Benzyl alcohols, allylation

Alkylation of I -dike tones with allylic and benzylic alcohols. Allylic and benzylic alcohols can alkylate 1,3-dikcloncs and other active hydrogen compounds in the... 

Physical properties Benzyl alcohol Allyl alcohol Di acetone alcohol Furfuryl alcohol Teirahydrofurfuryl alcohol Texanol ester-alcohoP... 

A white solid, m.p. 178 C. Primarily of interest as a brominaling agent which will replace activated hydrogen atoms in benzylic or allylic positions, and also those on a carbon atom a to a carbonyl group. Activating influences can produce nuclear substitution in a benzene ring and certain heterocyclic compounds also used in the oxidation of secondary alcohols to ketones. 

Benzyl and allyl alcohols which can generate stabilized caibocations give Friedel-Crafts alkylation products with mild Lewis acid catalysts such as scandium triflate. ... 

Certain functional groups may be protected from reduction by conversion to anions that resist reduction. Such anions include the alkoxides of allylic and benzylic alcohols, phenoxide ions, mercaptide ions, acetylide ions, ketone carbanions, and carboxylate ions. Except for the carboxylate, phenoxide, and mercaptide ions, these anions are sufficiently basic to be proton-ated by an alcohol, so they are useful for protective purposes only in the... 

The rearrangement of an ether 1 when treated with a strong base, e.g. an organo-lithium compound RLi, to give an alcohol 3 via the intermediate a-metallated ether 2, is called the Wittig rearrangement. The product obtained is a secondary or tertiary alcohol. R R can be alkyl, aryl and vinyl. Especially suitable substrates are ethers where the intermediate carbanion can be stabilized by one of the substituents R R e.g. benzyl or allyl ethers. 

In 1983, Nozaki, Takai, Hiyama, and their coworkers disclosed that vinyl and aryl iodides or bromides are reduced with chromium(n) chloride, and that the resulting organochromium(in) species react smoothly with a host of aldehydes to give allylic or benzylic alcohols in excellent yields.6 As shown in Scheme 1, the chromium(n) chloride-mediated carbonyl addition can be conducted efficiently at... 

Allylic or benzylic alcohols can be symmetrically coupled by treatment with... 

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

On reacting aldehydes such as propionic aldehyde, however, with a 1 1-mixture of a silylated allyl- or benzyl alcohol such as 589 and phenylthiotrimethylsilane 584 in the presence of TMSOTf 20 0,S-acetals such as 591 are obtained, via the probable intermediate 590, in high yields [63]. The a-ketoamide 592 is converted by methylthiotrimethylsilane 593/F3B-OEt2 into the bisthioketal 594 in 81% yield [145]. Ethylenethioketals such as 595 are cleaved by MesSiBr 16 or Me3SiI 17 in... 

C-Substitution Reactions of Silylated Allyl or Benzyl Alcohols... 

Previous studies by Sorokin with iron phthalocyanine catalysts made use of oxone in the oxidation of 2,3,6-trimethylphenol [134]. Here, 4 equiv. KHSO5 were necessary to achieve full conversion. Otherwise, a hexamethyl-biphenol is observed as minor side-product. Covalently supported iron phthalocyanine complexes also showed activity in the oxidation of phenols bearing functional groups (alcohols, double bonds, benzylic, and allylic positions) [135]. Besides, silica-supported iron phthalocyanine catalysts were reported in the synthesis of menadione [136]. 

These are generally oxidised with the same kinetics as saturated alcohols but more rapidly. In addition to the example of allyl alcohol - discussed previously (p. 377), several reports exist of oxidations of benzylic alcohols. The importance of a 1 1 complex K = 0.8 0.2 at 25 °C, [HCIO4] = 0.525 M) in the Ce(IV) oxidation is clear from agreement of spectroscopic and kinetic data . For a... 

Benzylic, allylic and propargylic positions enhance the cathodic cleavage rate of C— heteroatom bonds as, for example, in the reduction of benzylic and allylic halides or alcohols . Similar activated sulphones, due to their acidity, are in a class apart. Figure 8 shows the similitude between the cathodic behaviour of an allylic sulphone and its isomer, i.e., the corresponding vinylic sulphone when the electrolyses are run in an aprotic solvent. However, in the presence of an excess of proton donor, discrepancies appear. 

Loss of catalytic activity resulting from internal displacements is not usually a serious problem below temperatures of about 100 C. However, highly active R-groups, such as benzyl, methyl and allyl, undergo internal displacement more readily, particularly in the presence of strong nucleopfiles. For instance, the presence phenolates and thiolates may lead to the formation of benzyl alcohol, ethers, or sulphides from benzyl-substituted quaternary ammonium salts. 

Stabilized carbocations can be generated from allylic and benzylic alcohols by reaction with Sc(03SCF3)3 and results in formation of alkylation products from benzene and activated derivatives.39... 

Scheme 12.2 shows various types of alcohols that are most susceptible to Mn02 oxidation. Entries 1 and 2 illustrate the application of MnOz to simple benzylic and allylic alcohols. In Entry 2, the Mn02 was activated by azeotropic drying. Entry 3 demonstrates the application of the reagent to cyclopropylcarbinols. Entry 4 is an application to an acyloin. Entry 5 involves oxidation of a sensitive conjugated system. 

Another possible alternative oxidant that has recently been investigated is an Fe(VI) species, potassium ferrate, K2Fe04, supported on montmorillonite clay.14 This reagent gives clean, high-yielding oxidation of benzylic and allylic alcohols, but saturated alcohols are less reactive. 

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