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

Organocatalysis with a fluorous tag: Asymmetric reduction of imines with trichlorosilane catalyzed by amino acid-derived formamides

Asymmetric reduction of ketimines 1 with trichlorosilane can be catalyzed by N-methylvaline-derived Lewis-basic formamides 3a−d with high enantioselectivity (≤95% ee) and low catalyst loading (1−5 mol %) at room temperature in toluene. Appending a fluorous tag, as in 5a−c, simplifies the isolation procedure, while preserving high enantioselectivity (≤92% ee)

Dendron-anchored organocatalysts: the asymmetric reduction of imines with trichlorosilane, catalysed by an amino acid-derived formamide appended to a dendron

Asymmetric reduction of ketimines 1a-f with trichlorosilane can be catalysed by the Lewis-basic N-methylvaline-derived formamide anchored to a soluble dendron (11c) with good enantioselectivity (<= 94% ee) and low catalyst loading (typically 5 mol%) at room temperature in toluene. This protocol represents an improvement and simplification of the isolation procedure and recovery of the catalyst