Hydroborations allenes, pinacolborane

Hydroboration of allenes with pinacolborane provides the allylboronate or vinylboronates regioselectively depending on the bulk and basicity of the supporting phosphine ligand (eq 12). 

As exemplified with 23, the highly regioselective platinum-catalyzed hydroboration of alkoxy-substituted allenes with pinacolborane provided the corresponding 2)-y-alkoxyallylboronates by total anti-Markovnikov addition at the terminal double bond (Equation 12) [45]. Alkyl- and aryl-substituted allenes devoid of an alkoxy group, how-... 

Hydroboration of allenes 65 with pinacolborane in the presence of Pt(DBA)2 and a trialkylphosphine provides either the allyl boronate 66 or the vinyl boronate 67 regioselectively, depending on the stereoelectronic factors of the phosphine employed (Equation 2) <1999CL1069>. Allyl and vinyl boronates are synthetically important because of their ability to undergo nucleophilic addition to carbonyl compounds as well as transition metal-catalyzed cross-coupling. 

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