Site‐Fixed Hydroboration of Terminal and Internal Alkenes Using BX3/iPr2NEt**

AbstractAn unprecedented and general hydroboration of alkenes with BX3 (X=Br, Cl) as the boration reagent in the presence of iPr2NEt is reported. The addition of iPr2NEt not only suppresses alkene polymerization and haloboration side reactions but also provides an “H” source for hydroboration. More importantly, the site‐fixed installation of a boryl group at the original position of the internal double bond is readily achieved in contrast to conventional transition‐metal‐catalyzed hydroboration processes. Further application to the synthesis of 1,n‐diborylalkanes (n=3–10) is also demonstrated. Preliminary mechanistic studies reveal a major reaction pathway that involves radical species and operates through a frustrated Lewis pair type single‐electron‐transfer mechanism.