Anisyl and ferrocenyl adducts of methylenepyran-containing β-diketone: Synthesis, spectral, structural, and redox properties

Abstract

International audienceWittig 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

Reversible Redox Switching of Chromophoric Phenylmethylenepyrans by Carbon–Carbon Bond Making/Breaking

“…[36][37][38][39] Interestingly, electrochemical studies have shown that methylenepyran compounds can undergo fast dimerization by σ C−C bond making upon oxidation at moderate potential values (E p ~ 0.3 V vs. Fc) in organic solvents. 37,38,40,41 The resulting bispyrylium species is reduced irreversibly around −0.8 V vs. Fc leading back to the initial methylenepyran by C−C bond breaking (Scheme 1). [40][41][42][43] Bispyrylium compounds are much less sensitive to self-deprotonation than their bisdithiolium analogues.…”

“…37,38,40,41 The resulting bispyrylium species is reduced irreversibly around −0.8 V vs. Fc leading back to the initial methylenepyran by C−C bond breaking (Scheme 1). [40][41][42][43] Bispyrylium compounds are much less sensitive to self-deprotonation than their bisdithiolium analogues. 30,40,43 Such stability is of high importance when considering prospective application in the field of organic redox switches.…”

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…[87,112,[261][262][263][264][265] In most cases, ligands with strong RAHB systemsh ave lower reactivity towards metal ions, [55] but in some cases am etal ion can directly deprotonate the ligand, destroying the RAHB system and enteringt he chelating pocket. [87,112,[261][262][263][264][265] In most cases, ligands with strong RAHB systemsh ave lower reactivity towards metal ions, [55] but in some cases am etal ion can directly deprotonate the ligand, destroying the RAHB system and enteringt he chelating pocket.…”

“…[265] In the obtained organometallic complex, an enolization takes place exclusivelya way from the ferrocenyl group with formation of as ix-membered pseudoaromatic keto-enolr ing with as trong RAHB system,c onfirmed by 1 HNMR spectroscopy and X-ray analysis. [265] In the obtained organometallic complex, an enolization takes place exclusivelya way from the ferrocenyl group with formation of as ix-membered pseudoaromatic keto-enolr ing with as trong RAHB system,c onfirmed by 1 HNMR spectroscopy and X-ray analysis.…”

A facile access to new diazepines derivatives: Spectral characterization and crystal structures of 7-(thiophene-2-yl)-5-(trifluoromethyl)-2,3-dihydro-1 H -1,4-diazepine and 2-thiophene-4-trifluoromethyl-1,5-benzodiazepine

“…Thus, it is attractive to obtain new heterocycles with potential biological properties from easy and minimum step reactions, involving inexpensive starting materials such as -diketones which can be functionalized in three different sites of the molecule. In the last few years, our groups have been interested in the synthesis of -diketones [5][6][7] as starting materials to be used in the preparation of heterocycles [8,9] and tridentate Schiff base ligands [10][11][12], via condensation with aliphatic M A N U S C R I P T…”