Abstract
Direct cross-coupling between simple arenes and heterocyclic amines under mild conditions is undoubtedly important for C–N bonds construction. Selective C(sp2)-H amination is more valuable. Herein we show a selective C(sp2)-H amination of arenes (alkyl-substituted benzenes, biphenyl and anisole derivatives) accompanied by hydrogen evolution by using heterocyclic azoles as nitrogen sources. The reaction is selective for C(sp2)-H bonds, providing a mild route to N-arylazoles. The KIE (kinetic isotope effect) experiment reveals the cleavage of C–H bond is not involved in the rate-determining step. Kinetic studies indicate the first-order behaviour with respect to the arene component. It is interesting that this system works without the need for any sacrificial oxidant and is highly selective for C(sp2)-H activation, whereas C(sp3)-H bonds are unaffected. This study may have significant implications for the functionalization of methylarenes which are sensitive to oxidative conditions.
Highlights
Direct cross-coupling between simple arenes and heterocyclic amines under mild conditions is undoubtedly important for C–N bonds construction
Inputting energy by photocatalysis and employing the cobalt catalyst to take two electrons, we show an external oxidant-free oxidative C(sp2)-H amination of arenes, especially the methylarenes, whereas the C(sp3)-H bonds of the methylarenes are unaffected (Fig. 1c)
The KIE of 1.04 was observed from an intermolecular competition. It revealed that the C–H bond cleavage of arene might not be involved in the rate-determining step
Summary
Direct cross-coupling between simple arenes and heterocyclic amines under mild conditions is undoubtedly important for C–N bonds construction. The transition metal-catalysed (Pd, Cu and so on) cross-coupling of aryl halides (Ar–X) with azoles have served as a powerful tool for constructing C–N bonds[3,4,5,6,7,8]. Using simple arenes (Ar–H) to replace Ar–X is undoubtedly the most step- and atomeconomical method, representing an ideal route for C–N bonds construction. Methylarenes, a group of the most important raw chemical materials, have been widely utilized as acyl, alkyl, carboxylate and/or alcohol sources[18], providing the selective formation of C– C and C-heteroatom bonds. As pioneering work for arene C–H functionalization, the visible-light-mediated C(sp2)-H amination using azoles as nitrogen sources and O2 as terminal oxidant has been achieved recently[31]. Ru(bpy)3(PF6)[2] Eosin Y Vitamin B2 Acr þ -Mes ClO4À Acr þ -Mes ClO4À — Acr þ -Mes ClO4À
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