Boration of Alkyne

Pinacolborane (PBH, 537) sluggishly hydroborates alkynes and alkenes. Hydro-boration of alkyne with PBH is catalyzed by hydrozirconocene chloride (HCp2ZrCl) [206], CpNi(Ph3P)Cl and Rh(CO)(Ph3P)2Cl [207] at room temperature. Hydrobora-tion of 4-octene with PBH at room temperature gives either terminal or internal boranes 538 or 539 regioselectively, depending on the catalyst used [207]. PBH is more stable than CBH, and easier to handle. 

Selected 1-alkenylboronates synthesized by Equation (56) are shown in Scheme 17. The reaction afforded cyclic and acyclic vinylboronic esters possessing various functional groups, which are not available by conventional hydro-boration of alkynes or by a transmetallation method, for example 160-167. 

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