We present the first trans-selective diborylation reaction of alkynes. By means of theoretical calculation-assisted reaction analysis, we designed a pseudo-intramolecular reaction of diboron, propargyl alcohol, and a base to facilitate B-B bond activation and C-B bond formation with high efficiency. This approach provides synthetically versatile and densely functionalized 4-borylated 1,2-oxaborol-2(5H)-oles (vinyldiboronates) in a straightforward manner. Detailed computational analysis showed that the directing alkoxide functionality markedly lowers the activation energy of B-C bond formation.