Ester elimination reactions

The allyl cyanoacetate 731 can be converted into an a, /3-unsaturated nitrile by the decarboxylation-elimination reaction[460], but allyl malonates cannot be converted into unsaturated esters, the protonation and allylation products being formed instead. 

Sulfonate esters are subject to the same limitations as alkyl halides Competition from elimination needs to be considered when planning a functional group transforma tion that requires an anionic nucleophile because tosylates undergo elimination reactions just as alkyl halides do... 

Hydrolysis. Esters are cleaved (hydroly2ed) into an acid and an alcohol through the action of water. This hydrolysis is cataly2ed by acids or bases. The mechanistic aspects of ester hydrolysis have received considerable attention and have been reviewed (16). For most esters only two reaction pathways are important. Both mechanisms involve a tetrahedral intermediate and addition-elimination reactions i7i7... 

Because of thetr electron deficient nature, fluoroolefms are often nucleophihcally attacked by alcohols and alkoxides Ethers are commonly produced by these addition and addition-elimination reactions The wide availability of alcohols and fliioroolefins has established the generality of the nucleophilic addition reactions The mechanism of the addition reaction is generally believed to proceed by attack at a vinylic carbon to produce an intermediate fluorocarbanion as the rate-determining slow step The intermediate carbanion may react with a proton source to yield the saturated addition product Alternatively, the intermediate carbanion may, by elimination of P-halogen, lead to an unsaturated ether, often an enol or vinylic ether These addition and addition-elimination reactions have been previously reviewed [1, 2] The intermediate carbanions resulting from nucleophilic attack on fluoroolefins have also been trapped in situ with carbon dioxide, carbonates, and esters of fluorinated acids [3, 4, 5] (equations 1 and 2)... 

The nucleophilic attack of nitrogen bases leads to a variety of products as the result of addition or addition-elimination reactions The regioselectivity resembles that of attack by alcohols and alkoxides an intermediate carbanion is believed to be involved In the absence of protic reagents, the fluorocarbanion generated by the addition of sodium azide to polyfluonnated olefins can be captured by carbon dioxide or esters of fluonnated acids [J 2, 3] (equation I)... 

Conversion to p-toluenesulfonate esters (Section 8.14) Alcohols react with p-toluenesulfonyl chloride to give p-toluenesulfonate esters. Sulfonate esters are reactive substrates for nucleophilic substitution and elimination reactions. The p-toluenesulfonate group is often abbreviated —OTs. 

This mechanism of a -elimination reaction is supported by experimental findings with " S- and C-labeled starting materials." The Chugaev reaction is analogous to the ester pyrolysis, but allows for milder reaction conditions—i.e. it occurs at lower temperatures. It is less prone to side reactions, e.g. the formation of rearranged products, and is therefore the preferred method. 

For the regioselectivity similar rules as for the ester pyrolysis do apply. With simple, alkylsubstituted amine oxides a statistical mixture of regioisomeric olefins is obtained. On the other hand with cycloalkyl amine oxides the regioselectivity is determined by the ability to pass through a planar, five-membered transition state. This has been demonstrated for the elimination reaction of menthyl dimethylamine oxide 10 and neomenthyl dimethylamine oxide 11 ... 

The reaction proceeds by an Ei-mechanism. The /3-hydrogen and the carboxy-late are cleaved synchronously from the substrate molecule, while forming a new bond. This elimination reaction belongs to the class of -eliminations in the case of the ester pyrolysis, the substrate molecule passes through a six-membered cyclic transition state 4 ... 

In Europe, interest has centered particularly on polyhydroxybutyrate, which can be made into films for packaging as well as into molded items. The polymer degrades within 4 weeks in landfills, both by ester hydrolysis and by an ElcB elimination reaction of the oxygen atom p to the carbonyl group. The use of polyhydroxybutyrate is limited at present by its cost—about four times that of polypropylene. 

Resistance to streptogramin type B antibiotics can be mediated in staphylococci and enterococci by plasmids carrying a vgb gene [2]. The Vgb enzyme is a lyase that linearizes the cyclic hexadepsipeptide by cleavage of the ester bond via an elimination reaction. 

Volume 8 Volume 9 Volume 10 Volume 12 Volume 13 Proton Transfer Addition and Elimination Reactions of Aliphatic Compounds Ester Formation and Hydrolysis and Related Reactions Electrophilic Substitution at a Saturated Carbon Atom Reactions of Aromatic Compounds Section 5. POLYMERISATION REACTIONS (3 volumes)... 

The addition of dry HCl to a mixture of a nitrile and an alcohol in the absence of water leads to the hydrochloride salt of an imino ester (imino esters are also called imidates and imino ethers). This reaction is called the Pinner synthesisThe salt can be converted to the free imino ester by treatment with a weak base such as sodium bicarbonate, or it can be hydrolyzed with water and an acid catalyst to the corresponding carboxylic ester. If the latter is desired, water may be present from the beginning, in which case aqueous HCl can be used and the need for gaseous HCl is eliminated. Imino esters can also be prepared from nitriles with basic catalysts. ... 

Dialkyl esters of cystine (39) and lanthionine (40) undergo a surprising thermolysis reaction at between 25 C and 80 °C to afford cis and trans methyl 2-methylthiazolidine-2,4-dicarboxylates (43) in protic solvents. A two stage process is proposed for this transformation. An initial i-elimination reaction gives the thiol (41) and the enamine (42). Thiol addition to the imine tautomer of (42) is then followed by loss of ammonia and an intramolecular cyclisation to give (43) <96CC843>. 

The first compound is an antibiotic isolated from Streptomyces aureus [20], while the second compound is a cytotoxic antibiotic isolated from Dysidea fragilis, a marine sponge [21]. A logical approach to the synthesis of azirines would be an elimination reaction of a suitably M-substituted aziridine. Thus, AT-chlorination of aziridine-2-carboxylic esters was carried out using ferf-butyl hypochlorite (Scheme 8). 

The regiochemistry of this elimination reaction resembles that observed by Davis et al. (see Scheme 9) [23]. The special nature of the bonds in three-mem-bered rings is probably responsible for this exclusive regiochemistry. It is of interest to note that 3,3-dimethylaziridine-2-carboxylic ester indeed leads to the corresponding 3H-azirine ester upon Swern oxidation here there is, of course, no choice. 

The conversion of long-chain alkanoate CoA esters into the alkenoate CoA esters by acyl-CoA oxidase involves an anti elimination reaction. The stereochemistry of the reaction in Candida lipolytica was established using stearoyl-CoA-labeled with H at the 2 R)-, 3(R)-, and 3(5)-positions (Kawaguchi et al. 1980). 

Because in this case an elimination reaction could occur to form an a,/ -unsaturated ester, use of two equivalents of the phosphorane should be avoided.1The (a-acylalk-ylidene)triphenylphosphorane can be subjected to a subsequent Wittig reaction with an aldehyde.[4] [5],[8]... 

In the reduction of acids there is a tendency for the lithium salt, RCO20Li to separate from the ethereal solution, and thus bring reduction to a halt this can be avoided by first converting the acid to a simple, e.g. Me or Et, ester. In the reduction of the latter, the initial nucleophilic attack by AIH4 results in an addition/elimination reaction—OR is a good leaving group in (40)—followed by normal attack, as above, on the resultant carbonyl compound (41) to yield the primary alcohol (42) ... 

---