Bayer Villiger reaction lactonization

Other mechanisms of ketone oxidation are also known and will be discussed in Chapter 8. Peracid, which is formed from aldehyde, oxidizes ketones with lactone formation (Bayer-Villiger reaction). 

Once formed, alcohols esterify to some extent with the acids generated in an oxidation reaction. Except for lactones, esters do not appear to be generated directly in oxidation mechanisms [10, 37, 38]. The Bayer-Villiger reaction of intermediate peracids and ketones is sometimes proposed as a source of esters [39] but it appears to be too slow to be a significant source except in the case of cycloparaffins [10, 40]. The ester group and its immediate neighboring groups appear to be remarkably resistant to oxidation. 

When the 2-alkylcyclopentanones are subjected to the Bayer-Villiger reaction, the resultant lactones are found to have sweet, buttery, peach and coconut odours. These are useful in floral fragrances, but their major use is as butter flavour in margarines. 

Ketones. The predominant synthetic use of peroxygens in ketone oxidation is the Bayer-Villiger reaction, which converts them to esters (cyclic ketones to lactones). The predominant product is determined by the relative stability of the carbocations of R and R in RCOR, and an approximate ranking is ... 

The first eiample of an Ireland-Qaisen rearrangement of an allyl lactone employed in natural product synthesis was that of Danishefsky and Tsuzuke in 1980 (Scheme 4.137) [132]. The allyl lactone possessed an exocyclic alkene, and hence resulted in a net 7-membered ring lactone to carbocycle conversion. A Bayer-Villiger reaction converted the pentenoic add to the 3° hydroxyl group of widdrol. 

The key step in the biosynthesis of brassinosteroids is the conversion of castasterone to brassinolide. This reaction is a lactonization of the steroidal B-ring or a Bayer-Villiger-oxidation. Tomato cell suspension cultures have been extensively studied in respect to the metabolism of 24-< / i-castasterone and 24-ep/-brassinolide [21, 22, 32, 33]. A microsomal fraction of tomato cell cultures, induced by 24-epi-castasterone, was able to convert this substrate into 24-epi-brassinolide (Fig. (11)). The specific enzyme activity was determined to be 230 fkat/mg protein with NADPH serving as the only accepted electrondonor [24],... 

The chemical properties of cyclic ketones also vary with ring size. Lower members (addition reactions, than corresponding acyclic ketones. The Cg—C12 ketones are unreactive, reflecting the strain and high enol content of medium-sized ring systems. Lactones are prepared from cyclic ketones by the Bayer-Villiger oxidation reaction with peracids. S-Caprolactone is manufactured from cyclohexane by this process ... 

Fig (9) Methyl dihydroabietate (64b) has been converted to compound (68). The standard organic reactions have been utilized for its conversion to nitrite (72) which on irradiation followed by oxidation yields lactone (74). Cleavage of lactone ring followed by hydrogenation and esterification produced (76) which was converted to (77) by Friedel-Crafts acylation and Bayer-Villiger oxidation. This yields psiferic acid (1) tty hydrolysis. 

The conversion of cyclic ketones to produce lactones via a Bayer Villiger-type reaction can be performed using UHP as shown in reaction 5. These types of reactions involve using UHP with trifluoroacetic anhydride in the presence of disodium hydrogen phosphate which acts as a buffer. The active species in these solutions is trifluoroperoxyacetic acid which is generated in situ. 

Cyclobutanones 131, obtained easily by the 2 + 2 cycloaddition of olefines and ketenes, subjected to Bayer-Villiger-oxidation undergo ring enlargement to the y-lactones 128 of interest. Reaction scheme 83 describes such a reaction, starting from isobutene and Q-dichloro-4-pentenoic acid chloride 132. 

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