Previously reported 3-diazotetramic acids have been successfully involved in Rh(II)-catalyzed condensation with aliphatic and aromatic nitriles delivering compounds bearing a hitherto unexplored polysubstituted fused oxazole scaffold. The latter was found to be somewhat labile to the addition of nucleophiles (water and benzylamine) which leads to oxazole ring opening and may constitute an entry into polysubstituted pyrrolinones after due investigation of scope.