Science of Synthesis

Jain, N. F.; Masse, C. E., Science of Synthesis, (2007) 20, 712.

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 (3–10 mol%), 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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References

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• 8.Meeeee-Meee, (8888) M 8-8, 888.
• 8.Meeeee-Meee, (8888) M 88e, 888.