Keto aldehydes cleavage

The obvious Vfittig disconnection gives stabilised ylid (5fi) and keto-aldehyde (57). We have used many such long-chain dicarbonyl compounds in this Chapter and they are mostly produced from available alkenes by oxidative cleavage (e.g. ozonolysis). In this case, cyclic alkene (58) is the right starting material, and this can be made from alcohol (59) by elimination,... 

Chiral 4,4-dialkyl-l-cyclopentenones.1 The chiral bicyclic lactam 2, derived from levulinic acid and 1, on monoalkylation exhibits slight if any selectivity regardless of the electrophile. However, a second alkylation exhibits high endo-selectivity. This product (3), after reductive cleavage, furnishes a keto aldehyde that is cyclized by base to a chiral 4,4-disubstituted-2-cyclopentenone (4). Either antipode of 4 can be prepared by the sequence of alkylation. 

Terminal alkynes under these conditions undergo oxidative cleavage to the carboxylic acid, presumably because the intermediate keto aldehyde would yield the unstable a-keto acid. 

For reducing ozonides or sterically hindered peroxides, magnesium and methanol proved to be a better and mild reducing agent <2004JOC2851>. Thus, the bicylic ozonide prepared from 1-phenylcyclopentene, which is prone to base-mediated cleavage, was cleanly reduced by Mg/MeOH to the keto-acid with the ketonic methyl ester as a by-product, whereas reduction with zinc and acetic acid affords mainly the keto-aldehyde with the keto-acid as a by-product (Equation 7). 

Oxidative cleavage of the terminal olefin in 40 and 41 gave the keto aldehydes 42 and 43. 

Cleavage of a-keto acetals. Nafion-H is recommended as a catalyst for hydrolysis of these acetals to the unstable a-keto aldehydes. The reaction is carried out in two steps (equation I). 

The mono-pincer ruthenium(II) complex was successfuUy employed in the oxidative cleavage of olefins to aldehydes, dialdehydes or keto-aldehydes. 

R = CHN2) followed by acid-catalysed cleavage of the resultant cyclopropyl ketone. Lithium aluminium hydride reduction of (441) gave two epimeric alcohols (443) which, on Collins oxidation, yielded the keto-aldehyde (444). Reaction of (444) with sodium triethylphosphonoacetate afforded the two isomeric keto-esters (445 R = H, R = COjEt) and (445 = CO2EL = H) which, on... 

Indirect electrooxidation of cyclic aziridines using NaCl or NaBr as a redox catalyst results in C(l)-C(2) bond cleavage under formation of the corresponding keto nitriles. This reaction is explained by the intermediate generation of an azaallenyl cation, which is hydrated to the o -hydroxyimine. Further oxidation by Cl" then would lead to the open-chain keto A-chloroimine, which by HCl elimination forms the keto nitrile, while its hydrolysis leads to the keto aldehyde as a side product [32] ... 

In summary, the uncatalysed oxidation of hydrocarbons at temperatures of up to 120°C leads to alkylhydroperoxides, ROOH, dialkylperoxides, ROOR, alcohols, ROH, aldehydes, RCHO and ketones, RR C=0. In addition, cleavage of a dihydroperoxide II of Reaction (4.4) leads to diketones, RCO(CH2)jCOR keto-aldehydes, RCO(CH2)jCHO, hydroxy ketones, RCH(OH)-(CH2)jCOR and so forth. Under metal-catalysed conditions or at higher temperatures, considered in Sections 4.2.2 and 4.2.3, degradation leads to a complex mixture of final products. 

The synthesis of compound (8> is discussed in Chapter 36. Cleavage of (7> by ozone with reductive work-up (Table 26.1) gives the keto aldehyde (6) and cyclisation gives the most substituted double bond. 

Oxidation of 12 with excess Collins Reagent in methylene chloride yields the sensitive keto aldehyde 13. A pinacol cyclization of the keto aldehyde 13. to the tricyclic intermediate 14 is accomplisehd by reaction with finely powdered metallic Titanium inTHF. 2, 13 Oxidation to the ketol without appreciable glycol cleavage can be readily accomplished via an oxysulfonium intermediate. 14, 15 "phe ketol can then be converted to the MEM ether derivative by treatment with MEM chloride and diisopropylethylamine in methylene chloride at reflux to give the MEM ether derivative 15. ... 

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