Oxygenation of 2,6-di-t-butylphenols with superoxo Co(III) complexes

Superoxo Co(III) complexes, [Co(CN)₅O₂][X]₃ where X = Et₃N⁺ and (Ph₃P)₂N⁺, mediate the dioxygen incorporation into 2,6-di-$\text{t}$-butylphenols ($\text{1}$) with the same regioselectivity as that in the base-catalyzed oxygenation of $\text{1}$. The superoxo species acts as a base but is not incorporated into the substrate.     

Mechanism of selective p-quinol formation in the cobalt schiff base complex-catalyzed oxygenation of 4-alkyl-2,6-di-t-butylphenols

The selective formation of $\text{p}$-quinols in the Co(Salpr)-catalyzed oxygenation of 4-alkyl-2,6-di-$\text{t}$-butylphenols in MeOH has been found to involve the rate determining reduction of peroxy-$\text{p}$-quinolato Co(III) complex formed in the initial fast step. An ionic mechanism of the reduction of the OO bond in the peroxy complex by MeOH has been discussed based on kinetic studies. The reactive species in the catalytic cycle is found to be [Co(III)(Salpr)(OH)].     

Oxygenation of 4-(N-alkylimino)methyl-2,6-di-t-butylphenols mediated by Co(II)-Schiff base complex

4-(N-Alkylimino)methyl-2,6-di-$\text{t}$-butylphenols ($\text{1}$), Schiff bases of 3,5-di-$\text{t}$-butyl-4-hydroxybenzaldehyde can be oxygenated in the presence of Co(Salpr), a five coordinate Co(II)-Schiff base complex to give N-alkyl-3-$\text{t}$-butyl-5-formyl-2-hydroxy-2-pivaloyl-1,2-dihydropyridines ($\text{2}$ as the main product together with 3-formyl-2,5-di-$\text{t}$-butyl-2,4-cyclopentadienone ($\text{3}$) and 2,6-di-$\text{t}$-butyl-4-formyl-6-hydroxy-4,5-epoxy-2-cyclohexenone ($\text{4}$). These products result from dioxygen incorporation into the ortho position of $\text{1}$.     

Oxygenation of 2,6-di-t-butylphenols bearing electron-withdrawing group at 4-position mediated by Co(II)-schiff base complex

4-Acyl-2,6-di-$\text{t}$-butylphenols except 3,5-di-$\text{t}$-butyl-4-hydroxybenzaldehyde were oxygenated in the presence of Co(Salpr) exclusively at the ortho position to give the corresponding 3,5-di-$\text{t}$-butyl-6-hydroperoxy-2,4-cyclohexadienone derivatives in quantitative yield.     

Selective formation of peroxy-p-quinolato Co(III) complexes in the oxygenation of 4-alkyl-2,6-di-t-butylphenols with Co(II)-Schiff's base complexes

The oxygenation of 4-alkyl-2,6-di-$\text{t}$-butylphenols ($\text{2}$) with Co(II)-Schiff's base complexes in aprotic solvents such as CH₂Cl₂, THF, Py, and DMF leads to highly selective formation of the corresponding peroxy-$\text{p}$-quinolato Co(III) complexes. The reaction proceeds by mechanism involving a rate determining hydrogen abstraction by superoxo Co(III) species from $\text{2}$ giving phenoxy radical, rapid step of electron transfer from Co(II) complex to the phenoxy radical, and dioxygen incorporation into phenolato Co(III) complex thus formed.     

Acylation of 4-substituted 6-hydroperoxy-2,6-di-t-butyl-2,4-cyclohexadienones

Acylation of 4-aryl-2,6-di-$\text{t}$-butyl- and 2,4,6-tri-$\text{t}$-butyl- 6-hydroperoxy-2,4-cyclohexadienones gave unexpected products, 4-acyloxy-5,6-epoxy-2-cyclohexenones and 2-acyloxy-5,6-epoxy-3-cyclohexenones. The reaction involves a rapid homolysis of the peroxy bond of peroxy esters transiently formed in the pre-existing slow step.     

Reaction of superoxo Co(III) complexes with 2,6-di-t-butyl-p-benzoquinone methides

Superoxo Co(III) complexes derived from Co(Salpr) and [Co(CN)₅]^3? reacted with 2,6-di-$\text{t}$-butyl-$\text{p}$-benzoquinone methides to give 2,6-di-$\text{t}$-butyl-$\text{p}$-benzoquinone and 2,6-di-$\text{t}$-butyl-2,5-cyclohexadienonespirooxiranes as the main products, which are considered to result from nucleophilic attack by the superoxo species on the exo double bond of the quinone methides.     

Conformation,in solution,of c-4-t-butyl-1-phenyl-r-1-(N-piperidyl)cyclohexane hydrochloride. The conformational energy of t-butyl

Although the hydrochloride of $\text{c}$-4-$\text{t}$-butyl-1-phenyl-$\text{c}$-1-(N-piperidyl)cyclohexane crystallizes in the conformation with axial $\text{t}$-butyl, it exists as an almost equimolar mixture of the two chair conformers in CD₂ Cl₂ solution. The position of equilibrium allows one to calculate ΔG°_{$\text{t}$-Bu} as ?4.9 kcal/mol.     

Synthesis of di-t-alkylamines

Di-$\text{t}$-alkylamines can be synthesized efficiently by a three-step process: (1) oxidation of a $\text{t}$-alkylamine to a $\text{t}$-alkylnitroso compound with peracetic acid in ethyl acetate (2) conversion of the $\text{t}$-alkylnitroso compound to a tri-$\text{t}$-alkylhydroxylamine by successive trapping of two $\text{t}$-butyl radicals and (3) sodium naphthalide reduction to the di-$\text{t}$-alkylamine.     

Solvent effects on the nitrogen hyperfine splitting constant of the t-butyl-t-butoxy nitroxyl radical

A decrease in nitrogen hyperfine splitting constant (N-hfsc) with increasing solvent polarity is reported for $\text{t}$-butyl $\text{t}$-butoxy nitroxyl radical produced by trapping $\text{t}$-butoxyl radical with 2-methyl-2-nitrosopropane.     

Activation of methylenetriphenylphosphorane by reaction with t-butyl- or sec-butyllithium

Experimental details are provided to support a previous report that α-methylenetriphenylphosphorane ($\text{1}$) may be activated for reaction with unreactive substrates such as epoxides and hindered ketones by α-metallation to $\text{2}$.