Crystallographic evidence for cyclopropane ring formation in isotwistenes obtained by thermal cascade reactions of cyclopentadienone with acyclic conjugated dienes.

The molecular structure of the double Diels-Alder (DDA) adduct derived from three-step thermal cascade reactions of 2,5-bis(methoxycarbonyl)-3,4-diphenylcyclopentadienone with ethyl sorbate is elucidated by single crystal X-ray analysis. The structural features and the reaction mechanism of the adduct are discussed on the basis of density functional theory (DFT) calculation results.