Carbonylation, selective oxidation

Benzoic acid and naphthoic acid are formed by the oxidative carbonylation by use of Pd(OAc)2 in AcOH. t-Bu02H and allyl chloride are used as reoxidants. Addition of phenanthroline gives a favorable effect[360], Furan and thiophene are also carbonylated selectively at the 2-position[361,362]. fndole-3-carboxylic acid is prepared by the carboxylation of 1-acetylindole using Pd(OAc)2 and peroxodisulfate (Na2S208)[362aj. Benzoic acid derivatives are obtained by the reaction of benzene derivatives with sodium palladium mal-onate in refluxing AcOH[363]. 

The alkyl derivatives of thiazoles can be catalytically oxidized in the vapor phase at 250 to 400°C to afford the corresponding formyl derivatives (21). Molybdenum oxide, V2O5, and tin vanadate are used as catalysts either alone or with a support. The resulting carbonyl compounds can be selectively oxidized to the acids. 

Oxidation of alcohols to carbonyls (2° alcohols can be selectively oxidized)... 

Attempts to achieve selective oxidations of hydrocarbons or other compounds when the desired site of attack is remote from an activating functional group are faced with several difficulties. With powerful transition-metal oxidants, the initial oxidation products are almost always more susceptible to oxidation than the starting material. When a hydrocarbon is oxidized, it is likely to be oxidized to a carboxylic acid, with chain cleavage by successive oxidation of alcohol and carbonyl intermediates. There are a few circumstances under which oxidations of hydrocarbons can be synthetically useful processes. One group involves catalytic industrial processes. Much effort has been expended on the development of selective catalytic oxidation processes and several have economic importance. We focus on several reactions that are used on a laboratory scale. 

Dehydration of cortisone (198) affords the diene 199. This is then converted to ketal 200. The selectivity is due to hindrance about both the 11- and 20-carbonyl groups. The shift of the double bond to the 5,6-position is characteristic of that particular enone. Treatment of protected diene 200 with osmium tetroxide results in selective oxidation of the conjugated double bond at C-16,17 to afford the cis-diol (201). Reduction of the ketone at C-ll (202) followed by hydrolysis of the ketal function gives the intermediate 203. Selenium dioxide has been... 

Manganese dioxide (Mn02) supported on silica provides an expeditious and high-yield route to carbonyl compounds. Benzyl alcohols are selectively oxidized to carbonyl compounds by use of 35 % Mn02 doped silica under MW irradiation conditions (Scheme 6.28) [96]. 

Chemistries such as gasification, carboxylation, carbonylation, partial oxidation, and salt splitting may see much greater emphasis in manufacturing. These chemistries will need concurrent development of more selective catalytic and biocatalytic systems and promoters, as well as processes requiring much less ex-... 

Etard reagents (chromyl chloride and some derivatives) suffer from the problem that occasionally they can exhibit a lack of selectivity and low yields. They are useful in the selective oxidation of aromatic side-chains to a carbonyl group, aldehyde or ketone but in many instances, the formation of the initial complex is slow and yields are low because of difficulties in the work-up which lead to undesired over-reaction. Attempts have been made to solve the problems by the use of sonication [134]. A simple preparation of the liquid reagent was proposed and the Etard reaction itself together with the hydrolytic step were conducted under sonication, with some success (Scheme 3.25). 

The oxidation of alcohols to carbonyl compounds has been studied by several authors and a variety of methods have been used. Papers concerned vith such oxidations are illustrated (Scheme 3.26). Good results have been obtained using pyridinium chlor-ochromate (PCC) adsorbed onto silica gel for the selective oxidation of unsaturated substrates e.g. terpene [135] and furanyl derivatives [136]. Steroidal homoallylic alcohols can be converted to the corresponding 4-ene-3,6-diones using tetrapropylammo-nium per-ruthenate (TPAP) in catalytic amounts [137]. In this case, the oxidising agent is N-methyl morpholine N-oxide (NMO). 

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-... 

The ready condensation of sucrose with excess triphenylmethyl chloride in pyridine to a tri-trityl ether is, however, more easily explained by XV or II, which have three, instead of two (c/. I), primary alcohol groups to react selectively in the condensation. Fleury and Courtois oxidized sucrose for twenty-four hours at 14° with an excess of suitably buffered periodic acid and found that three moles of the oxidant were consumed and one mole of formic acid was eliminated. This highly selective oxidant is known to cleave unsubstituted 1,2 glycols quantitatively to two carbonyl groups and to eliminate the center carbon atom... 

Lead tetraacetate is a selective oxidizing agent causing oxidative cleavage of polyhydroxy compounds. It cleaves compounds that have hydroxyl groups on adjacent carbon atoms, breaking the carbon-carbon bonds to form carbonyl compounds, such as aldehydes, ketones or acids. The reaction is carried out in organic solvents. A typical example is as follows ... 

They used this new oxidizing reagent for a rapid and selective oxidation of primary and secondary benzylic alcohols to the corresponding aldehydes and ketones in good to excellent yields. BTPCP was later used for oxidation of various alkylbenzenes under neutral conditions in aqueous CH3CN to the corresponding carbonyl compounds in good yields (equation 34) °. ... 

The coupling of the same boronic acid was also achieved with 4-chlorobenzoyl chloride (6.5.), Running the reaction under anhydrous conditions the desired 2-(4 chlorobenzoyl)thiophene was obtained in good yield.7 The opening step in this process is the selective oxidative addition of the palladium into the carbonyl-chlorine bond giving an acylpalladium complex, which on subsequent transmetalation and reductive elimination gives the observed product. 

By a suitable choice of activating reagents, primary and secondary alcohols can be selectively oxidized to carbonyl compounds in good yields at room temperatures. Typical activating reagents ate acetic anhydride, sulfur trioxide—pyridine, dicyclohexyl catbodiimide, and phosphorus pentoxide (40). 

Alkali periodates (in aqueous solution)646 and ammonium periodate (in anhydrous aprotic solvent),647 when applied in the presence of a catalytic amount of 0s04, are selective oxidizing agents used to form carbonyl compounds. Os04 apparently transforms the alkene to an 1,2-diol that is subsequently cleaved by the periodate to the carbonyl compound end products. The periodate also serves to regenerate Os04. 

Molybdenum-peroxo compounds have been shown to achieve a variety of selective oxidations they a-hydroxylate enolizable ketones, presumably via epoxidation of the enolate (equation 27) 163 they cause Baeyer-Villiger lactonization of cyclic ketones, probably via the formation of five-membered trioxametallacycles (equation 28) 164 they oxidize alcohols to carbonyl compounds... 

Associated with BiCl3 and LiCl, RhCl3 acts as a very effective catalyst for the selective oxidation of secondary alcohols to carbonyl compounds by 02 under mild conditions. Selectivities up to 90% and turnovers numbering up to 200 have been obtained (equation 62).213... 

Palladium compounds are effective catalysts for the selective oxidative transformation of primary and secondary alcohols into carbonyl compounds. Although conventional PdCl2/CuCl2 catalysts can operate at 70-120 °C and under 02 pressure (3 atm),465 milder procedures using a PdCl2/NaOAc mixture are effective at room temperature and atmospheric 02 pressure (equation... 

The treatment of 1,2-diols with Dess-Martin periodinane may lead either to a 1,2-dicarbonyl compound,14 or to an oxidative breakage of a C-C bond14,72 depending on stereoelectronic factors. When a 1,2-dicarbonyl compound is obtained, very often, one of the carbonyl groups tautomerizes to the enol form. Under controlled conditions, very often, it is possible to selectively oxidize one of the alcohols in a 1,2-diol, particularly when this alcohol is an allylic one.73... 

IBX is able to transform tosylhydrazones and oximes into carbonyl compounds under very mild conditions.99 It is possible to selectively oxidize alcohols with IBX in the presence of sulfides.83,100 In fact, IBX has a lesser tendency to oxidize sulfides than Dess-Martin periodinane and in some sulfur-containing substrates it can be the oxidant of choice.36... 

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