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Boron-mediated aldol reaction of carboxylic esters.

This Account outlines the unique features of the boron-mediated aldol reaction of carboxylic esters, which include (i) facile isomerization of E-enolate to Z-enolate and (ii) formation of a doubly borylated enolate upon enolization of acetate esters. The first carbon-bound boron enolates were spectroscopically characterized, and they appeared to be responsible for these unique properties. Furthermore, complementary anti- and syn-selective boron-mediated asymmetric aldol reactions of chiral propionate esters have been developed. A novel double aldol reaction of acetate esters has been discovered, and a plausible mechanism of the double aldol reaction is proposed.