Stereoselective Z -enolate formation of esters and its application in diastereoselective aldol addition reactions as reported in J. Am. Chem. Soc. (1989) 111 , 3441–3442

Boron compounds such as 9-chloro-9-borabicyclo[3.3.1]nonane ( B –Cl–9–BBN) and sterically hindered amine bases such as diisopropylethylamine ( i -PrEtN) almost quantitatively give Z -boron enolates, which in turn lead to the syn -Aldol as main product.