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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.

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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