First synthesis and cycloaddition reactions of 1-azaazulene N-ylide

2-Substituted 1-azaazulene N-ylides were generated by the treatment of appropriate 1-trimethylsilylmethyl-1-azaazulenium triflates with CsF; the triflate salts were prepared from 1-azaazulenes and trimethylsilylmethyl triflate. The 1,3-dipolar cycloadditions of 2-chloro-1-azaazulene N-ylide, prepared in situ, with acetylenic esters gave 2a-azabenz[cd]azulene derivatives and 3a-azacyclopent[a]naphthalene derivatives. These structures were determined by X-Ray crystal structure analysis. A similar reaction of 2-piperidino-1-azaazulene N-ylide gave 3a-azacyclopent[a]azulene derivative as major product.