Cycloheptyne Formation from Cyclohexylidenemethyliodonium Salt in Fluoro Alcohols

Abstract

Solvolysis of cyclohexylidenemethyl(phenyl)iodonium tetrafluoroborate was carried out in 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) in the presence of base. The reaction is much faster in TFE than in HFP. Products in TFE include solely un-rearranged enol ether 2 together with iodobenzene, while the main product in HFP is ring-expanded 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.