Stereocontrol of intramolecular Diels-Alder reactions by an allylic diphenylcyclopropyl group.

Intramolecular Diels-Alder reactions of ester-linked 1,3,8-nonatrienes carrying a diphenylcyclopropyl substituent attached to C1 proceed with high levels of stereoselectivity. The stereochemical outcomes of these reactions are explained by reference to B3LYP/6-31G(d) transition structures. Experimentally, the diphenylcyclopropane rings remain intact through these IMDA reactions, notwithstanding their predicted extremely high degree of asynchronicity (the B3LYP-computed lengths in the IMDA transition structures differ by as much as 1.1 angstroms), providing support to the notion that these reactions are concerted processes.