed for the synthesis of spiro-substituted benzo[b]furo[3,4-e][1,4]diazepine derivatives. The reaction is a multicomponent domino green process and can be readily performed by reacting inexpensive starting materials of benzene-1,2-diamines, tetronic acid and 2,2-dihydroxy-2H-indene-1,3-dione in aqueous solution under microwave irradiation. The present synthesis shows attractive characteristics, such as the use of water as reaction media, convenient one-pot operation, short reaction periods of 10–18 min and reduced waste production without the use of any strong acids or metal promoters. This synthesis serves as a nice addition to GAP (Group-Assistant-Purification) chemistry in which purificationviachromatography and recrystallization can be avoided, and the pure products were obtained simply by washing the crude products with 95% EtOH.