Synthesis and stability of 1,1-dialkyl-1H-azulenium cations |
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Authors: | Mitsunori Oda Nobue Nakajima Takanori Kajioka |
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Affiliation: | a Department of Chemistry, Faculty of Science, Shinshu University, Asahi 3-1-1, Matsumoto, Nagano 390-8621, Japan b Department of Applied Chemistry, Faculty of Engineering, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan |
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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 pKR+ 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 pKR+ 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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Keywords: | Carbocations pKR+ values Tropylium ions Nazarov cyclizations Intermolecular charge-transfer interaction |
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