Photoinduced Rearrangement Research Articles

Synthesis of Oxadihydrophenanthroquinolizidinones by Photoinduced Rearrangement of 3‐Biphenyl‐1‐hydroxypropyl‐pyridin‐2(1H)‐ones

Synthesis of Oxadihydrophenanthroquinolizidinones by Photoinduced Rearrangement of 3‐Biphenyl‐1‐hydroxypropyl‐pyridin‐2(1H)‐ones

A Porous Crystalline Nitrone-Linked Covalent Organic Framework.

Herein, we report the synthesis of a nitrone-linked covalent organic framework, COF-115, by combining N, N', N', N'''-(ethene-1, 1, 2, 2-tetrayltetrakis(benzene-4, 1-diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid-state 13 C multi cross-polarization magic angle spinning NMR spectroscopy of the 13 C-isotope-labeled COF-115 and Fourier-transform infrared spectroscopy. The permanent porosity of COF-115 was evaluated through low-pressure N2 , CO2 , and H2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF-115 and the isoreticular imine-linked COF indicated a superior potential of N-oxide-based porous materials for atmospheric water harvesting and CO2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF-115 to the associated amide-linked material was successfully demonstrated.

A Porous Crystalline Nitrone‐Linked Covalent Organic Framework**

AbstractHerein, we report the synthesis of a nitrone‐linked covalent organic framework, COF‐115, by combining N, N′, N′, N′′′‐(ethene‐1, 1, 2, 2‐tetrayltetrakis(benzene‐4, 1‐diyl))tetrakis(hydroxylamine) and terephthaladehyde via a polycondensation reaction. The formation of the nitrone functionality was confirmed by solid‐state 13C multi cross‐polarization magic angle spinning NMR spectroscopy of the 13C‐isotope‐labeled COF‐115 and Fourier‐transform infrared spectroscopy. The permanent porosity of COF‐115 was evaluated through low‐pressure N2, CO2, and H2 sorption experiments. Water vapor and carbon dioxide sorption analysis of COF‐115 and the isoreticular imine‐linked COF indicated a superior potential of N‐oxide‐based porous materials for atmospheric water harvesting and CO2 capture applications. Density functional theory calculations provided valuable insights into the difference between the adsorption properties of these COFs. Lastly, photoinduced rearrangement of COF‐115 to the associated amide‐linked material was successfully demonstrated.

Photoinduced Decarbonylative Rearrangement of Diazabicyclo[2.2.2]Octenones: A Photochemical Approach of Diazabicyclo[4.1.0]heptene Skeleton from Masked o-Benzoquinone

We report a photoinduced decarbonylative rearrangement of diazabicyclo[2.2.2]octenone in the facile synthesis of a functionalized diazabicyclo[4.1.0]heptene skeleton, a unique derivative of the hydropyridazine type structure which could be found in a variety of biologically active natural products. The scope of functional group compatibility in the photoreaction was examined by taking advantage of the easy access of the heterobicyclo[2.2.2] structure from the Diels-Alder reaction of masked o-benzoquinones. 4-Phenyl-1,2,4-triazoline-3,5-dione served as the dienophile which provided the adjacent N-N unit in hexahydropyridazine-type products of subsequent photorearrangement.

Intramolecular crankshaft-type rearrangement in a photoisomerised glycoconjugate.

High-resolution NMR spectroscopy revealed that a novel glycoconjugate, consisting of two β-glucopyranoses attached to a quinazolinone-like structure, exhibited photoisomerization around the -N-N[double bond, length as m-dash] and [double bond, length as m-dash]CH-C- bonds of the -N-N[double bond, length as m-dash]CH-C- linkage in the same timeframe (the so-called "crankshaft rotation") upon exposure to UV light. Experimental NMR data combined with DFT calculations discovered that the attachment of carbohydrate residues to photoactive compounds significantly changed the isomerization process and intramolecular rearrangement compared to the unglycosylated system, while the overall molecular structure remained virtually unchanged.

Skeletal photoinduced rearrangement of diarylethenes: ethene bridge effects.

A skeletal photorearrangement involving UV-induced 6π-electrocyclization of diarylethenes with various ethene bridges has been studied. It has been found that deprotonation is the predominant step among the three possible alternative reaction pathways (radical abstraction, deprotonation, or sigmatropic shift) following 6π-electrocyclization, and incorporation of an electronegative carbonyl group into the geminal position to the phenyl residue results in a reduction in the reaction time and an increase in the yield of the desired product. The significant increase in the reaction time in less polar solvents (toluene, TCM) also indicates a large contribution of the deprotonation step to the skeletal photorearrangement of diarylethenes. Performing the reaction in toluene in the presence of tertiary amines leads to a reduction in the reaction time and an increase in the yield of the desired product. The best results were achieved when the reaction was carried out in toluene in the presence of DIPEA. The experimental results are in good agreement with the DFT calculations.

Pnictogen-Bridged Diphenyl Sulfones as Photoinduced Pnictogen Bond Forming Emission Motifs.

In this study, pnictogen (Pn)-bridged diphenyl sulfones were synthesized as motifs for photoinduced dynamic rearrangement. The newly synthesized sulfones exhibited dual fluorescence at 298 K. Density functional theory calculations revealed that the longer-wavelength fluorescence was derived from the geometries after structural relaxation through photo-driven pnictogen bond formation between the O atom lone pair of the sulfonyl moiety and the antibonding orbital of the Pn-C bond. This is the first report on emission dynamics driven by pnictogen bond formation upon photoexcitation.

Understanding of Photo-Induced Reversible Rearrangement from Borepin to Borirane.

The first reversible photoisomerization between a borepin and a borirane was reported in the photo-induced reactions of B(npy)Ar2 (npy=2-(naphthalen-1-yl) pyridine, Ar=phenyl or electron rich aryl; S. Wang, et al. Angew. Chem. Int. Ed. 2019, 58, 6683-6687). In this work, the detailed mechanisms of the unprecedented reversible photoisomerization between the borepin (compound a) and the borirane (compound b) of B(npy)Ph2 in the first excited singlet (S1 ) state and the ground (S0 ) state were studied by carrying out calculations with the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT). The calculation results show that photoexcitation of a-S0 at 365 nm and b-S0 at 450 nm populate their S1 state with evident charge transfer characteristics. The photoisomerization is triggered in the S1 state and ends in the S0 state, at which the intersection points in a (S1 /S0 )x intersection seam participate in and promote phenyl migration and ring-closure processes. Furthermore, we reveal that the not large energy difference (less than 0.6 eV) and similar conjugation properties of π electrons between a-S0 and b-S0 are responsible for their unique photo-reversible reactivity, compared with those of the isomers of the thermally reversible compound B(ppy)Mes2 . Our results contribute to an understanding of the excited-state reactivity of organoboron compounds and will be useful to support the design of new boron-based photo-responsive materials.

Curtius-Type Rearrangement of Sulfinyl Azides: A Matrix Isolation and Computational Study.

The highly unstable methyl sulfinyl azide, CH3S(O)N3, has been synthesized and characterized for the first time. In the gas phase, CH3S(O)N3 decomposes quickly at room temperature (300 K) with an estimated half-life (t1/2) of 7 min. Upon irradiation at 266 nm in cryogenic Ar (10 K) and Ne (3 K) matrices, the azide extrudes molecular nitrogen by yielding the novel sulfinyl nitrene intermediate CH3S(O)N in the closed-shell singlet ground state, which has been characterized with matrix-isolation IR and UV-vis spectroscopy. Prolonged irradiation at 266 nm causes Curtius rearrangement of the nitrene to form N-sulfinylamine CH3NSO and S-nitrosothiol CH3SNO. By high-vacuum flash pyrolysis (HVFP) at 800 K, CH3S(O)N3 also decomposes and furnishes CH3S(O)N with minor fragmentation products HNSO and CH2 in the gas phase. A similar photo-induced Curtius-type rearrangement of trifluoromethyl sulfinyl azide CF3S(O)N3 to CF3NSO and CF3SNO has also been observed in matrices. According to the theoretical calculations at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311++G (3df,3pd) level of theory, the rearrangement of CH3S(O)N3 prefers a stepwise pathway by initial formation of the nitrene intermediate CH3S(O)N. In line with the thermal persistence of CH3S(O)N in the gas phase, the barriers for its subsequent rearrangement are higher than 30 kcal mol-1.

Photo-Fries-type rearrangement of cyclic enamides. An efficient route to structurally diverse five-membered enaminones.

A simple, efficient and user-friendly protocol for the preparation of structurally diverse enaminones from enamides has been developed. The strategy is based on a photo-induced intramolecular Fries-type rearrangement. The photochemical transformation proceeds under mild reaction conditions, applies to a broad substrate range, is highly economic, and limits the amount of waste produced. The proposed methodology was used as a key step in the synthesis of dihydrojasmone an important fragrance compound.

A Self-Catalyzed Visible Light Driven Thiol Ligation.

We introduce a highly efficient ligation system based on a visible light-induced rearrangement affording a thiophenol which rapidly undergoes thiol-Michael additions. Unlike conventional light-triggered thiol-ene/yne systems, which rely on the use of photocaged bases/nucleophiles, (organo)-photo catalysts, or radical photoinitiators, our system provides a light-induced reaction in the absence of any additives. The ligation is self-catalyzed via the pyridine mediated deprotonation of the photochemically generated thiophenol. Subsequently, the thiol-Michael reaction between the thiophenol anion and electron deficient alkynes/alkenes proceeds additive-free. Hereby, the underlying photoinduced rearrangement of o-thiopyrinidylbenzaldehyde (oTPyB) generating the free thiol is described for the first time. We studied the influence of various reactions conditions as well as solvents and substrates. We exemplify our findings in a polymer end group modification and obtained macromolecules with excellent end group fidelity.

Molecular Cage Promoted Aerobic Oxidation or Photo-Induced Rearrangement of Spiroepoxy Naphthalenone

Herein, we report a Pd4L2-type molecular cage (1) and catalyzed reactions of spiroepoxy naphthalenone (2) in water, where selective formation of 2-(hydroxymethyl)naphthalene-1,4-dione (3) via aerobic oxidation, or 1-hydroxy-2-naphthaldehyde (4) via photo-induced rearrangement under N2 have been accomplished. Encapsulation of four molecules of guest 2 within cage 1, i.e., (2)4⊂1, has been confirmed by NMR, and a final host-guest complex of 3⊂1 has also been determined by single crystal X-Ray diffraction study. While the photo-induced ring-opening isomerization from 2 to 4 are known, appearance of charge-transfer absorption on the host-guest complex of (2)4⊂1 allows low-power blue LEDs irradiation to promote this process.

UVA-Triggered Drug Release and Photo-Protection of Skin.

Light has attracted special attention as a stimulus for triggered drug delivery systems (DDS) due to its intrinsic features of being spatially and temporally tunable. Ultraviolet A (UVA) radiation has recently been used as a source of external light stimuli to control the release of drugs using a “switch on- switch off” procedure. This review discusses the promising potential of UVA radiation as the light source of choice for photo-controlled drug release from a range of photo-responsive and photolabile nanostructures via photo-isomerization, photo-cleavage, photo-crosslinking, and photo-induced rearrangement. In addition to its clinical use, we will also provide here an overview of the recent UVA-responsive drug release approaches that are developed for phototherapy and skin photoprotection.

Density Functional Theory Evaluation of a Photoinduced Intramolecular Aryl Ether Rearrangement.

Recently, a new approach of converting (hetero)aryl ethers to C–C coupled products via a photoinduced intramolecular rearrangement has been reported. Although this reaction is photocatalyst-free, it requires excitation in the ultraviolet (UV) range. To help refine this process, three different 2-(hetero)aryloxybenzaldehydes are selected from the available substrate scope in which the general mechanism based on experimental results is evaluated using density functional theory calculations. The reaction takes place in the triplet state after photoexcitation and includes three main steps: the addition of carbonyl carbon to the ipso carbon of the aryl ether followed by the C–O cleavage of the resulting spirocyclic intermediates and then the transfer of the formyl proton to afford 2-hydroxybenzophenone-type products. This agrees with the experiments, but the calculated pathways show considerable differences between the three substrates. Above all, either the first or the second step can be rate-determining but not the C–H activation. The important factor behind the differences is the spin-density rearrangement, which is mainly responsible for the barrier of the ether cleavage. Based on the obtained insights, the strategy to improve the ∼250 nm excitation has been briefly discussed, and promising molecules are proposed to improve the scope of this process.

Reversibly Photo-Modulating Mechanical Stiffness and Toughness of Bioengineered Protein Fibers.

Light‐responsive materials have been extensively studied due to the attractive possibility of manipulating their properties with high spatiotemporal control in a non‐invasive fashion. This stimulated the development of a series of photo‐deformable smart devices. However, it remained a challenge to reversibly modulate the stiffness and toughness of bulk materials. Here, we present bioengineered protein fibers and their optomechanical manipulation by employing electrostatic interactions between supercharged polypeptides (SUPs) and an azobenzene (Azo)‐based surfactant. Photo‐isomerization of the Azo moiety from the E‐ to Z‐form reversibly triggered the modulation of tensile strength, stiffness, and toughness of the bulk protein fiber. Specifically, the photo‐induced rearrangement into the Z‐form of Azo possibly strengthened cation–π interactions within the fiber material, resulting in an around twofold increase in the fiber's mechanical performance. The outstanding mechanical and responsive properties open a path towards the development of SUP‐Azo fibers as smart stimuli‐responsive mechano‐biomaterials.

Synthesis and highly efficient light-induced rearrangements of diphenylmethylene(2-benzo[b]thienyl)fulgides and fulgimides.

2-Benzo[b]thienyl fulgides and fulgimides containing bulky diphenylmethylene substituents were synthesized in the form of their ring-opened E- or Z-isomers. In contrast to the majority of known fulgides/fulgimides, that form colored ring-closed structures under UV irradiation, the obtained compounds undergo an irreversible transformation leading to decoloration of their solutions. This rearrangement with the formation of the dihydronaphthalene core appeared to be by 2–3 orders of magnitude more efficient than for the known diphenylmethylene(aryl(hetaryl))fulgides. The molecular structures of E- and Z-isomers and of products of the photoinduced rearrangement completed by 1,5-H shift reaction, 3a,4-dihydronaphtho[2,3-c]furans(pyrroles) C, were established based on the data of 1H and 13C NMR spectroscopy and X-ray diffraction studies.

Algorithmic Discovery of Tactical Combinations for Advanced Organic Syntheses

Summary Whereas most organic molecules can be synthesized from progressively simpler substrates, syntheses of complex organic targets often involve counterintuitive sequence of steps that first complexify the structure but, by doing so, open up possibilities for pronounced structural simplification in subsequent, downstream steps. Such complexifying/simplifying reaction sequences, called tactical combinations (TCs), can be quite powerful and elegant but also inherently hard to spot—indeed, only some 500 TCs have so far been cataloged, and even fewer are routinely used in synthetic practice. This paper describes computer-driven discovery of large numbers of viable TCs (over 46,000 combinations of reaction classes and ∼4.85 million combinations of reaction variants), the vast majority of which have no prior literature precedent. Examples—including a concise wet lab synthesis of a small natural product—are provided to illustrate how the use of these newly discovered TCs can streamline the design of syntheses leading to important drugs and/or natural products.

Syntheses of Benzofuranoquinolines and Analogues via Photoinduced Acceptorless Dehydrogenative Annulation of o-Phenylfuranylpyridines.

A strategy for the syntheses of benzofuranoquinolines and its analogues via the irradiation of o-phenylfuranyl/thienylpyridines/pyrimidines in DCM with UV light at rt under an argon atmosphere is described. The mechanism of this reaction through the process of 6π-electrocyclization, [1,5]-hydrogen shift, and 1,3-eneamine tautomerism leading to H2 evolution was elucidated. Notably, the syntheses of cis-8b-methyl-8b,13a-dihydrobenzo[f]benzofuro[3,2-h]quinolone via the photoinduced rearrangement of 2-(3-methylbenzofuran-2-yl)-3-phenylpyridine relevant to the mechanism of this reaction highlights the importance of the developed methodology.

Theoretical study on photo-induced ring closure and rearrangement of diarylethenes

Theoretical study on photo-induced ring closure and rearrangement of diarylethenes

Visible-Light-Promoted Oxo-Sulfonylation of Ynamides with Sulfonic Acids.

A visible-light-promoted oxo-sulfonylation of ynamides with sulfonic acids is reported, giving rise to a collection of functionalized α-sulfonylated amides in a straightforward manner. The reaction proceeds sequentially through a cascade of electrophilic addition and photoinduced sulfonyl radical-sustained skeleton rearrangement. The high atom economy, mild reaction conditions, and wide substrate scope comprised the merits of this synthetic transformation.