Furopyridines. I. Synthesis of furo[2,3-c]pyridine

The parent framework of furo2,3-c]pyridine has been synthesized. 3-Furoic acid chloride ( 2 ) was reduced with bis(triphenylphosphine) copper(1) tetrahydroborate to afford 3-furaldehyde ( 3 ) which was condensed with malonic acid to give β-(3-furyl)acrylic acid ( 4 ). The acrylic acid 4 was converted to the acid azide ( 5 ), which in turn was cyclized to give furo2,3-c]pyridin-7(6H)-one ( 6 ) by heating at 180° in diphenylmethane. The pyridone 6 was chlorinated with phosphorus oxychloride, followed by reduction with zinc and acetic acid to give furo2,3-c]pyridine ( 8 ).