Reactions of 4,4-Diphenylcarbena-2,5-cyclohexadiene and Related Systems in Dimethyl Sulfoxide

Article abstract of DOI:10.1021/jo00265a014

Thermal decomposition of the lithium salt of the tosylhydrazone of 4,4-diphenyl-2,5-cyclohexadienone (10) in dimethyl sulfoxide produces 4,4-diphenyl-2,5-cyclohexadienone, p-benzylbiphenyl, 3,4-diphenyltoluene, 6,6-diphenyl-1-methylene-2,4-cyclohexadiene, and o-terphenyl, while similar treatment of the lithium salt of the tosylhydrazone of 4,4-diphenylcyclohexenone (26) generates 4,4-diphenylcyclohexenone, 5,5-diphenyl-1,3-cyclohexadiene, 4,4-diphenyl-1-methylene-2-cyclohexene, and 6,6-diphenyl-1-methylene-2-cyclohexene.Thermolysis of the lithium salt of the tosylhydrazone of 4,4-diphenylcyclohexanone (32) in dimethyl sulfoxide yields 4,4-diphenylcyclohexene, 4,4-diphenylcyclohexanone, and 4,4-diphenyl-1-methylcyclohexanol.The kinetics of the thermal decomposition of tosylhydrazone lithium salts 10, 26, and 32 in dimethyl sulfoxide in the temperature range 90-125 deg C were analyzed by evaluating the rate constants for the two consecutive first-order steps.The second step, for parent salts 10, 26, and 32, decomposition of diazo compound to carbene, exhibited values for k₂ (110 deg C) of 8.22, 197, and 363 h^-1, ΔG(activ)s of 27.2 +/- 3.1, 24.8 +/- 3.1, 24.2 +/- 0.9 kcal mol^-1, and Δ(activ)s of -10.7 +/- 5.7, -6.3 +/- 5.8, and -8.1 +/- 1.7 eu.The activation parameters for decomposition of the diazo compounds are interpreted in terms of an increasing dipole moment in the transition state relative to ground state.Product formation from carbene intermediate is viewed in terms of a competition of a singlet oxygen abstraction reaction with intersystem crossing to triplet.