Dynamic Kinetic Resolution via Asymmetric Conjugate Reduction:  Enantio- and Diastereoselective Synthesis of 2,4-Dialkyl Cyclopentanones

Herein, we report the kinetic and the dynamic kinetic resolutions of racemic 3,5-dialkyl-2-cyclopenten-1-ones. Kinetic resolution, with good selectivity factors (25−52), was achieved by conjugate reduction with catalytic CuCl/NaOt-Bu/(S)-p-tol-BINAP and stoichiometric quantities of poly(methylhydrosiloxane) (PMHS). When stoichiometric amounts of NaOt-Bu and t-BuOH were included in the reaction mixture, rapid racemization of the starting material occurred allowing for the dynamic kinetic resolution of the cyclopentenone substrates. In this process, chiral 2,4-dialkylcyclopentanones were isolated with high stereoselectivity (ee ≥ 91%, dr ≥ 90:10) and in high yield (≥89%).