Chlorochromates, in oxidation

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

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. 

The pyridinium chlorochromate (PCC) oxidations of pentaamine cobalt(III)-bound and unbound mandelic and lactic acids have been studied and found to proceed at similar rates.Free-energy relationships in the oxidation of aromatic anils by PCC have been studied. Solvent effects in the oxidation of methionine by PCC and pyridinium bromochromate (PBC) have been investigated the reaction leads to the formation of the corresponding sulfoxide and mechanisms have been proposed. The major product of the acid-catalysed oxidation of a range of diols by PBC is the hydroxyaldehyde. The reaction is first order with respect to the diol and exhibits a substantial primary kinetic isotope effect. Proposed acid-dependent and acid-independent mechanisms involve the rapid formation of a chromate ester in a pre-equilibrium step, followed by rate-determining hydride ion transfer via a cyclic intermediate. PBC oxidation of thio acids has been studied. ... 

Ketone rac-13 was transformed into the corresponding silylenolether and by Pd(II)-mediated Saegusa oxidation [14] into a, -unsaturated ketone rac-14. By alkylative enone transposition comprising methyl lithium addition and pyridinium chlorochromate (PCC) oxidation [15], rac-14 was finally converted into the racemic photo cycloaddition precursor rac-6. In conclusion, the bicyclic irradiation precursor rac-6 was synthesized in a straightforward manner from simple 1,5-cyclooctadiene (11) in nine steps and with an overall yield of 21%. 

Oxidation of 8-hydroxymethyl-2-isopropyl-l 1 //-pyrido[2,l-b]quinazolin-11-one with pyridinium chlorochromate in methylene chloride gave the 8-carboxaldehyde, which was converted into its 8-aminomethyl derivatives by reacting with amines followed by reduction of the Schiff bases with sodium cyanoborohydride in acetic acid (87JOC2469). 

This methodology was applied to the synthesis of L-streptose [91] and methyl a-D-mycaroside [95 a], The difficulty of this photochemical oxidation originates from the sensitivity of pyruvates to hydrolysis. This approach seems limited to small quantities of substrates but does not need any separation technique as in oxidation by pyridinium chlorochromate [95 b]. Nethertheless, photolysis of pyruvates of partially protected derivatives of a-D-g/ucofuranose and P-D-fructofuranose in benzene yields the corresponding oxidized products in excellent yields [96]. 

In the following experiments cyclohexanol is oxidized to cyclohexanone using pyridinium chlorochromate in dichloromethane. The progress of the reaction can be followed by thin-layer chromatography. On a larger scale this reaction would be carried out using sodium dichromate in acetic acid because the reagents are less expensive, the reaction is faster, and much less solvent is required. 

Alternatively, pyridinium chlorochromate in dichloromethane has successfully been used to obtain both aldehydes and ketones, 516,517,540,547,607,785 - 788,790-802 most cases from the corresponding alcohols, although the silyl ether of a secondary alcohol has been oxidized to the corresponding ketone, In order to facilitate the reaction, sodium acetate, molecular sieves, " alumina, and Celite have been added (Table 2), The closely related reagent pyridinium dichromate, however, has been far less frequently utilized. ... 

Pyridinium chlorochromate as oxidant in organic synthesis 82S245. Pyridinium compounds, kinetics and mechanism of nucleophilic sub-... 

Schemes have been devised to substitute less toxic metals for more toxic ones. Potassium ferrate on K10 mont-morillonite clay has been used to replace potassium chromate and potassium permanganate in the oxidation of alcohols to aldehydes and ketones in 54-100% yields.153 The potassium ferrate is made by the action of sodium hypochlorite on iron(III) nitrate or by treatment of iron(III) sulfate with potassium peroxymonosulfate.154 After the oxidation, any excess oxidizing agent, and its reduced form, are easy to recover by filtration or centrifugation. In another case, manganese-containing reagents have been substituted for more toxic ones containing chromium and selenium (4.21).155 Selenium dioxide was used formerly in the first step and pyridinium chlorochromate in the second.

The synthetic utility of a-silyl esters has been amply demonstrated by several examples. The basis for this chemistry is the observation that ester lithium enolates can be directly C-silylated with methyldiphenylchlorosilane, a reagent which avoids the more common O-silylation153. The a-silyl-y-valerolactone 80 was converted in two steps and high yield to racemic ancepsenolide by condensation of its lithium enolate with decane 1,10-dicarboxaldehyde followed by isomerization to the endocyclic double bonds of the natural product154 (equation 160). Treatment of the a-silyl-y-butyrolactone 81 or 80 with a Grignard reagent followed by pyridinium chlorochromate (PCC) oxidation provides 4-oxo aldehydes and 1,4-diketones, respectively155 (equation 161). 

The discovery route utilized the pyridinium chlorochromate (PCC) oxidation of 2-cyclohexylethanol in CH2CI2 in presence of molecular sieves. It is a simple process, as the aldehyde is simply isolated by filtration of the reaction mixture through silica gel. However, this process was proven to be difficult to scale up due to difficulties of filtration of the chromium salts. Furthermore, the environmental issues created by the large amount of toxic chromium salts make this process unsuitable for large-scale synthesis. Two other processes (Scheme 6.7) were therefore developed and tested to prepare the required 2-cyclohexyl acetaldehyde at the pilot-plant scale ... 

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