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ABSTRACT: [reaction: see text] High stereoselectivities were found in a wide range of superacid-catalyzed Pictet-Spengler cyclization reactions. Particularly in the cases of 2-alkyl-N-benzylidene-2-phenethylamines, an enhanced stereoselectivity was observed under the superacid conditions as compared with the corresponding weak acid (TFA)-catalyzed (monocationic) cyclization reaction of the N-benzylidene-2-(3',4'-dimethoxy)phenethylamines that bear electron-donating groups on the cyclizing aromatic ring. The computational study also supported the energetic favorability of the cyclization of the N,N-diprotonated imine and revealed a significantly early transition-state structure.
Organic Letters 07/2003; 5(12):2087-90. DOI:10.1021/ol034526a · 6.36 Impact Factor