Heterocycles by Cycloaddition. XII. Cycloaddition-Extrusion of a Mesoionic 1,3-Dithiolium-4-olate and a Mesoionic Oxazolium-5-olate with a Phosphirene. Formation of Six- and Five-membered Heterocycles

The reaction of a mesoionic dithioliumolate (6) w ~t h triphenylphosphirene (7) gave a cycloadduct (8).Pyrolysis of the cycloadduct (8) gave a 1,4-thiaphosphinine (11) and a thiophene (9).Acid treatment or photolysis of the cycloadduct (8) gave the thiophene (9) exclusively.The reaction of a mesoionic oxazolium-5-olate ( I t ) and the phosphirene (7) gave a pyrrole (15) as the only isolable product.Thanks largely to extensive works by Huisgen and his coworkers, 1,3-dipolar cycloaddition is now widely