Electrophilic Borylation of Terminal Alkenes with BBr3/2,6-Disubstituted Pyridines

A variety of terminal alkenes, as well as heteroaromatic compounds, are borylated by the combined use of BBr3/2,6-dichloropyridine (B3) or BBr3/2,6-lutidine (B5). α,α-Diarylalkenes prefer the former reagent combination, while other alkenes prefer the latter. Mechanistic considerations strongly suggest that the former and latter reactions proceed through electrophilic substitution reactions with BBr3 and [BBr2·B5]+BBr4–, respectively.