Enantioselective catalysis of the Henry reaction by a chiral macrocyclic ytterbium complex in aqueous media

A chiral macrocyclic ytterbium cationic complex catalyses the nitro-aldol reaction between alpha-ketocarboxylates and nitromethane under ambient aqueous conditions, leading to the formation of for example, methyl-2-hydroxy-2-methyl-3-nitropropanoate in 96% yield and 59% enantiomeric purity. Monitoring of the paramagnetically shifted intermediate Yb species by (1)H NMR allows several different species on the catalytic cycle to be identified and is consistent with the intermediacy of stereoisomeric chelated pyruvates of differing reactivity towards the nucleophile, as well as product inhibition of turnover.