LAUSR

A cobalt-catalyzed enantioconvergent radical Negishi C(sp)−C(sp) cross-coupling of racemic benzyl chlorides with arylzinc reagents has been developed in good yield with moderate enantioselectivities. This strategy provides an expedient access toward a range of enantioenriched 1,1-diarylmethanes. Key to this discovery is the utilization of a chiral multidentate anionic N,N,Pligand to strongly coordinate with the cobalt catalyst and tune its chiral environment, thus achieving the enantiocontrol over the highly reactive prochiral alkyl radical species. T metal catalyzed enantioconvergent C(sp)− C(sp) cross-coupling of racemic alkyl electrophiles and organometallic reagents represents a powerful tool in the synthesis of enantioenriched three-dimensional molecules. Recent emphasis on sustainability and economy has led to the use of an earth-abundant transition metal catalyst as a new horizon in the cross-coupling reactions. In this context, the first-row transition metals (Ni, Co, Fe, and Cu) have high-spin electronic configurations and easily convert racemic alkyl electrophiles to the prochiral alkyl radical species via a singleelectron transfer process, thus providing a general mechanism for enantioconvergence. As such, tremendous progress has been made by Fu and others in developing chiral nickel catalysis to realize the enantioconvergent C(sp)−C(sp) cross-coupling of racemic alkyl electrophiles in the past two decades (Scheme 1). Very recently, the chiral iron and copper catalysis have been designed for such transformations. Owing to the earth-abundant, low-cost, and nontoxic nature of cobalt catalyst, it has been widely used in the crosscoupling of alkyl electrophiles with organometallic reagents in the past three decades. However, the enantioconvergent cross-coupling has been much less developed. The main reason might be that the cobalt-catalyzed C(sp)−C cross-coupling occurs easily even in the absence of any ligand, and this background reaction would thwart the development of a chiral ligand-induced enantioconvergent process. It is thus a challenging task to design suitable chiral ligands to promote the enantioconvergent cross-coupling. Until now, only limited examples have been demonstrated by using chiral bisoxazoline ligands in the enantioconvergent C(sp)−C(sp) crosscoupling of racemic α-bromo esters or fluorinated benzyl bromides since the seminal work of Zhong and Bian. Therefore, the development of new chiral ligands to tune the chiral environment of cobalt catalyst and realize the enantioconvergent cross-coupling of more alkyl halides is highly desirable. Special Issue: Organometallic Solutions to Challenges