title: Stereoselectivity of superacid-catalyzed Pictet-Spengler cyclization reactions.
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.
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakamura
authors.forename: Masaru
authors.initials: M
authors.lastname: Tanaka
authors.forename: Tooru
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Masanobu
authors.initials: M
authors.lastname: Uchiyama
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ohwada