Cobalt-catalyzed homo-coupling of aryl and alkenyl bromide using atmospheric oxygen as oxidant

An efficient procedure for the synthesis of symmetric biphenyl and olefinic compounds was reported by cobalt-catalyzed direct homo-coupling reaction of aryl and alkenyl bromide in the presence of metallic magnesium using atmospheric oxygen as the oxidant. All tested aromatic bromides could give corresponding biaryls in good yields (up to 85%). Moreover, under the same conditions, β-bromostyrene could also afford the corresponding conjugated dienes in moderate yields, and the coupling is highly stereoselective to give trans-products. This mild and practicable method opened a new way to the preparation of symmetric biaryls and conjugated dienes.