Baeyer-Villiger oxidation pathway

Bac2 pathway, 239, 384 Baeyer-Villiger oxidation, 127 Barton reaction, 337 Base catalysis general, 75... 

Alternative reactions employ coupling reagents such as DCC (Steglich Esterification), preformed esters (transesterification), carboxylic acid chlorides or anhydrides. These reactions avoid the production of water. Another pathway for the production of esters is the formation of a carboxylate anion, which then reacts as a nucleophile with an electrophile (similar reactions can be found here). Esters may also be produced by oxidations, namely by the Baeyer-Villiger oxidation and oxidative esterifications. 

Sever, R. R., Root, T. W. Computational Study of Tin-Catalyzed Baeyer-Villiger Reaction Pathways Using Hydrogen Peroxide as Oxidant. 

All these degradation pathways were shown to involve a Baeyer-Villiger oxidation of a cycloalkanone that led to formation of the corresponding lactone. Further degradation then occured via hydrolysis of this lactone by a lactone hydrolase which has, in some cases, been isolated. As an example, the reaction sequence for the degradation of cyclopentanol by Pseudomonas sp. NCIMB 98721351 is shown in Fig. 16.5-7. 

The major pathway to 3,4-dihydro-2/f-l,5-benzodioxepin-2-ones (140) is the Baeyer-Villiger oxidation of flavanones (139) <91SC2263>. Reaction of catechol with carbon suboxide gave benzo-dioxepindione (141) <90MI 9l2-02>. 

The epoxidation with in situ generated dioxiranes often requires careful control of the reaction pH. Since Oxone rapidly autodecomposes at high pH, early epoxidations were usually carried out at pH 7-8. In contrast, higher pH was found to be beneficial to epoxidation with ketone 2. For example, conversion of /ra 5-P-methylstyrene 11 to its epoxide 12 increased from 5% at pH 7-8 to > 80% at pH > 10 while a high enantioselectivity (90-92% ee) was retained. Analysis of the reaction cycle implied that a Baeyer-Villiger oxidation from intermediate 8 could be one of the possible decomposition pathways for ketone 2. A higher pH would facilitate the formation of anion 9 and subsequent formation of dioxirane 10, thus... 

Ottolina G, de Gonzalo G, Carrea G, Danieli B (2005) Enzymatic Baeyer-Villiger oxidation of bicyclic diketones. Adv Synth Catal 347(7-8) 1035-1040. doi 10.1002/adsc.200505027 PaUcovits R (2010) Pentenoic acid pathways for cellulosic biofuels. Angew Chem Int Ed Engl 49 4336-4338. doi 10.1002/anie.201002061... 

Wright, J.L.C., Hu, T., McLachlan, J.L., Needham, J., and Walter, J.A. (1996) Biosynthesis of DTX-4 Confirmation of a polyketide pathway, proof of a Baeyer-Villiger oxidation step, and evidence for an unusual carbon deletion process./. Am. Chem. Soc., 118, 8757-8758. 

Scheme 3.62 Pathways a-k (a) nucleophilic addition of the ketone by peroxymonosulfate (b) formation ofthe oxy-anion intermediate (c) formation of the dioxirane (d) epoxidation of an olefin by the dioxirane (e) epimerization of the stereogenic centers of the ketone (f) hydration of the ketone (g) self-decomposition of peroxymonosulfate (h) Baeyer-Villiger oxidation (i) consumption of the dioxirane by peroxymonosulfate (j) self-decomposition ofthe dioxirane. (k) racemic epoxidation of the olefin by peroxymonosulfate itself...

FIGURE 8.35 Degradation of (a) mandelate, (b) 4-hydroxyacetophenone by side-chain oxidation pathways, (c) acetophenone by Baeyer-Villiger monooxygenation. 

It was postulated (169) that these amides are 8,8a-secobenzophenanthridine alkaloids produced by oxidative cleavage of ring B of the corresponding benzophenanthridines. The success of Baeyer-Villiger-type oxidations of the immonium bond of benzophenanthridine skeletons (168,171,172,175) indicates that this type of oxidation could be a real biological pathway. 

The Baeyer-Villiger rearrangement of cyclohexanone and acetophenone with TS-I/H2O2 proved to be poorly selective [117]. Notably, Ti-P and Sn-P have different chemoselectivities in the oxidation of unsaturated ketones, leading selectively to corresponding epoxides and lactones, respectively [118]. The different oxidation pathways were attributed to the preferential adsorption of hydrogen peroxide on Ti-sites and of the carbonyl group on Sn-sites. 

Several 21,22-seco-diacids (150) have been prepared in the 20/S,28-epoxy-18a,19/8H-ursane series by oxidation of the corresponding 22-hydroxymethylene-21-ketones (151). Reaction of the 21-ketone (152) with oxygen in an alkaline medium afforded the a-hydroxy-acid (153) and the seco-diacid (150). ° Several interesting reactions were observed during this work. ° While pyrolysis of the a-acetoxy-acid (154) yielded the ketone (155) pyrolysis of the seco-diacid anhydride resulted in loss of carbon monoxide and formation of the lactone (156). Lead tetra-acetate oxidation of the ketone (155) [or the hydroxy-acid (153)] followed a Baeyer-Villiger pathway to the lactone (156). The ketone (155) was very susceptible to reduction in the presence of alcoholic alkali. The mass spectral fragmentation of a series of compounds based on 20/8,28-epoxy-18a,19/8H-ursane has been examined. ... 

Forney and Markovetz isolated undecyl acetate directly from growing cultures of Pseudomonas aeruginosa. They showed that all early intermediates in the pathway arise biologically and sequentially from their precursors, indicating involvement of a Baeyer-Villiger type oxidation. In a further study they also showed that cell-free... 

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