Vinyl esters synthesis

Tsuda156 reported the preparation of poly(vinyl 2-furylacrylate) by the reaction of 2-furylacrylyl chloride with poly(vinylalcohol) in NaOH-water-methyl ethyl ketone. Up to 80% of the hydroxyl groups were esterified. The interest of this technique is obvious here, considering that the vinyl ester of 2-furylacrylic acid does not polymerize119 A similar procedure was employed by Gandini and Rieumont26,1 9 for the synthesis of poly(vinyl 2-furoate) another product unobtainable via a standard polymerization process (see Section 1II-B-3). 

Combination of lipase-catalyzed transesterification with unsaturated vinyl esters as acyl donors and ring-closing metatheses (RCMs) have also been reported [146-148]. Two groups applied this strategy for the synthesis of goniothalamin from cinnamaldehyde [147,148]. The key steps were a transesterification using vinyl acrylate as acyl donor, followed by an RCM, as depicted in Figure 6.55. 

Scheme 7.10 Controllable selective synthesis of N-acyl or O-accylpropanolol vinyl esters catalyzed by lipases.

Vinyl ethers and vinyl esters are not employed extensively in organic transformations. During the synthesis of phlegmarine, however, the stereogenic center at C-10 was to be introduced stereoselectively by catalytic hydrogenation-hydrogenolysis of the vinyl triflate (Scheme 4.7). 

It is remarkable that better enantioselectivities are achieved when CALB-catalyzed acylations of the alcohol are carried out in organic solvent rather than in water. Excellent enantioselectivities are obtained when the process is carried out with vinyl esters [22]. However, in some cases the use of vinyl or alkyl esters as acyl donors has the drawback of the separation of the ester (product) and the alcohol (substrate). A practical strategy to avoid this problem is the use of cyclic anhydrides [23]. In this case an acid is obtained as product, which can be readily separated from the unreacted alcohol by a simple aqueous base-organic solvent liquid-liquid extraction. This methodology has been successfully used for the synthesis of (-)-paroxetine as indicated in Scheme 10.11 [24]. 

The same authors recently described the synthesis of similar rhodium-complexed dendrimers supported on a resin having both interior and exterior functional groups. These were tested as catalysts for the hydroformylation of aryl alkenes and vinyl esters (52). The results show that the reactions proceeded with high selectivity for the branched aldehydes, with excellent yields, even up to the tenth cycle. The hydroformylation experiments were carried out with first- and a second-generation rhodium-complexed dendrimers as catalysts, with a mixture of 34.5 bar of CO and 34.5 bar of H2 in dichloromethane at room temperature. Each catalyst was easily recovered by simple filtration and was reusable for at least six more cycles without... 

The synthesis route to vinyl ester-based polymers starting from ethylene is shown in Fig. 2. The basic monomer for PVAc and its related polymers is VAM. The worldwide production capacity for VAM was estimated to be close to 5,900 ktons in 2009 with an actual production of around 5,500 ktons [13]. About 50% of the VAM is converted to PVAc and VAc-containing polymers, and around 30% is converted to PVA. The remaining 20% is converted in other ways, including the production of PVB [13]. As can be seen from Fig. 2, basically only ethylene and air are needed for the production of PVAc and its polymer analogous products PVA and PVB. 

The synthesis of long-chain fatty acid esters of carbohydrates is inherently more demanding. It was found that glucose did not react with vinyl laurate in a pure ionic liquid medium, but in biphasic tert-butyl alcohol/[BMIm][PF6], glucose could be acylated by the vinyl esters of O, 2-Cu, fatty acids. The best results were obtained with CaLB, which was twice as active as TIL, and the selectivity for acylation at C-6 was high [114]. The esterification of glucose with palmitic acid, which is, in an industrial context, to be preferred over transesterification, has recently been demonstrated in tert-butyl alcohol/[BMIm][PF6] medium [115]. 

Regioselective reactions in systems which contain multiple functional groups are an area ideally suited for biocatalysis. Linhardt and co-workers at the University of Iowa s Division of Medicinal and Natural Products Chemistry recently published the synthesis of a series of 1 -O-acyl sucrose derivatives [31], Using Chiro-CLEC -BL (the CLC of subtilisin) and vinyl esters of the acylating agent in pyridine as solvent, the authors prepared l -O-lauryl sucrose, l -O-myristyl sucrose, and l -O-stearyl sucrose in 80-90% yield (Fig. 9). Their method represents a green alternative to the tin chemistry previously used [32],... 

Harvey and Ratts have discovered an interesting vinyl azide synthesis from allenic esters.40 Treatment of allenes (83a and b) with... 

The base-catalyzed condensation of a-azido esters and ketones with aromatic aldehydes has recently been developed as a new vinyl azide synthesis.42,43 The yields range from moderate to excellent in some cases. The thermal decomposition of ethyl a-azidocinnamate (87) in xylene gives only 2-ethoxycarbonylindole (88).44 The unstable 2-ethoxycarbonyl-3-phenyl-l-azirine could be detected if the thermolysis was carried out at a lower temperature. This fact indicates that the 1-azirine is probably an intermediate leading to the indole, although the intermediacy of the vinyl nitrene could not be established. This result is similar to that observed by Isomura et al. on the pyrolysis of terminal vinyl azides.27,28... 

In addition to free fatly acids and their esters as previously described, compounds with antioxidant potency were also used as acyl donors. In order to investigate the synthesis of hybrid antioxidants, the enzymatic acylation of escuhn catalyzed by immobilized CALB in the ionic liquids [bmtm]BF4 and [bmim]PF6 was investigated using several phenolic acids as well as their corresponding vinyl esters. 

Cyclopropene can also be used as the aUcene component and affords bicyclo[3.1.0]hexen-2-ones upon reaction with alkyne dicobalt octacarbonyl complexes in the presence of NMO (Scheme 250). Vinyl ethers and vinyl esters serve as ethene equivalents in Pauson-Khand reactions. For example, reaction of vinyl benzoate with complex (169) furnished cyclopentenone (170) (Scheme 251). This reaction was used in a synthesis of (-l-)-taylorine and nortaylorine. Allenes participate in intermolecular Pauson-Khand reactions affording alkylidene-substituted cyclopentenones (Scheme 252). ... 

The most obvious route to vinyl azide synthesis lies in the addition of hydrazoic acid to an alkyne. Unfortunately, this reaction has been found to be successful with only one group of compounds, the esters of acetylene dicarboxylic acid (equation 1). Acetylene mono-... 

Bomscheuer, U.T., and T. Yamane, Fatty Acid Vinyl Esters as Acylating Agents A New Method for the Enzymatic Synthesis of Monoacylglycerols, J. Am. Oil Chem. Soc. 72 193-197 (1995). 

The first vinyl ester prepared was vinyl acetate, in 1912, by homogeneous mercury sulfate catalysis [29]. For the vinyl esters of lower carboxylic acids, the reaction was soon carried out in the gas phase over, for example, zinc salts of the corresponding carboxylic acids (such as zinc acetate) heterogenized on active charcoal [30]. By 1965, vinyl acetate was prepared almost exclusively by this method. Since then, this synthesis has been largely superseded by the ace-toxylation of ethylene, the petrochemical preparation of which is highly economic (Section 2.1.4.1). 

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