Reactions of an imidazo[4,5-c]isoxazole-6-carboxylate with electron deficient acetylenes

The synthesis of the first examples of the imidazo[4,5-c]isoxazole ring system has recently been reported,(2) but little is known about the chemistry of this heterocycle. In this paper we describe our investigation into the behaviour of an imidazo[4,5-c]isoxazole-6-carboxylate ester with acetylenic esters and ketones. A complex reaction sequence is found to occur, involving addition of two molecules of alkyne followed by ring opening and fragmentation, leading to the formation of 2-pyrrol-2-yl imidazoles in moderate yield. The mechanism and scope of the reaction is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.