Synthesis and some reactions of N-amino-2-methoxy-1-azaazulenium salt: leading to 3,3a-diazacyclopent[a]azulene and 2a,3-diazabenz[cd]azulene systems

Abstract

N-Amino-2-methoxy-1-azaazulenium salt 2 has been synthesized from 2-methoxy-1-azaazulene with O-mesitylenesulfonylhydroxylamine and its structure has been characterized by X-ray crystal analysis. The salt 2 reacts with ethyl cyanoacetate in the presence of potassium carbonate in acetonitrile to give ethyl (1-amino-1,2-dihydro-1-azaazulen-2-ylidene)cyanoacetate 4, which undergoes cyclization with potassium carbonate in ethanol to give ethyl 2-amino-3,3a-diazacyclopent[a]azulene-1-carboxylate. Reaction of 2 with diethyl ethoxymethylenemalonate in the presence of potassium carbonate in acetonitrile gives ethyl 2-methoxy-2a,3-diazabenz[cd]azulene-5-carboxylate and ethyl 3,3a-diazacyclopent[a]azulene-1-carboxylate as cyclization products. Cycloaddition of the salt 2 with an acetylenic ester proceeds regioselectively and gives 3,3a-diazacyclopent[a]azulene derivatives and 2a,3-diazabenz[cd]azulene derivatives.