The deuterated 3-methylcyclohexanones 1-5 are of interest as substrates for spectroscopic and theoretical studies1 $2. Recently, we reported the preparation of a series of racemic, deuterated 3-methylcyclohexanones, and the detailed assignment and interpretation of the Raman optical activity (ROA) spectrum of the parent compound.2 Ongoing studies of C-H stretching vibrational circular dichroism and low-frequency ROA required the chiral series of deuterated 3-methylcyclohexanones 1-3. We now report the efficient, enantioselective synthesis of these compounds.
Chiral 3-methylcyclohexanones and 2 were prepared as shown in Scheme 1. Alkylation of imine4 1, derived from 1,4-~yclohexanedione monoketal 5 and amine 6 , with methyl iodide followed by hydrolysis and reduction with LiAlDh afforded alcohol 8 as a mixture of diastereomers. Using the sequence developed for the racemic aeries3, 4 was converted to (2_R)-4-d2-methylcyclohexanone 1, identical in all respects (except optical rotation) to an authentic sample of racemic material. Based on the observed rotation of L9 we estimate the optical purity of our synthetic material to be greater than 60%.