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Phosphoric Acid Catalyzed Friedel-Crafts Reaction of Indoles with Imines
Q. Kang, Z.-A. Zhao, S.-L. You*
Shanghai Institute of Organic Chemistry, P. R. of China
24 April 2007 (online)
Here the authors report a chiral phosphoric acid catalyzed enantioselective Friedel-Crafts reaction of indoles with N-sulfonyl aldimines. After screening different 3,3′-substituents on the binol motif, 1-naphthyl-substituted catalyst 1 has been found to be highly effective for this reaction. With 20 mol% of catalyst 1, good to high yields (83-90%) and high enantioselectivities (er = 91:9 to >99:1) were obtained for different aromatic aldimines. A non-aromatic cyclohexyl aldimine has also been used; however, lower yield (56%) and lower enantioselectivity (er = 79:21) were obtained.