Investigation of the Compatibility of Racemization and Kinetic Resolution for the Dynamic Kinetic Resolution of an Allylic Alcohol

Allylic alcohols, such as methyl styryl carbinol (MSC), are required as single enantiomers for use as chiral building blocks, flavor additives, and aroma compounds in perfumes. This paper investigates the use of dynamic kinetic resolution (DKR) for this purpose, by determining concentration-time data for all species in the racemization, kinetic resolution (KR), and DKR of MSC in toluene. Racemization was catalyzed by ruthenium p-cymene combined with a number of different bases, while Novozym 435 catalyzed the KR. Results showed that the racemization is the rate-limiting step in MSC DKR because the hydrogenation step of the catalyst cycle is deactivated by the KR products. Furthermore, the racemization bases and ruthenium p-cymene made the KR less enantiospecific by either catalyzing nonenantiospecific allylic acetate formation or interfering with enzyme enantiospecifity. Nevertheless, DKRs using ruthenium p-cymene combined with triethylamine, trioctylamine, or P1-t-Oct gave enantiopure (R)-allylic acetate yields above 68% at 80 -97% ee.