Enantioselective synthesis of ( S)-α-methylphenylalanine using ( S)-BINOLAMs as new phase-transfer catalysts

Abstract

A series of ( S)-bis(aminomethyl)binaphthols [( S)-BINOLAMs] 4 have been prepared and used as catalysts in the enantioselective C-alkylation reaction of the aldimine Schiff bases of alanine esters 5 under solid–liquid phase-transfer catalysis (PTC) conditions employing NaOH as base in toluene at room temperature. ( S)-3,3′-Bis[(diethylamino)methyl]-2,2′-dihydroxy-1,1′-binaphthalene 4a gave the best e.e.s. ( S)-α-Methylphenylalanine 7 was isolated, after hydrolysis of the iminoester, in 85% yield with an e.e. of 68%.