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.
1H and 13C NMR Studies of conformational substituent effect in 4- and 5-monosubstituted derivatives of benzocycloheptene
作者:D. Ménard、M. St-Jacques
DOI:10.1016/s0040-4020(01)91866-6
日期:1983.1
Values of-ΔG° for the axial ⇌ equatorial conformational equilibrium of the chair form of 5-substituted (2–8) and 4-substituted (9–14) derivatives of bezocycloheptene were measured from their 1H and/or 13C NMR spectra recorded under conditions of slow exchange (T < 80°C). Strikingly different conformationalsubstituenteffects are noted in each series of compounds. The results are compared with equivalent
苯环庚烯的5-取代(2-8)和4-取代(9-14)衍生物的椅子形式的轴向赤道构象平衡的-ΔG°值是通过其1 H和/或13 C NMR光谱测量的在缓慢交换条件下(T <80°C)记录。在每个系列的化合物中都发现了截然不同的构象取代基效应。将结果与发布的类似六元环导数的等效能量参数进行比较,并根据空间和静电相互作用进行解释。测量了对13 C NMR化学位移的取代基影响,并将其与环己烷环报道的取代基进行了比较。