2- -1 -alkene carboxylate ester

SnCLrinduced cyclizations between alkenes and enol acetates result in cycloalkanes or bicycloalkanes in high yield (Eq. 59). It is interesting to note that the MesSiOTf-catalyzed reaction can yield fused rather than bicyelo products. Alkenic carboxylic esters, allylic alcohols, sulfones, and sulfonate esters are also cyclized in the presence of SnCU alkenic oxiranes, however, often cyclize in poor yield [89a]. 

The Japp-Klingeraann coupling of aryidiazonium ions with enolates and other nucleophilic alkenes provides an alternative route to arylhydrazones. The reaction has most frequently been applied to P-ketoesters, in which deacylation follow S coupling and the indolization affords an indole-2-carboxylate ester. 

Carboxylic esters 1, having an O-alkyl group with a /3-hydrogen, can be cleaved thermally into the corresponding carboxylic acid 2 and an alkene 3. This reaction often is carried out in the gas phase generally the use of a solvent is not necessary. 

The alkylation of activated halogen compounds is one of several reactions of trialkylboranes developed by Brown (see also 15-16,15-25,18-31-18-40, etc.). These compounds are extremely versatile and can be used for the preparation of many types of compounds. In this reaction, for example, an alkene (through the BR3 prepared from it) can be coupled to a ketone, a nitrile, a carboxylic ester, or a sulfonyl derivative. Note that this is still another indirect way to alkylate a ketone (see 10-105) or a carboxylic acid (see 10-106), and provides an additional alternative to the malonic ester and acetoacetic ester syntheses (10-104). 

Carboxylic esters are produced by the addition of carboxylic acids to alkenes, a reaction that is usually acid catalyzed (by proton or Lewis acids ) and similar in mechanism to 15-5. Since Markovnikov s rule is followed, hard-to-get esters of... 

Similar additions have been successfully carried out with carboxylic acids, anhydrides, acyl halides, carboxylic esters, nitriles, and other types of compounds. These reactions are not successful when the alkene contains electron-withdrawing groups such as halo or carbonyl groups. A free-radical initiator is required, usually peroxides or UV light. The mechanism is illustrated for aldehydes but is similar for the other compounds ... 

Direct elimination of a carboxylic acid to an alkene has been accomplished by heating in the presence of palladium catalysts.Carboxylic esters in which the alkyl group has a P hydrogen can be pyrolyzed, most often in the gas phase, to give the corresponding acid and an alkene. No solvent is required. Since rearrangement and other side reactions are few, the reaction is synthetically very useful and is often carried out as an indirect method of accomplishing 17-1. The yields are excellent and the work up is easy. Many alkenes have been prepared in this manner. 

The reagent titanocene dichloride reduces carboxylic esters in a different manner from that of 10-86, 19-36, or 19-38. The products are the alkane RCH3 and the alcohol R OH. The mechanism probably involves an alkene intermediate. Aromatic acids can be reduced to methylbenzenes by a procedure involving refluxing first with trichlorosilane in MeCN, then with tripropylamine added, and finally with KOH and MeOH (after removal of the MeCN). The following sequence has been suggested ... 

Addition of carboxylic esters to activated alkenes (Michael)... 

Free-radical addition of carboxylic esters to alkenes... 

Choi and Sakakura et al. reported that iron(III) triflate, in situ formed from FeCls and triflic acid, efficiently catalyzes the intermolecular addition of carboxylic acids to various alkenes to yield carboxylic esters. The reaction is applicable to the synthesis of unstable esters, such as acrylates (Scheme 40) [50]. 

Unlike the case of the Ni-catalyzed reaction, which afforded the branched thioester (Eq. 7.1), the PdCl2(PPh3)3/SnCl2-catalyzed reaction with 1-alkyne and 1-alkene predominantly provided terminal thioester 6 in up to 61% yield in preference to 7. In 1983, a similar hydrothiocarboxylation of an alkene was also documented by using a Pd(OAc)2/P( -Pr)3 catalyst system with t-BuSH to form 8 in up to 79% yield (Eq. 7.6) [16]. It was mentioned in the patent that the Pt-complex also possessed catalyhc activity for the transformation, although the yield of product was unsatisfactory. In 1984, the hydrothiocarboxylation of a 1,3-diene catalyzed by Co2(CO)g in pyridine was also reported in a patent [17]. In 1986, Alper et al. reported that a similar transformation to the one shown in Eq. (7.3) can be realized under much milder reaction conditions in the presence of a 1,3-diene [18], and the carboxylic ester 10 was produced using an aqueous alcohol as solvent (Eq. 7.7) [19]. 

Some care must be taken in drawing conclusions from the E/Z or syn/anti selectivity of a given catalyst/alkene combination. The intrinsic stereoselectivity may be altered in some cases by subsequent isomerizations initiated by the catalyst. For example, epimerization of disubstituted vinylcyclopropanes is effectively catalyzed by palladium compounds the cis - trans rearrangement of ethyl chrysanthemate or of chrysanthemic acid occurs already at room temperature in the presence of PdCl2 L2 (L = MeCN, EtCN, PhCN)96 Oxycyclopropane carboxylic esters undergo metal-... 

Hydroxycarbonylation and alkoxycarbonylation of alkenes catalyzed by metal catalyst have been studied for the synthesis of acids, esters, and related derivatives. Palladium systems in particular have been popular and their use in hydroxycarbonylation and alkoxycarbonylation reactions has been reviewed.625,626 The catalysts were mainly designed for the carbonylation of alkenes in the presence of alcohols in order to prepare carboxylic esters, but they also work well for synthesizing carboxylic acids or anhydrides.137 627 They have also been used as catalysts in many other carbonyl-based processes that are of interest to industry. The hydroxycarbonylation of butadiene, the dicarboxylation of alkenes, the carbonylation of alkenes, the carbonylation of benzyl- and aryl-halide compounds, and oxidative carbonylations have been reviewed.6 8 The Pd-catalyzed hydroxycarbonylation of alkenes has attracted considerable interest in recent years as a way of obtaining carboxylic acids. In general, in acidic media, palladium salts in the presence of mono- or bidentate phosphines afford a mixture of linear and branched acids (see Scheme 9). 

The OPLS parameters (charges and Lennard-Jones terms) were obtained primarily via Monte Carlo simulations with particular emphasis on reproducing the experimental densities and heats of vaporization of liquids. Those simulations were performed iteratively as part of the parametrization, so better agreement with experiment is obtained than in previous studies where the simulations were usually carried out after the parametrization. Once the OPLS parametrization was completed, further simulations were also performed in order to test the new set of parameters in the calculation of other thermodynamic and structural properties of the system, besides its density and its heat of vaporization. Parameters have now been generated, among others, for water, alkanes, alkenes, alcohols, amides, alkyl chlorides, amines, carboxylic esters and acids, various sulfur and nitrogen compounds, and nitriles. A protein force field has been established as well. 

The Ziegler-like character of the initial catalyst systems prohibited the use of alkenes containing functional groups, even very simple ones as carboxylic esters, amides or ethers, as they will coordinate to the electrophilic metal, or... 

Tetraalkylammonium bromide was found to be a good catalyst for the conjugate addition of thiols to a,p-unsaturated nitriles, carboxylic esters, ketones, aldehydes, and nitro alkenes. The reactions proceeded rapidly and gave high yields of products (typically, 90%) (160). 

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