Chiral - and -symmetric BINOL-derived bis(phosphoric acid) catalysts, which have OP([double bond, length as m-dash]O)(OH)/OP([double bond, length as m-dash]O)(OH)(OR) moieties at the 2,2'-positions, were developed and used for the enantioselective aza-Friedel-Crafts reaction of 2-methoxyfuran with α-ketimino esters for the first time. The intramolecular conjugated double hydrogen bond network is a key to increasing the Brønsted acidity and preventing deactivation of the catalysts. Highly functionalized α-amino acid derivatives with a chiral quaternary carbon center could be transformed into versatile optically active - and -heterocycles and an α-aryl-substituted serine.
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| http://dx.doi.org/10.1039/c8sc02290a | DOI Listing |
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