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Morifumi Fujita, Kenji Ihara, Wan Hyeok Kim, Tadashi Okuyama, Generation of Cycloheptyne during the Solvolysis of Cyclohexylidenemethyliodonium Salt in the Presence of Base, Bulletin of the Chemical Society of Japan, Volume 76, Issue 9, September 2003, Pages 1849–1855, https://doi.org/10.1246/bcsj.76.1849
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Abstract
Solvolysis of 4-methylcyclohexylidenemethyl(phenyl)iodonium tetrafluoroborate (1) and its R isomer (69% ee) was carried out in 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) in the presence of bases such as acetate, pyridine, triethylamine, and alkoxide. The reaction is much faster in TFE than in HFP. Products in TFE include solely un-rearranged (racemized) enol ether 2 together with iodobenzene, while the main product in HFP is ring-expanded (partially racemized) 1-alkoxycycloheptene 3. Results show that 2 is formed via α-elimination with alkylidenecarbene as an intermediate, while the reaction in HFP to give 3 involves a cycloheptyne intermediate that is mostly derived from an intermediate cyclohept-1-enyl cation via the E1-type pathway.