C- Alkylation directed

Note Pyrazine may be C-alkylated directly, e.g., by alkyl radicals also by addition to give an alkylated hydropyrazine, sometimes amenable to subsequent... 

Under the conditions of most alkylation reactions, the products of O- and C-alkylation are usually not interconvertible, so it is not valid to predict C-alkylation directly on the basis of thermodynamic considerations. But, the transition state B and D resemble the products C and E, respectively, to a significant extent. It is therefore expected that the transition state for C-alkylation will be lower in energy, anticipating to some extent the greater stability of the product. This is depicted in Figure 1.2. The competition between O- and C-alkylation will then depend upon the interplay among (1) solvation effects, (2) nucleophilicity of the C and O ends of the enolate ion, and (3) transition-state structure. 

C-alkylation, directed condensation, -cycloaddition, direction of -functionalization, — halogenation, directed nitration, direction of -ring opening, —... 

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See also in sourсe #XX -- [ ]

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