Synthesis of 2-(2-Pyridyl)-2-azirines via Metal-Free C-C Cross-Coupling of Bromoazirines with 2-Stannylpyridines.

A high-yield method for the introduction of a 2-pyridyl substituent in the C2 position of the three-membered ring of 2-bromo-2-azirine-2-carboxylic acid derivatives by the direct cross-coupling with 2-(trialkylstannyl)pyridines has been described. The reaction works well with 3-, 4-, or 5-substituted 2-stannylpyridines and can be also employed for the synthesis of 2-(thiazol-2-yl)-2-azirines. According to DFT calculations, the reaction proceeds through the sequence of S2'-substitution of bromine, 1,4-stannyl shift, and [2,3]-sigmatropic shift of the pyridine ring.