Alkynes, metal mediated reagents

Other metal-mediated reactions of azide reagents to terminal alkynes have also been reported. Indium(ll) triflate catalyzed tandem azidation/l,3-dipolar cycloaddition of various (o,(o-dialkoxyalkynes 134 with trimethylsilyl azide yielded fused 1,2,3-triazoles 135 <05TL8639>. A new ruthenium-catalyzed process for the regioselective synthesis of 1,5-disubstituted-1,2,3-triazoles has been developed <05JA15998>. 

Allylindiums were found to be highly active reagents to react with terminal alkynes to yield allylated products.451 In a similar fashion efficient allylation can be mediated by indium metal under mild conditions 452... 

Zirconium Reagents. Ethenylation can be effected via hydrozirconated terminal alkynes (Scheme 83). The alkenylzirconocene gives the -aUcenyl product. The reaction is carried out in the presence of zinc chloride. Presumably metal metathesis occurs before the palladium-mediated coupling takes place. The coupling is regiospecific with initial... 

A practical and high yielding application of DlB-induced oxidative [4+2] annulations of o-phenylenediamines 135 and electron-deficient alkynes 136 was described for the preparation of quinoxaline derivatives 137 (Scheme 30). The oxidative [4+2] annulations between diaminobenzene (4e center) and electron-poor alkynes (2e center) were successfully mediated by 1(111) reagent. Formation of quinoxalines was proposed to involve an initial generation of enamine which was likely to undergo DlB-mediated oxidative [4+2] annulations and aromatization. This metal-free and green protocol is very useful in the synthesis of diverse bioactive quinoxaline scaffolds (Scheme 30) [46]. 

The Si-B bond in silylboranes are activated in the manner similar to disilanes by the group 10 transition metal catalysts to mediate silylboration of such unsaturated substrates including alkenes, alkynes, 1,2-, and 1,3-dienes. Catalytic enantioselective silylboration of 1,2-dienes has been achieved with a chiral palladium catalyst to give a-boryl-substituted chiral allylsilanes. The resulting C-B bonds are converted into various types of C-C, C-N, and C-O bonds by the rich chemistry of organoboron reagents (Scheme 3 1). ... 

---