A novel synthetic approach to 2,3,6-trisubstituted pyridines, their 4,5-dideuterated derivatives, 4,5-13C2- and doubly-labeled D2‑13C2-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-13C2 in the mixture with water or deuterium oxide was applied as 13C2-acetylene and D2-13C2-acetylene source.