ABSTRACT
The electron-rich and conformationally rigid (R,S,R,S)-Me-PennPhos ligand (shown schematically) appears to chelate rhodium and form well-defined chiral pockets. This allows, for example, efficient differentiation between the two enantiotopic approaches available to a substrate in a hydrogenation reaction. The Rh-Me-PennPhos complex is the first catalyst for the highly enantioselective asymmetric hydrogenation of cyclic enol acetates. For example, 3,4-dihydronaphth-1-yl acetate can be hydrogenated with up to 99% ee.
ABSTRACT
Even alkyl methyl ketones undergo asymmetric hydrogenation with high enantioselectivity when a rhodium complex of the conformationally rigid chiral ligand 1 (Me-PennPhos; R=CH3 ) is used as the catalyst. Basic additives such as 2,6-lutidine contribute to the achievement of high enantiomeric excesses.
