Condensation of acylpyridines with amines. Part II. Pyrido[1,2-a]pyrido[1′,2′:3,4]imidazo[2,1-c]pyrazi-5,8-di-inium salts from pyridine-2-carbaldehyde and aminoacetaldehyde dimethyl acetal

Abstract

The anil formed from pyridine-2-carbaldehyde and aminoacetaldehyde dimethyl acetal is converted by acids, in the absence of appreciable quantities of water, into the monoquaternary salts (III). Treatment of these salts with aqueous acids or with alcoholic perchloric acid gives 6,7-dihydro-6-hydroxypyrido[1,2-a]pyrido[1′,2′:3,4]imidazo[2,1-c]pyrazi-5,8-di-inium salts (IV; R = H) or the corresponding methoxy-compounds (IV; R = Me) respectively. Subsequent dehydration of the hydroxy-diquaternary salts (IV; R = H) with thionyl chloride gives the title compounds (V). Pyridine-2-carbaldehyde condenses with 2-bromoethylamine hydrobromide giving 6,7-dihydropyrido[1,2-a]pyrido[1′,2′:3,4]imidazo[2,1-c]pyrazi-5,8-di-inium dibromide (XI; X = Br).