The Huisgen 1,3-dipolar cycloaddition reaction of organic azides and alkynes has gained considerable attention in recent years due to the introduction in 2001 of Cu(1) catalysis by Tornoe and Meldal, leading to a major improvement in both rate and regioselectivity of the reaction, as realized independently by the Meldal and the Sharpless laboratories. The great success of the Cu(1) catalyzed reaction is rooted in the fact that it is a virtually quantitative, very robust, insensitive, general, and orthogonal ligation reaction, suitable for even biomolecular ligation and in vivo tagging or as a polymerization reaction for synthesis of long linear polymers. The triazole formed is essentially chemically inert to reactive conditions, e.g. oxidation, reduction, and hydrolysis, and has an intermediate polarity with a dipolar moment of ∼5 D. The basis for the unique properties and rate enhancement for triazole formation under Cu(1) catalysis should be found in the high ∆G of the reaction in combination with the low character of polarity of the dipole of the noncatalyzed thermal reaction, which leads to a considerable activation barrier. In order to understand the reaction in detail, it therefore seems important to spend a moment to consider the structural and mechanistic aspects of the catalysis. The reaction is quite insensitive to reaction conditions as long as Cu(1) is present and may be performed in an aqueous or organic environment both in solution and on solid support.

Cu-catalyzed azide-alkyne cycloaddition.

The modification of polymers after the successful achievement of a polymerization process represents an important task in macromolecular science. Cycloaddition reactions, among them the metal catalyzed azide/alkyne ‘click’ reaction (a variation of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides) represents an important contribution towards this endeavor. They combine high efficiency (usually above 95%) with a high tolerance of functional groups and solvents, as well as moderate reaction temperatures (25–70 °C). The present review assembles recent literature for applications of this reaction in the field of polymer science (linear polymers, dendrimers, gels) as well as the use of this and related reactions for surface modification on carbon nanotubes, fullerenes, and on solid substrates, and includes the authors own publications in this field. A number of references (>100) are included.

http://www.c2p2-cpe.com/imgBase/download/Click%20Review.pdf

‘Click’ Chemistry in Polymer and Materials Science

The preparation of urea by Wöhler constituted a landmark achievement in organic chemistry, and it laid the ground for the early days of target-oriented organic synthesis.1 Since then, significant progress has been achieved in this discipline; many powerful single bond forming reactions and asymmetric variants have been developed. These discoveries have paved the way for the stereoselective assembly of complex organic molecules, a task deemed inconceivable by early practitioners. A great many strategies were invented by chemists in order to facilitate the synthesis of complex natural products.2 One avenue in emulating nature’s efficiency would * To whom correspondence should be addressed. E-mail: dennis.hall@ ualberta.ca. † Novartis Institute for Biomedical Research. ‡ Department of Chemistry, University of Alberta. Chem. Rev. 2009, 109, 4439–4486 4439

Natural product synthesis using multicomponent reaction strategies.

CuI‐Catalyzed Alkyne–Azide “Click” Cycloadditions from a Mechanistic and Synthetic Perspective

In recent years, there has been an ever-increasing need for rapid reactions that meet the three main criteria of an ideal synthesis: efficiency, versatility, and selectivity. Such reactions would allow medicinal chemistry to keep pace with the multitude of information derived from modern biological screening techniques. The present review describes one of these reactions, the 1,3-dipolar cycloaddition ("click-reaction") between azides and alkynes catalyzed by copper (I) salts. The simplicity of this reaction and the ease of purification of the resulting products have opened new opportunities in generating vast arrays of compounds with biological potential. The present review will outline the accomplishments of this strategy achieved so far and outline some of medicinal chemistry applications in which click-chemistry might be relevant in the future.

Click chemistry reactions in medicinal chemistry: applications of the 1,3-dipolar cycloaddition between azides and alkynes.

Regioselective synthesis of [1,2,3]-triazoles catalyzed by Cu(I) generated in situ from Cu(0) nanosize activated powder and amine hydrochloride salts

Microwave-assisted one step high-throughput synthesis of benzimidazoles

One-pot total syntheses of the quinazolinobenzodiazepine alkaloids sclerotigenin (1), (±)-circumdatin F (2), and (±)-asperlicin C (3) via novel microwave-assisted domino reactions were achieved in 55%, 32%, and 20% yields, respectively, from commercially available starting materials. A two-step total synthesis of (±)-benzomalvin A (4) was accomplished with an overall yield of 16%. Additionally, analogues of circumdatin E were synthesized via the three-component one-pot sequential reactions promoted by microwave irradiation. Finally, a two-step formal total synthesis of (±)-asperlicin E (5) was also realized by using this microwave-assisted protocol.

/pdf/microwave-assisted-concise-total-syntheses-of-3pkosp6nem.pdf

Microwave-assisted concise total syntheses of quinazolinobenzodiazepine alkaloids.

Design and synthesis of a quinazolinone natural product-templated library with cytotoxic activity.

A straightforward and efficient method for the regioselective synthesis of functionalized 1,4-disubstituted [1,2,3]-triazoles, from terminal alkynes and azides, has been established utilizing Cu(0) as the source of the catalytic species. The presumed catalytic Cu(I) species is generated by the combination of 10 mol % copper nanosize activated powder and 1 equiv of an amine hydrochloride salt. The addition of an amine hydrochloride salt into the reaction mixture enhanced the dissolution of copper metal, and subsequently facilitated the formation of the Cu(I)-acetylide intermediate required for the regioselective cycloaddition.

Yuko Isome

Papers

Regioselective synthesis of [1,2,3]-triazoles catalyzed by Cu(I) generated in situ from Cu(0) nanosize activated powder and amine hydrochloride salts

Microwave-assisted one step high-throughput synthesis of benzimidazoles

Microwave-assisted concise total syntheses of quinazolinobenzodiazepine alkaloids.

Design and synthesis of a quinazolinone natural product-templated library with cytotoxic activity.

Regioselective Synthesis of [1,2,3]‐Triazoles Catalyzed by Cu(I) Generated in situ from Cu(0) Nanosize Activated Powder and Amine Hydrochloride Salts.