Amide-directed catalytic asymmetric hydroboration of trisubstituted alkenes.
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.
Smith
Sean M
SM
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0304, USA.
Takacs
James M
JM
D000475:Alkenes / Q000737:chemistry*; D000577:Amides / Q000737:chemistry*; D001895:Boron / Q000737:chemistry*; D002384:Catalysis; D013237:Stereoisomerism
D000475:Alkenes; D000577:Amides; D001895:Boron