Medium-sized cyclophanes. Part XVIII. Iodine-induced cycloisomerization of methyl-, ethyl-, and isopropyl-[2.2]metacyclophanes. π-Basicity and additional strain energy terms as controlling factors
作者:Takeo Sato、Tetsuo Takemura
DOI:10.1039/p29760001195
日期:——
Methyl-, ethyl-, and isopropyl-[2.2]metacyclophanes (4)–(14), in which up to eight alkyl groups are present, have been prepared. The relative rates of iodine-induced cycloisomerization were determined by competitive experiments and gave the order of reactivity as (12) > (9)≃(10) > (11) > (5) > (8) > (4) > (3). The presence of alkyl groups adjacent to the bridging methylene enhanced the rate. For the
制备了甲基,乙基和异丙基[2.2]甲基环已烷(4)-(14),其中最多可存在八个烷基。通过竞争实验确定碘诱导的环异构化的相对速率,并给出反应顺序为(12)>(9)≃(10)>(11)>(5)>(8)>(4)>(3) )。与桥连的亚甲基相邻的烷基的存在提高了该速率。对于甲基系列,除(13)和(14)未恢复原状外,该速率随甲基数目的增加而增加。尽管乙基化合物(10)具有与甲基衍生物(9)相似的反应性,但是异丙基化合物(11)具有降低的反应活性,这与较低的π络合平衡常数相符。结果归因于两个因素: