Cycloaddition alkynes

Besides short ELPS, longer ELPs have also been conjugated to synthetic polymers. In one approach, Cu(I)-catalyzed azide-alkyne cycloaddition click chemistry was applied. For this purpose, ELPs were functionalized with azides or alkynes via incorporation of azidohomoalanine and homopropargyl glycine, respectively, using residue-specific replacement of methionine in ELP via bacterial expression [133]. More recently, an alternative way to site-selectively introduce azides into ELPs was developed. Here, an aqueous diazotransfer reaction was performed directly onto ELP[V5L2G3-90] using imidazole-1-sulfonyl azide [134]. 

Rhodium also has been reported as a catalyst for [2+2+2] alkyne cycloaddition in water. Uozumi et al. explored the use of an amphiphilic resin-supported rhodium-phosphine complex as catalyst (Eq. 4.60). The immobilized rhodium catalyst was effective for the [2+2+2] cycloaddition of internal alkynes in water,113 although the yields of products were not satisfactory. 

Gramlich PME, Wirges CT, Manetto A, Carell T (2008) Postsynthetic DNA modification through the copper-catalyzed azide-alkyne cycloaddition reaction. Angew Chem Int Ed... 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

M. Meldal and C. W. Tomqe, Cu-catalyzed azide-alkyne cycloaddition, Chem. Rev., 108 (2008) 2952-3015. 

Agard, N.J., Prcschcr, J.A., and Bertozzi, C.R. (2004) A strain-promoted [3+2] azide-alkyne cycloaddition for covalent modification of biomolecules in living systems. /. Am. Chem. Soc. 126, 15046-15047. 

Sun, X.-L., Stabler, C.L., Cazalis, C.S., and Chaikof, E.L. (2006) Carbohydrate and protein immobilization onto solid surfaces by sequential diels-alder and azide-alkyne cycloadditions. Bioconjugate Chem. 17, 52-57. 

CuO nanostructures of variable shapes CuO nanospheres (5-10 run), CuO nanorods (WXL = 24-27 nmxl24-140 run) and CuO nanowires (WXL= 8-10 nmx230-270 nm) have been synthesised to study the effect of shape of the catalyst on the Cu(I)-catalyzed click azide-alkyne cycloaddition. Cu(I) species were generated in situ by the reduction of CuO nanostructures in the presence of sodium... 

Keywords Azide-alkyne cycloaddition, triazoles, CuO-nanowires, CuO-nanorods, CuO-nanospheres Reference ... 

Ir-diphosphine complexes have been shown to catalyze a number of potentially interesting C—C coupling reactions [41]. Special mention should be made of the various transformations of alkynes (cycloaddition, isomerization, dimerization, alkynylation), selected aldol and carbonylation reactions, even though the synthetic potential of some of these reactions has not been explored. 

Fused triazoles were synthesized in a similar manner through the Huisgen azide-alkyne cycloaddition, which was carried out by simple heating the Ugi adducts at 100°C. Five different fused triazole scaffolds 160-164 were obtained by placing the additional functions in different components or changing the distance between them and the Ugi-reacting group [131]. 

The Dotz benzannulation reaction, based on the alkyne cycloaddition to chromium carbene complexes, is the most important application of Fischer carbene complexes. Among the various Fischer carbene complexes, alkoxy and aminocarbene complexes of chromium undergo a novel inter- and intramolecular tandem alkyne insertion/ carbene annotation sequence to give 9H-carbazoles and nf/-benzo[fl]carbazoles. 

Another approach for the synthesis of networks relies on the polycondensation of multifunctionalized polyesters with the appropriate multifunctionalized agent, provided that one of the partner is at least tri-functionalized. Toward this end, several reaction have been reported, such as the Michael addition of amines onto acrylates [184], the coupling of ketones and oxyamines [185], the click copper(II)-catalyzed azide-alkyne cycloaddition [186], and esterification reactions [25, 159, 187]. Interestingly, if esterification reactions are used, the crosslinks are then degradable. 

Scheme 29 Preparation of tricyclic [1-lactams 86-89 using nitrone-alkene(alkyne) cycloadditions...

The reaction chosen to connect the tethers in situ was the Huisgen azide-alkyne cycloaddition (Scheme 10.5). The Huisgen cycloaddition forms 1,2,3-triazoles as a nearly 1 1 mixture of regioisomers (10.28 and 10.29). The reaction is slow at room temperature. However, if the azide and alkyne are positioned ideally, such as when bound in close proximity by AChE, then the reaction occurs at room temperature. 

Diaz, D.D., Punna, S., Holzer, P., Mcpherson, A.K., Sharpless, K.B., Fokin, V.V. and Finn, M.G. (2004) Click chemistry in materials synthesis. 1. Adhesive polymers from copper-catalyzed azide-alkyne cycloaddition. J. Polym. Sci. Polym. Chem., 42, 4392. 

Copper(I)-catalyzed azide-alkyne cycloaddition as a selective bioconjugation technique... 

Beatty KE, Fisk JD, Smart BP et al (2010) Live-cell imaging of cellular proteins by a strain-promoted azide-alkyne cycloaddition. Chembiochem 11 2092-2095... 

This strategy has also been extended to [6 + 2]-cycloaddition [61]. Thus, substituted cyclooctatetraenes can be prepared in two steps employing a Cr-(0)-promoted [67t + 27t] thiepin dioxide-alkyne cycloaddition, followed by photoactivated sulfur dioxide extrusion (Scheme 9.37) [62]. 

M. F. Semmelhack, J. J. Bozell, L. Keller, T. Sato, E. Spiess, W. Wulff, and A. Zask, Synthesis of Naphthoquinone Antibiotics by Intramolecular Alkyne Cycloaddition to Carbene-Chromium Complexes, Tetrahedron 41, 5803-5812 (1985). 

A copper catalysed click (azide-alkyne cycloaddition) reaction has been used to prepare a fluorous-tagged TEMPO catalyst (Figure 7.20). TEMPO is a stable organic free radical that can be used in a range of processes. In this case, its use in metal-free catalytic oxidation of primary alcohols to aldehydes using bleach as the terminal oxidant was demonstrated. The modified TEMPO can be sequestered at the end of the reaction on silica gel 60 and then released using ethyl acetate for reuse in further reactions in this way the TEMPO was used four times with no loss in activity. 

A number of examples exist involving reactions of CpCo(CO)2 and silylated alkynes. Cycloaddition of MesSiC CH gives a 3 1 mixture of 2,5- and 2,4-bis(trimethylsilyl)cyclopentadienone complexes. The use instead of [C5Me5]Co(CO)2 reverses the regioselectivity to 1 3.7, presumably due to the increased steric crowding about cobalt (equation 9). This effect has yet to be exploited in synthesis. 

Rodionov VO, Fokin VV, Finn MG. Mechanism of the ligand-free Cu-I-catalyzed azide-alkyne cycloaddition reaction. Angew. Chem. Int. Ed. 2005 44 2210-2215. 

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