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Several α,β‐unsaturated ketones were treated with dimethyl diazomalonate and ethyl acetodiazoacetate under bis(acetyl‐acetonato)copper(II) catalysis. Dihydrofuran derivatives, obviously arising from carbonyl ylides, were isolated in high yields. Structural identifications were carried out using 2D‐NMR‐spectroscopic data.

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.

1,3-Dioxole derivatives were synthesized from copper(II)-catalyzed cyclization reactions of carbonyl ylides derived from 3-methylenebicyclo[2.2.1]heptan-2-one and dimethyl diazomalonate. The reaction mechanisms leading to all possible products have been extensively investigated by density functional theory. The generally accepted mechanism proposed by Doyle12 for the carbene transformation reactions were applied to this system for the first time to shed light on the reaction mechanism and to understand the catalytic activity of Cu(acac)2. Calculations have shown that the reaction mechanisms leading to different products greatly depend on the conformations of copper-stabilized carbonyl ylides, which are treated as reactants in our calculations. The conformational effects and donor−acceptor type stabilizations between the catalyst and the carbonyl ylide observed in the reactants and the transition state geometries seem to be the main reasons for the observed product selectivity. Our theoretical results are in good agreement with the experimental results, and the calculations successfully predict the experimental 75:25 product distribution.

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