Conjugation Chemistry/Click Chemistry

"Click Chemistry" is a term which was first described by K. B. Sharpless in 2001 to describe reactions that afford products in high yields and in excellent selectivities by carbon-hetero bond formation reactions. The term "Click" means joining molecular pieces as easily as clicking together the two pieces of a seat belt buckle. In general, the definition of click chemistry is described as follows:

1. Give very high chemical yields of desired products.
2. Combination of readily available simple building blocks.
3. Generate almost no byproducts.
4. Simple product isolation by non-chromatographic methods.
5. Reaction proceeds in water, as well as in organic solvents.

While there are a number of reactions that fulfill this criteria, the Hüisgen 1,3-dipolar [3+2] cycloaddition of azides and alkynes has emerged as the frontrunner.¹⁾ In general, the 1,2,3-triazole ring is not almost oxidized or reduced, which makes it possible to strongly connect two substrates.

In the Hüisgen reaction, metal catalysts, such as copper sulfate, are generally required for reaction acceleration. In especial, it has been reported that the combination of tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (= TBTA) (Product No. T2993) and catalysts shows excellent reactivity.^2,3)。
This reaction system affords desired products in almost 100% yield with no need of repurification, such as recrystallization or column chromatography. Thus, this methodology is an eco-friendly reaction. Moreover, the combination of various alkynes and azides allows it to rapidly construct large compound libraries, and 1,2,3-triazole itself exhibits various kinds of biological activities, such as anti-allergenic or anti-bacterial activities. In addition, the reaction proceeds even in water, and thus, click chemistry has been widely used in many research fields.

References

• 1) R. Huisgen, Angew. Chem. Int. Ed. Engl. 1963, 2, 565.
• 2) Q. Wang, T. R. Chan, R. Hilgraf, V. V. Fokin, K. B. Sharpless, M. G. Finn, J. Am. Chem. Soc. 2003, 125, 3192.
• 3) T. R. Chan, R. Hilgraf, K. B. Sharpless, V. V. Fokin, Org. Lett. 2004, 6, 2853.