Iminium ions imine conjugate bases

Hydride shifts are more difficult to ascertain. This process gives a iV-protonated iminium ion, which is the conjugate acid of an imine. The latter could also result when proton transfer occurs from the alkylnitrenium ion to a base. Chiapperino and... 

Other pertinent mechanistic evidence is provided as well. The authors report no observation of any intermediates. A control experiment showed that the iminium ion derived by C-protonation of 27 (Ar = Ph, L = H) and/or its conjugate base imine would,... 

The greater scope of this reaction was attributed to the dual cyclic Bronsted acid/H-Bond donar cocatalysis mechanism. The catalytic cycle initially involves imine protonation by the chiral thiourea catalyst 170 associated via H-bonding to the conjugate base (X ) of a weak Bronsted acid (H-X, benzoic acid in this case) additive. Intramolecular cyclization of the protonated iminium ion 146, followed by rearomatization regenerates the Bronsted acid cocatlayst (benzoic acid). Note for brevity, the plausible rearrangement (RR) step of the inital CCij-spiroalkylated adduct to the final tetrahydrohydroisoquinoline scaffold 147 is not shown. 

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