4,4,5,5-Tetramethyl-1,3,2-dioxaborhexacyclopentane (5.69 ml, 39.2 mmol, 1.1 equivalent) and di(cyclopentadienyl)zirconium(IV) chloride hydride (0.55 g, 2.14 mmol, 0.06 eq) were added to a stirred solution of ethoxyacetylene (2.5 g, 35.7 mmol, 1 equivalent) in DCM (60 ml). The reaction mixture was stirred at room temperature for 12 h. After the starting material was consumed, the reaction mixture was filtered through a neutral alumina pad topped with a diatomaceous earth layer and washed with DCM (50 ml). The resulting filtrate was evaporated under vacuum to obtain crude (E)-1-Ethoxyethene-2-ylboronic acid pinacol ester, which was a brown liquid (6.5 g).
