1,5-Asymmetric Induction in Boron-Mediated Aldol Reactions of β-Alkoxy Methylketones

Good levels of substrate-controlled, 1,5-syn-stereoinduction are obtained in boron-mediated aldol reactions of β-trichloromethyl-β-alkoxy and β-trifluoromethyl-β-alkoxy methylketones with achiral aldehydes, independent of the nature of the β-alkoxy protecting group (TBS or PMB). In the case of boron aldol reactions of β-aryl-β-alkoxy methylketones, the 1,5-anti-adducts were obtained with high levels of diastereoselectivity only with a β-OPMB group.