Hydrides imines, chemoselectivity

A convenient new one-pot procedure for the selective reduction of ketones in the presence of aldehydes (the less usual chemoselectivity) is outlined in Scheme 9. ° The aldehyde is protected as an imine and the ketone is then reduced in situ with a hindred hydride reagent the aldehyde is regenerated on hydrolytic work-up. Conjugated and aromatic aldehydes are protected satisfactorily by this sequence, and moderate discrimination between aliphatic and aromatic aldehydes, with preferential reduction of the aromatic aldehyde, can also be achieved. These authors claim better selectivity than previous methods based on ketalization or hydration of aldehydes with lanthanoid cation catalysts (4,141). 

Chemoselective hydrogenation of aldehydes, ketones, and imines is achieved employing catalytic amounts of an iron complex containing both an acidic and a hydridic hydrogen atom (Scheme 4-325). This iron complex was synthesized first by Kndlker et Isolated C=C double bonds, C triple bonds, C-X, -NO2, epoxide, and ester functions are tolerated under those conditions. The same iron complex also catalyzes the transfer hydrogenations of acetophenone with isopropanol. ... 

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