substitution reactions. However, attempts to observe the formation of 4 from various precursors by NMR methods (which succeed for the 1-adamantyl cation 5) failed, suggesting that 4 does not survive on longer timescales. DFT calculations suggest that the retro-Prins process (β-cleavage, Grob fragmentation) to give enantiomeric (1R,5R)- and (1S,5S)-7-methylene-2-oxoniabicyclo[3.3.1]non-2-ene cations 22 is the
这 2-氧杂-5-
金刚烷基碳阳离子4被证明是在几个S N 1取代反应中的可行中间体。但是,尝试通过NMR方法观察到各种前体形成4的尝试(对于1-
金刚烷基阳离子5而言成功)失败了,这表明4不能在更长的时间尺度上存活。DFT计算表明,逆-Prins过程(β裂解,Grob断裂)可得到对映体1 R,5 R)- 和 (1 S,5 S)-7-亚甲基-2-氧杂双环[3.3.1] non-2-ene阳离子22是用于唯一现实的单分子退路4。在6-31G(d)基础集的情况下,B3LYP计算预测4比22更稳定11 kJ mol -1,并且将4和22隔离的势垒仅计算为15 kJ mol -1,因此快速平衡这些物种可能在实验室时间尺度上。讨论了这项研究对Prins环化机理的意义。