Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 17, Pages 9627-9634Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202017220
Keywords
cycloaddition; homogeneous catalysis; mechanochemistry; polycyclic aromatic compounds; pyridines
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Funding
- Singapore Ministry of Education [MOE2016-T2-2-043, RG114/18]
- Zhejiang Provincial Natural Science Foundation of China [LY18B020007]
- A*STAR [AME IRG A1783c0003, A2083c0050]
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The study presents a simple and inexpensive catalytic system based on cobalt(II) iodide, 1,3-bis(diphenylphosphino)propane, and Zn for the [2+2+2] cycloaddition of various nitriles and diarylacetylenes to synthesize a broad range of polyarylated pyridines. DFT studies support a reaction pathway involving oxidative coupling of two alkynes, insertion of the nitrile into a cobaltacyclopentadiene, and C-N reductive elimination, leading to the synthesis of tetra- and pentaarylpyridines that can be used as precursors for nitrogen-containing polycyclic aromatic hydrocarbons.
The transition-metal-catalyzed [2+2+2] cycloaddition of nitriles and alkynes is an established synthetic approach to pyridines; however, these cycloadditions often rely on the use of tethered diynes or cyanoalkynes as one of the reactants. Thus, examples of efficient, fully intermolecular catalytic [2+2+2] pyridine synthesis, especially those employing unactivated nitriles and internal alkynes leading to pentasubstituted pyridines, remain scarce. Herein, we report on simple and inexpensive catalytic systems based on cobalt(II) iodide, 1,3-bis(diphenylphosphino)propane, and Zn that promote [2+2+2] cycloaddition of various nitriles and diarylacetylenes for the synthesis of a broad range of polyarylated pyridines. DFT studies support a reaction pathway involving oxidative coupling of two alkynes, insertion of the nitrile into a cobaltacyclopentadiene, and C-N reductive elimination. The resulting tetra- and pentaarylpyridines serve as precursors to hitherto unprecedented nitrogen-containing polycyclic aromatic hydrocarbons via mechanochemically assisted multifold reductive cyclodehydrogenation.
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