SHORT COMMUNICATIONSImidazo[1,2-a]pyridine is one of the widely used pharmacophores. Published data contain numerous compounds with imidazo[1,2-а]pyridine fragment possessing different types of bioactivity [1]. The basic and the most investigated method of constructing the bicyclic imidazo[1,2-a]pyridine structure consists in the application of substituted 2-aminopyridines. Various methods of production of one of popular 2-aminopyridines, (2-aminopyridin-4-yl)methanol 1, are described in [2][3][4][5]. However the basic drawback of the known methods is their multistage character and low efficiency. Unlike the methods applied previously, implying the preliminary acylation of 2-amino-4-methylpyridine 2, we developed a method of direct oxidizing the methyl group in compound 1 without preliminary protection of amino group obtaining in one stage 2-aminoisonicotine acid 3, the precursor of alcohol 1. The use of elemental sulfur as an oxidizer [6] made it possible to realize a one-pot synthesis of the methyl ester of 2-aminoisonicotine acid 4, suitable for reduction into the target compound 1 with lithium aluminum hydride (Scheme 1).Overall yield of two stages is more than 49% that more than twice exceeds the yield of the best of described methods [2].Methyl 2-aminoisonicotinate (4). A mixture of 108 g of 2-amino-4-methylpyridine, 110 g of sulfur, and 300 g of DMF was heated at 140-160°С during 20 h, then kept at 10 mmHg. To the residue 250 mL of 30% NaOH was added and the mixture was boiled while stirring for 50 h.
An analytical expression for the elastic interaction energy of radiation point defects of the dipole type with the basal dislocation loop of the hcp metal is obtained using the Green's function method for hexagonal crystals in the Krener approach. It was used for numerical calculation of the bias for the basal dislocation loop of zirconium in a toroidal reservoir. The toroidal geometry of the reservoir allows one to perform the calculation for a loop of any size and without any correction of the elastic field in its region of influence. The dependencies of the loop bias on its radius and nature are obtained for various shapes of dipole defects.
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