Pyridinium chlorochromate, oxidation

Perhaps the most important reaction of alcohols is their oxidation to carbonyl compounds. Primary alcohols yield either aldehydes or carboxylic acids, secondary alcohols yield ketones, but tertiary alcohols are not normally oxidized. Pyridinium chlorochromate (PCC) in dichloromethane is often used for oxidizing primary alcohols to aldehydes and secondary alcohols to ketones. A solution of Cr03 in aqueous acid is frequently used for oxidizing primary alcohols to carboxylic acids and secondary alcohols to ketones. 

In this reaction only the cyclopropane ring is opened to form III/66. This compound is in equilibrium with the y-lactol III/67, which, in case of R=H, was transformed oxidatively (pyridinium chlorochromate) to the furanone III/68. The synthesis of thiophene derivatives in a similar reaction is shown in Scheme III/ll, also. 

Halogenation of enol ethers and enol esters, leading directly to a-halo ketones is realized by use of molecular halogen or halide salts and metal oxidants. Pyridinium chlorochromate (PCC)/l2, Cr03/TMS-Cl/l2, AgOAcfi2, T10Ac/l2. ° Pb(OAc)4 and metal halides and Cu(OAc)2/l2 are useful classes of reagents for this conversion, and some examples are listed in Table 1. 

A-methylmorpholine A-oxide = pyridinium chlorochromate = 2-phenylsulfonyl-3-phenyloxaziridine = pyridinium p-toluenesulfonate = pyridinium / -toluenesulfonate = pyridine... 

Sol 4. (a) Oxidative annulation of alkenols to form six-membered rings may be accomplished with mildly acidic oxidant pyridinium chlorochromate (PCC). This process is postulated to occur via initial oxidation of the citronellol (I) to... 

The uses of the versatile oxidant pyridinium chlorochromate have been reviewed. Pyridinium chlorochromate has been used for the oxidation of methyl 5-hydroxypentanoate to the aldehyde, an intermediate useful in the synthesis of leukotrienes, and the same reagent oxidatively cleaves secondary vicinal diols to the corresponding aldehydes. The reactivity of the chlorochromate ion as an oxidant can be influenced by the counter-ion. For example, the 4-dimethylaminopyridinium salt is a mild, selective reagent for the oxidation of allylic and benzylic alcohols. Pyridinium fluorochromate oxidizes primary and secondary alcohols to aldehydes and ketones respectively in dichloromethane solution, and shows a less pronounced acidity compared with the chloro-... 

Pyridinium chloride, N-(4-pyridyl)-hydrochloride quaternization, 2, 175 reactions with amines, 2, 241 Pyridinium chlorochromates as oxidizing agents, 2, 170 reactions, 2, 34 Pyridinium dichromate as oxidizing agent, 2, 170 Pyridinium l-dicyanomethylide... 

Oxidation of tim5-4-(2,2,2-tnfluoro-l-hydroxy 1 tnfluoromethylethyl)cyclo-hexanol with pyridinium chlorochromate results m the correspondmg cyclic ketone whereas oxidation with nitnc acid m the presence of a catalyst causes ring cleavage [50] (equation 46)... 

Conditions that do pennit the easy isolation of aldehydes in good yield by oxidation of primaiy alcohols employ vaiious Cr(VI) species as the oxidant in anhydrous media. Two such reagents ar e pyridinium chlorochromate (PCC), C5H5NH ClCi03, and pyridinium dichromate (PDC), (C5H5NH)2 Ci207 both are used in dichloromethane. 

Pyridinium chlorochromate. In this case, the alcohol that is cleaved is simultaneously oxidized to give a ketone. ... 

Secondary alcohols are oxidized easily and in high yield to give ketones. For large-scale oxidations, an inexpensive reagent such as Na2Cr207 aqueous acetic acid might be used. For a more sensitive or costly alcohol, however, pyridinium chlorochromate is often used because the reaction is milder and occurs at lower temperatures. 

Q Primary alcohols can be oxidized to give aldehydes (Section 17.7). The reaction is often carried out using pyridinium chlorochromate (PCC) in dichloro-methane solvent at room temperature. 

What product would you obtain by reduction of digitoxigenin (Problem 27.39) with LiAl.H4 By oxidation with pyridinium chlorochromate ... 

The C2-symmetric epoxide 23 (Scheme 7) reacts smoothly with carbon nucleophiles. For example, treatment of 23 with lithium dimethylcuprate proceeds with inversion of configuration, resulting in the formation of alcohol 28. An important consequence of the C2 symmetry of 23 is that the attack of the organometallic reagent upon either one of the two epoxide carbons produces the same product. After simultaneous hydrogenolysis of the two benzyl ethers in 28, protection of the 1,2-diol as an acetonide ring can be easily achieved by the use of 2,2-dimethoxypropane and camphor-sulfonic acid (CSA). It is necessary to briefly expose the crude product from the latter reaction to methanol and CSA so that the mixed acyclic ketal can be cleaved (see 29—>30). Oxidation of alcohol 30 with pyridinium chlorochromate (PCC) provides alde-... 

Entries 5 to 7 are examples of oxidation of boranes to the carbonyl level. In Entry 5, chromic acid was used to obtain a ketone. Entry 6 shows 5 mol % tetrapropylam-monium perruthenate with Af-methylmorpholine-lV-oxide as the stoichiometric oxidant converting the borane directly to a ketone. Aldehydes were obtained from terminal alkenes using this reagent combination. Pyridinium chlorochromate (Entry 7) can also be used to obtain aldehydes. Entries 8 and 9 illustrate methods for amination of alkenes via boranes. Entries 10 and 11 illustrate the preparation of halides. 

Xb was utilized in the elaboration of the hydrindan XIII and subsequently compound XIV. We expected that Xa could be converted to XIII in the same manner as was in the Sih synthesis. This was confirmed in practice (Scheme II). Oxidation of 569 mg (2.68 mmol) of Xa with pyridinium chlorochromate in methylene chloride furnished 532 mg (94%) of enone Ila (7,21). Treatment of 130 mg of Xa witlj a slight excess of Jones reagent (3,22) afforded 126 mg (98%) of Ila. Allylic brominatlon of Ila with a 20% excess of N-bromosuccinimide (NBS) in refluxing carbon tetrachloride provided Xlla in 98% yield. 

A biomimetic synthesis of benzo[c]phenanthridine alkaloids from a protoberberine via the equivalent of a hypothetical aldehyde enamine intermediate has been developed (130,131). The enamide 230 derived from berberine (15) was subjected to hydroboration-oxidation to give alcohol 231, oxidation of which with pyridinium chlorochromate afforded directly oxyche-lerythrine (232) instead of the expected aldehyde enamide 233. However, the formation of oxychelerythrine can be rationalized in terms of the intermediacy of 233 as shown in Scheme 41. An alternative and more efficient... 

This complex, formerly called pyridine perchromate and now finding application as a powerful and selective oxidant, is violently explosive when dry [1], Use while moist on the day of preparation and destroy any surplus with dilute alkali [2], Preparation and use of the reagent have been detailed further [3], The analogous complexes with aniline, piperidine and quinoline may be similarly hazardous [4], The damage caused by a 1 g sample of the pyridine complex exploding during desiccation on a warm day was extensive. Desiccation of the aniline complex had to be at ice temperature to avoid violent explosion [4]. Pyridinium chlorochromate is commercially available as a safer alternative oxidant of alcohols to aldehydes [5], See Chromium trioxide Pyridine Dipyridinium dichromate See Other AMMINECHROMIUM PEROXOCOMPLEXES... 

The pyranocoumarin 105 can be prepared via a three-component Diels-Alder reaction between 4-hydroxycoumarin, ethyl vinyl ether and an a-dicarbonyl compound. Similarly to the above, upon treatment of 105 with sulfuric acid in THF, hydrolysis and rearrangement occur to give the furofurochromenone 106. The hemiacetal functionality in 106 may then be oxidized with pyridinium chlorochromate (PCC) to give the lactone 107 <2001EJ03711> (Scheme 28). 

A variety of oxidizing agents are available to prepare aldehydes from 1° alcohols such as pyridinium chlorochromate (PCC) and pyridinium dichromate (PDC). 

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