Redon Sophie, Li Yun, Reinaud Olivia
Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques (CNRS UMR 8601), Université René Descartes, 45, rue des Saints-Pères, 75270 Paris Cedex 06, France.
J Org Chem. 2003 Sep 5;68(18):7004-8. doi: 10.1021/jo034557j.
The electrophilic ipso-reactions of a tBu-calix[6]arene that presents alternate O-methyl and O-2-methylen-N-methyl-imidazolyl groups (1) at the small rim have been studied. Whereas 1 underwent per-sulfonation in sulfuric acid, it selectively reacted with nitric acid to yield a tris-nitro derivative. The ipso-nitration occurred regioselectively on the calixarene anisol units. The reaction has been studied with various tBu-calixarenes (2-11) presenting alternate anisol and phenol ether units. The regioselectivity of the process appeared to be correlated to the presence of a protonable site on the O-substituent. It is proposed that the corresponding protonated heteroatom (N for the amines, O for the amides and the carboxylic acid), situated in the gamma or epsilon position of the phenoxy moieties, deactivates the corresponding aromatic ring by removing electron density through intramolecular hydrogen bonding. The high control operated by the O-substituents at the small rim even allowed the selective ipso-nitration of partially detertiobutylated calixarene 1(H3). Hence, these findings open new routes to a wide range of nonsymmetrically substituted calixarenes at the large rim.
对一种在小环处带有交替的O - 甲基和O - 2 - 亚甲基 - N - 甲基 - 咪唑基的叔丁基杯[6]芳烃（1）的亲电本位反应进行了研究。虽然1在硫酸中发生全磺化反应，但它与硝酸选择性反应生成三硝基衍生物。本位硝化反应区域选择性地发生在杯芳烃苯甲醚单元上。对带有交替苯甲醚和酚醚单元的各种叔丁基杯芳烃（2 - 11）的该反应进行了研究。该过程的区域选择性似乎与O - 取代基上存在可质子化位点相关。有人提出，位于苯氧基部分γ或ε位置的相应质子化杂原子（胺的N、酰胺和羧酸的O），通过分子内氢键去除电子密度，使相应的芳环失活。小环处的O - 取代基实现的高度控制甚至允许对部分去叔丁基化的杯芳烃1(H3)进行选择性本位硝化。因此，这些发现为在大环处制备多种不对称取代的杯芳烃开辟了新途径。
