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Download filePalladium(II)-Catalyzed Direct Ortho Arylation of 4‑Methyl‑N‑phenylpyridin-2-amines via C–H Activation/C–C Coupling and Synthetic Applications
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posted on 2014-03-10, 00:00 authored by Jean-Ho Chu, Hao-Ping Huang, Wen-Ting Hsu, Shih-Tien Chen, Ming-Jung WuThe
direct ortho arylation of 4-methyl-N-phenylpyridin-2-amines
via palladium(II)-catalyzed C–H activation is described. Treatment
of 4-methyl-N-phenylpyridin-2-amine with potassium
aryltrifluoroborate using 10 mol % of palladium(II) acetate as the
catalyst, 2 equiv of copper(II) acetate as the oxidant, and 1 equiv
of p-benzoquinone in tert-butyl
alcohol gave ortho-arylated products in modest to excellent yields.
This reaction shows good functional group compatibility. A series
of 1H NMR titration experiments and controlled experiments
elucidating the reaction mechanism were carried out. The key intermediate,
4-methyl-N-phenylpyridin-2-amine palladacycle, was
isolated and characterized by X-ray crystallography. The advanced
transformations of ortho-phenylated 4-methyl-N-phenylpyridin-2-amine
to N-(4-methylpyridin-2-yl)-9H-carbazole,
biphenyl-2-amine, and 3-methyl-6-phenylpyrido[1,2-a]benzimidazole were successfully demonstrated as potential synthetic
applications.
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Keywords
Synthetic ApplicationsTheortho arylationPalladiumtransformationmethylactivationoxidantmolyieldseriespalladacyclecrystallographyMethylreaction mechanismbiphenyl2 equivcatalystpalladiumexperiments elucidatingacetateOrtho Arylation1 H NMR titration experimentsgroup compatibilityActivationapplicationpotassium aryltrifluoroborate1 equiv