Vinylboronates, hydrogenation

Fig. 2.11 Hydrogenation of vinylboronates. Conditions (i) 3 mol%, R-BINAP, -20°C, CICh2CH2CI, 65%, 7 days, then HjOj, NaOH ...

Diboration of phenyl vinylsulfide to give 15 is best performed with a phosphine-free Pt catalyst, as Wilkinson s catalyst affords the Z-(phenylthio)-vinylboronate ester side product, 16, presumably due to (3-hydrogen elimination being competitive with B-C reductive elimination (Equation 12). 

A mixture of 2-phenyl-1-ethynyidiisopropoxyborane and Lindlar catalyst in 1,4-di-oxane containing a little pyridine hydrogenated for 1.5 h, crude vinylboronic acid ester hydrolysed by stirring with water for 1 h, the resulting boronic acid filtered, suspended in pentane, and esterified with 1,3-propanediol Z-2-(2-phenylvinyl)-1,3,2-dioxaborinane. Y 82% (stereochemical purity > 99%). F.e.s. M. Srebnik et al., Tetrahedron Letters 29, 2635-8 (1988). 

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