Photoinduced Skeletal Rearrangement of Diarylethenes: Photorelease of Lewis Acid and Synthetic Applications

Abstract

The skeletal photorearrangement including 6πelectrocyclization induced by UV light of ortho-halogen-substituted diarylethenes has been studied. It has been found that the reaction pathways leading to bi-or tricyclic frameworks depend on the kind of halogen substituent and solvent. Photocyclization with halogen abstraction leads to bicyclic fused aromatics, while the tricyclic frameworks are formed due to the tandem 6π-electrocyclization/ sigmatropic shift reaction. THF is preferred as the solvent in the former process and chloroform in the latter reaction. It was found for the first time that, owing to the ability of this series of diarylethenes to undergo skeletal photorearrangement with the release of the bromide cation, they can be used both as brominating agents and as Lewis acids for catalyzing electrophilic reactions.

Atom-economic and Self-reported Thiol Activation through Visible Light Induced Photo-rearrangment for Efficient Click-ligation

“…5) and release of the free thiol group through intramolecular rearrangement and cleavage. [50][51][52][53] The clear isosbestic points also suggested an exclusive transformation from the above intermediate (Supplementary Fig. 6).…”

Traffic Lights for Catalysis: Stimuli‐Responsive Molecular and Extended Catalytic Systems

“…[51] Although the majority of studies in the area of stimuliresponsive photocatalysts utilize azobenzene or hydrazone derivatives as described above, [1,50,51,69] other classes of relatively less explored photoswitches offer other avenues for switchable catalysis. [52,[73][74][75] For example, some overcrowded alkenes (i.e., tetrasubstituted alkenes with bulky substituents such as 9-(6-bromo-3,5,8-trimethylthiochroman-4-ylidene)-N,N-dimethyl-9H-fluoren-2-amine) exhibit photoswitchable behavior similar to E-to-Z isomerism. [73] A photoresponsive tetrasubstituted alkene core has been used to build molecular motors for controlling the catalytic activity in the Michael reaction between (E)-3-bromo-βnitrostyrene and 2,4-pentanedione.…”

“…[52,54,74,75,77] In this direction, diarylethene derivatives (Scheme 2) have played a significant role. [52,74,78] Their photoisomerization is based on reversible bond formation leading to alternation between conjugated and non-conjugated forms. [52,74,78] For instance, photocyclization of diarylethene derivatives is accompanied by changes in π-conjugation of the photoswitch backbone and, in some cases, release of substituent groups.…”

“…[52,74,78] Their photoisomerization is based on reversible bond formation leading to alternation between conjugated and non-conjugated forms. [52,74,78] For instance, photocyclization of diarylethene derivatives is accompanied by changes in π-conjugation of the photoswitch backbone and, in some cases, release of substituent groups. [52] Indeed, Shirinian and co-workers have shown the ability of a series of halogenated diarylethene derivatives to release bromine cations upon photoisomerization (Figure 3 and Table 1, #20).…”

Green-Light Responsive Perylene Bisimides for Atom-Economic Thiol Generation and Click-Ligation

“…Intriguingly, the original broad absorption bands could be gradually restored after immediate irradiation with λ = 730 nm, indicating the probable existence of a reversible transformation at the beginning period of irradiation, albeit significant fatigue after three cycles was detected (Figure c). A reasonable photorearrangement mechanism is hence assumed with two steps: (1) visible-light-induced photocyclization of PBIs was triggered to form the unstable intermediate PBI-1/2b (Scheme and Figure S8); followed by (2) the eventual formation of semi-CDIs via [1,9]-H sigmatropic migration (Figure S6, S9) and release of the free thiol group through intramolecular rearrangement and cleavage. − It is worth noting that the bathochromic band of intermediate PBI-2b was not observed for PBI-2a (Figure S9), most presumably due to the absorption band overlap between the isomerized PBI-2b structure and PBI-2a according to the TD-DFT calculation (Table S1–S3, see SI for details). Moreover, the solvent-dependent photoreaction of both PBIs was observed (Figure S10), which might result from the possible charge-transfer character between the electron-donating thiophene/benzothiophene pendant and the electron-withdrawing PBI core. , …”