Catalytic Boration of Alkyl Halides with Borane without Hydrodehalogenation Enabled by Titanium Catalyst

An unprecedented and general titanium-catalyzed boration of alkyl (pseudo)halides (alkyl-X, X=I, Br, Cl, OMs) with borane (HBpin, HBcat) is reported. The use of titanium catalyst can successfully suppress the undesired hydrodehalogenation products that prevail using other transition-metal catalysts. A series of synthetically useful alkyl boronate esters are readily obtained from various (primary, secondary, and tertiary) alkyl electrophiles, including unactivated alkyl chlorides, with tolerance of other reducing functional groups such as ester, alkene, and carbamate. Preliminary studies on the mechanism revealed a possible radical reaction pathway. Further extension of our strategy to aryl bromides is also demonstrated.