The formation of the pyridine ring in the synthesis of dipyrido-[3′,2′:4,5]thieno[3,2-b: 3,2-d]pyridines

Abstract

While continuing our investigations into the reactivity of substituted 3-aminothieno[2,3-b]pyridines [1, 2], we found a new reaction leading to closure of the pyridine ring during the formation of a pentacyclic heteroaromatic 22π-electronic system dipyridothienopyridine.During an attempt to reduce the carbonyl group of compounds 1a-d with sodium borohydride in ethanol the corresponding dipyrido[3',2':4,5]thieno[3,2-b:3,2-d]pyridines 3a-d were isolated from the reaction mixture instead of the expected amino alcohols 2. The mechanism of the transformations that occur is not quite clear and will be the subject of further investigations. N S Me NH 2 R O MeO NaBH 4 N S Me N S N Me R MeO OMe N S Me NH 2 R OH MeO 2 1a-d 3a-d 1, 3 a R = Ph; b R = C 6 H 4 Br-4; c R = C 6 H 3 Cl 2 -2,4; d R = MeThe 1 H NMR spectra were recorded in trifluoroacetic acid (compounds 3a-c) and DMSO-d 6 (compound 3d) on a Bruker DRX-500 instrument (500 MHz).Synthesis (General Procedure). Compound 1 (0.005 mol) was dissolved by heating in ethanol (20 ml), and sodium borohydride (7.5 mmol) was added while the reaction mixture was stirred. The obtained solution was boiled for 3 h, cooled, and neutralized with a 10% solution of hydrochloric acid. The flocculent precipitate was separated and washed with boiling DMF, water, and ethanol. The products were recrystallized from ethanol. __________________________________________________________________________________________

Phenylfurylthieno[2,3-b]pyridyl-methanes. synthesis and reactions of the furan ring transformation

“…We showed in [14] that the direct conversion of amino ketones 1 into the corresponding alcohols by the action of NaBH 4 was not possible. In their place derivatives of 6-phenyl-7,12-dithia-1,5,8-triazaindeno[1,2-a]fluorene were formed, products of intermolecular dimerization accompanied by the elimination of benzonitrile.…”