Asymmetric catalysis. Part 153: Metal-catalysed enantioselective α-ketol rearrangement

Abstract

Promoted by catalytic amounts of Ni complexes tertiary α-hydroxyketones 1a, 3a–5a undergo rearrangement, forming chiral isomers 1b, 3b–5b. The best enantioselection was obtained with the model system 1-benzoylcyclopentanol 4a/2-hydroxy-2-phenylcyclohexanone 4b. In a ligand screening 2-[4-(S)-tert-butyloxazolin-2-yl]pyridine gave the highest enantiomeric excess of 46% (S)-4b. The analogous isomerisation reactions of α-hydroxyimines 6a, 7a forming chiral α-aminoketones 6b, 7b were established.