Facial selectivity in the 4 + 2 reactions of a diene derived from carvone

Abstract

The facial selectivities of cyclohexadienes bearing isopropenyl and isopropyl groups as plane-nonsymmetric substituents were assessed in 4 + 2 reactions with N-phenylmaleimide, tetracyanoethylene and 4-phenyl-1,2,4-triazoline-3,5-dione. The only adducts were those arising by attack of the dienophile on the face of the diene opposite the isopropenyl or isopropyl group. In spite of some mechanistic similarities that tetracyanoethylene and 4-phenyl-1,2,4-triazoline-3,5-dione might have with the 4 + 2 addition of singlet oxygen, these dienophiles show none of the ability that singlet oxygen has shown to add syn to a plane-nonsymmetric isopropyl group.