Asymmetric aldol reaction using boron enolates.


The protocol for the prepn. of boron enolate and its subsequent reaction with aldehyde is described, providing convenient access to β-hydroxy ketone I in good yields and with high stereoselectivities. The reaction consists of three steps: first, the ketone is rapidly converted to the corresponding boron enolate II, by exposure to a chlorodialkylborane and tertiary amine base, which is then reacted in situ with the aldehyde. Finally, oxidative workup of the resultant boron aldolate provides aldol adduct. The reaction procedure requires approx. 28 h to complete over a 2-day period, consisting of 5 h to set up the reaction, whereupon the reaction mixt. is left at -20 °C overnight (16 h), followed by 7 h for workup and purifn.

Nature Protocols