Direct esterifications, 4-dimethylaminopyridine

In a more comprehensive ongoing investigation [117], fatty acid-based monomers with acrylate functionality were prepared under mild and green conditions by direct esterification of unsaturated fatty acids, namely 10-undecenoic (Cll l), oleic (C18 l) and linoleic (Cl 8 2) acids, with 2-hydroxyethyl methacrylate (HEMA) inthe presence of N,N -dicyclohexylcarbodiimide and 4-dimethylaminopyridine. Scheme 4 4 shows the structure of these novel monomers, whose additional originality is that they were synthesised directly from the corresponding fatty acid. 

Two strategies have been developed for the preparation of esters of diazoacetic acid. If the alcohol is inexpensive, it is first converted (diketene) into the corresponding acetoacetate (120 equation 49). Diazo transfer with subsequent deacylation then yields the diazoacetate (121). If the alcohol is particularly valuable or sensitive, it may alternatively be esterified with a more direct precursor to diazoacetate. One reagent that has been used for this purpose is glyoxalic acid 2,4,6-triisopropylbenzenesulfonylhydrazone (TIPPS) (123 equation 50). Esterification of the alcohol (122) with (123), using dicyclohexylcarbo-diimide followed by addition of 4-dimethylaminopyridine, gives the diazoacetate (124). ... 

Among the diverse mechanistic studies directed to prevent the use of high temperatures during the process, the esterification of benzoic acid 1 with DMC, at 90°C, in the presence of a variety of amine bases (1 equiv) was investigated (Scheme 20.2). Although different types of bases were studied, (e.g. A -methyl-morpholine (NMM), tributylamine, 4-dimethylaminopyridine (DMAP), ammonium hydroxide) only l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) yielded methyl benzoate 2 in quantitative yield. With the rest of the amines tested, the ester 2 was not obtained even after prolonged reaction times. 

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