Baeyer-Villiger process

The high chemoselectivity for the Baeyer-Villiger process was utilized in the synthetic elaboration of another hetero-bicyclic substrate. The biooxidation only provides the expected unsaturated lactone in a desymmetrization reaction without compromising the olefin functionality. The biotransformation product was then converted to pivotal intermediates for C-nucleosides like showdomycin, tetrahydro-furan natural products like kumausyne, and goniofufurone analogs in subsequent chemical operations (Scheme 9.17) [161]. 

The Baeyer-Villiger process for conversion of open-chain ketones to esters, or cyclic ketones to lactones by a peracid involves an intermediate a-hydroxyperester (235) step, as shown in equation 83. Determination of 235 in the reaction mixture involves selective reduction of the peroxyacid with diphenyl sulfide and reduction of 235 with excess iodide, followed by titration of the liberated iodine. The presence of various transition metal ions may affect the determination by accelerating the final step of the synthetic process, thus... 

Where the selectivity of BVMOs regarding the Baeyer-Villiger process versus a heteroatom oxidation is concerned, usually the oxygenation at the carbonyl center is favored. This was demonstrated in a study of heterocyclic substrates of type 6 to give good yields of the corresponding lactone product 7 (Scheme 21.3) [61, 62]. 

The (1S,5R)-2-oxabicydo-octenone (see Fig. 5) is formed with 96% ee from one ketone enantiomer of racemic bicyclo[3.2.0]hept-2-en-6-one, which is synthesized in a cycloaddition reaction from cyclopentadiene and dichloroacetylchloride with subsequent Zn-reduction. The key limitation to the biocatalytic Baeyer-Villiger process is product inhibition [26]. In order to overcome product inhibition problems, in situ product removal was required. 

Figure 16.5-74. Involvement of enzymatic Baeyer-Villiger processes in the degradation of non-steroidal polycyclic compounds.

Application of dynamic kinetic resolution has also been reported in a whole-cell enzymatic Baeyer-Villiger process. While this was initially done using slightly basic conditions, Furstoss and Alphand have more recently reported the use of a weakly basic anion exchange resin to promote racemization of the slow oxidizing enantiomer 99 to the fast enantiomer 100.53 Baeyer-Villiger oxidation using recombinant E. coli to overexpress the CHMO from A. calcoaceticus provided excellent yield and % ee of lactone 101. 

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 ... 

When a ketone 1 is treated with hydrogen peroxyde or a peracid, a formal insertion of oxygen can take place to yield a carboxylic ester 2. This process is called the Baeyer-Villiger oxidation ... 

In miscellaneous oxidative processes of indoles, two methods for the preparation of 3-hydroxyindoles have been reported. The first approach involves initial Vilsmeier-Haack reaction of indole-2-carboxylates 176 to afford the corresponding 3-formyl analogs 177. Activation of the aldehyde with p-toluenesulfonic acid (PTSA) and Baeyer-Villiger oxidation with m-chloroperoxybenzoic acid (wi-CPBA) then affords high yields of the 3-hydroxy compounds 178 <00TL8217>... 

Bacteriological sulfur, 23 577-578 Bacteriophages, 3 135 12 474 in fermentation, 11 46 Bacteriorhodopsin, 20 826, 840 photochromic material, 6 603 Bacteriosins, 12 76. See also Bacteriocins Bacteriostatic water, 18 714 Bacterium lactis, 11 7 Baculovirus expression system, 5 346 Baddeleyite, 21 489 26 623-624 colorants for ceramics, 7 346t Badische Anilin und Soda Fabrik (BASF) terpenoid manufacture process, 24 481 Baeyer-Villiger oxidation reactions, 14 592 chiral recognition by enzymes, 3 675 microbial, 16 401 Baffled shellside flow, 13 262 Baffles, in stirred tank geometries,... 

Acidic products result from further oxidation of aldehydes (or ketones), again by a radical process. Oxidation of an aldehyde to a carboxylic acid in the presence of air involves a peroxy acid (compare peroxyacetic acid. Section 8.1.2). Finally, a reaction between the peroxy acid and a molecule of aldehyde yields two carboxylic acid molecules this is not a radical reaction, but is an example of a Baeyer-Villiger oxidation. Baeyer-Villiger... 

Oxidoreductases are, after lipases, the second most-used kinds of biocatalysts in organic synthesis. Two main processes have been reported using this type of enzymes-bioreduction of carbonyl groups [39] and biohydroxylation of non-activated substrates [40]. However, in recent few years other processes such as deracemization of amines or alcohols [41] and enzymatic Baeyer-Villiger reactions of ketones and aldehydes [42] are being used with great utility in asymmetric synthesis. 

Acyclic and cyclic ketones may be oxidized to esters or lactones, respectively, by a variety of oxidants including peracids or peroxides associated with suitable catalysts. This reaction is known as Baeyer-Villiger (BV) oxidation and it was originally applied to the oxidation of menthone and tetrahydrocarvone with monopersulfuric acid (equation 69). With the increase of environmental concern, much research has focused on the development of catalytic BV processes based on green and cheap oxidants like hydrogen peroxide and relatively non-toxic metals (Re, Pt, Ti). ... 

The Baeyer-Villiger oxidation of ketones represents a powerful synthetic method that breaks carbon-carbon bonds in an oxygen insertion process to deliver lactones. A recent comprehensive review by ten Brink et describes the different... 

The same Pt species that epoxidize double bonds are active in Baeyer-Villiger oxidation of ketones. Strukul has shown that this synthetically interesting process can be carried out also enantioselectively, in the presence of appropriate diphosphine ligands121-123. For this reaction a mechanism has been proposed that involves again a quasi-peroxo metallacycle intermediate, even though in this reaction the metal catalyst plays primarily the role of a Lewis acid while the real oxidant is H2O2 itself (Scheme 9). 

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