Process development of potassium channel opener, TCV-295, based on convenient ring formation of 2H-1,3-benzoxazine and selective N-oxidation of the pyridyl moiety

An efficient process for potassium channel opener, TCV-295, based on a novel and convenient 4-(2-pyridyl)-2H-1,3-benzoxazine ring formation from o-hydroxybenzoylpyridine by the NH4I/piperidine/2,2-dimethoxypropane system and the following selective pyridine-N-oxidation using dimethyldioxirane, has been developed. Additionally, the combination reagent of ammonium halide and sec- or tert- amine conveniently converted o-hydroxyphenyl arylketones with several ketones (or benzaldehyde) to various novel 4-aryl-2H-1,3-benzoxazines.