Iron‐Catalysed C(sp2)‐H Borylation with Expanded Functional Group Tolerance†

Comprehensive Summary Arene C(sp 2 )‐H bond borylation offers direct and efficient access to aryl boronic esters. Using in situ catalyst activation and photoirradiation, the iron‐catalysed C(sp 2 )‐H borylation reaction of carboarenes, pyrroles, and indoles has been developed using only bench‐stable pre‐catalysts and reagents. Good functional group tolerance was observed including those not reported using previous methods (ArNH 2 , ArOH, ArSiR 3 , ArP(O)(OR) 2 , ArC(O)NR 2 ). Mechanistic studies revealed iron‐catalysed reductive deoxygenation, C—F protodefluorination, and a demethylation of aryl methyl ethers by C—O sigma bond hydroboration.