Cyclopentanone Baeyer-Villiger oxidation

The reduction of the unsaturated ketone (560) can be controlled to give mainly the cw-cyclopentanone (561). Upon treatment with sodium hydroxide isomerization to the trans compound occurs. Both isomers undergo a Baeyer-Villiger oxidation to the corresponding tetrahydropyranones, of which the cis isomer is rather unstable (Scheme 213) (82GJC29). 

More recently, the formal total syntheses of some bioactive natural products bearing a tetrahydrofurane moiety were achieved by enzymatic Baeyer-Villiger oxidation using cyclopentanone monooxygenases (CPMOs) from Comamonas sp. 

Ueno, S., Ebitani, K., Ookubo, A. and Kaneda, K. (1997). The active sites in the heterogeneous Baeyer-Villiger oxidation of cyclopentanone by hydrotalcite catalysts. Appl. Surf. Sci. 121, 366. 

The anhydrous reagent gives improved results in the Baeyer-Villiger oxidation of cyclic ketones to lactones. Thus cyclopentanone afforded 8-valerolactone in... 

The basic sites of HT (type A in Figure 2.44) are active in the Baeyer-Villiger oxidation of various carbonyl compounds, for example, the oxidation of a substrate in the presence of O2 and an aldehyde (e.g., benzaldehyde) through the intermediate formation of a peracid. An example is the oxidation of cyclopentanone to 5-valer-olactone [275]. The base property of hydrotalcites can be tuned by changing the Mg/Al ratio and the content of interlayer anion species, for example, Cl and S04 ... 

Baeyer-Villiger oxidation is also a common feature during the catabolic degradation of a variety of other compounds, including monocyclic, bicyclic or polycyclic molecules. For monocyclic compounds, one of the first reports describing formation of a lactone from racemic a-substituted cyclopentanone by various Pseudomonas sp. was by Shaw1341. This could be regarded as the first indication that these reactions were to prove of interest for asymmetric synthesis since the lactone product displayed some optical activity (Fig. 16.5-6). 

Another prominent route to develop 1,5-difunctionlized molecular skeletons is the oxidative cleavage of cyclopentene derivatives (Scheme 2.57). In Corey s terminology of retrosynthesis this is the reconnect operation (reconnection of the two functionalities). Other reactions that faU under this heading include the Baeyer-Villiger oxidation and the Beckmann rearrangement of cyclopentanones. 

Miscellaneous. Sodium bromide or sodium iodide can be used with Amberlyst 15 to effect regioselective ring-opening reactions of substituted aziridlne-2-carboxylates to a-halo- -amino esters. 1,3 Dicarbonyl compounds can be brominated using potassium bromate/potasslum bromide in the presence of Dowex resin.Amberlyst 15 bound sulfonic acid groups are oxidized by aqueous hydrogen peroxide at 70 °C and the peracid that is formed has been used in Baeyer-Villiger oxidation of cyclopentanone. ... 

Another interesting way to construct 8-lactones is the Baeyer-Villiger oxidation [72] of cyclopentanones. For example, Hacini and Santelli have reported an efficient synthesis of the Prelog-Djerassi lactone methyl ester using Baeyer-Villiger oxidation [73] (Scheme 30). Hydrolysis of enol ether 162 derived from —)-trans-pulegenic acid furnished an inseparable diastereomeric mixture of the corresponding dimethylacetals. Ozonolysis of the olefin and subsequent... 

Adger et al. have reported an enantioselective method for the synthesis of 5-lactones via application of enzymatic Baeyer-Villiger oxidation [75] (Scheme 32). Oxidation of cyclopentanone derivative 168 using a monooxygenase... 

Yamamoto et al. have reported the synthesis of optically active 8-lactones by Baeyer-Villiger oxidation of chiral cyclopentanones [77] (Scheme 34). Asymmetric hydrogenation of enones 175 and 176 in the presence of 0.01 equivalent of Ru2Cl4[(5)-p-Tolyl-Binap]2NEt3 catalyst afforded chiral ketones 177 and 178 in good yield and with excellent enantioselectivity. These chiral ketones were found to show a fundamentally jasmine-like floral odor. Chiral ketones 177 and 178 were then transformed to 8-lactones 179 and 180 by Baeyer-Villiger oxidation with... 

In view of the biological importance of the 6-lactone moiety, extensive efforts have been devoted for the development of various methods for the synthesis of saturated 8-lactones. Ammig the various methods, the more classical methods include lactonization of the 8-hydroxy acid derivatives, Baeyer-Villiger oxidation of cyclopentanones, and oxidation of lactols. Besides, more challenging and attractive methods such as oxidative lactonization, radical cyclization, and carbonylatimi have also been used efficiently for the synthesis of 8-lactones. The past two decades have witnessed remarkable growth in the development of catalytic and asymmetric methods for the synthesis of 6-lactones in optically pure form. In the next decade, new and more exciting advances in the development of efficient and catalytic enantioselective methods and their application in the synthesis of complex 8-lactone natural products can be expected. 

A final oxidation type that has been observed is the catalysis of Baeyer-Villiger-type oxidations of cyclic ketones to lactones.53 Understandably, the strained cyclobutanone is the best substrate, giving 80% conversion after 24 h at 25°C (tert-butanol solvent). Larger ring ketones proceed more slowly, although selectivity remains high. Elevated temperatures increase the rate without sacrificing selectivity cyclopentanone is converted to the lactone in 72% yield after 1 h at 70°C in THF. Complex 4 was presumed to be the active species. 

Baeyer-Villiger reaction. This peracid has been used for the Baeycr-Villiger reaction with cyclopentanones and cyclohexanones. The reaction is carried out with 1.25 molar equiv. of benzeneseleninic acid and 10 molar equiv. of H2O2 in THF or CH2CI2 buffered to pH 7. Yields are comparable to those with other peracids. One example, 1 2, was reported where oxidation was achieved only with this peracid. 

Seven-membered cyclic orthocarbonates are also available via a formal double Baeyer-Villiger reaction by oxidation of a cyclopentanone diethyl acetal with m-chloroperbenzoic acid, for example the synthesis of orthocarbonates (167) and (168) (Scheme 31) <82JAI769>. However, only moderate yields (15-37%) of pure seven-membered cyclic orthocarbonates have been obtained, as complications arise with the separation of the complex reaction mixture. Moreover, precautions should be taken, because these reactions become very violent after an induction period. However, this procedure provides a simple method for the oxidative removal of the carbonyl group from a ketone via the intermediacity of an orthocarbonate. This is accomplished by treatment of the crude reaction mixture with LAH in ethereal solution to give the corresponding diols, thereby avoiding the crucial product separation. 

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