Divergent Synthesis of Pyrazolo[1,5-<i>a</i>]pyridines and Imidazo[1,5-<i>a</i>]pyridines via Reagent-Controlled Cleavage of the C–N or C–C Azirine Bond in 2-Pyridylazirines
Anastasiya V. Agafonova, Artem A. Golubev, Ilia A. Smetanin, Alexander F. Khlebnikov, Dar’ya V. Spiridonova, Михаил С. Новиков
Abstract
The three-membered ring in 2-(2-pyridyl)azirine-2-carboxylic esters and thioesters can undergo selective cleavage of either the N–C2 bond under copper(II) catalysis or the C–C bond under the action of HCl to provide isomeric azirine ring expansion products of pyrazolo[1,5- a ]pyridine or imidazo[1,5- a ]pyridine series, respectively. Mild catalytic reaction conditions for the formation of pyrazolopyridines make it possible to obtain them directly from 4-bromoisoxazoles by a one-pot, three-stage procedure without isolating the intermediate 2-bromoazirines and 2-(2-pyridyl)azirines.
Topics & Concepts
AzirineChemistryReagentPyridineCleavage (geology)Ring (chemistry)CatalysisBond cleavageMedicinal chemistryStereochemistryOrganic chemistryEngineeringFracture (geology)Geotechnical engineeringSynthesis and Catalytic ReactionsCatalytic C–H Functionalization MethodsPhenothiazines and Benzothiazines Synthesis and Activities