Click chemistry continued

Insofar as heterogeneous Cu(I)-catalyzed click chemistry is concerned, new catalysts continue to appear. Nanoparticles of copper can be generated and used in aqueous solution, from which crystalline products often precipitate. Inclusion of copper (as CuCl) into Lewis acidic zeolites, using in particular Cu(I)-USY (pore size 6-8 A), is one such catalyst employed in toluene. Other solvents such as DCM, CH3OH, CH3CN, and benzene were not recommended, and yields of 1,4-disubstituted triazoles can be highly variable. 

Synthesis of new materials based on click chemistry between a terminal acetylene and an azide unit to form a triazole continues to be of great interest. The Click-cycloaddition requires Cu(I) species. The Cu(I) species can be generated easily by in situ reduction of CUSO4 with ascorbic acid (eq 27). Application of microwave (MW) energy to promote this useful reaction has helped to reduce reaction times and increase reaction rates considerably. 

Click processes occur through simple reaction conditions such as air/moisture insensitivity, solventless or aqueous media, readily available precursors and reagents, and simple product isolation - mostly precluding chromatographic separation (unlike most organic syntheses). The utilization of click chemistry in combination with combinatorial screening will speed up the discovery of new pharmaceuticals that our society will continue to rely upon. ... 

Figure 3.14 Continued) (c) MALDI of the final PEK product bearing barbiturates at both chain ends according to Petraru et al. (2004). (Reprinted with permission from L. Petraru, D. Famik, R. Saf, W.H. Binder, Supramolecular, telechelic poly(etherketones) bearing barbituric acid as hydrogen bonding unit, Polymer Preprints, 45, 2, 690-691, 2004. 2004 Division of Polymer Chemistry, Inc. of the American Chemical Society.) (d) Synthesis of telechelic PCLs with hydrogen bonds via azide-alkine click reactions.

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