Orientation specific Diels–Alder addition of isoprene to an activated 4,4-dimethylcyclohexenone. An improved route to himachalenes

Abstract

Diels–Alder addition of isoprene to enone-ester 3 proceeds exclusively to the para-addition product 6. The specificity of this route constitutes a significant improvement in the previously reported total synthesis of himachalenes via 6. The mechanistic significance of the observed specificity of addition is discussed.