Highly diastereo- and enantioselective kinetic resolution (KR) of a series of racemic planar-chiral 1-R-2-vinylcymantrenes ( rac - 1 ; R = Br, Me, I) was realized by an asymmetric metathesis dimerization (AMD) reaction catalyzed by a chiral molybdenum-alkylidene precatalyst. The Mo/( R )- L1 precatalyst promoted the AMD/KR reaction of rac - 1a (R = Br) to give ( E )-( R , R )- 2a of 99% ee together with unreacted recovered ( S )- 1a of 45% ee at 37% conversion. The diastereoselectivity of this reaction was excellent with chiral - 2a / meso - 2a = 96:4 molar ratio, and the selectivity factor ( k rel ) was calculated to be 754 based on a second-order equation. In all the three substrates examined, the dimerized products, chiral - 2 , were obtained in >98% ee thanks to the outstanding enantioselectivity.
Imazu et al. (Tue,) studied this question.