Stereo- and Regiocontrolled Methylboration of Terminal Alkynes.

A scalable and operationally simple synthesis of trisubstituted alkenyl boronic esters has been achieved using a Zr-catalyzed carboalumination of terminal alkynes followed by in situ transmetalation with i-PrOBpin. The products are formed in good yields and with excellent regioselectivity and perfect stereoselectivity. The new procedure provides a significant improvement over the previously reported syntheses.