ACCURATE CALCULATIONS OF REACTIVITIES AND DIASTEREOSELECTIVITIES IN COMPLEX-MOLECULES - AN AM1 STUDY OF 1,3-DIOXOLAN-4-ONES AND RELATED OXYGEN HETEROCYCLES

The AMI semiempirical method has been used to calculate the heats of f ormation and preferred conformations of a variety of dioxolanes and re lated compounds, and of the radicals derived from them. The heats of f ormation and conformations of the transition structures for hydrogen-a tom transfer from trialkylstannane to some of these radicals have also been determined. Among the major conclusions of this study are the fo llowing: the results of the calculations are highly consistent with ex perimental data; the regiochemistry of hydrogen-atom abstraction from dioxolanes is controlled mainly by thermochemical factors; the Sn---H- --C bond angle in the transition structure for hydrogen-atom transfer is close to 180 degrees; the calculated activation energies for reacti ons of dioxolanonyl radicals with trialkylstannane agree with observed diastereoselectivities; and the bond lengths and charge distribution in radicals bearing an a-ether and an alpha-carbonyl substituent are c onsistent with captodative stabilization.