Conjugate addition reactions chiral Bronsted bases

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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