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.
4-甲基
环己烯基甲基(苯)
碘铵四
氟硼酸盐(1)及其R异构体(69% ee)的溶剂解反应在存在
醋酸盐、
吡啶、triethylamine和烷氧基化合物的情况下,在
2,2,2-三氟乙醇(
TFE)和
1,1,1,3,3,3-六氟丙烷-2-醇(
HFP)中进行。在
TFE中的反应速度远快于在
HFP中的反应。
TFE中的产物仅包括未重排的(消旋化的)烯醇醚2以及
碘苯,而
HFP中的主要产物是扩环的(部分消旋化的)1-烷氧基
环庚烯3。结果表明,2是通过α-消除反应形成的,烷基烯基碳烯作为中间体,而在
HFP中生成3的反应涉及一个主要来源于中间体环庚-1-烯阳离子的环庚炔中间体,通过E1型路径实现。