γ-Cyclodextrin-Directed Enantioselective Photocyclodimerization of Methyl 3-Methoxyl-2-naphthoate

Abstract

Irradiation of methyl 3-methoxyl-2-naphthoate (2,3-NA) in methanol solution with light lambda > 280 nm produces anti-head-to-head cubane-like photocyclodimer 1 and [4+4] intermediate 2, which is, to the best of our knowledge, the first incidence of directly obtaining the intermediate in photocyclodimerization of naphthalene analogues. X-ray crystal structural analysis has realized the chirality of 1, and the optically pure enantiomers 1(a) and 1(b) have been achieved by HPLC resolution. To understand the fundamental photocyclodimerization of naphthalene analogues mediated by native gamma-CD, the neutral 2,3-NA was selected as a typical reactant in this work. UV-vis, fluorescence, and (1)H NMR analysis reveal that gamma-CD can encapsulate 2,3-NA to make a stable 2:1 inclusion complex 2,3-NA@gamma-CD both in aqueous solution and in the solid state. Irradiation of 2,3-NA@gamma-CD results in photocyclodimerization with remarkable selectivity and efficiency, whereas no photocyclodimers could be detected in host-free aqueous solution and the neat solids. More importantly, the use of native gamma-CD as a chiral reaction vessel turns out to be an effective and versatile strategy for the enantioselective photocyclodimerization of 2,3-NA. The ee values of 48% in aqueous solution and up to 34% in the solid state for anti-head-to-head photocyclodimer 1 have been achieved upon irradiation of the inclusion complex of 2,3-NA@gamma-CD under ambient temperature and pressure. All of the observations indicate that native gamma-CD with hydrophobic interaction only is capable of regulating the orientation of naphthalene analogue 2,3-NA within the cavity of gamma-CD, and thereby leading to the highest ee value of 48% obtained so far for the photocyclodimerization with native gamma-CD in solution.

A fixable supramolecular cyclic polymer based on the cucurbit[8]uril-stabilized π–π interaction

“…S8) showed that Np groups were cleaved from PEG backbone, leading to the formation of byproduct. We supposed that here the methylene linkage was not suitable for photo-dimerization, as previous works had only shown successful photo-induced dimerization when carbonyl group was utilized 21,22 .…”

Supramolecular complexation and photocyclodimerization of methyl 3-methoxy-2-naphthoate with modified γ-cyclodextrins

“…Native γ-CD forms a 1:2 host-guest complex with NA as proven by the Job plot showing the largest intensity change at a mole fraction of 0.33 [7]. This seems reasonable, since the large γ-CD cavity is capable of accommodating two aromatic guest molecules of suitable size.…”

“…However, recent studies revealed that the supramolecular approach enables us to more critically control the photochirogenic process and significantly improve the stereochemical outcomes through noncovalent chiral interactions in both ground and excited states [2][3][4][5]. We thus applied the supramolecular approach to the enantiodifferentiating photocyclodimerization of methyl 3-methoxy-2-naphthoate (NA) [6][7][8]. As shown in Scheme 1, the photocyclodimerization of NA is a two-step (two-photon) process, composed of the first intermolecular [4 + 4] photocyclodimerization in anti-head-to-head fashion and the subsequent intramolecular [2 + 2] photocyclodimerization of the [4 + 4] cyclodimer to give chiral cubane-like cyclodimer 1 upon absorption of a second photon.…”

“…The irradiated solution was extracted with dichloromethane and the extract was subjected to high-performance liquid chromatography (HPLC) analysis on a Daicel OJ-H column with an n-hexane/2-propanol eluent [7,8].…”

Supramolecular Host-Guest Asymmetric Induction In Organic Synthesis

“…CD have also the remarkable property of accommodating various organic molecules in aqueous solution by hydrophobic interactions and have been extensively used to improve the efficiency and selectivity of chemical reactions [20]. They represent an important class of molecular reaction vessels due to their unique characteristics of high solubility in water, availability, inherent chirality, and transparence in the UV-visible regions.…”