Sharpless-type click reaction

Among the chemical procedures listed above, click chemistry can be considered an efficient method that covers a wide range of different, requested functionalizations. The key reaction, called Sharpless-type click reaction , is a variant of the Huisgen 1,3-dipolar cycloaddition reaction between C—C triple bonds, C—N triple bonds, and alkyl-, aryl-, and sulfony 1-azides. 

Roth, T., Groh, P.W., Palfi, V. et al. (2005) Supramolecular three-arm star polyisobutylenes by sharpless-type click reactions. Polymer Preprints, 46,1166. 

Some of the important click reactions are (Kolb and Sharpless 2003 Adzima and Bowman 2012) azide-alkyne azide-sulfonyl cyanide benzyne-azide cycloaddition and hetero Diels-Alder reactions nucleophilic ring opening of strained molecules such as epoxides, aziridines, etc. non-aldol-type reactions and additions to carbon-carbon multiple bonds through oxidation-type reactions such as epoxidation, hydrox-ylation, etc. For more details, the reader is referred to a recent review by Adzima and Bowman (2012). 

Click chemistry is a chemical concept enunciated by Barry Sharpless, Scripps Research Institute, USA, in 2001, which highlights the importance of using a set of powerful, highly reliable, selective reactions under simple reaction conditions to join small molecular units together quickly for the rapid synthesis of new compounds via heteroatom links and create molecular diversity. Several types of reactions have been identified that fulfill the criteria- thermodynamically favored reactions that lead specifically to one product such as nucleophilic ring opening reactions of epoxides and aziridines, nonaldol type carbonyl reactions, additions to carbon-carbon multiple bonds, Michael additions, and cycloaddition reactions. The best-known cHck reactions are the copper-catalyzed reaction of azides and alkynes or the so-called CuAAC reaction and the thiol-ene reaction. 

A somewhat different but mechanistically related reaction is the [2 -f 3] cycloaddition of a functionalized alkyne or nitrile to an azide to form a disubstituted triazole (120) or tetrazole ring (121, 122), linking the respective functionalities irreversibly (Scheme 14b). This click chemistry was used by Sharpless and co-workers (120) in 2001 as a tool to probe biochemical catalysis and substrate activation. The ease of the Cu(I)-catalyzed reaction has created a true explosion (120-160) of simple coupling-functionalization chemistry of all types of biochemical components (sugars, DNA, proteins, enzymes, substrates, inhibitors) (131, 135, 136, 139, 142, 155, 157-160), polymers (126, 134, 140, 147, 154),... 

S.2.2.4. Triazoles from Azides. Cycloadditions of this type constitute a valuable synthetic route to the triazole ring system. This is shown in Scheme 5.30. This combination dates back to the early work of Huis-gen, but in more recent times it was discovered to be subject to catalysis by Cu(I) compounds. The reactions are fast under mild conditions, have high regiospecificity, and occur in a variety of solvents including water. In addition, reaction products are easily isolated. Reactions with these characteristics have become known as comprising click chemistry this term was coined by K. B. Sharpless. The first and most commonly used reaction referred to by this name is indeed the azide-alkyne cycloaddition, and new interest has developed in triazole hemistry since the discoveiy of the copper catalysis. In addition to its use in organic... 

Amongst the list of highly efficient chemical transformations that were outlined in the definitive click chemistry paper by Sharpless and colleagues was carbonyl chemistry of the nonaldol type (Kolb et al, 2001). One such reaction is oxime formation, resulting from the catalyst-free/ambient temperature reaction of aldehydes/ketones with aminooxy functionalities (Scheme 2.7). 

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