Dye-sensitized Photooxygenation Research Articles

Regioselective Photooxidation of Citronellol: A Way to Monomers for Functionalized Bio-Polyesters.

Dye-sensitized photooxygenation reaction of bio-based double bond-containing substrates is proposed as sustainable functionalization of terpenes and terpenoids to transform them into polyoxygenated compounds to be employed for the synthesis of new bio-based polyesters. As proof of concept, citronellol 1 has been regioselectively converted into diol 4 using singlet oxygen (1O2), a traceless reagent that can be generated from air, visible light and zeolite supported-photosensitizer (Thionine-NaY). With our synthetic approach, diol 4 has been obtained in two-steps, with good regioselectivity, using green reagents such as light and air, and finally a solvent-free oxidation step. From this compound, a citronellol-based copolyester of poly(butylene succinate) (PBS) has been synthesized and fully characterized. The results obtained evidence that the proposed copolymerization of PBS with the citronellol-based building blocks allows to obtain a more flexible and functionalizable material, by exploiting a largely available natural molecule modified through a green synthetic path.

Rearrangements vs Fragmentations in the Dye-sensitized Photooxygenation of N-Aryl α-Furanamides

Rearrangements vs Fragmentations in the Dye-sensitized Photooxygenation of N-Aryl α-Furanamides

Spiroketals of monosaccharides by dye-sensitized photooxygenation of furyl ketoses

[4+2] Cycloaddition of singlet oxygen to suitably substituted furans followed by reduction of the corresponding endoperoxides afforded functionalized enediones which quickly cyclized into the titled spiroketals. The reported method represents a green synthetic one-pot procedure for novel [6,6]-, [5,6]-, and [5,5]-spiroketals of sugars.

Synthesis of Polyfunctional Drimanes from Drim-7,9(11)-diene and Drim-8-en-7-one

A series of 15 new polyfunctional drimanic compounds have been obtained by synthesis via dye-sensitized photooxygenation, bromination with N-bromosuccinimide, and electrochemical transformation of drim-7,9(11)-diene 1 and drim-8-en-7-one 2. Three alternative syntheses of 12-acetoxy-drim-7,9(11)-diene 8 and two of 11-bromo-drim-8(9)-en-7-one 10 have been accomplished. For the first time a drimanic compound 12 with an aromatic ring B has been synthesized and the experimental conditions for the selective bromination at C11 and C12 methyl groups of drim-8-en-7-one 2 have been optimized. The synthesized compounds are suitable intermediates for the preparation of natural drimane-type compounds and some of them have shown good antimicrobial and antifungal activities. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]

Photooxygenations in a bubble column reactor

A novel column reactor was constructed and successfully applied to dye-sensitized photooxygenation reactions in aqueous alcohol solutions. The air flow pattern within the narrow glass column could be controlled via the size of the air inlet capillary. Using a 500 μm capillary, a slug flow pattern was realized which allowed for superior mass transfer and light transparency within a thin solvent layer. These features subsequently gave higher conversion rates and isolated yields.

Dye-Sensitized Photooxygenation of 2,5-Bis(glycosyl)furans

The dye-sensitized photooxygenation of 2,5-bis(glycosyl)furans followed by warming up to r.t. provides 1,1- linked disaccharides separated by a functionalized spacer. Asymmetrical disubstituted glycosyl furans give the corresponding Bayer-Villiger type-rearranged products in a molar ratio depending on the sugars and the protecting groups. The migratory aptitudes have been rationalized by both theoretical calculations and experimental data. The 1,1- disaccharides obtained are new sugar derivatives structurally related to some mimetics of Sialyl Lewis X. Keywords: [4+2]-Cycloaddition, endoperoxides, glycosyl furans, glycosides, photooxygenation, singlet oxygen, thermal rearrangement, rearrangement, dichloromethane, disaccharidic systems

ChemInform Abstract: Photochemical Reactions of Tetrahydroquinoxalin-2(1H)-ones and Related Compound.

Photochemical behaviors of the pyrazinone derivatives 5,6,7,8-tetrahydroquinoxalin-2(1H)-ones 1a–c and 1,5,6,7,8,9-hexahydro-2H-cyclohepta[b]pyrazin-2-one 1d were investigated. Dye-sensitized photo-oxygenation of 1a-c gave the 1:1 adducts 5a–c of the corresponding 3,8a-epidioxy-3,5,6,7,8,8a-hexahydroquinoxalin-2(1H)-one 4 and H2O, whereas 1d gave 3,9a-epidioxy-1,3,5,6,7,8,9,9a-octahydro-2H-cyclohepta[b]pyrazin-2-one 4d (Scheme 2). The different kind of products was interpreted as being the result of the ring strain and steric hindrance of endoperoxides produced from 1a–d with singlet oxygen. Irradiation of 1a–b in the presence of alkenes gave tricyclic azetidine derivatives 9 by [2 + 2] cycloaddition of the CN bond of 1 to the alkene.

ChemInform Abstract: Carbonyl Oxide Chemistry. Part 1. Mechanism of Formation and Reactions of Carbonyl Oxides Obtained by Dye-Sensitized Photooxygenation of Some 2-Alkoxyfurans.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Mechanisms of Dye-Sensitized Photooxygenation of Olefins

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Dye-Sensitized Photooxygenation of 2,3-Dihydrothiophenes: Formation of Stable 1,2-Dioxetanes from 4,5-Dialkyl-Substituted Derivatives.

We report on the photooxygenation of 2,3-dihydrothiophenes and of 5,6-dimethyl-3,4-dihydro-2H-thiopyran in some detail

ChemInform Abstract: Dye-Sensitized Photooxygenation of 2,3-Dihydrofurans: Competing (2 + 2) Cycloadditions and Ene Reactions of Singlet Oxygen with a Rigid Cyclic Enol Ether System.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dye-sensitized photochemical transformation of some pharmaceutical drugs by singlet molecular oxygen

Dye-sensitized photo-oxygenation of thiopentone and phenytoin by singlet molecular oxygen has been carried out under various reaction conditions, including variation of solvents and sensitizers. The product has been isolated and characterized by elemental analysis, physical, chemical and spectral data. A suitable mechanism has been proposed for the formation of photo product. To confirm the participation of singlet oxygen in the reaction, singlet oxygen scavengers have been used in the photo-oxygenation reaction.

Dye-sensitized photooxygenation of sugar furans: novel bis-epoxide and spirocyclic C-nucleosides

Dye-sensitized photooxygenation of 2-methyl 5-(2,3,5-tri- O-acetyl-β- d-ribofuranosyl)furoate leads to (1 S,4 R)- endo-peroxide, highlighting a high facial diastereoselectivity. This endo-peroxide rearranges into syn-(1 R,2 R:3 S,4 R)-diepoxide C-nucleoside, while by Et 2S-reduction followed by NEt 3 catalysis affords a spirocyclic C-nucleoside.

New Insight into the Reaction of Singlet Oxygen with Sulfur-Containing Cyclic Alkenes: Dye-Sensitized Photooxygenation of 5,6-Dihydro-1,4-dithiins

The reaction of 3-methyl-5,6-dihydro-1,4-dithiins with singlet oxygen affords dicarbonyl compounds and/or ring-contracted ketosulfoxides, the latter regio- and stereoselectively, depending on the nature of the substituent at C-2 and on the reaction conditions. In competition with normal fragmentation, the intermediate dioxetanes, derived from [2 + 2] cycloaddition of singlet oxygen to the double bond, undergo an intramolecular oxygen transfer to the sulfur-1 atom, leading to labile epoxide intermediates. The latter convert to cis- and trans-ketosulfoxides through a non-concerted S-4 migration. This pathway is promoted by the electron-withdrawing group at C-2 and, for monosubstituted amide, by the solvent basicity. S-Oxidation of dithiins is insignificant, except for the monosubstituted amide derivative or in the presence of protic species, and occurs selectively at the S-1 atom.

Green photochemistry: Production of fine chemicals with sunlight

Abstract Three photochemical reactions were investigated under solar irradiation conditions with moderately concentrated sunlight: the photoacylation of naphthoquinone with butyraldehyde and the dye-sensitized photooxygenations of citronellol and 1,5-dihydroxynaphthalene, respectively. All reactions were easily performed on multigram-to-kilogram scales using cheap and commercially available starting materials, and yielded important key intermediates for industrial applications.

Dye-sensitized photooxygenation of sugar-furans as synthetic strategy for novel C-nucleosides and functionalized exo-glycals

The methylene blue-sensitized photooxygenation of β-ribofuranosyl furan 1e followed by in situ Et 2S treatment afforded the conformationally stable β-ribofuranoside 4e almost quantitatively. The latter was converted to pyridazine C-nucleoside 6e by cyclization with NH 2NH 2 and to pyrazoline 7e through a 1,3-dipolar cycloaddition with diazomethane. Attempts to epoxidize the double bond failed both by dimethyldioxirane (DMDO), which left 4e unchanged, and by NEt 3/ t-BuOOH or NaOO- t-Bu which respectively afforded the new and unexpected exo-glycals E, Z- 8e and the novel furan derivative 9.

Christopher Foote's Discovery of the Role of Singlet Oxygen [1O2 (1Δg)] in Photosensitized Oxidation Reactions

The chemistry of singlet molecular oxygen [1O2 (1Delta g)], its importance in atmospheric, biological, and therapeutic processes, and its use as a reagent in organic synthesis have been of considerable interest. Many aspects of singlet oxygen chemistry have emanated from the work of Christopher S. Foote and co-workers. Singlet oxygen is a historically interesting molecule with an unusual story connected with its discovery. Foote and Wexler conducted experiments in the 1960s where evidence was obtained supporting 1O2 generation via two independent routes: (1) a photochemical reaction (dye-sensitized photooxidation) and (2) a chemical reaction (NaOCl with H2O2). An important factor in the discovery of 1O2 as the critical reaction intermediate in dye-sensitized photooxygenations was Foote's reassessment of the chemical literature of the 1930s, when 1O2 was suggested to be a viable intermediate in dye-sensitized photooxidation reactions. Experiments that used silica gel beads provided evidence for a volatile diffusible oxidant such as 1O2. However, a contemporaneous quarrel surrounded this early work, and the possible existence of solution-phase 1O2 was ignored for over 2 decades. Not long after Foote's initial studies were published in 1964, the idea of singlet oxygen as an intermediate in photooxidation chemistry gained increasing recognition and verification in organic, gas phase, and biological processes. There are many documented impacts that 1O2 has had and continues to have on biology and medicine, for example, photodynamic therapy and plant defenses.

Christopher S. Foote (1935–2005): Singlet Oxygen

Christopher S. Foote (1935–2005): Singlet Oxygen

Dye-Sensitized Photooxygenation of Furanosyl Furans: Synthesis of a New Pyridazine C-Nucleoside

The dye-sensitized photooxygenation of furanosyl furans easily affords C- or O-glycosides with cis-alpha,beta-unsaturated 1,4-dioxo aglycones. The reaction, performed on a ribofuranosyl furan, provides a useful new entry to a novel pyridazine C-nucleoside that can be achieved through a simple one-pot procedure.

Dye-Sensitized Photooxygenation of the CN Bond. 5. Substituent Effects on the Cleavage of the CN Bond of C-Aryl-N-aryl-N-methylhydrazones1

The title compounds are cleaved cleanly at the C=N bond by singlet oxygen ((1)O(2), (1)Delta(g)) yielding arylaldehydes and N-aryl-N-methylnitrosamines. These reactions take place more rapidly at -78 degrees C than at room temperature. The effects of substituent variation at both the C-aryl and N-aryl groups were studied using a competitive method. Good correlations of the resulting rate ratios with substituent constants (sigma(-) or sigma(+)) were obtained yielding small to very small rho values indicative of small to very small changes in charge distribution between the reactant and the rate determining transition state. Electron withdrawing groups on the C-aryl moiety retard reaction somewhat by preferential stabilization of the hydrazone. Electron donors on the other hand slightly stabilize the rate determining transition state. Substituents on the N-aryl group have almost no effect. Inhibition by 3,5-di-tert-butylphenol was not observed showing that free (uncaged) radical intermediates are not involved in the mechanism. We postulate a mechanism in which the initial event is exothermic electron transfer from the hydrazone to (1)O(2) leading to an ion-radical caged pair. Subsequent covalent bond formation between the hydrazone carbon and an oxygen atom is rate controlling. The transition state for this step also has a lower enthalpy than the starting reactants, but the free energy of activation is dominated by a large negative TDeltaS++term leading to the negative temperature dependence. Direct formation of a C-O bond in the initial step is not unambiguously ruled out. Subsequent steps lead to C-N cleavage.