Chiral SPINOL‐Derived Borophosphate‐Catalyzed Asymmetric 1,4‐Reduction of Exocyclic α,β‐Unsaturated Ketones

An asymmetric 1,4‐reduction of exocyclic α,β‐unsaturated ketones, yielding diverse optically active α‐substituted tetralones, has been achieved using a chiral SPINOL‐derived borophosphate catalyst. The enantioselectivity‐determining step of the reaction involves the protonation of a highly active boron enolates intermediate. This catalytic reduction system, comprising chiral SPINOL‐derived borophosphate and pinacolborane, has potential for broader application in other asymmetric reduction reactions.