Electrocyclic Ring Opening of Cyclopropyl Radical

Abstract

THE electrocyclic transformations of cyclopropyl to allyl in the particular cases of the cation and anion have received considerable theoretical attention and are now reasonably well understood1–6. Both simple symmetry arguments1,2 and detailed calculation3–6 agree on the stereochemistries of the ring openings, but the situation is not so clear for cyclopropyl radical. We have previously indicated3 that the prediction of a conrotatory ring opening based on simple symmetry arguments is likely to be in error. We report here the results of an INDO SCF MO (ref. 7) study of the cyclopropyl-allyl system which suggests that the ring opening transformation should occur in a disrotatory fashion in direct contradiction to predictions based on simple arguments involving conservation of orbital symmetry.