An iridium/electron-deficient bipyridine-catalyzed selective α-Me-C(sp3)-H borylation of methyl sulfides was disclosed. The reaction exhibited high site-selectivity at the C(sp3)–H bond of α-methyl group when aryl methyl sulfides were used as substrates (up to 65% yield with 99:1 r.r. ratio). In contrast, the borylation mostly occurred at the aryl ring and gave C(sp2)–H borylated products when using 4,4'-di-tert-butyl-2,2'-bipyridine as a ligand (up to 76% yield with 5:95 r.r. ratio). DFT calculation revealed that the C–H cleavage step of this reaction is the rate-determining step, the electrostatic interaction (π-π stacking) between substrate and the electron-deficient bipyridine ligand contributing to the energy difference between the major sp3 pathway (19.4 kcal/mol) and the minor sp2 pathway (23.7 kcal/mol) is the key factor for controlling the unique site-selectivity. This selective α-Me-C(sp3)–H borylation proceeded in many aryl methyl sulfides, as well as aliphatic methyl sulfide, with high functional group tolerance and good yields. Furthermore, the boryl group of the borylated product was readily transformed into other functional groups, which demonstrates the applicability of this methodology

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