Batch and Continuous-Flow Huisgen 1,3-Dipolar Cycloadditions with an Amphiphilic Resin-Supported Triazine-Based Polyethyleneamine Dendrimer Copper Catalyst

A polystyrene poly(ethylene glycol) (PS PEG) resin-supported triazine-based polyethyleneamine dendrimer copper catalyst (PS-PEG-TD2-CuSO4) was prepared and characterized by means of CP-MAS NMR, UV-vis/NIR, FTIR, SEM-EDX, XPS, and ICP-AES analyses. PS-PEG-TD2-CuSO4 was highly active in the Huisgen 1,3-dipolar cycloaddition of various organic azides with alkynes in water as well as the three-component reaction of alkynes, alkyl bromides, and sodium azide under batch conditions to give the corresponding triazoles in excellent yields with high recyclability of the catalyst. TEM analysis suggested that the copper nanoparticles generated in situ through reduction of PS-PEG-TD2-CuSO4 with sodium ascorbate serve as the active catalytic species. The application of PS-PEG-TD2-CuSO4 catalyst in a continuous-flow Huisgen reaction for the synthesis of 1,2,3-triazoles was also examined. The cycloaddition of organic azides with alkynes was completed within 22 s in the continuous-flow system containing PS-PEG-TD2-CuSO4 to give the corresponding triazoles in up to 99% yield. Moreover, the continuous-flow system accomplished the long-term continuous-flow cycloaddition for 48 h producing 10 g of a triazole as well as the successive flow reaction producing various kinds of triazoles.