Sterically hindered alcohols, oxidation with

A similar oxidation by dimethyl sulfoxide (DMSO) has attracted much attention because of the gentle conditions under which it takes place and the high yields of the resulting carbonyl compounds, especially those obtained from sterically hindered alcohols. In addition to dimethyl sulfoxide, an activator of DMSO is needed for the formation of a complex with the alcohol, and a base is required for the abstraction of a proton from the complex to initiate its collapse to the aldehyde (or ketone). The course of the reactions is summarized in equation 217. 

Dimethyl sulfoxide-Acetic anhydride [1, 305, after citation of ref. 43J. Albright and Goldman433 have reported further on the oxidation of secondary alcohols to ketones with DMSO-Ac20 at room temperature. In the case of yohimbine and the steroid secondary alcohols studied, oxidation apparently was faster than acetylation. The method is particularly useful for sterically hindered alcohols. The following mechanism is proposed ... 

Initially, Swem et al. reported the oxidation of sterically hindered alcohols to carbonyls with a dimethyl sulfoxide-trifluoroacetic anhydride complex.7 These reactants included primary alcohols such as 2,2-dimethyl-l-phenyl-propanol 3 and secondary alcohols, for example, 2-adamantanol 4. 

This reaction has been used to convert primary and secondary alcohols into corresponding aldehydes and ketones, especially for the sterically hindered alcohols. This reaction has been commonly used in carbohydrate transformation. However, for the oxidation of phenols with DMSO/AC2O, the thiomethoxymethylation of the corresponding phenols occurs." ... 

X0 to hydroxy compounds. Lower temperatures favor ketone formation and sterically hindered carbonyls, such as 2-thienyl t-butyl ketone, are not reduced. The sensitivity of desulfurization to steric factors is evident by the failure to desulfurize 2,5-di-i-butyl-3-acetylthiophene. The carbonyl groups of both aldehydes and ketones can be protected by acetal formation, as particularly cyclic acetals are stable during desulfurization in methanol at room temperature. " The free aldehydes give primary alcohols on desulfurization. Another method to obtain only keto compounds is to oxidize the mixtures of ketone and secondary alcohol with CrOs after the desulfurization. - Through the desulfurization of 5,5 -diacetyl-2,2, 5, 2"-terthienyl (228), 2,15-hexadecandione (229) has been obtained, which... 

Barium oxide and sodium hydride are more potent catalysts than silver oxide. With barium oxide catalysis, reactions occur more rapidly but O-acetyl migration is promoted. With sodiun hydride, even sterically hindered groups may be quantitatively alkylated but unwanted C-alkylation Instead of, or in addition to, 0-alkylatlon is a possibility. Sodium hydroxide is a suitable catalyst for the alkylation of carboxylic acids and alcohols [497J. 

Reaction of styrene oxide with tetraallyltin in the presence of Bi(OTf)3 (2 mol%) affords the corresponding l-phenyl-4-penten-2-ol (Fig. 5). In a similar fashion, various aryl substituted epoxides react smoothly with tetraallyltin to give the corresponding homoallylic alcohols. This method give generality as cycloalkyl oxiranes and sterically hindered ones give the corresponding homoallylic alcohols. 

Oxidation of primary, secondary and benzylic alcohols with TBHP or CHP, mainly catalyzed by Mo and Zr derivatives, were performed by different authors. As an example, Ishii, Ogawa and coworkers reported the conversion of secondary alcohols such as 2-octanol to ketones mediated by catalyst 39 and TBHP. The oxidation of cyclic alcohols depended on steric factors. Zirconium alkoxides may act as catalysts in the conversion of different alcohol typologies with alkyl hydroperoxides . Secondary alcohols, if not severely hindered, are quantitatively converted to the corresponding ketones. The selectivity for equatorial alcohols is a general feature of the system, as confirmed by the oxidation of the sole cis isomer 103 of a mixture 103-bl04 (equation 68). Esters and acids could be the by-products in the oxidation of primary alcohols. 

Manufacturing processes and equipment are similar to those employed for alcohol ethoxylate preparation. In the absence of steric hindrance, ethylene oxide reacts with both hydrogens of primary amines at relatively low temperatures (90—120°C) without added catalysts (105). When the nitrogen atom is hindered, as it is in the Triton RW products, only one of the amino hydrogens reacts with ethylene oxide. Once this reaction is complete, a basic catalyst is added and ethoxylation proceeds in the manner of the alcohol-based nonionics. In IV-alkyl-l,3-propanediamine, all three amino hydrogens are available for reaction with ethylene oxide. N-Alkyl-1,3-propanediamines are prepared from fatty monoamines and acrylonitrile, followed by reduction of the resulting 3-cyanoethylalkyl amine. 

Evidence of variables that influence the relative rates of reaction of olefins and alcohols was obtained from experiments with compounds that have both olefinic and alcoholic functions and by the competitive oxidation of mixtures of olefins and alcohols. The data of Table VI show that when the double bond has no substituents, as in allyl alcohol, but-3-en-l-ol, or 2-methylbut-3-en-l-ol, only the epoxide is formed but when the double bond has substituents, the epoxida-tion rate is decreased and ketone and aldehyde products from the oxidation of the OH group are formed. This effect is more pronounced with a greater degree of substitution. Since the double bond and the OH group are part of the same molecule, the difference must arise from the different abilities of the reactants to coordinate and react at the titanium center restricted transition-state shape selectivity is a possibility. The terminal double bond, sterically less hindered, interacts strongly with titanium, preventing coordination of the competing OH... 

Quite unsurprisingly, apart from stereoelectronic factors, DDQ oxidation of unsaturared alcohols is also subject to steric factors. For instance, the highly hindered allylic alcohol 94 could not be oxidized with DDQ in benzene at room temperature, being necessary to employ Jones oxidation.103... 

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