Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, P. le Aldo Moro 5, 00185 Roma, Italy.
J Org Chem. 2013 Jul 19;78(14):6935-46. doi: 10.1021/jo400489m. Epub 2013 Jul 3.
Resorc[4]arenes 1 and 2, which previously proved to entrap NO(+) cation within their cavities under conditions of host-to-guest excess, were treated with a 10-fold excess of NOBF4 salt in chloroform. Kinetic and spectral UV-visible analyses revealed the formation of isomeric 1:2 complexes as a direct evolution of the previously observed event. Accordingly, three-body 1-(NO(+))2 and 2-(NO(+))2 adducts were built by MM and fully optimized by DFT calculations at the B3LYP/6-31G(d) level of theory. Notably, covalent nitration products 4, 5 and 6, 7 were obtained by reaction of NOBF4 salt with host 1 and 2, respectively, involving macrocycle ring-opening and insertion of a nitro group in one of the four aromatic rings. In particular, compounds 4 and 6, both containing a trans-double bond in the place of the methine bridge, were oxidized to aldehydes 5 and 7, respectively, after addition of water to the reaction mixture. Calculation of the charge and frontier orbitals of the aromatic donor (HOMO) and the NO(+) acceptor (LUMO) clearly suggests an ipso electrophilic attack by a first NO(+) unit on the resorcinol ring, mediated by the second NO(+) unit.
Resorc[4]arenes 1 和 2 之前被证明在主客体过量的条件下能够将 NO(+)阳离子捕获在其空腔内，随后用 10 倍过量的 NOBF4 盐在氯仿中处理。动力学和光谱紫外可见分析表明，形成了异构体 1:2 配合物，这是之前观察到的事件的直接演变。因此，三原子 1-(NO(+))2 和 2-(NO(+))2 加合物通过 MM 构建，并通过 DFT 计算在 B3LYP/6-31G(d)理论水平上完全优化。值得注意的是，NOBF4 盐与主体 1 和 2 反应分别得到了共价硝化产物 4、5 和 6、7，涉及大环环的开环和一个硝基基团在四个芳环之一中的插入。特别是，化合物 4 和 6 都在亚甲基桥的位置含有反式双键，在向反应混合物中加水后，分别被氧化为醛 5 和 7。对芳香供体（HOMO）和 NO(+)受体（LUMO）的电荷和前沿轨道的计算清楚地表明，第一个 NO(+)单元通过第二个 NO(+)单元对间位的苯酚环进行亲电攻击。
