Enantioselective Lewis Acid-Catalyzed Mukaiyama−Michael Reactions of Acyclic Enones. Catalysis by <i>a</i><i>llo</i>-Threonine-Derived Oxazaborolidinones
Mukaiyama-Michael reaction of acyclicenones with a trimethylsilyl ketene S,O-acetal in high enantioselectivity. A range of alkenyl methyl ketones is successfully employed as Michael acceptors affording ee values of 85-90% by using 10 mol % of the catalyst. The use of 2,6-diisopropylphenol and tert-butyl methyl ether as additives is found to be essential to achieve high enantioselectivity in these reactions.