14387-13-4

In this paper, we confirmed the dearomative addition of tertiary alkyl radicals onto BHT derivatives to form highly congested vicinal quaternary carbons to produce tert-alkylated styrenes in the presence of copper catalyst. Although there are three candid

The reaction of quinone methide 1 and phenol 2 in equimolar amounts was investigated in pentane at 30 deg C.Products were isolated by means of column chromatography on SiO2.There was a marked difference in product distribution between the reactions in the presence and absence of added Et3N.Dienones 3 and 10 were obtained only from the former reaction, while formation of 1,2-bis(4-hydroxyphenyl)ethane 18 and 4,4'-dihydroxybiphenyl 20 was overwhelming in the latter reaction.Other products from both reactions were relatively small quantities of 4,4'-stilbenequinone 17, 4,4'-diphenoquinone 21, and bis(4-hydroxyphenyl)methane 24, but dienone 4 was not obtained.Compounds 20 and 24 obtained from the latter reaction were formed by isomerization of dienones 19 and 23, respectively, during chromatography.The reaction is initiated by dimerization of 1 to generate biradical 11.Subsequent processes involving hydrogenation-dehydrogenation, coupling-dissociation, and dienone-phenol rearrangement account for the formation or the lack of formation of the products.The difference in product distribution is ascribed to capability of Et3N to catalyze the isomerization.Quinone methide 1 also adds to 2 to give 23.The decay of 1 in the presence of both 2 and phenol 6 gave dienone 8 additionally.The formation of 24 and 4 was facilitated by conducting the reaction of 1 and 2 in DMSO.Dehydrogenation of 10 and 3 with PbO2 afforded spirodienones 27 and 28, respectively.Compounds 27 and 28 were unstable, and their decay in solution was investigated in the presence or absence of added 2.The results show that the decay is initiated by homolytic scission of the C-C bond connecting the dienone rings in the cyclopentane (in 27) and cyclohexane (in 28) rings.Compound 28 is novel in that it bears two kinds of such C-C bonds.Reversibility of the dimerization of 1 is suggested.

Dimer 3 dissociates in solution to give the phenoxy radical 4.When solid 3 is dissolved in a solution of phenol 11a, radical 4 dehydrogenates the phenol to afford phenol 5 and phenoxy radical 12.Radical 12 couples with more 4 to afford principally bis(cyclohexadienone) 16a and a minor amount of the dimeric bis(cyclohexadienone) 13.The preferential formation of 16a over 13 is explained as the result of a solvent-cage reaction.Compounds 13 and 16a are isomerized in the presence of silica gel or triethylamine to 4,4'-dihydroxybiphenyl 14 and phenolic dienone 17a, respectively.Compound 13 is relatively stable in hexane at 30 deg C, while 16a slowly dissociates under these conditions to afford parent radicals 4 and 12.If 11a is present, radical 4 either recombines with 12 or dehydrogenates the phenol.Two radicals of 12 generated by the dissociation of 16a and the subsequent dehydrogenation of 11a couple to give 13.Therefore, dissolving 3 in hexane containing excess 11a and keeping the resulting solution at 30 deg C results in the preferential formation of 13.Dissolving 3 in triethylamine containing phenols 11 or 21 similarly affords dienones 17 or 23.The yields of these dienones increase with increasing electron-donating capability of the substituent of the phenol ring.

Both monomeric and dimeric oxidation products are formed during the oxidation of 2,6-di-tert-butyl-4-methylphenol (ionole) by oxygen in a water-propanol solution of ammonia.Two nitrogen-containing compounds 3,3'-5,5'-tetra-tert-butylindophenol and 2,6-di-tert-butyl-4-cyanophenol are also formed, and their amounts in the reaction mixture increase with increase in temperature (45-120 deg C).

Cyclic voltammetry of 2,6-di-tert-butyl-4-methylphenol (1) in acetonitrile in the presence of an aliphatic amine such as ethyl-, diethyl-, or triethylamine shows an ill-defined anodic wave - a socalled kinetic wave - around 0.5V vs. aqueous saturated calomel electrode, indicating an electron-transfer process preceded by a slow chemical reaction.Based on the estimated pKa value of 1 (pKa=12.55 in water at 25 deg C), the chemical reaction was ascribed to a slow hydrogen-bonding association of 1 and the added amine.Controlled potential electrolysis of 1 at the potential of the anodic wave gave an unsymmetrical dimer, 2,6-di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxyphenyl)-4-methyl-2,5-cyclohexadiene-1-one, as the main product.Side-chain aminated derivatives of 1, Ar-CH2NHEt, Ar-CH2NEt2, and Ar-CH2N+NEt3 (Ar=3,5-di-tert-butyl-4-hydroxyphenyl), are suggested to be the intermediates; that is, the process of dimer formation is explained in terms of cross-coupling of the phenoxyl radicals derived from 1 and the side-chain aminated phenols followed by expulsion of the aminomethyl group.Keywords - electrochemical oxidation; cyclic voltammetry; conrolled potential electrolysis; 2,6-di-tert-butyl-4-methylphenol; oxidative dimerization; phenol coupling

The use of iodine as an oxidizing agent for phenolic compounds has been explored.The reaction has been conducted in methanol containing such alkali as potassium hydroxide and, depending on the nature of the substituents and on the amount of iodine employed, leads to iodination, oxidation to give a stable phenoxy radical, oxidative dimerization, or benzylic oxidation.In general the reaction proceeds smoothly at room temperature, and under appropriate conditions yields of products are good to excellent.Oxidative dimerization of 2,4- and 2,6-di-tert-butylphenols invol-ves iodination followed by iodine-catalyzed dimerization.The oxidation of 4-methylphenols with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in methanol has been carried out for comparison.