Asymmetric Ring-Closing Metathesis Catalyzed by Chiral Molybdenum Alkylidene Complexes.

Kinetic resolution was observed in ring-closing metathesis of racemic dienes catalyzed by the newly developed chiral molybdenum alkylidene complexes (R,R)-Mo(CHCMe(2)Ph)(NAr)(TBEC) 1 (Ar = 2,6-i-Pr(2)C(6)H(3), TBEC = 2',2',2",2"-tetrakis(trifluoromethyl)-1,2-bis(2'-hydroxyethyl)cyclopentane) and (R,R)-Mo(CHCMe(2)Ph)(NAr)(TBEH) 2 (Ar = 2,6-i-Pr(2)C(6)H(3), TBEH = 2',2',2",2"-tetrakis(trifluoromethyl)-1,2-bis(2'-hydroxyethyl)cyclohexane). In the case of a prochiral symmetric triene substrate, optically active cyclized product was formed by catalytic ring-closing metathesis with 1, which opens the possibility of a new version of two-directional synthesis. Although the observed enantiomeric excesses were modest to low, this data demonstrates the feasibility of asymmetric induction by chiral alkylidene catalysts in ring-closing metathesis.