Alcohols benzyhc, oxidation

The mechanism of the reaction was not studied, but a catalytic cycle similar to that in Scheme 15.6a is likely. Subsequently, there have been numerous other reports of nitroxyl/NOj catalytic systems for aerobic alcohol oxidation [30], including the chemoselective oxidation of primary over secondary ahphatic alcohols [31], and application to the oxidation of hgnin, in which secondary benzyhc alcohols are oxidized in preference to primary aliphatic alcohols [32]. 

Oxidation of Alcohols. Alkoxymagnesium bromides of secondary alcohols and allylic and benzyhc alcohols are oxidized to the corresponding ketones or aldehydes with N-chlorosuccinimide in the presence of r-BuOLi. The method is ineffective for primary saturated and some unsaturated alcohols, but oxidations of the former substrates to aldehydes occur readily if t-butoxymagnesium bromide is substituted for f-BuOLi. Secondary alcohols (eq 2) and primary benzylic (eq 3) and allylic alcohols are oxidized to the corresponding carbonyl compounds in good yields using 2—3 equiv of a 1 1 mixture of copper(II) bromide—r-BuOLi in THF at rt. However, the reagent is not effective for the conversion of primary aliphatic alcohols to aldehydes. 

In Summary Benzyhc oxidations of alkyl groups take place in the presence of permanganate or chromate benzyhc alcohols are converted into the corresponding ketones by manganese dioxide. The benzyhc ether function can be cleaved by hydrogenolysis in a transformation that allows the phenylmethyl (benzyl) substituent to be used as a protecting group for the hydroxy function in alcohols. 

In addition, Mg/Al and Co/Al LDHs containing Ru + in the layers have also been used as precursors to mixed oxides that are highly efficient catalysts for the oxidation of allylic and benzyhc alcohols [73,74]. 

Ley et al. performed oxidations of activated (benzyhc, allylic) alcohols by employing polymer-attached perruthenate catalysts and oxygen as oxidant. Triethylammo-... 

TABLE 10. Summary of Hammett p values and kinetic isotope effects in the oxidation of benzyhc alcohols ... 

Minisci and coworkers followed Ishii s procedure, and implemented it in the oxidation of benzyhc alcohols to benzaldehydes in almost quantitative yields" (Table 12). A,Af-dimethylbenzylamines were converted into aldehydes in good yields, by using catalytic amounts of either HPI or A-hydroxysuccinimide (HSI) for the formation of the corresponding aminoxyl radical intermediates. Because the attempted oxidation of primary and secondary amines caused the degradation of catalyst HPI, protection of the amino group in those substrates by acetylation was considered. This led one to develop... 

Typical examples are listed in Table 2.1. A few oxidations are effected by RuO but in general it is too powerful an oxidant for this purpose. The system RuCyaq. NaCl-CCy Pt anode oxidised benzyl alcohol to benzaldehyde and benzoic acid and p-anisaldehyde to p-anisic acid [24], and a wide range of primary alcohols and aldehydes were converted to carboxylic acids, secondary alcohols to ketones, l, -diols to lactones and keto acids from RuOj/aq. NaCl pH 4/Na(H3PO )/Pt electrodes (Tables 2.1-2.4). The system [RuO ] "/aq. K3(S303)/Adogen /CH3Cl3 oxidised benzyhc alcohols to aldehydes [30]. The oxidation catalyst TPAP (( Pr N)[RuO ]) (cf. 1.3.4) is extremely useful as an oxidant of primary alcohols to aldehydes and secondary alcohols to ketones without... 

Oxidation of Cu with O2 is markedly slower than the analogous oxidation by TEMPO. The existence of a copper-centered dehydrogenation step was supported by investigating kinetic isotope effects and Hammett correlation studies using different substituted benzyhc alcohols. The /1-hydrogen abstraction was postulated to occur in a concerted mechanism with an -coordinated TEMPO radical bgand (Scheme 4). As such, this TEMPO-mediated copper-catalyzed oxidation of alcohols bears resemblance... 

The stoichiometric selective oxidation of the benzyhc alcohol function in (di)hydroxy-substituted benzylalcohols (Eq. 14) has been demonstrated by Nolte et al., using host-guest chemistry to steer the regiospecificity in the reaction [167-170]. The host-receptor used to construct dicopper complex 21 is based on the building block diphenylglycoluril, which was functionahzed... 

Benzylic methylene groups are more readily oxidized to benzyhc alcohols when compared to simple alkanes. Typical reagents include manganese-salen and PhIO ° or peroxides. a-Hydroxy ethers are also generated by reaction of this regents with ethers.A-Benzyl phthahmide reacts with NBS, NaOAc, and acetic... 

This ionic hquid was a good alternative to the traditional toxic solvents and catalysts in the selective oxidation of benzyhc alcohols to carbonyl compounds. The... 

Peterson KP, Larock RC (1998) PaUadium-catalyzed oxidation of primary and secondary ally-hc and benzyhc alcohols. J Org Chem 63 3185-3189... 

Hu R, Lei M, Wei H, Wang Y (2009) Ionic liquid-H O resulting in a highly chemoselective oxidation of benzyhc alcohols in the presence of aliphatic analogues catalyzed by immobihzed TEMPO. Chinese J Chem 27 587-592... 

Oxidation. Heating an alcohol with Fe(N03)3 9H2O at 80° leads to its conversion into the carbonyl compound. However, the scope of the oxidation is not well studied, and its applicability (to give good 3delds) may he hmited to benzyhc alcohols. ... 

KRs based on the oxidation of a chiral secondary alcohol to a prochiral ketone has been of considerable interest as the later can be usually recycled into the racemic starting material by simple hydride reduction [2d, 55]. The first broadly applicable method for this purpose was reported by Noyori et al. [56], under catalytic hydride transfer conditions similar to those employed for the asymmetric hydrogenation of ketones. For example, excellent results (s>50) have been reported for the KR of benzyhc alcohols by using a chiral diamine-ruthenium complex in the... 

In 2013, Adimurthy and co-workers reported a TM-free NaOH-catalyzed N-alkylation reaction of 2-aminothiazoles, 2-aminobenzothiazoles, aminopyrimidines, and aminopyridines with benzyhc and heterobenzyhc alcohols under air (Scheme 43) [203]. In condition optimization, the authors found the model reaction of 2-aminobenzothiazole and 4-chlorobenzylalcohol under air afforded a higher yield of the product (93 %) than the one under nitrogen (90 %). Therefore, along with other results of mechanistic studies and the authors own previous work on based-catalyzed imine synthesis from alcohols and amines [204], they proposed that alcohol oxidation to aldehyde by air in the presence of bases is the initiation step of... 

Methyltrioxorhenium (MTO) also catalyzes the oxidation of alcohols with H2O2 via a peroxometal pathway [137,138]. Primary benzyhc and secondary aliphatic alcohols afforded the corresponding aldehydes and ketones, respectively, albeit using two equivalents of H2O2. In the presence of bromide ion the rate was increased by a factor 1000 [137]. In this case the active oxidant could be hypobromite (HOBr), formed by MTO-catalyzed oxidation of bromide ion by H2O2. 

The results obtained in the oxidation of representative primary and secondary aliphatic alcohols and allylic and benzyhc alcohols using this system are shown in Tables 1 and 2. 

However, these methods suffer from low activities and/or narrow scope. Uemura and coworkers reported an inproved procedure involving the use of Pd(OAc>2 (5m%) in combination with pyridine (20m%) and 3A molecular sieves (500 mg per mmol of substrate) in toluene at 80°C. This system catalyzed the smooth aerobic oxidation of primary and secondary aliphatic alcohols to the corresponding aldehydes and ketones, respectively, in addition to benzyhc and allyhc alcohols. Representative examples are summarized in Table 6. 1,4- and 1,5-Diols afforded the corresponding lactones. 

A variety of secondary and benzyhc alcohols can be oxidized by O2 in the presence of 2-methylpropanal, a sacrificial aldehyde both in the presence and absence of a metal catalyst in a homogeneous phase. The results are compared in Figure 58. Co(acac)2 is the most efficient catalyst as compared with Cu, Ni, Pd, Fe, Mn acac complexes. Depending on the substrate, yield enhancements by a factor of 1.5 - 24 ate observed for... 

A representative example of the use of triazole reagents as organocatalysts in synthetic transformations [519] is the oxidation of allylic, propargyHc, and benzyhc alcohols to the corresponding carboxylic esters by Mn02 in alcohol solvents, which is mediated by l,4-dimethyl-l,2,4-triazolium iodide (30) in the presence of DBU as a base [520], for example ... 

Authors found that the vinylalumination reaction is fully diastereoconvergent as the reaction of both cis- and trans-stilbene oxides 90 led to the exclusive formation of the same anti-configured homoallyUc alcohol 39a, which was subsequently cyclized to fS,y-diphenyl-a-methylene-y-lactone trans-29aa under acidic conditions (Scheme 4.23). This experimental result was rationalized by the intermediacy of the corresponding benzyhc carbocation in the reaction. 

The experiments by Canonica et al. (1981) suggest a third plausible formation of simple isoquinoHnes with no carbon-1 substituent in plants mainly producing alkaloids of the benzylisoquinoline type. Treatment of the benzylisoquinoline N-methylcoclaurine with ascorbic acid oxidase, an enzyme widespread in plants, resulted in benzyhc fission giving about 40% yield of corypalline, its quaternary 1,2-dehydroderivative and benzyl alcohol. Thus, both isoquinolones and simple isoquinolines may be formed directly by the action of oxidative enzymes in benzyl-isoquinoline-producing plants. 

Jeffrey C. PeUetier of Wyeth Research, Collegeville, PA has developed (Tetrahedron Lett. 2007, 48,7745) a easy work-up Mitsunobu procedure for the conversion of a primary alcohol such as 1 to the corresponding primary amine 2. Shlomo Rozen of Tel-Aviv University has taken advantage (J. Org. Chem. 2007, 72, 6500) of his own method for oxidation of aprimary amine to the nitro compound to effect net conversion of an amino ester 3 to the alkylated amino ester 5. Note that the free amine of 3 or 5 would react immediately with methyl iodide. Keith A. Woerpel of the University of California, Irvine has uncovered (J. Am. Chem. Soc. 2007,129,12602) a Cu catalyst that, with 7, effected direct conversion of sUyl ethers such as 6 to the aUyl silane 8. An Ag catalyst gave 9, which also shows arllyl silane reactivity. Biswanath Das of the Indian Institute of Chemical Technology, Hyderabad has established (Tetrahedron Lett. 2007, 48, 6681) a compact procedure for the direct conversion of an aromatic aldehyde such as 10 to the benzylic halide 11. This will be especially useful for directly generating benzyhc hahdes that are particularly reactive. 

MW irradiation also permitted a shorter reaction time for the selective solvent-free oxidation of primary, secondary, aUylic, and benzyhc alcohols with pyridinum sulfonate chlorochromate and pyridinum sulfonate fluoro-chromate as oxidizing agents, compared with the use of solvent. For example, cholest-5-en-3-ol acetate and cholest-5-en-3-ol benzoate were chemoselectively oxidized at position 7 in solvent-free conditions with 82% and 87% conversion, respectively. 

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