Novel Route From Imines To Amines

Researchers have developed a novel synthetic approach for converting imines to amines enantioselectively. The carbon atom of an imine is normally electron-poor and acts as an electrophile, reacting with a carbon nucleophile to form a new carbon-carbon bond in an amine product. In unusual “umpolung” (German for “polarity reversal”) reactions, the carbon atom of the imine is instead made electron-rich so it is able to react as a nucleophile with carbon electrophiles. Such umpolung reactions also form amines but potentially create new opportunities to access otherwise hard-to-get products. Umpolung reactions of imines have been developed only rarely before, and now Li Deng and coworkers at Brandeis University have added to the repertoire (Nature 2015, DOI: 10.1038/nature14617). Chiral phase-transfer catalysts they discovered catalyze asymmetric umpolung reactions of imines with enal electrophiles. Tiny amounts of the catalysts deprotonate imines, forming intermediates that react with enals to form amines stereoselectively and with high yields. Dieter Seebach of ETH Zurich comments that the approach “opens up a useful route to highly enantioenriched, synthetically and structurally useful products.”