Formation of Four-membered rings Using the Intramolecular Wittig Reaction: Convenient Generation of Functionalised Butadienes

Flash vacuum pyrolysis of the stable ylides 5, readily available by conjugate addition of ylides 3 to alpha,beta-unsaturated ketones 4, results in an intramolecular Wittig reaction with the delta-carbonyl to give cyclobutenes which under the conditions involved undergo electrocyclic ring-opening to afford the synthetically useful 1,3-dienes 7.</p