2.4.6- Tri-r-butylphenol

Oxidation of 44 is completely inhibited by the addition of a small amount of 2,4,6-tri-r-butylphenol. Consequently, the oxidation of the Si—Si bond with oxygen displays the following features 1) a Si—Si bond which is either angle-strained or substituted with more than two fluorine atoms is easily oxidized 2) a radical mechanism is operative 3) the insertion of oxygen into the Si—Si bond proceeds stereospecifically62. Incorporation of molecular oxygen was also observed in the direct photolysis of the cyclopolysilanes 80 and 81 (equations 88 and 89)91. 

Urethanes analogous to the amides of the previous section undergo similar deprotonation followed by alkylation and condoisation reactions. For example, 2,4,6-tri-r-butylphenol may be converted into the corresponding urethane which can be further functionalized (equation 32). N-Carbomethoxy-3-pyrroline has been convoted into both the trail pheromone for the Pharaoh ant and gq)hyrotoxin 223 by using regiospecific alkylations (Scheme 3). ° Similar tqjproaches were used in the preparation of the natural product supinidine. Piperidines also have been alkylated via the r-BOC-protected amines. ... 

We have also prepared the 0-bonded silanetriol (2,4,6-rBu3C6H2)OSi(OH)3 (18) starting from 2,4,6-tri-r-butylphenol (Scheme 4) [27]. However, the synthesis of other O-bonded silanetriols proved to be difficult due to the ready cleavage of the Si-O(aryl) bond... 

Preparation. Dialkyl acetals of DMF are generally prepared by transacetal-ization of the dimethyl or diethyl acetal, but this reaction is not useful in the case of the di-r-butyl acetal. Replacement of one methoxy group of DMF dimethyl acetal occurs on refluxing in f-butyl alcohol conversion to the di-f-butyl acetal is effected in the presence of 2,4,6-tri-r-butylphenol (equation I). 

It has been shown that mononuclear cobalt superoxo complexes react with 2,4,6-tri-r-butyl-phenol. The anion [Co(CN)j(02)] acts as a base in the oxidation of the phenol. The neutral complex Co(salptr)(02) forms a peroxy adduct with 2,4,6-tri-r-butylphenol. An X-ray study on this adduct has revealed the structure shown in (10). ... 

The phenoxy radical, derived from an H-abstraction reaction by NO, couples with another -NO molecule to give 4-nitrocyclohexa-2,5-dienone, which readily rearranges, after a keto-enol tautomerism to 2,6-di- -butyl-4-nitrophenol. 2,4-di-t-butylphenol and 4-r-butylphenol react in the same way, whereas the presence of three substituents on the aromatic ring of 2,4,6-tri-r-butylphenol and 2,6-di- butyl-4-methylphenol does not allow keto-enol tautomerism in these cases 2,4,6-tri- -butyl-4-nitrocyclohexa-2,5-dienone and 2,6-di-r-butyl-4-methylnitrocyclohexa-2,5-dienone were the sole nitro compounds obtained. The reaction between NO and 2,6-di-t-butylphenol or 2,4-di- -butylphenol in methanol resulted in phenoxyl radical dimerisation together with nitration. As shown in (Scheme 5.100), phenoxyl radical dimerises to give an... 

Fig.1. Two-stage polymerization of methyl methacrylate (MMA) in CH2CI2 at room temperature with the enolatealuminum porphyrin (2, R=Me)-methylaluminum bis(2,4,6-tri-tert-butylphenolate) (3f) (1.0 1.0) system. GPC profiles of the polymers formed at the first stage (I) [MMA]o/[l (X=Me)]o=50, 100% conversion Mn=7,000, Mw/Mn= 1.12 and the second stage (II) [MMA]o/[2]q=200, 100% conversion Mn=47,600,Mw/Mn= 1.05...

The tert-butoxy radical is liberated by photolysis of XXXVIa (Scheme 9). Its formation was confirmed by reactions which produce more stable radicals detectable by the ESR method135. The heptane solution of XXXVIa was irradiated by light 360—480 nm in the presence of 2,6-di-tert-butyl-4-methylphenol or 2,4,6-tri-tert-butylphenol. These sterically hindered phenols were transformed by the liberated tert-butoxyl into phenoxyls. Their identification by the ESR method is the indirect evidence of tert-BuO formation. The direct evidence was achieved by means of nitro-sobenzene CVI (R=H) and nitrosodurene CVI (R=Me) as spin-traps. The nitroxide radical CVII (R=H or Me) is formed in both cases and was identified by ESR spectrum135. This spin-adduct is unstable. The intensity of its spectrum gradually decreases during irradiation and the spectrum of another radical appears which is less intense but invariable in time. Judging from its hyperfine structure, it may be formulated as CVIII (R=H or Me). More detailed data on the character of substituents RJ-R2 is not yet known. 

Treatment of 2,4,6-tri-r rr-butylphenol with bromine in cold acetic acid gives the compound CigH29BrO in quantitative yield. The infrared spectrum of this compound contains absorptions at 1630 and 1655 cm Its NMR spectrum shows only three peaks (all singlets), at 8 1.2, 1.3, and 6.9, in the ratio 9 18 2. What is a reasonable structure for the compound ... 

The behaviour of the most sterically hindered 2,6-di-rerr-butylphenol (25) and its derivatives was very dependent upon the reaction conditions. In the presence of a base favouring electron-transfer (such as BTMG), oxidation reactions took place with triphenylbismuth dichloride or triphenylbismuth carbonate leading to the diphenoquinone (26). Para-phenylation with formation of (27) was observed for the first time in the reaction of the potassium phenolate of 2,6-di-re rr-butylphenol with triphenylbismuth dichloride and in the reaction of the phenol (25) with tetraphenylbismuthonium tosylate in the presence of BTMG. Even ortho- and para-phenylation with concomitant de-rerr-butylation occurred in the reaction of the potassium salt of 2,4,6-tri-re r/-butylphenol with triphenylbismuth dichloride. 2... 

Trimethyl-2,4,6-tris-(3,5-di-r-butyl-4-hydroxy-benzyl)-benzene Calcium bis-(ethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate) 2,2 -Methylene-bis-(4-methyl-6-tert-butylphenol) 2,2 -Methylenebis-(6-tert-butyl-4-methylphenol) monoacrylate... 

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