Stereoselective Cobalt-Catalyzed Cross-Coupling Reactions of Arylzinc Chlorides with α-Bromolactones and Related Derivatives.

α-Bromolactones bearing a substituent in the β-position undergo a highly trans-diastereoselective arylation with arylzinc chlorides in the presence of 10-20% CoCl2 and 10-20% PPh3 in THF under mild conditions (25 °C, 16 h) leading to optically enriched α-arylated lactones and protected aldol products (99% ee) in 52-96% yield. The synthetic utility of this arylation was demonstrated by the stereoselective preparation of an artificial rotenoid MOM-protected munduserol derivative.