Biocatalytic asymmetric reduction of prochiral bulky-bulky ketones

Biocatalytic asymmetric reduction of prochiral bulky-bulky ketones is an attractive approach to produce their corresponding valuable enantiopure alcohols. These ketones contain alkyl or aryl groups that exhibit subtle differences in size, and thus their asymmetric reduction is challenging. Bulky-bulky ketones include acyclic ketones that comprise an aryl ring in each side of the ketone or aryl and another relatively bulky group such as cyclohexyl or long chains; they also include prochiral cyclic ketones that comprise two moieties that are similar in their sizes such as tetralones and tetrahydrofuran-3-one. This review summarizes recent examples of biocatalytic asymmetric reduction of bulky-bulky ketones, a transformation that is not easily accomplished not only by enzymes, but also by organo- and organometallic catalysis. Moreover, it has identified gaps that limits the efficiency of the biocatalytic asymmetric reduction of bulky-bulky ketones, and has proposed various strategies to improve this efficiency.