Dynamic kinetic resolution of a tertiary alcohol†
In spite of the tremendous success of dynamic kinetic resolutions for a broad range of compound classes, tertiary alcohols and their corresponding esters have still remained as one of the most challenging substrates for this type of process. This is due to the size and steric hindrance of tertiary alcohols as well as to the difficulty in finding reaction conditions for the racemization of such compounds being at the same time compatible with the resolution reaction, which preferably is carried out with an enzyme. In this study, the first example of a dynamic kinetic resolution of a racemic tertiary alcohol is presented. The desired synthesis of the resulting enantiomerically pure ester was achieved by combining a lipase-catalyzed kinetic resolution with an in situ racemization utilizing a bio-compatible oxovanadium-catalyst. First, the two individual reactions were examined, improved and adjusted to be compatible with each other. Subsequently, addition of both catalysts in tailor-made portions led to the desired combined process and delivered the product with >99% ee and a conversion exceeding 50%, thus proving such a desired dynamic kinetic resolution of a tertiary alcohol.