Studies on the enantioselective addition of enol silyl ethers to imines catalyzed by optically active
palladium diaquo complexes 3 or binuclear palladium μ-hydroxo complex 4 are described, with particular
focus on the mechanistic aspects. Asymmetric induction in the reaction using [Pd((R)-binap)(H2O)2]2+(BF4
-)2
(3a) was quite sensitive to the reaction conditions, suggesting unfavorable effects of HBF4 generated from 3a
in situ. Novel optically active binuclear μ-hydroxo complexes [{Pd((R)-binap)(μ-OH)}2]2+(BF4
-)2 (4a), [{Pd((R)-tol-binap)(μ-OH)}2]2+(BF4
-)2 (4b), [{Pd((R)-binap)(μ-OH)}2]2+(TfO-)2 (4c), and [{Pd((R)-tol-binap)(μ-OH)}2]2+(TfO-)2 (4d) were prepared and were found to be better catalysts for the asymmetric Mannich-type
reaction. Benzoylalanine derivatives 5 were obtained in excellent chemical and optical yields (up to 90% ee).
Mechanistic studies using 1H NMR and electrospray ionization mass spectrometry indicated that a unique
binuclear palladium-sandwiched enolate 12 was involved in the reaction of enol silyl ether 1 with imine 2
catalyzed by 4.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.