Abstract
1,1-Ethylene-1H-azulenium tetrafluoroborate ( 1b) and its alkyl substituted derivatives, 6-t-butyl ( 1c) and 4-isopropyl-3,8-dimethyl ones ( 1d), were synthesized starting from their corresponding azulenes by a three-step sequence which includes reduction, cyclopropanation and hydride abstraction reactions. The cation 1 b and its 6-t-butyl derivative 1c, generated in deuterated acetonitrile at −20 °C, were characterized by low-temperature NMR spectroscopy. On the other hand, the cation 1d was isolated as slightly unstable, greenish-yellow crystals. While the cation 1 b in solution underwent expansion of the cyclopropane ring at elevated temperatures, 1 c and 1 d just decomposed. All the cations were found to react easily with nucleophiles to give thermodynamically controlled, stable addition products at their cyclopropane methylene carbons.
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