The effect of microwave irradiation on carbodiimide-mediated esterifications on solid support

The esterification of a polymer-supported alcohol (PS Wang resin) with benz oic acid was investigated using microwave irradiation. Activation of the ca rboxylic acid was carried out using diisopropylcarbodiimide, either via the O-acylisourea or symmetrical anhydride protocols. In the microwave-assiste d solid-phase coupling using the O-acylisourea method the main product of t he reaction was 1-benzoyl-1,3-diisopropylurea, formed by rearrangement of t he thermolabile isourea intermediate. On the other hand, significant rate e nhancements were observed for the coupling of benzoic anhydride to Wang res in using microwave hash heating in 1-methyl-2-pyrrolidone as solvent. React ion times were reduced from 2 to 3 days using conventional conditions, to 1 0 min by microwave dielectric heating. (C) 2001 Elsevier Science Ltd. All r ights reserved.