Unsaturated compounds ester preparation

Various alkylating agents are used for the preparation of pyridazinyl alkyl sulfides. Methyl and ethyl iodides, dimethyl and diethyl sulfate, a-halo acids and esters, /3-halo acids and their derivatives, a-halo ketones, benzyl halides and substituted benzyl halides and other alkyl and heteroarylmethyl halides are most commonly used for this purpose. Another method is the addition of pyridazinethiones and pyridazinethiols to unsaturated compounds, such as 2,3(4//)-dihydropyran or 2,3(4//)-dihydrothiopyran, and to compounds with activated double bonds, such as acrylonitrile, acrylates and quinones. 

Prochiral aryl and dialkyl ketones are enantioselectively reduced to the corresponding alcohols using whole-cell bioconversions, or an Ir1 amino sulfide catalyst prepared in situ.695 Comparative studies show that the biocatalytic approach is the more suitable for enantioselective reduction of chloro-substituted ketones, whereas reduction of a,/ -unsaturated compounds is better achieved using the Ir1 catalyst. An important step in the total synthesis of brevetoxin B involves hydrogenation of an ester using [Ir(cod)(py) P(cy)3 ]PF6.696... 

Polymers Catalytic reactions involving C=C bonds are widely used for the conversion of unsaturated fatty compounds to prepare useful monomers for polymer synthesis. Catalytic C-C coupling reactions of unsaturated fatty compounds have been reviewed by Biermann and Metzger [51]. Metathesis reactions involving unsaturated fatty compounds to prepare co-unsaturated fatty acid esters have been applied by Warwel et al. [52], Ethenolysis of methyl oleate catalyzed by ruthenium carbenes developed by Grubb yields 1-decene and methyl 9-decenoate (Scheme 3.6), which can be very useful to prepare monomers for polyolefins, polyesters, polyethers and polyamide such as Nylon 11. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

The same procedure was applied to several unsaturated nitriles 125, prepared from various acyclic carboxylic esters with a terminal double bond 124. The intermediate carbonylic compound 126 cyclized either during silica gel chromatography, or on sequential treatment with calcium hydride followed by aqueous ammonium chloride. The result was a five- or six-membered cyanocycloalkenone 127 (Scheme 45 and Table 17) <1999JOC2830>. 

Selenenyl halides are relatively stable, though moisture sensitive, compounds that are generally prepared by the reactions shown in Scheme 7 and behave as electrophihc selenium species. " They react with ketones and aldehydes via their enols or enolates to afford a-seleno derivatives (e.g. (17) in equation 11). Similar a-selenenylations of /3-dicarbonyl compounds, esters, and lactones can be performed, although the latter two types of compounds require prior formation of their enolates. Moreover, the a-selenenylation of anions stabilized by nitrile, nifro, sulfone, or various types of phosphorus substituents has also been reported (equation 12). In many such cases, the selenenylation step is followed by oxidation to the selenoxide and spontaneous syn elimination to provide a convenient method for the preparation of the corresponding a ,/3-unsaturated compound (e.g. 18 in equation 11). Enones react with benzeneselenenyl chloride (PhSeCl) and pyridine to afford a-phenylselenoenones (equation 13). 

A convenient procedure has been developed for the synthesis of cyano ester is prepared and treated with hydrogen cyanide in a single operation. For this purpose, a hot mixture of the carbonyl compound, cyanoacetic ester, and pyridyl acetate s treated with ethanol and potassium cyanide. 

Selenoxide elimination occurs under relatively mild conditions in comparison to the elimination reactions described above. Selenoxides undergo spontaneous yn-elimi-nation at room temperature or below and thus have been used for the preparation of a variety of unsaturated compounds. The selenide precursors can be obtained by displacement of halides or sulfonate esters with PhSeNa. Oxidation of the selenides with hydrogen peroxide or tert-huiyX hydroperoxide, sodium periodate, or peroxycar-boxylic acids furnishes the corresponding selenoxides. Their eliminations usually favor formation of the less substituted olefin in the absence of heteroatom substituents or delocalizing groups. Since selenium compounds are toxic, they should be handled with care. 

Functionalized P-amino-a, -unsaturated lactones, esters and nitriles can be prepared by nucleophilic vinylic substitution of halogen atoms by amines on the corresponding 3-halo-a,3-unsaturated compounds (12), (13) and (15) (Scheme 9). 3-Bromo-2-butenoates ( )-(13) and (Z)-(13) reacted with secondary amines to give ( )-p-aminopropenoates ( )-(14) regardless of the initial stereochemistry, while the reaction with primary amines yielded a mixture of ( )- and (Z)-(14), when R = H, with the latter predominant. In contrast, the substitution of ( )- and (Z)-nitriles, ( )-(15) and (Z)-(15), with second-... 

Michael addition of l-(alkoxycarbonyl)methylphosphonate anions to unsaturated compounds provides a methodology for the elaboration of new reagents and also for the preparation of phosphonylated heterocycles. Thus, in the presence of basic catalysts, diethyl l-(ethoxycarbonyl)alkyl- and l-(ethoxycarbonyl)methylphosphonates add to a.p-nnsaturatcd esters and nitriles.Addition of diethyl l-(ethoxycarbonyl)methylphosphonates under basic conditions to methyl or ethyl acrylates, acrylonitrile, and benzalacetophenone occurs readily and gives rise to products of addition to one and two molecules of the unsaturated compound (Scheme 8.14). ° - ° Reaction of a-substituted phosphonoacetates with acrylates is less vigorous, and attempts at addition to crotonic and methacrylic esters fail. mi-zos-zos... 

Sulfur- and Selenium-containing Compounds. A new route to a-thioalkyl-phosphonates (292) and -phosphinates (294) has been reported from the reaction of selenothioic acid S-esters (291) with phosphites and phosphinites, respectively. By-products (293), derived from the P(III) ester alkylating the Se atom, are formed in many cases. a-Phosphono-p-substituted a,P-unsaturated dithioesters (296), prepared from diethyl phosphonodithioacetate (295), undergo Diels-Alder reactions with enol and thioenol ethers to give excellent yields of novel 5-... 

Some typical reactions of 1,1 -difluoroethene with nucleophiles are summarized in Scheme 2.18. Alkoxides [3], trialkylsilyl anion [4], ester enolates [5], and diphenylphosphinyl anion [6] attack the gem-difluorinated carbon of 5. However, it is noteworthy that nucleophilic substitution and proton abstraction are in some cases competitive, and thus s -butyl lithium abstracts the (3 -vinylic proton predominantly to generate vinyllithium. The lithium species can be trapped with an aldehyde, providing difluoroallyl alcohol, which is then hydrolyzed to a, (3-unsaturated carboxylic ester (11) [ 7 ] (Scheme 2.19). Some synthetically useful examples are shown in Schemes 2.20 and 2.21. Tetrathiafulvalene derivative (14) is prepared from difluorinated derivative (13) [8]. An elegant intramolecular version was demonstrated by Ichikawa, which provided a range of cyclized compounds (17), including dihydrofurans, thiophenes, pyrroles, and cyclopentenes, and also corresponding benzo derivatives (20) [2]. 

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