Ketones by Baeyer-Villiger oxidation

Transformation of cyclic ketones into lactones by Baeyer-Villiger oxidation 99EJ0737. 

Lactone (15) can be derived by Baeyer-Villiger oxidation of syrnmetrica) ketone (16) whose further analysis follows the usual strategy for symmetrical ketones,... 

Scheme 13.17 depicts a synthesis based on enantioselective reduction of bicyclo[2.2.2]octane-2,6-dione by Baker s yeast.21 This is an example of desym-metrization (see Part A, Topic 2.2). The unreduced carbonyl group was converted to an alkene by the Shapiro reaction. The alcohol was then reoxidized to a ketone. The enantiomerically pure intermediate was converted to the lactone by Baeyer-Villiger oxidation and an allylic rearrangement. The methyl group was introduced stereoselec-tively from the exo face of the bicyclic lactone by an enolate alkylation in Step C-l. 

Oxidative degradation of the catalyst (e.g. lactone formation by Baeyer-Villiger oxidation) competes with oxygen transfer and is the reason a relatively high catalyst loading is required. In their search for more robust, yet (comparatively) readily available ketone catalysts, Shi et al. prepared the carbamates 12a-c [20-22], Use... 

Fig. 17.32. Oxidative cleavage of an asymmetric ketone with complementary regiose-lectivities. Lactone A is obtained by Baeyer-Villiger oxidation of menthone [2-methyl-5-(l- methylethyl)cyclo-hexanone]. Alternatively, one may first convert menthone into the silylenol ether B and cleave its C=C double bond with ozone to obtain a silyl ester containing an a-methoxyhydroperoxide group as a second functional group (which resembles the unstable structural element of the so-called ether peroxides cf. Figure 1.38). The latter is reduced with NaBH4tothe hydroxylated silyl ester C. The hydroxycarboxylic acid is obtained by acid-catalyzed hydrolysis. It cyclizes spontaneously to give lactone D.

Alternative methods for the formation of the catechol (5) were examined, and these serve to show other methods for introduction of the hydroxy group. Nitration of triene (6) followed by reduction to the amine and diazotization in the presence of methanol gave the phenol (8), but only in poor yield. The best method developed appears to be acetylation of the triene (6) with titanium tetrachloride/acetyl chloride to give the ketone (9), followed by Baeyer-Villiger oxidation to die acetate (10), which on hydrolysis afforded the catechol (8) in 70% overall yield. 

Ha and Hart [78] introduced a new functional group conversion of the 4-styryl group in azetidinones of type 142 (Scheme 24). Namely, the trans isomer of 142, readily available from the lithium enolate 147 and the imine 141, was iV-deprotected and the resulting N-H azetidinone converted to the bromohy-drin 148. Dehalogenation and further Jones oxidation of the resulting diastereomeric alcohols 149 produced the ketone 150, which was transformed into the 4-acetic acid derivative 151 by Baeyer-Villiger oxidation. 

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... 

CuOTf-catalyzed photobicyclization of 1,6-heptadien-3-ols produces bicyclo[3.2.0]heptan-2-ols (eq 21)P In conjunction with pyrolytic fragmentation of the derived ketones, these CuOTf-catalyzed photobicyclizations provide a synthetic route to 2-cyclopenten-l-ones from 1,6-heptadien-3-ols (eq 28). The derived ketones can also be converted into lactones by Baeyer-Villiger oxidation and, in conjunction with pyrolytic fragmentation, CuOTf-catalyzed photobicyclizations provide a synthetic route to enol lactones of glutaraldehydic acid from 1,6-heptadien-3-ols (eq 28). ... 

The reaction of ketones with peroxy acids is both novel and synthetically useful An oxygen from the peroxy acid is inserted between the carbonyl group and one of the attached car bons of the ketone to give an ester Reactions of this type were first described by Adolf von Baeyer and Victor Vilhger m 1899 and are known as Baeyer—Villiger oxidations... 

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