1,4-Diphenyl-1,4-butadiyl Diradicals from Thermolysis of cis- and trans-3,6-Diphenyl-3,4,5,6-tetrahydropyridazine

Abstract

Reduction of 3,6-diphenyl-2,3,4,5-tetrahydropyridazine with sodium amalgam in ethylene glycol at 130° produces a 1:2 mixture of cis- and trans-3,6-diphenylpiperidazine (cis- and trans-4) from which trans-4 was obtained by fractional crystallization. Oxidation of cis- and trans-4 with oxygen gave cis- and trans-3,6-diphenyl-3,4,5,6-tetrahydropyridazine (cis- and trans-1). For thermolysis of trans-1 at 62.5° Ea = 25.3 ± 1.1 kcal/mol and ΔS≠ = 0.4 ± 3 e.u. At 63° the relative yields of styrene, cis- and trans-1,2-diphenylcyclobutane (cis- and trans-7) formed from cis-1 are 55.3, 30.1, and 18.6% and those formed from trans-1 are 59.1, 1.7, and 39.2%, respectively. For the 1,4-diphenyl-1,4-butadiyl diradical from thermolysis of cis-1kcleav/krot = 1.1 and kcyc/krot, = 1.5 whereas for that of trans-1kcleav/krot = 10 and kcyc/krot = 14. At 205° cis-7 decomposes to yield a 4.8:1 ratio of styrene: trans-7. This is near the ratio expected if the initial geometries of the diradicals produced from cis-1 and cis-7 are similar.