Heterocyclic alcohols, oxidation

The reaction of the a-bromo aldoxime 52e (R = R = Me) with unsaturated alcohols has been extended to the heterocyclic systems furfuryl alcohols and 2-thiophene methanol [29b]. The furanyl and thiophenyl oximes 63a-c were treated with NaOCl and the resulting heterocyclic nitrile oxides were found to undergo spontaneous intramolecular dipolar cycloaddition to produce the unsaturated tricyclic isoxazolines 64a-c in high yield (Eq. 5). In these cases, the heterocyclic ring acts as the dipolarophile with one of the double bonds adding to the nitrile oxide [30]. 

Varieties of primary and secondary alcohols are selectively oxidized to aldehyde or carbonyl compounds in moderate to excellent yields as summarized in Table 3. As can be seen, /(-substituted benzyl alcohols (e.g., -Cl, -CH3, -OCH3, and -NO2) yielded > 90% of product conversion in 3-4 h of reaction time with TOP in the range of 84-155 h (entries 2-5, Table 3), Heterocyclic alcohols with sulfur- and nitrogen-containing compoimds are found to show the best catalytic yield with TOP of 1517 and 902 h for (pyrindin-2-yl)methanol and (thiophene-2-yl) methanol, respectively (entries 9 and 10, Table 3). Some of aliphatic primary alcohols (long chain alcohols) and secondary alcohols (cyclohexanol, its methyl substituted derivatives and norboman-2-ol) are also selectively oxidized by the membrane catalyst (entries 11-14 and 15-17, Table 3) with TOP values in the window of 8-... 

Major oxidations are aromatic, aliphatic, alicyclic, heterocyclic, N-oxidation, S-oxidation, dealkylation. Other enzymes also catalyze phase 1 reactions microsomal flavin monooxygenases, amine oxidases, peroxidases, and alcohol dehydrogenase. 

They include aromatic hydroxylation, hydrocarbon and alcohol oxidation, alkene epoxidation, nitro-aromatic reduction, dehydrogenation, carbonylation, cyclization, heterocycle functionalization, etc. 

Asymmetric induction has been observed in the hydroboration of heterocyclic rings such as dihydrofuran, dihydropyrrole, dihydropyran, and dihydrothiophenes.Table 5.6 ° shows the hydroboration-oxidation sequence that gives heterocyclic alcohols in good yield and with excellent % ee from heteroatom containing... 

Many reports of aerobic alcohol oxidation involve homogeneous Pd- [7] and Ru-based [8] catalysts that are effective with benzylic, allylic, and ahphatic primary and secondary alcohols. These catalysts are often inhibited by coordinating functional groups such as heterocycles, amines, and oxygen- or sulfur-containing moieties and are capable of oxidizing alkenes. Efforts to develop scalable applications of Pd-based catalysts raised concerns about large-scale prospects for these... 

Oxidation of heterocyciic alcohols. This reagent is useful for oxidation of heterocyclic primary alcohols, particularly those containing nitrogen. Note that oxidation of a nonaromatic heterocyclic alcohol can lead to a lactone or a ketone instead of an aldehyde. ... 

Oxidation of Benzylie and Heterocyclic Alcohols. Conjugated aromatic aldehydes or ketones can be efficiently prepared by treatment of benzylic alcohols with Mn02 (eq 20). Numerous functional groups are tolerated (eqs 21-24). 

The oxidation reaction can be extended to heterocyclic alcohols (eq 27) and the Corey procedure gives the expected esters (eq 28).2> ... 

Cr(III)M0gO24Hg] promotes H2O2 oxidation of aliphatic, benzylic, and heterocyclic alcohols to the corresponding aldehydes and ketones in 50% H20-MeCN by becoming oxidized to the intermediate [Cr(V)M0gO24Hg] which is the active catalyst. " ... 

Direct fluorination of aliphatics and non-C moieties Direct fluorination of benzenoid aromatics Direct fluorination of heterocyclic aromatics Oxidations of alcohols, diols and ketones with fluorine Photo-oxidation of a-terpinene and cyclopentadiene Oxidation of benzyl alcohol to benzaldehyde Homogeneously catalyzed oxidation of butyraldehyde Oxidation of sulfite to sulfate Photochlorination of aromatic isocyanates... 

Brown et a/ [1] have elegantly hydroborated a variety of heterocyclic olefins, which on oxidation yield the corresponding alcohols in excellent yields. In the case of heterocyclic olefin containing a double bond a to the heteroatom, the hydroboration reaction is highly regioselective, placing boron at the (3-carbon atom. The use of 9-BBN for the synthesis of variety of heterocyclic alcohols is given in Chart 6.21. 

A systematic mechanistic study of the K2[0s02(0H)4]-catalysed and highly chemos-elective oxidation of allylic, electron rich/deficient benzylic, and heterocyclic alcohols with CAT using the LC-ESI-MS/MS method reveals the presence of imidotriooxoos-mium species which react further with alcohol to give the respective ketones. ... 

Thus, a rare one-pot reaction for assembling pyrrolo[l,2-fl]quinoxalines from 1-(2-nitrophenyl)pyrroles and various alcohols. The nitro reduction, alcohol oxidation, heterocycle formation, and heterocycle oxidation were realized in a cascade. A wide range of these fused heterocycles bearing different alkyl and aryl groups in position 4 have been elaborated from suitable substrates thereby 3-nitro-2-pyrrolopyridine was also compatible with this process, giving the corresponding fused tricyclic compounds. 

A series of tetradentate pyridyl-imine terminated Schiff-bases, bis(pyridyl-imine) terminated siloxane and other related polymers, can be used as ligands to host copper(II) ions. These CuBr2/polyL/TEMPO catalytic systems (polyL stands for polydimethylsiloxane derived pyridyl-imine terminated ligand) are effective for aerobic oxidations of primary and secondary alcohols under aqueous conditions. Chiral N,0-Hgands, e.g., inexpensive L-proline, can also be used to prepare copper catalysts that are particularly effective for the oxidation of sterically hindered, allylic or heterocyclic alcohols such as l-(3-pyridyl)ethanol, l-(2-furfuryl)ethanol. 

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. 

Typical nucleophiles known to react with coordinated alkenes are water, alcohols, carboxylic acids, ammonia, amines, enamines, and active methylene compounds 11.12]. The intramolecular version is particularly useful for syntheses of various heterocyclic compounds[l 3,14]. CO and aromatics also react with alkenes. The oxidation reactions of alkenes can be classified further based on these attacking species. Under certain conditions, especially in the presence of bases, the rr-alkene complex 4 is converted into the 7r-allylic complex 5. Various stoichiometric reactions of alkenes via 7r-allylic complex 5 are treated in Section 4. 

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