diphenylphosphonium diylides was investigated towards carbonic anhydride derivatives. Unsubstituted and substituted non-stabilized diylides react with phenylisocyanate and dicyclohexylcarbodiimide, leading to the formation of new monoylide type intermediates. These last ones react in situ with carbonylcompounds through a Wittig reaction leading respectively to α,β-unsaturated amides and amidines. Substituted semi-stabilized