Imidazo pyridine basicity

Fig. 13.2. Illustration of the basic concept of Basis Products, (a) The PGVL reaction scheme of VRXN-2-00051 (formation of the H-imidazo[1,2-a]pyridine ring system using aminoheterocycles and alpha-halo ketones) is used for the illustration (b) The Basis Products of A are formed by all A reactants with one constant reactant (B CAP, 1 -bromopropan-2-one). The Basis products of are formed by all reactants with a constant A reactant (A CAP, 2-amino pyridine). The blue triangle and yellow hexagon represent two such basis products. The red star represents a product molecule which is related to those two corresponding basis products.

Little work has been reported. From studies of proton/deuterium exchange rates, 2-methylpyrrolo[2,l-6]thiazole (478) was estimated to have a pKa of 6.4,394 a value comparable with that of 2-methylindolizine (pKa = 5.9).394 In the same way, the basicity of 3,4-dimethylimidazo-[l,5-a]benzimidazole (468b) (pA = 6.01) resembles that of imidazo-[l,2-a]pyridines (pA = 5.05-5.96).398 It would seem, therefore, that the basicity of azapentalenes parallels that of related indolizine derivatives [Eq. (40)]. 

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