Reactions of α,β-enones with diazo compounds: Part 3. On the nature of the 1,5-ring closure of α,β-enone ylides

Carbonyl ylides arising from ethyl acetodiazoacetate/dimethyl diazomalonate and α,β-enones with mainly s-cis conformations underwent disrotatory cyclization to produce dihydrofuran derivatives. This process proved to be sensitive to steric effects. The corresponding ylides arising from rather s-trans α,β-enals yielded dioxole derivatives. The mechanisms of the reactions are discussed.