Chemo- and regioselective click reactions through nickel-catalyzed azide–alkyne cycloaddition
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- Chemo- and regioselective click reactions through nickel-catalyzed azide–alkyne cycloaddition
- Kim, Woo Gyum; Baek, Seung-yeol; Jeong, Seo Yeong; Nam, Dongsik; Jeon, Ji Hwan; Choe, Wonyoung; Baik, Mu-Hyun; Hong, Sung You
- Issue Date
- ROYAL SOC CHEMISTRY
- ORGANIC & BIOMOLECULAR CHEMISTRY, v.18, no.17, pp.3374 - 3381
- Metal-catalyzed cycloaddition is an expeditious synthetic route to functionalized heterocyclic frameworks. However, achieving reactivity-controlled metal-catalyzed azide-alkyne cycloadditions from competing internal alkynes has been challenging. Herein, we report a nickel-catalyzed [3 + 2] cycloaddition of unsymmetrical alkynes with organic azides to afford functionalized 1,2,3-triazoles with excellent regio- and chemoselectivity control. Terminal alkynes and cyanoalkynes afford 1,5-disubstituted triazoles and 1,4,5-trisubstituted triazoles bearing a 4-cyano substituent, respectively. Thioalkynes and ynamides exhibit inverse regioselectivity compared with terminal alkynes and cyanoalkynes, affording 1,4,5-trisubstituted triazoles with 5-thiol and 5-amide substituents, respectively. Density functional theory calculations are performed for the elucidation of the reaction mechanism. The computed mechanism suggests that a nickellacyclopropene intermediate is generated by the oxidative addition of the alkyne substrate to the Ni(0)-Xantphos catalyst, and the subsequent C-N coupling of this intermediate with an azide is responsible for the chemo- and regioselectivity.
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