In the presence of a Co(II)-diamine catalyst system, a variety of secondary alkyl halides were diastereoselectively coupled with arylmagnesium reagents to form C-C bonds. Diastereoselectivity ranged from poor to excellent and was optimal with R1 = (+)-isomenthyl as a chiral auxiliary. In addition to these results, the non-diastereoselective coupling of a variety of alkyl halides was demonstrated, as well as the total synthesis of a synthetic prostaglandin.