Abstract
Asymmetric metathesis dimerization (AMD) reactions of a series of racemic planar-chiral 2-vinylphosphaferrocenes (rac-1) were examined in the presence of a chiral molybdenum-alkylidene precatalyst. The reactions proceeded in a highly enantio- and diastereoselective fashion to realize the efficient kinetic resolution (KR) of the racemic substrates. The AMD/KR reaction of rac-1a showed excellent diastereoselectivity (chiral-2a/meso-2a = >98/<2) to provide (E)-(S,S)-2a of >99% ee in 38% yield together with unreacted recovered (R)-1a of 63% ee in 58% yield. The selectivity factor (krel) of this reaction was estimated to be 1.5 × 103 based on a second-order equation. In all the cases examined, the dimerized products, chiral-2, were obtained in >98% ee even with near 50% conversions (i.e., close to the complete consumption of the more reactive enantiomers in rac-1) thanks to the outstanding enantioselectivity.
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