Assessing the Role of Benzylic C─H Bonds in Suppressing Radical Chemistry Initiated by Benzynes

Abstract

Reaction of KOtBu with haloarenes in arene solvent leads to the formation of biaryls through radical intermediates, and we recently (2026) showed that the radical chemistry is initiated by the formation of benzynes. Our original studies (2014) compared the reactivity of iodobenzene and 2-iodo-m-xylene; the latter substrate cannot form o-benzynes. Whereas iodobenzene led to the formation of biaryls (40%), for 2-iodo-m-xylene this was suppressed almost to 0%. However, in the intervening time, we came to suspect that the iodoxylene was not an ideal substrate due to the potential reactivity of the Ar-Me groups both to base and to hydrogen atom abstraction reactions. We have now examined two new substrates where the Ar-Me groups are replaced by Ar-Ph groups. These substrates cause much more efficient initiation of radical chemistry, arising from the formation of p- and m- benzynes through the reaction of iodobenzenes with base. Importantly, these substrates allow assessment of the role of the Ar-Me groups in 2-iodo-m-xylene in suppressing radical chemistry.