Photoinduced Rearrangement Research Articles

Formation of 2,2-dimethylchroman-4-ones during the photoinduced rearrangement of some aryl 3-methyl-2-butenoate esters. A mechanistic insight

Several aryl 3-methyl-2-butenoate esters upon irradiation lead to the formation of [1,3]-migrated photoproducts, phenol and, surprisingly 2,2-dimethylchroman-4-one derivatives. The starting photochemical reaction takes place from the singlet excited state of the ester and as a total mechanism two consecutive reaction pathways are proposed. The former involves the photo-Fries rearrangement of the esters in all the solvents studied and, depending on the proticity of the solvent, the latter involves an ESIPT process followed by thermal 6π-electrocyclic reaction and/or thermal (intramolecular oxa-Michael addition) cyclization of the ortho regioisomers photoformed. This second pathway is responsible of the formation of the 2,2-dimethylchroman-4-one derivatives.

Caged Gaseous Mediators and Their Control of Cellular Functions

Nitric oxide (NO) is historically well known as a toxic gas but now recognized as a physiological cellular mediator acting at very low concentrations. It is biosynthesized within the body, and modulates many signal transduction processes. For investigation of the functions of this gaseous mediator, it is necessary to use chemical donors that release NO specifically, and it is highly advantageous if the release can be made with precise spatiotemporal control. For this purpose, we have developed caged NO (photocontrollable NO-releasing compounds) with unique releasing mechanisms. One employs the photoinduced rearrangement of an arylnitro group and subsequent release of NO, and another uses photoinduced electron transfer to release NO. One of our caged NO was confirmed to induce a NO-dependent cellular response in vivo under photocontrol. Photocontrollable NO releasers are expected to become indispensable tools for physiological experiments, and are also potential therapeutic agents for photodynamic therapy.

Photoinduced Decarbonylative Rearrangement of Bicyclo[2.2.2]Octenones: Synthesis of the Marasmane Skeleton.

The marasmane sesquiterpenoid structure can be found in the skeleton of a variety of natural products bearing interesting bioactivity. The unique fused-5,6,3-tricyclic ring structure, in which the rings are cis-fused and the five- and three-membered rings are mutually trans, provides a synthetic challenge for organic chemists. In this work, we took advantage of the photoinduced decarbonylative rearrangement of bicyclo[2.2.2]octenone to develop a new methodology for construction of the highly functionalized fused-5,6,3-tricyclic ring structure in a concise reaction sequence.

Capturing ultrafast photoinduced local structural distortions of BiFeO3.

The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

Biomimetic syntheses of rubialatins A, B and related congeners.

The first total syntheses of rubialatins A and B, two newly discovered naphthohydroquinone dimers, were achieved with high efficiency and elegancy through rationally designed biomimetic approaches. The tandem ring contraction/Michael addition/aldol reaction followed by oxidation enabled the rapid access of prerubialatin from readily available precursors, which then diverted into rubialatins A and B via epoxidation and photoinduced skeletal rearrangement, respectively. Moreover, several new rubialatin congeners were also obtained along the synthetic tour, some of which were proved to be authentic natural products.

Photoinduced transformation of UVR8 monitored by vibrational and fluorescence spectroscopy.

Tryptophan residues at the dimer interface of the plant photoreceptor UVR8 promote monomerisation after UV-B absorption via a so far unknown mechanism. Using FTIR spectroscopy we assign light-induced structural transitions of UVR8 mainly to amino acid side chains without major transformations of the secondary structure of the physiologically relevant C-terminal extension. Additionally, we assign the monomerisation associated increase and red shift of the UVR8 tryptophan emission to a photoinduced rearrangement of tryptophan side chains and a relocation of the aspartic acid residues D96 and D107, respectively. By illumination dependent emission spectroscopy we furthermore determined the quantum yield of photoinduced monomerisation to 20 ± 8%.

Model of nonadiabatic-to-adiabatic dynamical quantum phase transition in photoexcited systems

We study the ultrafast dynamic process in photoexcited systems and find that the Franck-Condon or Landau-Zener tunneling between the photoexcited state and the ground state is abruptly blocked with increasing the state coupling from nonadiabatic to adiabatic limits. The blockage of the tunneling inhibits the photoexcited state from decaying into the thermalized state and results in an emergence of a metastable state, which represents an entanglement of electronic states with different electron-phonon coupling strengths. Applying this model to the investigation of photoexcited half-doped manganites, we show that the quantum critical transition is responsible for more than three orders of magnitude difference in the ground state recovery times following photoirradiation. This model also explains some elusive experimental results such as photoinduced rearrangement of orbital order by structural rather than electronic process and the structural bottleneck of one-quarter period of the Jahn-Teller mode. We demonstrate that in the spin-boson model there exist unexplored regions not covered in the conventional phase diagram.

Photoinduced Brook-Type Rearrangement of Acylcyclopolysilanes

Previously unknown 1,1,4-tris(trimethylsilyl)-4-acyldodecamethylcyclohexasilanes (Me3Si)2Si6Me12(Me3Si)COR (16a, R = tert-butyl; 16b, R = 1-adamantyl) have been synthesized by the reaction of the potassium silanides (Me3Si)2Si6Me12(Me3Si)K with acid chlorides ClCOR, and their photochemical rearrangement reactions have been studied. The molecular structures of 16a,b as determined by single-crystal X-ray diffraction analysis exhibit an unusual twist-boat conformation of the cyclohexasilane ring. When 16a,b were photolyzed with λ >300 nm radiation, they underwent Brook type 1,3-Si → O migration reactions to generate the cyclohexasilanes 17a,b with exocyclic Si=C bonds along with smaller amounts of the ring-enlarged species 19a,b with endocyclic Si=C double bonds. While 17a,b were stable enough to allow characterization by NMR and UV absorption spectroscopy, the less stable products 19a,b could only be observed in the form of their methanol adducts.

Synthesis of a new photochromic 2,2-diphenylpyrano[3,2-h]quinoline

The formation of new materials based on the bistable structures consisting of light-sensitive fragments tightly bonded to complex-forming centers of molecules is one of the priority areas at the junction of organic, coordination chemistry, and photochemistry. 2 H-Pyrano[3,2-h]quinoline diaryl derivatives are the examples of such compounds, the structure contains a coordination node formed by nitrogen atom of the quinoline ring and the oxygen atom of the annelated pyran heterocycle, which is a potential photochromic fragment of the 2H-chromene part of the molecules. In agreement with the literature data [1-5], photochromic derivatives of pyrano[3,2-h]quinoline are known, but they are spirocyclic compounds which contain indole as hetarene, however the pyrrole nitrogen affects the distribution of the electron density in the molecule substantially changing its properties. The basicity of this heteroatom is an important factor, which may effect the study of complex formation and its influence on the photochromic processes. Calculations [6] of an example of 2H-pyrano[3,2-h]quinoline containing a hydrogen atom at position 2 showed that changes in the magnetic properties of metal chelates under the influence of photoinduced cis-trans rearrangement makes it relevant to complex use the properties of these compounds and opens up opportunities to create controlled photomagnets. There are known methods for the synthesis of 2H-chromene derivatives containing annelated five- and six-membered heterocycles that use hydroxygroups of the corresponding heteroannelated phenols in reaction with diarylpropargyl alcohols [7-9]. We have attempted the synthesis of 2,2-diphenylpyrano[3,2-h]quinoline (3) from the reaction of 8-hydroxyquinoline (1) with 1,1-diphenyl-2-propyn-1-ol under the conditions described above, however the reaction products were the adducts of 8-hydroxyquinoline either with propargyl alcohol (2) formed under the influence of the medium, or directly with the catalyst itself.

Crossover from photodarkening to photobleaching in a-Ge_xSe_100-x thin films

In this Letter, we present the interesting results of photodarkening (PD), transition toward photostability, and a slow crossover from PD to photobleaching when composition of the chalcogenide glassy thin film changes from Ge-deficient to rich. A subsequent Raman analysis on these as-prepared and irradiated samples provide the direct evidence of photoinduced structural rearrangement, i.e., photocrystallization of Se and the removal of edge-sharing GeSe4 tetrahedra. Further, our experimental results clearly demonstrate that light-induced effects can be effectively controlled by choosing the right composition and provide valuable information on synthesizing photostable/sensitive glasses.

Thermally Persistent Fluorosulfonyl Nitrene and Unexpected Formation of the Fluorosulfonyl Radical

Thermally persistent triplet sulfonyl nitrene, FSO(2)N, was produced in the gas phase in high yields (up to 66%) by flash vacuum pyrolysis of FSO(2)N(3). Surprisingly, no rearrangement of FSO(2)N was observed, but the long-sought radical FSO(2) (22%) and traces of SO(2) (3%) were identified by IR ((15)N, (18)O, (34)S) spectroscopy. The photoinduced Curtius rearrangement of the nitrene to FNSO(2) was observed in solid noble gas matrices, and reactions of the nitrene with O(2), NO, and CO were studied.

Photoinduced Ultrafast Wolff Rearrangement: A Non‐Adiabatic Dynamics Perspective

One reaction, two routes: full-dimensional non-adiabatic dynamics simulations shed light on the ultrafast photoinduced Wolff rearrangement in an α-diazocarbonyl compound. The trajectories show both concerted asynchronous and stepwise processes leading to the corresponding ketene.

Interconversion of the Pallambins through Photoinduced Rearrangement

Interconversion of the Pallambins through Photoinduced Rearrangement

Interconversion of the Pallambins through Photoinduced Rearrangement

A new photoinduced interconversion of four naturally occurring 19-nor-7,8-secolabdane diterpenoids was discovered and analyzed. The photochemical mechanism, intramolecular diradical rearrangement reaction, was investigated by time-lapse monitoring of the end product formations with HPLC and UV, as well as detailed theoretical calculations.

Photochemistry and photophysics of the endoperoxide of mesodiphenylhelianthrene: a contribution to the localization of the S1(π*σ*) state of aromatic endoperoxides

The endoperoxide of mesodiphenylhelianthrene MDHPO has been studied in detail with respect to fluorescence and photo-induced rearrangement. MDHPO proved to be non-fluorescent, although its absorption spectrum is dominated at the low energy side by a strong ππ* band with a maximum at 429.5 nm. Irradiation of that band effects rearrangement to the corresponding diepoxide MDHDO, a reaction typical for S(1)(π*σ*) excited endoperoxides (EPOs). The absorption spectrum of the product MDHDO is blue shifted by only 3.5 nm. MDHDO has the same extended planar aromatic system like its precursor MDHPO, but MDHDO fluoresces strongly. These results set the excitation energy of the S(1)(π*σ*) state of MDHPO to ≤23 000 cm(-1), which is considered to be a generally realistic value of the S(1)(π*σ*) state energy of aromatic EPOs. The main reaction of S(1)(π*σ*) excited MDHPO is, however, chemical deactivation to ground state MDHPO via an oxygen biradical. The sequence of O-O bond opening and closing is the general way of repopulation of the S(0) state of aromatic EPOs from S(1)(π*σ*) excited states.

Matrix isolation studies of 185 nm light-induced cage reactions of o-chlorobenzaldehyde

VUV light photolysis of o-chlorobenzaldehyde (CBA) has been investigated by infrared spectroscopy in cryogenic Ar and O2 matrices. Previously reported photoinduced rotational isomerization from anti- to syn-CBA was confirmed in the Ar matrix. In addition, absorption bands associated with photoinduced rearrangement to benzoyl chloride were observed accompanying the weak bands due to the CO photolysis product. However, in the reactive O2 matrix, isomerization was observed and there was no evidence of benzoyl chloride formation. A kinetic analysis revealed that rearrangement was a minor process under the present excitation energy. The TD-B3LYP calculations show that as the excitation energy increases the predissociation channel will open and the repulsive 1(π, σC-Cl∗) and 1(n, σC-Cl∗) states are directly achievable by the 185nm excitation. Photoinduced rearrangement will be caused by the reaction of thus dissociated cage pairs.

Theoretical Studies on the Photoinduced Rearrangement Mechanism of α‐Santonin

α-Santonin is the first organic compound observed to feature a photoinduced rearrangement and is now known to undergo a series of photochemical processes under UV irradiation. On the basis of the considerable interest of this system as a prototype, and of the yet limited insights reached for the basic photo mechanisms, we calculate the high-level electronic structures and explore the potential energy surfaces (PES) of α-santonin in the ground and lowest-lying excited states, their couplings, and the possible photoinduced isomerization pathways. The calculations identify the low-lying singlet excited state (1)(nπ*) accessible under light irradiation, which decays to the low-energy (3)(ππ*) state through an intersystem crossing in the Franck-Condon region to initiate the photoinduced rearrangement. The initial reaction from the C3-C5 bond coupling, which takes place on the (3)(ππ*) state potential energy surface, leads to a three-membered alkyl-ring compound intermediate state INT. The following photochemical reactions have the possibility to arise from two distinct C-C bond cleavages, C4-C5 and C3-C4, denoted as path A and path B. Path A is favored both dynamically on the excited-state PES and thermodynamically on the ground-state PES in vacuo. Experiments show that it also becomes the dominant photoinduced rearrangement process in the crystal, which can be explained by considering the requirement for less space and the stacking effect under the confined environment. Path B is dynamical advantaged both on the ground- and excited-state PESs in a weak polar solvent, such as dioxane. Once the biradical intermediate B-INT is accessible on the ground-state PES, the formation of the product B-P is almost barrier free.

Degradation of Flumioxazin in Illuminated Water–Sediment Systems

The aerobic aquatic metabolism of flumioxazin was studied in two water-sediment systems under illumination and in darkness to investigate its degradation profiles. (14)C-Flumioxazin separately labeled at the 1- and 2-positions of the tetrahydrophthalimide moiety or uniformly labeled at the phenyl ring was applied to a overlying water at a rate equivalent to 600 g ai/ha by assuming uniform distribution in the water layer to a depth of 100 cm. Flumioxazin was rapidly degraded at 20 °C in the overlying waters irrespective of irradiation with half-lives of 0.1-0.4 day. Both various modes of liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy analyses showed four major degradates under irradiation. Two of them were formed via successive hydrolysis of the cyclic imide ring, and the others were 2-arizidinone derivatives via photoinduced rearrangement. The presence of sediment under illumination greatly reduced the formation of these degradates and accelerated their degradation. The partitions of flumioxazin and its degradates to the bottom sediment not only reduced their fractions in the water layer subjected to hydrolysis and photolysis but also enhanced their microbial degradation in the sediment. The illuminated water-sediment systems were considered to more adequately represent the behavior of flumioxazin and its degradates in the environment than the corresponding studies of aqueous photolysis and water-sediment in darkness.

Synthesis of (-)-Pyrenophorol

Macrodiolide antibiotics, which possess interesting structural and biological properties are found in fungi and marine sponges. These macrodiolides are classified into two groups; one includes homodimers that consist of two identical units, and the other includes heterodimers that consist of two different units. Macrodiolides such as pyrenophorol (1), pyrenophorin (2), and vermiculine (3), which have 16membered rings are homodimeric macrodiolides, and macrocylic dilactones such as colletallol (4) and grahamimycin A1, which have 14-membered rings, are heterodimeric macrolides (Fig. 1). Analogs with various degrees of unsaturation such as tetrahydropyrenophorol (5) and dihydropyrenophorin (6), have also been reported. These naturally occurring macrodiolides show antifungal and anthelmintic activities. Pyrenophorol (1) is isolated from the fungi Byssochlamys nivea and Stemphylium radicinum. Pyrenophorin (2), an analog of pyrenophorol (1), is originated from the fungi Pyrenophora avenae and Stemphylium radicinum. These macrodiolides have attracted significant attention of synthetic chemists because of their interesting biological properties and structural features. Kibayashi, Zwanenburg, and, recently, Yadav have reported the synthesis of (–)pyrenophorol. For the preparation of the key intermediate, chiral 4-hydroxy-2-alkenoate, Zwanenburg group exploited the photo-induced rearrangement of the corresponding expoxy diazomethyl ketone. On the other hand, Kibayashi group, synthesized (−)-pyrenophorol using C2 symmetric (R,R)-diepoxide as a chiral building block. Recently, Yadav group synthesized (–)-pyrenophorol employing the hydrolytic kinetic resolution developed by Jacobson and the McMillan α-hydroxylation. In connection with our interests in the synthesis of natural products, we, herein, report the total synthesis of (–)pyenophorol (1). Our synthetic approach is based on the utilization of a chiral building block 8, which was used in our previous synthesis of ophiocerins (Scheme 1). The chiral building block 8, prepared from D-glucose, has the potential to be used as a versatile chiral synthon. As summarized in Scheme 2, the key starting chiral building block 8 was prepared from methyl α-D-glucopyranoside (9), which was prepared from α-D-glucose, in four steps. Regioselective reductive opening of the epoxide ring in 8 was the key step to establish the required stereocenter.

Correction to “Photoinduced Rearrangement of Aromatic N-Chloroamides to Chloroaromatic Amides in the Solid State. Inverted ΠN–ΣN Occupational Stability of Amidyl Radicals”

Correction to “Photoinduced Rearrangement of Aromatic <i>N</i>-Chloroamides to Chloroaromatic Amides in the Solid State. Inverted Π_N–Σ_N Occupational Stability of Amidyl Radicals”