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20.5.1.2.1.2 Variation 2: Dicyclohexylcarbodiimide Activation of Acids

DOI: 10.1055/sos-SD-020-00659

Jain, N. F.; Masse, C. E.Science of Synthesis, (200720712.

Perhaps the most common approach to the synthesis of esters involves activation of the carboxylic acid component by treatment with a carbodiimide reagent followed by subsequent nucleophilic acyl substitution with the neutral alcohol component. The most commonly employed diimide activating reagent is dicyclohexylcarbodiimide; however, the use of dicyclohexylcarbodiimide alone in these esterification protocols has traditionally suffered from variable yields due to the formation of N-acylurea side products. This limitation has been overcome by the addition of catalytic amounts of 4-(dimethylamino)pyridine. A representative example of this approach involves treatment of (E)-cinnamic acid with dicyclohexylcarbodiimide, catalytic 4-(dimethylamino)pyridine (310mol%), and methanol or tert-butyl alcohol in dichloromethane at 0°C to afford the desired esters 3 (R1=Me, t-Bu) in 98 and 68% yield, respectively (Scheme 2).[‌2‌]

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