Synthesis of new recoverable catalysts and their application in asymmetric reduction of ketimines with trichlrosilane

Obtaining chiral amines from ketones via imine intermediates represents an attractive strategy that opens a straightforward route to valuable building blocks for the pharmaceutical and other fine chemicals industries. Metal-free oranocatalysis can be viewed as an attractive and broadly applicable methodology in which the metal is not vital for the key bond-forming event. Previously developed in our laboratory, N-methylvaline-derived formamides IIIa,b proved to be efficient catalysts for asymmetric reduction of prochiral ketimines with trichlorosilane, (up to 98%, 95% ee).136,137 Tagging the catalyst to a fluorous ponytail IIIc, soluble and insoluble polymers IIId, or gold nanoparticles IIIe simplified the isolation procedure, while preserving high activities and stereoselectivities (up to 98%, 91% ee). The recovered catalysts could be reused at least 5 times without the loss of activity or stereoselectivity. This technology appears to be particularly suited to the small-scale parallel chemistry.