Regio- and Stereoselectivity in the Reductions of Cyclic Enedione Systems

Reductions of cyclic enedione substrates by NaBH₄ and by LiAl(O-t-Bu)₃H very predominantly gave monoreduction products with very high regio- and stereoselectivity. The reductions involved axial delivery of the hydride. The results indicated that electronic factors were dominated by steric considerations in the transition state of the reduction, even though the seemingly more encumbered carbonyl was reduced.