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DOI: 10.1055/s-2006-941941
Enantioselective Construction of Secondary Boronic Esters
W. J. Moran, J. P. Morken*
University of North Carolina at Chapel Hill, USA
Publication History
Publication Date:
21 July 2006 (online)
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Significance
The method adresses the difficult problem of the preparation of secondary organoboron derivatives. In general, the hydroboration of 1,2-disubstituted alkenes suffers from low regioselectivity. Using an enantioselective Rh(I)/bis-phosphine catalytic hydrogenation, vinyl boronates 1 were transformed into chiral secondary boronic esters. The starting vinyl boronates were prepared from the alkyne by hydrobromination with BBr3 and subsequent transmetallation of the lithiated alkene to the borate with (pin)BOi-Pr. A variety of functional groups were tolerated under the mild reaction conditions. Importantly, examples 2c and 2f, bearing a pre-existing stereocenter, show that the reaction is reagent-controlled. Using the reported method, versatile secondary boronic esters can be accessed that are not available from other catalytic systems. Further derivatization of the boronic esters 2 was accomplished in situ by the preparation of chiral amine 3 and chiral alcohol 4.