trans-Hydroboration of Propargyl Alcohol Derivatives and Related Substrates.

The hydroboration of internal alkynes with pinacolborane as the reagent catalyzed by [Cp*RuCl]4 results in good to excellent levels of regio- as well as stereoselectivity, provided that the triple bond bears one linear and one singly-branched substituent. In such cases, the reaction follows an unusual trans-addition mode and places the boron entity distal to the branching point. The resulting alkenyl boronates, which are difficult to make otherwise, can be engaged in numerous enabling downstream processes.