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A novel synthetic approach to 2,3,6-trisubstituted pyridines, their 4,5-dideuterated derivatives, 4,5- 13 C 2 - and doubly-labeled D 2 - 13 C 2 -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 C 2 in the mixture with water or deuterium oxide was applied as 13 C 2 -acetylene and D 2 - 13 C 2 -acetylene source., (© 2023 Wiley-VCH GmbH.)