The Woodward-Hoffmann-De Puy rule revisited.

[structure: see text] An estimate of the kinetic advantage, in the gas phase and in MeOH, of one of the two allowed disrotatory movements in the electrocyclic ring opening of cyclopropyl derivatives has been theoretically obtained at the B3LYP/6-311++G level. Confirming the Woodward-Hoffmann-DePuy rule, the torquoselectivity of this process is attributed to charge donation from the dissociating C-C bond to the antibonding orbital of the breaking C-Br bond. Substituents do not modify the inherent torquoselectivity.