Ene Reaction Of Singlet Oxygen Research Articles

Highly active catalysts for the photooxidation of organic compounds by deposition of [60] fullerene onto the MCM-41 surface: A green approach for the synthesis of fine chemicals

A series of C60 catalysts supported on MCM-41 was prepared in the context of developing a highly active heterogeneous catalytic system for the singlet oxygen-mediated oxidation of organic substrates. Successive incipient wetness impregnation was used for preparing 3, 6, 9 and 12wt.% C60 onto MCM-41 surface. N2 adsorption, FT-IR, XRD, HR-TEM, DRS and TGA, have been used to characterize the photocatalysts.It was found that C60 is highly dispersed (especially in the 3 and 6wt.% C60 catalysts) within the mesopores or on the external surface of MCM-41, as clusters or crystallites/aggregates of very small size and presumably in the form of atomic layers. The mesoporous structure and characteristics (surface area, mesopore size and volume) of MCM-41 remain almost intact upon deposition of C60 on its surface.The photocatalytic activity was assessed in the photocatalytic oxidation of olefins via the singlet oxygen ene reaction by studying the photooxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5°C in CH3CN under oxygen atmosphere and using a 300W xenon lamp as the light source. To investigate further the potential applications of our catalysts we examined various types of photooxidations including the [4+2] or [2+2] cycloaddition, the heteroatom oxidation with sulfur or phosphorus containing compounds and the oxidation of phenols.The heterogeneous photocatalysts obtained were proved to be very active exhibiting higher substrate conversion, TON and TOF values, compared to those of the unsupported (solid) C60 and the corresponding photocatalysts supported on silica or γ-alumina. This was mainly attributed to the better dispersion of C60 on the MCM-41. The conversion achieved over the catalysts increases with the amount of the supported C60 up to a value of 6wt.% and then it decreases whereas the TON and TOF values decrease monotonically as the amount of the supported C60 increases following the increase in the size of the supported C60 crystallites/aggregates. Shadow effects were not observed under our experimental conditions.

Synthesis of 2-arylacrylic esters from aryl methyl ketones via Wittig reaction/singlet oxygen ene reaction

An efficient synthetic method has been developed for the synthesis of 2-arylacrylic esters from the corresponding aryl methyl ketones via Wittig reaction and singlet oxygen ene reaction. Wittig reaction to aryl methyl ketones with (methoxymethyl)triphenylphosphonium chloride in basic condition afforded the methyl enol ethers, and then 2-arylacrylic esters were obtained by singlet oxygen ene reaction, followed by tosylation and elimination in one-pot to the methyl enol ethers in good yields.

Synthesis of Withanolide A, Biological Evaluation of Its Neuritogenic Properties, and Studies on Secretase Inhibition

Neurons on steroids: A stereoselective synthesis of the neuritogenic steroid lactone withanolide A was achieved by singlet oxygen ene reaction, Wharton transposition, a Corey–Seebach homologation, and a vinylogous aldol reaction. Biological evaluation demonstrated neurite outgrowth, which supports the potential neuritogenic role of this compound in traditional Indian medicine.

Stereoselective synthesis of deoxycarbaheptopyranose derivatives: 5a-carba-6-deoxy-α- dl-galacto-heptopyranose and 5a-carba-6-deoxy-α- dl-gulo-heptopyranose

Two new deoxycarbaheptopyranoses, 5a-carba-6-deoxy-α- dl-galacto-heptopyranose and 5a-carba-6-deoxy-α- dl-gulo-heptopyranose were prepared starting from cyclohexa-1,4-diene. The addition of dichloroketene to cyclohexa-1,4-diene followed by the subsequent reductive elimination and Baeyer–Villiger oxidation in turn led to the formation of a bicyclic lactone. Reduction of the lactone moiety followed by acetylation gave a diacetate with cis-configuration. The introduction of additional acetate functionality into the molecule was achieved by singlet oxygen ene-reaction. The formed hydroperoxide was reduced and then acetylated. The triacetate was further functionalized either by direct cis-hydroxylation using OsO 4 or by epoxidation followed by a ring-opening reaction to give the title heptopyranose derivatives. One of the synthesized molecules, galacto-heptopyranose exhibited enzyme specific inhibition against α-glycosidase. On the other hand, they did not show any inhibition for α-amylase. However, both compounds, gulo-heptopyranose and galacto-heptopyranose increased the activity of α-amylase.

ChemInform Abstract: Unraveling the Mechanism of the Singlet Oxygen Ene Reaction: Recent Computational and Experimental Approaches

AbstractReview: about 60 refs.

ChemInform Abstract: Regio- and Diastereoselective Ene Reactions of Singlet Oxygen with Dialkyl-Substituted Acrylic Esters.

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: Photooxygenation of 2-Alkenyl-Substituted Chiral Oxazolines: Stereochemical Evidence Favoring the cis-Effect in the Regioselective Ene Reaction of Singlet Oxygen with α,β-Unsaturated Carbonyl Derivatives.

ChemInform Abstract: Photooxygenation of 2-Alkenyl-Substituted Chiral Oxazolines: Stereochemical Evidence Favoring the cis-Effect in the Regioselective Ene Reaction of Singlet Oxygen with α,β-Unsaturated Carbonyl Derivatives.

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.

ChemInform Abstract: Photooxygenation of Chiral Allylic Alcohols: Hydroxy-Directed Regio- and Diastereoselective Ene Reaction of Singlet Oxygen.

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.

Cover Picture: Fullerene Derivatives That Bear Aliphatic Chains as Unusual Surfactants: Hierarchical Self‐Organization, Diverse Morphologies, and Functions / Model Studies in Heterogeneous Catalysis / Functional Hybrid Materials with Polymer Nanoparticles as Templates / Systems Chemistry Approach in Organic Photovoltaics / Unraveling the Mechanism of the Singlet Oxygen Ene Reaction: Recent Computational and Experimental Approaches / Applied Biotransformations in Green Solvents

Cover Picture: Fullerene Derivatives That Bear Aliphatic Chains as Unusual Surfactants: Hierarchical Self‐Organization, Diverse Morphologies, and Functions / Model Studies in Heterogeneous Catalysis / Functional Hybrid Materials with Polymer Nanoparticles as Templates / Systems Chemistry Approach in Organic Photovoltaics / Unraveling the Mechanism of the Singlet Oxygen Ene Reaction: Recent Computational and Experimental Approaches / Applied Biotransformations in Green Solvents

Unraveling the Mechanism of the Singlet Oxygen Ene Reaction: Recent Computational and Experimental Approaches

The mechanism of the singlet oxygen ene reaction has been a subject of renewed interest within the last few years. The main question being whether this reaction proceeds through a concerted mechanism or if it involves discrete intermediates. In general, the majority of experimental and computational studies support a traditional stepwise mechanism involving a perepoxide-like intermediate. In this minireview we highlight the most prominent and recent theoretical, as well as experimental results relating to the challenging mechanism of the singlet oxygen ene oxyfunctionalization.

Diastereoselective schenck ene reaction of singlet oxygen with chiral allylic alcohols; access to enantiomerically enriched 1,2,4-trioxanes

A series of antimalarial chiral 1,2,4-trioxanes ( 1– 8) were synthesised in high enantiomeric purities. Enantioselective addition of R 2Zn reagent to 3-methyl-2-butenal catalysed by (+)-MIB or (−)-MIB yielded both the enantiomers of the chiral allylic alcohols 9– 11 (90–98% ee), which were subjected to diastereoselective photooxygenation in the presence of tetraphenylporphine (TPP) to obtain ( R, R)- threo- or ( S, S)- threo-β-hydroperoxy alcohols ( 12– 14). Reaction of β-hydroperoxy alcohols ( 12– 14) with different cyclic ketones produced optically active trioxanes 1– 8.

Theoretical Prediction of a Perepoxide Intermediate for the Reaction of Singlet Oxygen with trans-Cyclooctene Contrasts with the Two-Step No-Intermediate Ene Reaction for Acyclic Alkenes

B3LYP/6-31G* and CASMP2 calculations have been employed to study the ene reaction of singlet oxygen with trans-cyclooctene. These methods predict that the reaction involves a perepoxide intermediate, whereas alkenes such as tetramethylethylene are predicted by the same methods to occur by a two-step no-intermediate mechanism, with no perepoxide intermediate. The change in mechanism arises because the trans-cyclooctene imposes a substantial strain in the transition state for hydrogen abstraction. The perepoxide is formed through a polarized diradical intermediate that can lead to the observation of alkene isomerization. The polarized diradical also becomes a minimum because of the barrier to abstraction.

Synthesis of Benzo[c]xanthones from 2-Benzylidene-1-tetralones by the Ultraviolet Radiation-Mediated Tandem Reaction

A facile one-pot method to prepare benzo[c]xanthones from readily accessible benzylidene-1-tetralones by the ultraviolet radiation-mediated tandem reaction is reported. The overall transformation presumably involves cis-trans isomerization, oxa-6pi electrocyclization, singlet oxygen ene reaction, dehydration, and aromatization.

The Cyclopropyl Group as a Hypersensitive Probe in the Singlet Oxygen Ene Reaction Mechanism

Cyclopropyl-substituted olefins are employed as mechanistic probes in the singlet oxygen-alkene ene reaction. In MeOH and aprotic solvents [CHCl(3), (CH(3))(2)CO, CH(3)CN], only the allylic hydroperoxides bearing an intact cyclopropyl group are detected. The reaction mechanism is independent of solvent polarity. Our findings, to a certain experimental limit, exclude a biradical or dipolar intermediate.

Spiroperoxy Lactones from Furans in One Pot: Synthesis of (+)-Premnalane A

A [4+2]-cycloaddition between singlet oxygen and a furan, followed by an ene reaction and ketalization, in one synthetic operation, was used for the synthesis of (+)-premnalane A. The first example of a singlet oxygen ene reaction that furnishes exclusively a Z-double bond is noted.

Selective Formation of Allylic Hydroperoxides via Singlet Oxygen Ene Reaction

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

En Route to Improved Antimalarial Peroxides Following the Natural Role Model Artemisinin

AbstractThe synthesis of a series of 5‐cyclopropyl substituted 1,2,4‐trioxanes 3a‐3f by a sequence of singlet oxygen ene reaction with the 1‐cyclopropylated allylic alcohol 1 and subsequent peroxyacetalization reaction with aldehydes and ketones, respectively, is described. An important side reaction is the formation of cross‐peroxyacetalization products 4 and 5 from the Lewis‐acid catalyzed cleavage of the initially formed β‐hydroperoxy alcohol 2. The in vitro antimalarial activities of several derivatives 3 against Plasmodium falciparum are remarkably high.

Stereoelectronic and solvent effects on the allylic oxyfunctionalization of alkenes with singlet oxygen

The factors that control the stereochemistry of sensitized photooxygenation of alkenes via singlet oxygen (ene reaction) are selectively reported. We also introduce our most recent stereoelectronic effects on the singlet oxygen–ene reaction. The origin of site selectivity and solvent-dependent stereoselectivity in this classical ene reaction with simple as well as functionalized alkenes is highlighted. These studies and other similar studies have enhanced substantially the utility of singlet oxygen in the synthesis of natural and non-natural products.

Auxiliary controlled singlet-oxygen ene reactions of cyclohexenes

The photooxygenation of homochiral cyclohexene ketals, which are easily available from 2-cyclohexenone and l-tartrates, affords hydroperoxides and after reduction the corresponding allylic alcohols in good yields and high regioselectivities. This can be rationalized by electronic repulsions in a perepoxide intermediate and provides evidence for unfavorable 1,3 diaxial interactions with a dioxolane oxygen atom. Only low stereoselectivities were observed, due to the flexibility of the cyclohexene ring. However, the diastereomers could be separated and after cleavage of the auxiliary, 4-hydroxy-2-cyclohexen-1-one was isolated in enantiomerically pure form, which can serve as a building block for natural product synthesis.