Selective reagent for preparation of pinacol boronic esters, e.g. for preparation of allenyl or vinyl pinacol boronates from the Grignard or lithium reagents: Liebigs Ann. Chem., 881 (1987); Chem. Ber., 122, 1777 (1989); Tetrahedron Lett., 33, 6941 (1992).