ChemInform Abstract: Synthetic Studies Towards Gelsemine. Part 1. The Importance of the Antiperiplanar Effect in the Highly Regioselective Reduction of Non‐Symmetrical cis‐Hexahydrophthalimides.

Abstract

ChemInform Abstract The imides (II), prepared from (I) by Diels-Alder reactions and appropriate functionalization procedures, are submitted to NaBH4 reduction (→ (VIII)) and subsequent ethanolysis (→ (IV)-(VII)). The remarkable regioselectivity (i.e. (IV) + (V) vs. (VI) + (VII)) observed in the case of hexahydrophthalimides (IIc)-(IIf) is rationalized on the basis of pronounced conformational preferences: the succinimide moiety adopts a half-chair conformation with one CO group in an equatorial and the other in an axial position of the cyclohexane ring, the equatorial group being more susceptible to hydride attack due to the antiperiplanar effect and associated steric factors.