Carboxylic acids, conversion alkenes

Dehydrative decarboxylation.1 The conversion of (3-hydroxy carboxylic acids to alkenes by reaction with a DMF dialkyl acetal involves an anr/-elimination, and thus is complementary to the known syn-elimination of these hydroxy acids via a (3-lactone (5, 22 9, 504). These reactions were used to obtain both the (E)- and the (Z)-l-alkoxy-l,3-... 

Table 10 Conversion of Carboxylic Acids into Alkenes...

DMF dineopentyl acetal has been used as a reagent for dehydrative decarboxylation in order to avoid the possibility of competing 0-alkylation of the carboxyl group. This conversion of P-hydroxy carboxylic acids to alkenes by reaction with a DMF acetal involves an anti elimination, and it is thus complementary to the syn elimination of these hydroxy acids via the p-lactone. These reactions have been used to obtain both )- and (Z)-1 -alkoxy-1,3-butadienes (eq 6). For additional examples of alkenes obtained from p-hydroxy acids with DMF acetals, see Scheeren et al. ... 

In addition, also nonheme iron catalysts containing BPMEN 1 and TPA 2 as ligands are known to activate hydrogen peroxide for the epoxidation of olefins (Scheme 1) [20-26]. More recently, especially Que and coworkers were able to improve the catalyst productivity to nearly quantitative conversion of the alkene by using an acetonitrile/acetic acid solution [27-29]. The carboxylic acid is required to increase the efficiency of the reaction and the epoxide/diol product ratio. The competitive dihydroxylation reaction suggested the participation of different active species in these oxidations (Scheme 2). 

Esters can be formed when the hydrocarbonylation reaction is carried out in an alcohol.242 Although hydrocarbonylation is the basis for conversion of alkenes to carboxylic acids on an industrial scale, it has seen only limited application in laboratory synthesis. 

Recently, the conversion of alkenes or non-activated internal alkynes into the corresponding carboxylic acids and/or butenolides has been achieved through carboxylation of titanacycle intermediates of type 73 with carbon dioxide (Scheme 27).78... 

In the case of manganese porphyrin catalyzed epoxidations, the axial ligands have been used alone or together with other additives like carboxylic acids (Banfi and coworkers) and soluble bases (Johnstone and coworkers). For example, Mansny and coworkers showed that in the presence of imidazole, 2-methylimidazole or 4-imidazole chloromanganese(tetra-2,6-dichlorophenylporphyrin) catalyzes the epoxidation of varions aUtenes including 1-alkenes by Under these conditions alkene conversion... 

J. Goossen of the Max-Planck-Institut, Muhlheim, has found Chem. Commun. 2004,724) that in situ activation of the acid with phthalic anhydride and inclusion of the bis phosphine DPE-Phos substantially slow alkene isomerization, which can be essentially eliminated by running the reaction to only 80% conversion. Both linear and branched carboxylic acids work well. 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

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... 

Alcohols and carboxylic acids also readily add to metal-activated alkenes2 and industrial processes for the conversion of ethylene to vinyl acetate, vinyl ethers and acetals are well established. However, very little use of intermolecular versions of this chemistry with more complex alkenes has been developed. In... 

The conversion of an alkene to a halohydrin can also be considered as an epoxidation because this can be achieved by a simple ring closure.184 Although no reagent is yet available to perform an asymmetric conversion of an isolated alkene to a halohydrin, the reaction can be controlled through diastereoselection. One such case is the halolactonization of y,8-unsaturated carboxylic acids, N,N-dialkylamides.185189... 

Lipase has been employed to prepare peracids, usually in situ.m The lipase catalysed peracid production from carboxylic acids has been used for the mild epoxidation of alkenes.109 A number of immobilized lipases exist, including one from Candida Antarctica (Novozym 435), which catalyses the conversion of fatty acids to peroxy fatty acids.110... 

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