Synthesis and thermal decomposition of cis-3,4,5,6-tetrahydropyridazine-3,4-d2. Relative rates of rotation, cleavage, and closure for tetramethylene

The stereospecific syntheses of cis-3,4,5,6-tetrahydropyridazine-3,4-d₂ (6 ) and cis- and trans-cyclobutane-l,2-d₂ are reported. The thermal decomposition of cis-3,4,5,6-tetrahydropyridazine-3,4-d₂ (6 ) (gas phase, 439°C affords 67.1 ± 0.9% cis-ethylene-1,2-d₂, 16.1 ± 0.8% trans-ethylene-1,2-d₂,9.4 ± 0.4% cis-cyclobutane-1,2-dz, and 7.4 f 0.4% trans-cyclobutane-1.2-d₂. The relative rates of rotation, cleavage, and closure for this 1,2-diazene generated tetramethylene-d₂ are k(cleavage)/k(closure) = 2.2 ± 0.2 and k(rotation)/k(closure) = 12 ± 3. An extra stereospecific cleavage component (46%) superimposed on the 1,4-biradical pathway (54%) from the parent tetrahydropyridazine was found, similar to that observed in the 3,4-dimethyl-3,4,5,6-tetrahydropyridazinthe ermal reactions. Finally, the experimental data for the parent 1.4 biradical, tetramethylene, are compared to calculated values in the literature.