Three novel isotope-economic synthetic paths to ¹³C₂-labeled heterocycles are proposed. Using calcium carbide-¹³C₂ a number of 4,5-¹³C₂-triazoles, 4,5-¹³C₂-isoxazoles and 3,6-di(pyridin-2-yl)pyridazine-4,5-¹³C₂ were synthesized. New data on ¹H and ¹³C NMR spectra of ¹³C₂-labeled triazoles, isoxazoles and symmetrical pyridazine are described in details.

Comprehensive Summary

¹³C-Carbon is the most available source of carbon-13. It is a relatively inexpensive solid material, which can be easily converted to calcium carbide-¹³C₂. In current work, Ca¹³C₂ was used for in situ generation of ¹³C₂-acetylene in 1,3-dipolar cycloaddition and [4+2] cycloaddition reaction. For the first time, 1H-1,2,3-triazoles-4,5-¹³C₂ and isoxazoles-4,5-¹³C₂ were synthesized using calcium carbide-¹³C₂. A Diels-Alder type cycloaddition of 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine and Ca¹³C₂ was investigated, and the best way for the synthesis of 3,6-di(pyridin-2-yl)pyridazine-4,5-¹³C₂ was proposed for the first time. Here we perform a detailled description of NMR spectra of ¹³C₂-labeled triazoles, isoxazoles and 3,6-di(pyridin-2-yl)pyridazine.