CYCLOADDITION REACTION OF IMIDAZO[1,2-c]THIAIVZOLE TO ACETYLENIC DIPOLAROPHILES AND NOVEL CONVERSION OF CYCLOADDUCTS INTO 4,9c-DIAZAPENTALENO[1,6a,6 : ab]NAPHTHALENES
A nitrogen-bridged tetravalent sulfur compound, 1,3,6-triphenylimidazo[1,2-c]thiaIVzole, reacts with several acetylenic dipolarophiles giving excellent yields of regio- and periselective [3+2] cycloadducts to the azomethine ylide 1,3-dipole of the thiaIVzole. These cycloadducts undergo, in the presence of triethylamine, a rare desulfurization and a subsequent 10π cyclization yielding the derivatives of a new heterocyclic system, 4,9c-diazapentaleno[1,6a,6 :ab]naphthalene.