Potential antiallergics - Part 3: Synthesis and transformations of 1,4-dihydro-4-oxo-[1]benzothieno [3,2-b]pyridine-2-carboxylic acid esters

The title compounds 2a, b are obtained by reaction of potassium 3-aminobenz o[b]thiophene-2-carboxylate (1) with acetylenedicarboxylic acid esters in a cetic acid. The substance 2a gives the carboxylic acid 2c by saponification , reaction with phosphoryl chloride affords the 4-chloropyridine 3. The car binol 4, received by boranate reduction, was dehydrogenated with activated manganese dioxide to yield the carbaldehyde 5. Compound 2a reacts with meth yliodide to give a separable mixture of the O- and N-alkylated products 6a and 7a, while by reaction of 2b with ethyliodide only the 4-ethoxypyridine 6b is formed. The carboxylic acids 6c, 7b are obtained by alkaline hydrolys is of the esters 6a, 7a. The carbinols 8, 9, formed by reduction of the est ers 6a, 7a, are oxidized to give the carbaldehydes 10, 11. The 1H-tetrazole s 17, 18 are synthesized from the aldehydes 10, 11 via the aldoximes 13, 14 and the nitriles 15, 16. The aldehydes 10, 11 react with the beta-aminocro tonic acid esters 19 in acetic acid to yield the 1,4-dihydropyridines (DHP) 20, 21, which are dehydrogenated to form the pyridines (Py) 22, 23. The ha lf-wave potentials E-1/2 Of the redox system DHP/Py is determinated by diff erence pulse voltammetry using nifedipine as reference substance.