Reaction of Nitrosonium Cation with Resorc[4]​arenes Activated by Supramolecular Control: Covalent Bond Formation

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 obsd. event. Accordingly, three-​body 1-​(NO+)​2 and 2-​(NO+)​2 adducts were built by MM and fully optimized by DFT calcns. 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, resp., involving macrocycle ring-​opening and insertion of a nitro group in one of the four arom. rings. In particular, compds. 4 and 6, both contg. a trans-​double bond in the place of the methine bridge, were oxidized to aldehydes 5 and 7, resp., after addn. of water to the reaction mixt. Calcn. of the charge and frontier orbitals of the arom. 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.