کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1323426 1499878 2014 10 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی معدنی
پیش نمایش صفحه اول مقاله
Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties
چکیده انگلیسی


• Synthesis of anisyl and ferrocenyl adducts of methylenepyran-containing β-diketones using base-catalyzed Claisen condensation.
• Characterization by elemental analysis, IR and 2D NMR, HRMS-ESI+ and cyclic voltammetry.
• The X-ray crystal structures of the ferrocenyl adduct shows π-conjugation over the entire molecule.
• Both solution and solid state measurements show that the two compounds exist solely as their keto–enol tautomers.

Wittig reaction between the in situ generated [2,6-diphenyl-4H-pyran-4-yl phosphorane and methyl 4-formylbenzoate afforded the methyl 4-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl]benzoate precursor 2 in 75% yield. The anisyl and ferrocenyl adducts of methylenepyran-containing β-diketones 3 and 4, respectively, were prepared from the base-catalyzed Claisen condensation reaction between precursor 2 and 4-methoxyacetophenone or acetylferrocene, using t-BuO−K+ as basic initiator. Both β-diketones 3 and 4 were isolated as an orange and dark-red crystalline solids in 50% yield, respectively. The acetyl derivative 6, 1-acetyl-1′-methylenepyranyl-ferrocene, was synthesized following a classical Friedel–Crafts acylation reaction of the parent ferrocenylmethylenepyran 5, and isolated in 61% yield as a red microcrystalline powder. The condensation reaction between the electron-rich acetyl complex 6 and acetyl acetate, using lithium diisopropylamide as the active base initiator, provided the ferrocenylmethylenepyran-containing β-diketone, 1-(1,3-dioxobutyl)-1′-[(2,6-diphenyl-4H-pyran-4-ylidene)methyl] ferrocene 7, isolated in 20% yield as an orange powder. The composition and identity of the new compounds 2–4, 6 and 7 are supported by elemental analysis, FT-IR, one- and two-dimensional 1H and 13C NMR spectral data and mass spectrometry. Additionally, the molecular structures of compounds 2, 4 and 6 were ascertained by single-crystal X-ray diffraction study. FT-IR and NMR spectral data indicate that both β-diketones 3 and 4 do solely exist as their keto–enol tautomeric form in solution and in the solid state, whereas a mixture of keto–enol and β-diketone tautomers in a 73:27 spectroscopic ratio was observed for 7. In the three cases, enolization takes place exclusively away from the anisyl or ferrocenyl group with formation of a six-membered pseudo-aromatic keto–enol ring, confirmed by the crystal structure of 4. Cyclic voltammetric measurements revealed that all the compounds undergo a single one-electron oxidation, localized presumably at the methylenepyran unit. This first oxidation generates a radical cation that undergoes an intermolecular C–C bond coupling to form the corresponding dimer. Anodically shifted to the first oxidation, cyclovoltammogram of 4 exhibits one reversible two-electron oxidation while that of 6 and 7 present two successive reversible one-electron oxidations, attributed in the three cases to the ferrocenyl fragment of the dimer.

The title compounds are readily syntheized from the base-catalyzed Claisen condensation reaction. The electron-rich 1-ferrocenyl-3-methylenepyran substituted β-diketone (illustrated) does solely exist as its keto–enol tautomeric form both in solution and in the solid state. The pseudo-aromatic keto–enol ring allows partial conjugation between the two-redox active parts of the molecule.Figure optionsDownload as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Organometallic Chemistry - Volume 762, 15 July 2014, Pages 19–28
نویسندگان
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