Metalation of a-picoline by phenyl

Metalation of a-picoline by phenyl lithium, 23, 84 Metal bath, 20, 48... 

The reactivity of the 1-methyl group and of corresponding positions (i.e., a-carbon atoms) in other l-alkyl-j8-carbolines, analogous to that in a-picoline, quinaldine, and isoquinaldine, is due to the acidity of this center. Deprotonation yields a resonance-stabilized anion (288) which reacts readily with electrophilic reagents. Metallation with phenyl-lithium of the 1-methyl group of a l-methyl-j8-carboline derivative in which the indole nitrogen is protected, first described by Woodward... 

While the analysis of intermediates and/or products in the preceding examples unambiguously demonstrates the participation of zinc-coordinated nucleophiles in the chemical transformation, it generally is not possible to demonstrate unequivocally that the activation of a coordinated water molecule assumes the same mechanistic significance in metal ion-catalyzed hydrolytic reactions. This happenstance, as pointed out by Breslow et al. 19), is due (a) to the extremely labile nature of most aquo complexes, (b) to the invariance of water concentration in aqueous milieu, and (c) to the mechanistic ambiguity arising from the kinetic equivalance of the two mechanisms, A and B, illustrated below (here p-nitro-phenyl picolinate is used as the hypothetical example). 

---