Addition of carboxylic acids to alkenes

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... 

Scheme 40 Iron(III)-catalyzed intermolecular addition of carboxylic acids to alkenes...

Although a seldom used laboratory method, the addition of carboxylic acids to alkenes provides carboxylic esters. The addition is catalyzed by protic acids or Lewis acids and obeys Markovnikov s rule (equation 273).456-458... 

More recently, interest in the addition of carboxylic acids to alkenes has focused on the development of new catalytic systems such as clay,466 sheet silicate (montmorillonites) 467 wofatit468 and zeolites.469... 

The acyloxymercuration-demercuration of alkenes provides an alternative route to esters which is probably less prone to caibon skeleton rearrangements than the direct addition of carboxylic acids to alkenes (equation 282). This reaction has recently been reviewed.477 The reaction is most commonly run using mercury(II) acetate in acetic acid, though other mercury salts may be used and aprotic solvents can also be employed. Equilibria have been measured for the reaction of mercury(II) trifluoroacetate and alkenes in tetrahydrofuran, and were found to be solvent dependent.478... 

Addition of carboxylic acids to alkenes (e.g., norbomene) is promoted by FeCls-AgOTf in refluxing 1,2-dichloroethane. Unsaturated carboxylic acids give y-lactones. ... 

The Cu2+ montmorillonite was also found to be an effective catalyst for the addition of carboxylic acids to alkenes to give esters. Al3+-exchanged montmorillonite was shown to catalyse the reaction between ethanol and hex-l-ene producing 2- and 3-ethoxyhexanes. 

Gassman and Bottorff [134] have utilized this strategy for synthesising lactones (158) by the intramolecular addition of carboxylic acid to alkene radical... 

In addition to the gold-catalyzed chemistry described in the preceding section, ruthenium complexes also catalyzed the addition of carboxylic acids to alkenes (Scheme 2.20) [25]. A common air-stable ruthenium compound served as the catalyst for the reaction along with silver(I) triflate as an additive. While a range of monosubstituted terminal alkenes were successfully converted into esters in moderate to excellent yields (up to 95%), analogous reactions with internal or disubstituted alkenes were less successful. Both the gold- and ruthenium-catalyzed additions were attractive due to the availability of the catalysts used for the reactions. 

Need to convert an unactivated alkene into an ester Are the methods for ether/ester synthesis limited to alcohols and carboxylic acids This can be accomplished through the gold- or ruthenium-catalyzed addition of carboxylic acids to alkenes [22, 25] A number of heteroatom-containing compounds have been involved in oxygen-carbon(sp ) bond-forming reactions. The intramolecular iodinative cyclization of phosphoramidates serves as a representative example [37]... 

The addition of carboxylic acids to olefins, especially cyclic olefins has also been reported in the presence of Fe(OTf)3 (2 mol%) without solvent [18]. In the same paper and others, it was shown that triflic acid that could arise from catalyst decomposition, also promoted the addition of carboxylic acids to alkenes but with lower efficacy [19, 20]. 

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]. 

The addition of carboxylic acids to alkynes affords enol esters which are useful as intermediates in organic synthesis.470 As in the addition to alkenes, a catalyst is usually required for high conversions of alkynes to enol esters. Simple acid catalysis has been employed (equation 279),471 but the more common catalysts are Lewis acids, such as boron trifluoride etherate,472 silver nitrate,473 zinc acetate474 and zinc oxide (equations 280 and 281),47S-476... 

Esterification. Add-catalyzed esterification of carboxylic acid with alcohol produces water as a coproduct. However, a greener method of esterification of carboxylic acid is via the addition of olefin, which does not produce any co-products and therefore, displays 100% atom efficiency. Proton-exchanged montmorillonite (H+-mont) can be used as a catalyst for addition reactions of carboxylic acids to alkenes (Fig. 7) (38)a). For example, the reaction of benzoic acid with norbomene in the presence of the H+-mont catalyst gave 2-benzoyloxynorbomane. Even with less-reactive simple alkenes, such as cyclopentene and cyclohexene, the corresponding esters were obtained in excellent yields. 

The iodine-catalyzed addition of carboxylic acids to styrene derivatives generated high yields of esters and related compounds (Scheme 2.17) [24], This transition metal-free reaction used TBHP as the oxidant and was carried out under very mild conditions using an assortment of alkenes and carboxylic acids as substrates. The chemistry was quite tolerant of preexisting functional groups, and even aryl bromides were retained through the oxidation process. In addition to the styrene derivatives, aliphatic alkenes such as 1-octene were also successfully converted into esters using this approach. 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and alkenes. The most common is the reaction with carboxylic acids, illustrated above.Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesi-toic acid. This method has the advantage over 18-13 and 18-14 that it is just one laboratory step from the acid to the amine, but conditions are more drastic. Under the acid conditions employed, the isocyanate is virtually never isolated. 

Esterification of carboxylic acids with bulky alcohols is unsatisfactory. However, tertiary alkyl esters often can be prepared by addition of the acid to the appropriate alkene using an acid catalyst ... 

Reactions Initiated by the Addition of Alcohols or Carboxylic Acids to Alkenes... 

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