Control of reaction pathways in the photochemical reaction of a quinone with tetramethylethylene by metal binding

Abstract

The present study reports a novel supramolecular photochemical reaction that focuses on the direct electronic interactions between a host reaction substrate and guest metal salts. The reaction pathways in the photochemical reactions of quinone derivatives bearing a methoxy group and a long oligoether sidearm QEn (n = 0 and 3) with tetramethylethylene (TME) are changed upon noncovalent complexations of the host reactant with alkali and alkaline earth metal ions and a transition metal salt. The photochemical reaction of QEn with TME provides a mixture of [2 + 2] cycloadducts 1aEn and 1bEn, hydroquinone H2QEn, and monoallyl ether adducts of hydroquinones 2aEn and 2bEn. The photochemical reaction proceeds by the photoinduced electron transfer mechanism, where photoirradiation brings about formation of a radical ion pair [QEn˙(-), TME˙(+)] as the primary intermediate. We found that the yields and selectivity of these photoproducts are changed upon electronic interactions of QEn˙(-) with the metal salts. The photochemical reaction in the absence of metal salts provides H2QEn as its major product, whereas QE3, having the long sidearm, dominantly produces 2aE3 at the expense of 1aE3, 1bE3, and H2QE3 when it forms a size-favorable host-guest complex with divalent Ca(2+). In contrast, QEn selectively provides oxetanes 1aEn and 1bEn in the presence of Pd(OAc)2, which can form complexes with the quinone through metal-olefin and coordination interactions in the ground and photoexcited states of the quinone.

Crystal structure of 3,4-dimethoxyphenol

“…For the crystal structure of the related 4-[(2,3-dimethylbut-3en-2-yl)oxy]-3-methoxyphenol, see: Yamamoto et al (2014). For the crystal structure of 3,4,5-trimethoxyphenol, see: Jia et al (2012).…”

“…Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2014); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015) and olex2.refine (Bourhis et al, 2015); molecular graphics: OLEX2 (Dolomanov et al, 2009); software used to prepare material for publication: OLEX2 and publCIF (Westrip, 2010 Nguyen et al, 2015), we report herein the structure of 3,4-dimethoxyphenol. A similar 3,4-dialkoxyphenol complex has been structurally characterized (Yamamoto et al, 2014) and…”

A catalyzed E/Z isomerization mechanism of stilbene using para-benzoquinone as a triplet sensitizer

“…16 To the best of our knowledge, a stable product has not been known for Paternò-Büchi reaction with unsubstituted PBQ and stilbene; [16][17][18][19][20][21] however, there is a possibility to form an intermediate exciplex of PBQ and stilbene. [22][23][24][25][26] Additionally, the experimental study showed that the [Z]/[E] ratio in the steady-state depended on the concentration of PBQ sensitizer, although such concentration dependence was not found in the reaction which proceeds in the Dexter mechanism. 2 Those findings suggest that a specific intermolecular interaction plays an essential role in the isomerization of stilbene with PBQ sensitizer.…”

Switching of the π-electronic conjugations in the reduction of a dithienylethene-fused p-benzoquinone

“…7 We previously reported supramolecular [4 + 2] cycloaddition and [2 + 2] photocycloaddition reactions of a pbenzoquinone derivative bearing an oligoether side-chain that can bind a metal ion through electrostatic interaction. 8,9 The bound metal ion reduces or increases the p-electron density of the quinone, changing its reactivity in both thermal and photochemical reactions. However, to the best of our knowledge, physical operation of the chemical reactions of quinone with the light is an unprecedented subject.…”