EXPERIMENTAL-DETERMINATION OF THE RELATIVE RATES OF ROTATION, CLEAVAGE, CLOSURE, AND 1,5-HYDROGEN SHIFT FOR 3-METHYL-1,4-PENTANEDIYL - EVIDENCE FOR 1,4 BIRADICALS AS COMMON INTERMEDIATES FROM DIFFERENT PRECURSORS, 3,4 AND 3,6-)DIMETHYL-3,4,5,6-TETRAHYDROPYRIDAZINES AND 1,2-DIMETHYLCYCLOBUTANES

Thermal decomposition of cis- and trans-3, 6-dimethyl-3, 4, 5, 6-tetrahydropyridazine (11 and 12, respectively) affords propene, cis- and trans-1, 2-dimethylcyclobutanes, and 1-hexene. The stereochemistry of the products is consistent witha 1, 4-biradical intermediate(s) 2, 5-hexanediyl, which has the properties κ(rotation) ~ κ(cleavage) ~ κ(closure). At 439 °Cthe retention/inversion (r/i) ratios for the 1, 2-dimethylcyclobutane products are 1.7 and 1.7 from 11 and 12, respectively. At306 °C, these ratios are 1.9 and 2.2, respectively. The results indicate that when the thermal reactions of cyclic azo compoundsand cyclobutanes of similar substitution are compared at similar temperatures, the stereospecificities are similar. We concludethat stereoretention is dependent on both substitution and temperature, i.e., stereospecificity increases as substitution at theradical center increases and as the temperature is lowered. The thermal decomposition of cis- and trans-3, 4-dimethyl-3, 4, 5!tetrahydropyridazine (19 and 20, respectively) allows a dissection of direct vs. 1, 4-biradical pathways in six-membered cyrazo decompositions, e.g., 36% direct/64% 1, 4 biradical from cis-19 and 32% direct/68% 1, 4 biradical from trans-20. Thetive rates of rotation, cleavage, and closure for azo-generated 1, 4 biradicals, 3-methyl-l, 4-pentanediyl (8T and 8C), wdetermined. For 8T, κ (cleavage)/κ(closure) = 1.6 and κ (closure) κ (rotation) = 1.9. For 8C, κ (cleavage))κ (closure) = 1.8 andk(closure)/κ(rotation) = 0.7. These relative rates of rotation, cleavage, and closure generate similar trans-/cis-2-butene ratiosas found in the pyrolyses of cis- and trans-1, 2-dimethylcyclobutanes at the same temperature and phase. We conclude theypass the stereochemical test for identity, indicating evidence for common 1, 4-biradical intermediates from two different pre-cursors (1, 2-diazenes and cyclobutanes). Finally, the data are compared with the recent literature values reported for the dimerization of ethylene and 2-butenes. © 1979, American Chemical Society. All rights reserved.