Isomerization and Aromatization of the 1,3-Di-tert-butylcyclohexadienes in Strongly Basic Media

Article abstract of DOI:10.1021/jo00383a009

The five isomeric 1,3-di-tert-butylcyclohexadienes are equilibrated in t-BuOK/Me2SO at 30-55 deg C.In lithium ethylamide in ethylamine at 0 deg C, equilibration is accomplished within the set of three dienes which possess a tertiary hydrogen or between the other two dienes; however, one set is not transformed to the other.Aromatization accompanies the equilibration of the set of three but not the set of two.With a large excess of KAPA, the diene is transformed rapidly to the salt which aromatizes.With an excess of diene, the interconversion of all of the dienes accompanies aromatization (intraset isomerization being faster than interset interchange).In KAPA at 0 deg C, the introduction of dicyclohexyl-18-crown-6 inhibits aromatization; however, after a time reaction slows although the basicity of the solution remains strong enough to abstract a proton from a tertiary carbon.The effect of the base system upon the competitive reactions of cyclohexadienyl carbanions is understood in terms of the differing interactions of the carbanionic salts with the medium.