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In addition to (V-acyUminium ions, the protioiminium ions (X19) could be activi-ated in a similar anion-binding mechanism (Scheme 2.79). The same group then developed chiral thiourea (289a)-catalyzed two-component Pictet-Spengler reaction of tryptamines 21 and aldehydes under mild conditions. Benzoic acid used as the cocatalyst provided the products desired, with excellent results [110a]. Later, Lee... [Pg.100]

SCHEME 2.79 Chiral thiourea-catalyzed Pictet-Spengler reaction with protioiminium ions... [Pg.101]