Esters or Lactones

Allylalion of the alkoxymalonitrile 231 followed by hydrolysis affords acyl cyanide, which is converted into the amide 232. Hence the reagent 231 can be used as an acyl anion equivalent[144]. Methoxy(phenylthio)acetonitrile is allylated with allylic carbonates or vinyloxiranes. After allylation. they are converted into esters or lactones. The intramolecular version using 233 has been applied to the synthesis of the macrolide 234[37]. The /i,7-unsaturated nitrile 235 is prepared by the reaction of allylic carbonate with trimethylsilyl cyanide[145]. 

Silyl enol ethers are other ketone or aldehyde enolate equivalents and react with allyl carbonate to give allyl ketones or aldehydes 13,300. The transme-tallation of the 7r-allylpalladium methoxide, formed from allyl alkyl carbonate, with the silyl enol ether 464 forms the palladium enolate 465, which undergoes reductive elimination to afford the allyl ketone or aldehyde 466. For this reaction, neither fluoride anion nor a Lewis acid is necessary for the activation of silyl enol ethers. The reaction also proceed.s with metallic Pd supported on silica by a special method[301j. The ketene silyl acetal 467 derived from esters or lactones also reacts with allyl carbonates, affording allylated esters or lactones by using dppe as a ligand[302]... 

The product (6 hexanohde) is a cyclic ester or lactone (Section 19 15) Like the Baeyer-Vilhger oxidation an oxygen atom is inserted between the carbonyl group and a carbon attached to it But peroxy acids are not involved m any way the oxidation of cyclohexanone is catalyzed by an enzyme called cyclohexanone monooxygenase with the aid of certain coenzymes... 

BAEYER VILLIQER Ketone Oxidation Synthesis of esters or lactones trom ketones with retention of configuration... 

The Baeyer-Villiger oxidation of ketones to esters (or lactones) occurs by the following mechanism. 

Saponification of Esters or Lactones and Reaction of Persilylated Amides and Lactams with Alkali I 71... 

This reaction involves the two reactants carbon monoxide and alcohol and produces esters, or lactones. The starting material, which will be considered here, is an alkene or an alkyne but it is also possible to start from activated halides (aryl- or allyl- iodides and bromides) to produce the same kind of organic products. 

Cephalosporins Ester or lactone at the C(4) carboxy group /3-Lactam carbonyl C-atom more electrophilic, no intramolecular acylamido participation Increased up to 130-fold ... 

Cyclic peptides are important biologically active compounds that combine peptide properties with conformational bias and often improved serum stability and membrane penetration [1-3]. Depsipeptides are similar compounds, but they contain as part of their backbone one or more hydroxylated amino acid residues that add ester or lactone moieties to the peptide (Fig. 1) [4-6]. Cyclo- and... 

The reagent most commonly used for oxidation of ethers is RuO, and esters or lactones are the main prodncts early results are weU summarized by Gore [35], The first such oxidation of an ether was in 1958 when n-butylether gave n-butyl-n-... 

Benzyl-alkyl, dialkyl, cyclic and acyclic ethers were converted to esters or lactones by RuO or [RuO ] (RuClj/aq. Na(C10) or Ca(C10)j/CH2Cl2). It was not stated whether RuO or [RuO ] was the effective oxidant, but oxidation of jb-methoxy-benzyhnethyl ether apparently involved a one-electron transfer process, which might be more likely to occur with [RuO ] [426],... 

Traws-RuCljCdppp) (dppp=(l,2-diphenylphosphino)propane, sometimes abbreviated as (dpp) in the literature) is made from K2[Ru(H30)Cl5] and (dppp) in refluxing EtOH. Oxidation of a wide range of ethers to esters or lactones was effected by franx-RuCl Cdppp) or [RuCl(dppp)2]Vaq. Li(C10)/CH3Cl2 (Table 5.2) [931]. 

Abstract This chapter principally concerns oxidations of organic substrates containing N, O, S, P, As and Sb. Oxidations of amines are covered first, including primary amines to nitriles or amides secondary amines to imines or other products tertiary amines to N-oxides or other prodncts (Section 5.1) and the oxidation of amides (5.2). Oxidation of ethers to esters or lactones follows (5.3), then of sulfides to sulfoxides or sulfones (5.4) and of phosphines, arsine and stibines to their oxides (5.5). A final section (5.6) concerns such miscellaneous oxidations not covered by other sections in the book. 

Table 5.2 Oxidation of ethers to esters or lactones and suMdes to sulfoxides or sulfones... 

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). ... 

These new, uncharged amine bases are strong enough (pXa of 4 in acetonitrile is 42.62) to deprotonate esters or lactones, where they can even be used with advantage over the more conventional bases like LDA or metal hcxamethyldisilazanides. For example, the alkylation of dimethyl isopropylidene tartrate with n-alkyl iodide is not possible with the latter bases but can be achieved with phosphazene-base P4-t-Bu or phosphazene-base P4-t-Oct24. With phos-phazene-base P4- -Bu the yield of 8 is 41 % with 28 % of recovered starting material 6, whereas with phosphazene-base P4-i-Oct the yield of 8 is 71 % with only 9% of 6 left unreacted. (For alkylations of 6 with other more active electrophiles see later.)... 

Reactions presented below show that this method is used frequently to prepare magnesium enolates derived from functionalized carboxylic esters or lactones (equations 18-24, Tables 2 and 3). 

Asymmetric synthesis in aldol-type reaction involving magnesium ester or lactone enolates has also been reported. Enolate of (—)-menthyl or (-l-)-bornyl acetate reacts with substituted benzophenones or a-naphtophenones to yield, upon hydrolysis of the resulting esters, optically active /3-hydroxyacids. Although these results are interpreted in terms of a steric factor. Prelog s rules are not applicable to these reactions (equation 88). 

Now try this reaction which has a cyclic ester or lactone in it. The reaction is just like that for an ordinary ester,... 

Baeyer-VUliger Oxidations. The biological equivalent of the Baeyer-Villiger reaction is a useful transformation in providing a mild technique for converting ketones into esters or lactones. 

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