C₂ Symmetric Cubane-like Componds: Photochemical Sythesis And Derivation

Owing to environmental benign and economical advantage, photochemical reaction is appealing from synthetic perspective. However, short excited state lifetime and low activation energy for reaction in excited state leave little room for manipulating transient state when photochemical reaction is carry out in solution. In contrast to the great advance in thermal reaction, photochemistry still lies in the area of basic research. In this thesis, we studied the photocyclodimerization of alkyl 2-naphthoate derivatives to prepare a series of cubane-like photocyclodimers that cannot be made by thermal reactions. The detailed results are as follows:1. Irradiation of methyl 3-methoxyl-2-naphthoate (2,3-NA) in methanol with light l > 280 nm produces anti-head-to-head cubane-like photocyclodimer and the [4+4] intermediate, which is the first incidence of directly obtaining the intermediate in photocyclodimerization of naphthalene analogues.2. Spectroscopic analysis reveals thatγ-CD can encapsulate 2,3-NA to make a stable 2:1 inclusion complex 2,3-NA@γ-CD both in aqueous solution and in the solid state. Irradiation of 2,3-NA@γ-CD results in photocyclodimerization with remarkable selectivity and efficiency. Studies on the product distributions showγ-CD not only enhances the efficiency of photocyclodimerization but also facilitates the transformation from the [4+4] intermediate to cubane-like photocyclodimer. More importantly, the use of nativeγ-CD as a chiral reaction vessel turns out to be an effective strategy for the enantioselective photocyclodimerization of 2,3-NA. The stepwise photochemical-chiral delivery has been disclosed for the first time, which is well recognized to be a consequence of an in situ increase in the e.e. value upon irradiation of 2,3-NA in the presence ofγ-CD. 48% e.e. is the highest value reported so far for the photocyclodimerization with nativeγ-CD in solution under ambient temperature and pressure.3. Three 2,3-NA derivatives N(C)-P4-(C)N, N(O)-P4-(O)N and N(CO)-P4-(CO)N, bearing one or two tetra(ethylene glycol) chain(s), have been designed to provide a support on this stepwise two-photon process. The reactivity was found dependent on the substituted position of the long chain very much. CB[8] can template the intramolecular photocyclodimerization of N(C)-P4-(C)N with remarkable efficiency and selectivity in aqueous solution, whereas CB[8] also inhibits the photocyclodimerization of N(O)-P4-(O)N under the same condition.4. Two general derivation methods have been developed: carboxyl-functionalized cubane-like photocyclodimer was reacted with active alkyl halide to afford diacyl-substituted cubane-like photocyclodimer with remarkable efficiency under basic environment; on the other hand, the reaction of carboxyl-functionalized cubane-like photodimer and phenols or aromatic amines can be facilitated by N,N′-carbonyldiimidazole (CDIM). The easy modification of the cubane-like photocyclodimers would stimulate us to further develop of the fascinating cubane-like photocyclodimers of 2-naphthalenes.