The Influence of the 2-Alkoxy Group and of C-5 Substituents on the Direction of Reductive Cleavage of 2-Alkoxytetrahydrofurans by AlH<sub>2</sub>Cl in Ether Solution
作者:P. C. Loewen、Miss L. P. Makhubu、R. K. Brown
DOI:10.1139/v72-238
日期:1972.5.15
ring C—O bond cleavage. However, substituents at C-5 of 2-methoxytetrahydrofuran exert a strong effect on the ratio of ring to exo C—O bond cleavage. Thus, alkyl (electron donor) groups at C-5 promote an increase in the amount of exo cleavage, the proportion increasing from 62.5 to 100% as the C-5 alkyl group is changed from CH3 to t-C4H9. In contrast, electron withdrawing substituents, CH3OCH2— and
烷氧基为 CH3O、C2H5O、i-C3H7O 或 t-C4H9O 的 2-烷氧基四氢呋喃醚溶液的 AlH2Cl 氢解,仅产生那些由环 C-O 键断裂产生的产物。然而,2-甲氧基四氢呋喃的 C-5 处的取代基对环外 CO 键断裂的比例有很大影响。因此,C-5 处的烷基(电子给体)促进了外切量的增加,随着 C-5 烷基从 CH3 变为 t-C4H9,该比例从 62.5% 增加到 100%。相比之下,C-5 处的吸电子取代基 CH3OCH2- 和 C6H5 有利于环裂解的程度分别为 93% 和 84%。结果被解释为这些取代基通过它们的电子特性对达到导致环 C-O 或外型 C-O 键断裂的过渡态的相对容易程度的影响。然而,有证据表明这些取代基的体积空间效应也控制了,尽管在较小程度上......