Use of boron enolates in water. The first boron enolate-mediated diastereoselective aldol reactions using catalytic boron sources

Highly diastereoselective aldol reactions in water using a catalytic amount of diarylborinic acid have been developed. The reactions proceeded smoothly in the presence of a small amount of an anionic surfactant and a Brønsted acid. Water was the most suitable solvent, and organic solvents such as ether and dichloromethane were ineffective in this system. Use of bis(4-trifluoromethylphenyl)borinic acid gave high catalytic activity. It is most plausible to conclude that the active species of the reactions are boron enolates, and this is the first example of catalytic use of a boron source in boron enolate-mediated diastereoselective aldol reactions.