1,2,4‐Triazines and Calcium Carbide in the Catalyst‐Free Synthesis of 2,3,6‐Trisubstituted Pyridines and Their D‐, 13C‐, and Doubly D2‐13C2‐Labeled Analogues

A novel synthetic approach to 2,3,6-trisubstituted pyridines, their 4,5-dideuterated derivatives, 4,5-13 C2 - and doubly-labeled D2 -13 C2 -pyridines has been developed using catalyst-free [4+2] cycloaddition of 1,2,4-triazines and in situ generated acetylene or labeled acetylene. Calcium carbide and water or deuterium oxide were used for the in situ generation of acetylene and dideuteroacetylene. Calcium carbide-13 C2 in the mixture with water or deuterium oxide was applied as 13 C2 -acetylene and D2 -13 C2 -acetylene source.