Esterifications using other coupling reactions

The acid (10 mol) and a molar equivalent of triethylamine are dissolved in 20 ftl of acetonitrile, and a molar equivalent of CCBBT is added. The reaction mixture is cooled in ice and is then allowed to warm up to room temperature, with intermittent shaking, over 1.5 hours. Another equivalent of triethylamine together with 1.5 pi of MeOH is added, again with ice-cooling, and the mixture is again allowed to warm up to room temperature with intermittent shaking over 1.5 hours. The mixture is taken to dryness and the methyl ester(s) are extracted into ether. The ether may be briefly washed with sodium bicarbonate and with dilute HCl and water, dried over 

The acids (or the residues from an extract) are dissolved in a suitable solvent (benzene, dioxan, tetrahydrofuran or CCI4) and refluxed with a slight molar excess of KKr-dicyclohexyl-O-benzylisourea for an hour. The precipitate of dicyclohexylurea is centrifuged down, and the supernatant may be used directly for gas chromatographic analysis [119, 65]. 

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Due to the prevalence of many macrolide natural products, Yamaguchi s esterification has been used extensively in the total syntheses of such compounds. Increasingly, Yamaguchi s method has succeeded where other notable esterification conditions have failed. A recent example involves the coupling of two monomers to form the clavosolide A dimer.17 The Corey-Nicolaou protocol mentioned previously gave only a 30% conversion whereas the Yamaguchi esterification resulted in a clean reaction with a 66% yield. 

Palladium catalysts are widely used in liquid phase aerobic oxidations, and numerous examples have been employed for large-scale chemical production (Scheme 8.1). Several industrially important examples are the focus ofdedicated chapters in this book Wacker and Wacker-type oxidation of alkenes into aldehydes, ketones, and acetals (Scheme 8.1a Chapters 9 and 11), 1,4-diacetoxylation of 1,3-butadiene (Scheme 8.1b Chapter 10), and oxidative esterification of methacrolein to methyl methacrylate (Scheme 8.1c Chapter 13). In this introductory chapter, we survey a number of other Pd-catalyzed oxidation reactions that have industrial significance, including acetoxylation of ethylene to vinyl acetate (Scheme 8. Id), oxidative carbonylation of alcohols to dialkyl oxalates and carbonates (Scheme 8.1e), and oxidative coupling of dimethyl phthalate to 3,3, 4,4 -tetramethyl biphenylcarboxy-late (Scheme 8.1f). 

The hydrophobization of cellulose surface was often achieved thanks to the well-known aptitude of cellulose macromolecules to undergo esterification reactions. The main coupling agents used to esterify cellulose using nonswelling solvents, in order to limit the reaction to the fibre s surface, are summarized in Scheme 18.1, namely the classical acetic anhydride [24] (I), alkyl ketene dimer (AKD) II, alkenyl succinic anhydride (ASA) III, fatty acids (IV, with n var5fing from 6 to 22) or their chlorides, poly-(propylene-gra/f-maleic anhydride) (V), trifluoroethoxy-acetic acid (VI) and its anhydride, as well as several other perfluoro-derivatives, p5Tomellitic anhydride (VII), styrene-maleic anhydride copolymer (VIII) and methacrylic anhydride (IX). 

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