One-step synthesis of pyridines and dihydropyridines in a continuous flow microwave reactor

Abstract

The Bohlmann–Rahtz pyridine synthesis and the Hantzsch dihydropyridine synthesis can be carried out in a microwave flow reactor or using a conductive heating flow platform for the continuous processing of material. In the Bohlmann–Rahtz reaction, the use of a Brønsted acid catalyst allows Michael addition and cyclodehydration to be carried out in a single step without isolation of intermediates to give the corresponding trisubstituted pyridine as a single regioisomer in good yield. Furthermore, 3-substituted propargyl aldehydes undergo Hantzsch dihydropyridine synthesis in preference to Bohlmann–Rahtz reaction in a very high yielding process that is readily transferred to continuous flow processing.

Keywords

• Bohlmann–Rahtz
• continuous flow processing
• ethynyl ketones
• flow chemistry
• Hantzsch dihydropyridine synthesis
• heterocycles
• microwave synthesis
• multicomponent reactions
• pyridine synthesis