Asymmetric 1,4-dihydroxytations of 1,3-dienes, and other transformations, are initiated by the Pt-catalyzed enantioselective addition of bis(pinacolato)diboron (B-2(pin)(2)) to conjugated dienes. The studies reported in this communication suggest that both cyclic and acyctic substrates will participate in this reaction; however, dienes which are unable to adopt the S-cis conformation are unreactive. For most substrates, 1,4-addition is the predominant pathway. In addition to oxidation to the derived 2-buten-1,4-diol, stereosetective carbonyl allylation with the intermediate bis(boronate) ester is also described.