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. 2010 Feb 17;132(6):1740-1.
doi: 10.1021/ja908257x.

Amide-directed catalytic asymmetric hydroboration of trisubstituted alkenes

Sean M Smith  1 , James M Takacs
Affiliations

Amide-directed catalytic asymmetric hydroboration of trisubstituted alkenes

Sean M Smith et al. J Am Chem Soc. .

Abstract

Rhodium-catalyzed hydroborations of trisubstituted alkenes are generally slow and often suffer from competing alkene isomerization. In contrast, the trisubstituted alkene moieties contained within the framework of a beta,gamma-unsaturated amide undergo facile reaction, perhaps facilitated by carbonyl directing effects and two-point binding of the substrate to the rhodium catalyst. Stereoisomeric substrates, for example, (E)- and (Z)-3, cleanly give rise to diastereomeric products, and thus the rhodium-catalyzed reaction is stereospecific. In addition, simple TADDOL-derived phenyl monophosphite ligands in combination with Rh(nbd)(2)BF(4) afford highly enantioselective catalysts (seven examples, 91-98% ee). These catalysts provide an alternative methodology to prepare Felkin or anti-Felkin acetate-aldol products and related derivatives that are obtainable from the intermediate chiral organoboranes.

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Figures

Figure 1
Figure 1
Selective formation of either Felkin or anti-Felkin acetate-aldol products via stereospecific rhodium-catalyzed asymmetric hydroboration.
Figure 2
Figure 2
Comparing the yield of anti-6 (indicated by squares) and its enantiomeric excess (indicated by circles) over time with (red data) and without (blue data) added norbornene.
See this image and copyright information in PMC

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