Oxidative Cross-Coupling Reactions by Lei Aiwen & Wei Shi & Chao Liu & Wei Liu & Hua Zhang

Author:Lei, Aiwen & Wei Shi & Chao Liu & Wei Liu & Hua Zhang
Language: eng
Format: epub
ISBN: 9783527681006
Publisher: John Wiley & Sons, Inc.
Published: 2016-08-08T00:00:00+00:00

Scheme 3.75 Gold-mediated coupling between arenes and terminal alkynes.

Inspired by the above pioneering work, 9 years later, a gold-catalyzed oxidative cross-coupling between electron-rich arenes and terminal alkynes was developed by Nevado [209]. Using 5 mol% Ph3PAuCl as the catalyst in the presence of 1.5 equiv. of PhI(OAc)2 oxidant, various electron-rich arenes, heteroarenes, or even alkenes react with electron-deficient terminal alkynes smoothly to produce the corresponding products in good yields (Scheme 3.76). Phenylacetylene also affords the alkynylation product albeit in a lower yield due to the increased alkyne homocoupling by-product. Mechanistic investigation by 31P NMR confirms the formation of gold(I)–acetylide species in the reaction. Kinetic studies display the first order in both alkyne and arene substrates. Meanwhile, negligible kinetic isotope effects on both the substrates indicate that neither the C(sp)–H nor the C(sp2)–H bond cleavage is involved in the rate-determining step. Hence, starting from gold(I)–acetylide complex I, two possible pathways are proposed (Scheme 3.77). (A) Complex I is oxidized by PhI(OAc)2 to generate a gold(III)–alkynyl intermediate II; electrophilic aromatic substitution between intermediate II and arene affords complex III; final reductive elimination of complex III gives the alkynylated product. (B) Iodination of complex I with PhI(OAc)2 to generate an electrophilic alkynyl–iodonium complex IV; arylauration to the triple bond of complex IV affords a vinyl gold intermediate V; β-elimination delivers the arylated alkyne.

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