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2005
Enantioselective syntheses
O 0031
Catalytic Enantioselective Hydrogenation of Vinyl Bis(boronates). — The asymhydrogenation of prochiral vinyl bis(boronates) is accomplished in the presence
15- 033 metric
of the Walphos W001 and W008 catalysts. While W001 leads to high enantioselectivities in the case of aromatic bis(boronates) (I), W008 works best with aliphatic
bis(boronates) such as (III). To minimize the number of manipulations, a domino
one-pot alkyne diboration/hydrogenation procedure of (V) is shown to give the diol
(S)-(IIa) with only slightly lower selectivity than using the purified bis(boronate) (Ia)
as the starting material. An additional homologation step is included in the hydrogenation/homologation/oxidation protocol leading to the diol (VII); this reaction can be
accomplished as a one-pot procedure with only a single solvent swap (THF for toluene).
The reaction selectivity is remarkely dependent on the ligand:metal ratio; with an substoichiometric amount of ligand the opposite enantiomer (R)-(IIa) is formed. —
(MORGAN, J. B.; MORKEN*, J. P.; J. Am. Chem. Soc. 126 (2004) 47, 15338-15339;
Dep. Chem., Univ. N. C., Chapel Hill, NC 27599, USA; Eng.) — Kieslich
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