Formation, characterization, and some reactions of spiro[cyclobutane-1,1′-1′H-azulenium] ion

Starting from trimethylsilyl enol ether of 1-acetyl-1,3,5-cycloheptatriene, the title 1H-azulenium cation was synthesized by a five-step sequence that involves the Noyori-Mukaiyama aldol reaction, the Nazarov cyclization, the Shapiro reaction, and hydride abstraction. The Nazarov reaction of the aldol-type adduct resulted in formation of an unusual double-bond position isomer, which has never been obtained in similar reactions forming tetrahydroazulenones. The pK R + value of the title cation was found to be 9.8, which is less than that expected by inductive stabilization of the carbon number at the 1-position. The X-ray crystal structure of the title cation (ClO 4 -salt) reveals CH-O interactions and deformation of the azulenyl ion part.

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Synthesis, Stability, and Crystal Structure of an Azulenium Cation Containing an Adamantyl Group

Oda

Nakajima

Thạnh

et al. 2008

Eur J Org Chem

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Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

et al. 2006

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Abstract:Starting from trimethylsilyl enol ether of 1-acetyl-1,3,5-cycloheptatriene, the title 1,1-dimethyl-, 1,1-diethyl-and 1,1-dipropyl-1H-azulenium cations 6-8 were synthesized in five steps. The order of pK R + values of these cations was found to be 7>8>6. A comparison of the values between 1,1-dialkyl-and 1,1-spiroalkylated 1H-azulenium cations with the same number of carbon atoms at the 1-position provided the results of 7>1 and 8<3. The cation 8 shows a relatively lower pK R + value to those of 3 and 7 probably due to its slightly bulkier propyl groups from which solvation stabilization of 8 under the conditions suffers. An intermolecular charge-transfer interaction between the cations and dibenzo-24-crown-8 was also studied.

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Reductive coupling of (azulen-1-yl)carbonyl compounds by low-valent titanium; pinacol/pinacolone rearrangement versus pinacol and alkene generation

Razus

Dragu

Nica

et al. 2011

Tetrahedron Letters

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Formation, characterization, and some reactions of spiro[cyclobutane-1,1′-1′H-azulenium] ion

Cited by 4 publications

References 43 publications

Synthesis, Stability, and Crystal Structure of an Azulenium Cation Containing an Adamantyl Group

Synthesis, Stability, and Crystal Structure of an Azulenium Cation Containing an Adamantyl Group

Synthesis and stability of 1,1-dialkyl-1H-azulenium cations

Reductive coupling of (azulen-1-yl)carbonyl compounds by low-valent titanium; pinacol/pinacolone rearrangement versus pinacol and alkene generation

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