Esters from Baeyer-Villiger reaction

A variety of esters can be prepared from the corresponding ketones usiag peracids ia a process usually referred to as the Baeyer-Villiger reaction (95) ie, cyclopentanone is converted to 5-valerolactone upon treatment of the ketone with peroxytrifluoroacetic acid ... 

Bis(trimethylsilyl) peroxide, (CH3)3SiOOSi(CH3)3, is prepared from trimethylsilyl chloride, l,4-diaza[2,2,2]bicyclooctane, and Dabco s complex with 2 mol of hydrogen peroxide [127]. It is used alone [228] or in the presence of catalysts such as pyridinium dichromate [236] trimethylsilyl trifluoromethanesulfonate, CF3S03Si(CH3)3 [228, 237] or tris-(triphenylphosphine)ruthenium dichloride, [(C6H5)3P]3RuCl2 [236]. This reagent oxidizes primary alcohols to aldehydes (in preference to the oxidation of secondary alcohols to ketones [236]), ketones to esters or lactones Baeyer-Villiger reaction) [238], and nucleoside phosphites to phosphates [228]. All these oxidations require anhydrous conditions. 

Oxidations with m-chloroperoxybenzoic acid are carried out in solutions in hexane, dichloromethane, chloroform, methanol, or tetrahydro-furan at temperatures ranging from -78 to 40 C. The applications of m-chloroperoxybenzoic acid are epoxidation [287, 314, 315, 316] the Baeyer-Villiger reaction [286, 315, 317, 378] and the oxidation of primary amines to nitro compounds [379], of tertiary amines to amine oxides [320], of sulfides to sulfoxides [327, 322, 323, 324], and of selenides to selenones [325]. Secondary alcohols are oxidized to ketones in the presence of hydrogen chloride [326], and acetals are oxidized to esters with boron trifluoride etherate as a catalyst [327]. The addition of potassium fluoride to reaction mixtures facilitates product isolation, because both m-chloroben-zoic acid and the unreacted m-chloroperoxybenzoic acid are precipitated... 

A single enzyme is sometimes capable of many various oxidations. In the presence of NADH (reduced nicotinamide adenine dinucleotide), cyclohexanone oxygenase from Acinetobacter NCIB9871 converts aldehydes into acids, formates of alcohols, and alcohols ketones into esters (Baeyer-Villiger reaction), phenylboronic acids into phenols sulfides into optically active sulfoxides and selenides into selenoxides [1034], Horse liver alcohol dehydrogenase oxidizes primary alcohols to acids (esters) [1035] and secondary alcohols to ketones [1036]. Horseradish peroxidase accomplishes the dehydrogenative coupling [1037] and oxidation of phenols to quinones [1038]. Mushroom polyphenol oxidase hydroxylates phenols and oxidizes them to quinones [1039]. 

Saponification of the ester product from the Baeyer-Villiger reaction is easily accomplished, leading to the alcohol and the interesting functional group transform (C—C=0 C—OH) for acyclic ketones. Cyclic... 

The second reason the Baeyer-Villiger reaction is significant is that it cleaves a carbon-carbon bond. You have seen only a very small number of reactions capable of this (e.g., ozonolysis Chapter 12). The power of this method to be a synthetic tool lies both in its high selectivity when the carbonyl compound is not symmetrical (see discussion of migratory aptitudes) and in the subsequent chemistry available from the ester or acid, which will be covered shortly. 

Scheme 9.176. A representation of the reaction of the ethyl ester of cyclohexanone-2-car-boxylic acid with excess permethanoic acid (peracetic acid, CH3CO3H). The labile epoxide presumed to be produced from the corresponding enol is expected to rearrange to a ketone, which undergoes the Baeyer-Villiger reaction.

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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