[3+2] Cycloaddition Using Reusable Polymer-Supported Catalyst

Significance

A reusable polymer-supported copper(I) iodine catalyst 1 for the [3+2] cycloaddition reaction between azides and alkynes was prepared. The catalyst has exhibited good activity, stability, and recyclability. The complexation was carried out with 500 mg of Amberlyst A-21 (2.4 mmol of amine) and 1 mmol of CuI in acetonitrile to give the copper catalyst (1.23 mmol of Cu/g of resin). The [3+2] cycloaddition reaction of propiolic acid methyl ester (2) and ethyl azidoacetate (3) was found to proceed smoothly in the presence of 13 mol% catalyst in dichloromethane to give the triazole 4 in quantitative yield with high purity without chromatographical purification. The catalyst was recovered and reused four times without any loss of catalytic activity. 1,4-Disubstituted 1,2,3-triazoles were obtained in high yields (14 examples; average 91% yield) under similar conditions.