Synthesis of Sterically Congested 2,2'-Bi(Adamantyl)-Based Alcohol and Amines.

Abstract

Sterically congested chiral alcohol and amines have gained tremendous attention in the design of asymmetric catalysts. Herein, the synthesis of a sterically congested bis-adamantane framework-based chiral alcohol, (1R,2S,3S,4R)-4-(2-adamantyl)adamantan-2-ol, and amine, (1R,2S,3S,4R)-4-(2-adamantyl)adamantan-2-amine, is described. Access to these sterically encumbered compounds is found via the preparation of an enantioenriched 4-adamantyladamantan-2-one intermediate, which was synthesized in 6 steps from adamantan-2-one. The key step involved enzyme-catalyzed ester hydrolysis in giving unsaturated alcohol with an enantiomeric excess of >95%. This adamantylidene adamantanol was subjected to an acid-catalyzed intramolecular [1,4] shift to give the key chiral intermediate without racemization. This ketone intermediate was transformed into the target compounds via reduction and reductive amination protocols.