Sunlight oxidation of alkyl aryl tellurides to the corresponding carbonyl compounds: a new carbonyl precursor.

Alkyl aryl tellurides were efficiently transformed to the corresponding carbonyl compounds by photo-oxidation with sunlight without affecting various functional groups in the alkyl moiety. The tellurides can be used as a new carbonyl precursor, and the photolysis can be conducted without special equipment for light sources.

Laser photolysis and thermolysis of organic selenides and tellurides for chemical gas-phase deposition of nanostructured materials.

Laser radiation-induced decomposition of gaseous organic selenides and tellurides resulting in chemical deposition of nanostructured materials on cold surfaces is reviewed with regard to the mechanism of the gas-phase decomposition and properties of the deposited materials. The laser photolysis and laser thermolysis of the Se and Te precursors leading to chalcogen deposition can also serve as a useful approach to nanostructured chalcogen composites and IVA group (Si, Ge, Sn) element chalcogenides provided that it is carried out simultaneously with laser photolysis or thermolysis of polymer and IVA group element precursor.

Facile photochemical transformation of alkyl aryl selenides to the corresponding carbonyl compounds by molecular oxygen: use of selenides as masked carbonyl groups.

Alkyl aryl selenides with and without functional groups on the alkyl group were transformed efficiently into the corresponding carbonyl compounds, particularly primary alkyl aryl selenides in good yields, by a simple photolysis in the presence of air or oxygen. This transformation can be conducted without protection of functional groups. The yield of carbonyl compounds was much affected by the solvent viscosity, reaction temperature, concentration of dissolved oxygen in the solvents, wavelength of light, and structure of the aryl substituents. The present study indicates that aryl selenides can be considered as a masked carbonyl group that can be easily converted to a carbonyl group by very mild reaction conditions even in the presence of various unprotected functional groups. Therefore, this functional group transformation can be used as an important tool in organic synthesis due to its simplicity and mild reaction condition.

Factors controlling photochemical cleavage of the energetically unfavorable Ph-Se bond of alkyl phenyl selenides.

Primary photochemical paths of alkyl phenyl selenides (1) were investigated, and an origin of large deviations in the chemical yields of products obtained by carbon radical reactions induced by photolysis of phenyl selenides was clarified. KrF excimer laser photolyses of n-pentyl phenyl selenide (1a) yielded 1-pentene (2a), n-pentane (3a), n-decane (4a), dipentyl selenide (5a), benzene (6), dipentyl diselenide (7a), and diphenyl diselenide (7) as major photoproducts, with compounds 2a, 3a, 4a, 5a, and 7 formed by pentyl-Se bond cleavage, and 5a, 6, and 7a by Ph-Se bond cleavage. The selectivity of the photoproducts revealed the occurrence of an unexpected amount of Ph-Se bond cleavage (35% in n-hexane at 248 nm) during photolysis. Solvent viscosity, wavelength of light, and the structure of alkyl substituents were the major factors that controlled Ph-Se bond cleavage. The ratio of Ph-Se bond cleavage decreased with increasing solvent viscosity and laser wavelength. The effect of alkyl substituents on the ratio of bond cleavages, Ph-Se/total C-Se, was investigated for five alkyl phenyl selenides; the ratio decreased in the order pentyl > 2-methylallyl > allyl > 1-ethylpropyl > tert-butyl groups. The contribution of Ph-Se bond cleavage is most probably the origin of the large deviations in the yields of radical reactions induced by photolyses of 1, which can be minimized by selecting appropriate solvents and wavelength of light.

Stepwise photocleavage of C-O bonds of bis(substituted-methyl)naphthalenes with stepwise excitation by two-color two-laser and three-color three-laser irradiations.

Stepwise photocleavage of naphthylmethyl-oxygen (C-O) bonds of mono(substituted-methyl)naphthalenes [1- and 2-ROCH2Np, R = 4-benzoylphenyl (BP), phenyl (Ph), and methyl (CH3)] and bis(substituted-methyl)naphthalenes [1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np, R = BP and Ph] was observed to give the naphthylmethyl radicals (NpCH2* or ROCH2NpCH2*) in almost 100% yield with two-step or three-step excitation by the two-color two-laser or three-color three-laser irradiation, respectively, at room temperature. The C-O bond cleavage quantum yields of 1-PhOCH2Np, 2-PhOCH2Np, 1,8-(PhOCH2)2Np, and 1,4-(PhOCH2)2Np were higher than those of 1-BPOCH2Np, 2-BPOCH2Np, 1,8-(BPOCH2)2Np, and 1,4-(BPOCH2)2Np. No C-O bond cleavage occurred from 1,8-(HOCH2)2Np and 2-CH3OCH2Np in the higher triplet excited state (T(n)). The experimental results show that the C-O bond cleavage was determined not only by the position of the substituents on Np but also by the type of the substituents. The C-O bond cleavage of 1-ROCH2Np was more efficient than that of 2-ROCH2Np. In the case of 1,8-(ROCH2)2Np and 1,4-(ROCH2)2Np (R = BP and Ph), the first C-O bond cleavage from the T(n) states occurred to give ROCH2-substituted naphthylmethyl radicals (1,8- and 1,4-ROCH2NpCH2*) when the T1 states, generated with the 308-nm first laser irradiation, were excited using the 430-nm second laser. The second C-O bond cleavage occurred when 1,8- and 1,4-ROCH2NpCH2* in the ground state [1,8- and 1,4-ROCH2NpCH2*(D0)] were excited to the excited states [1,8- and 1,4-ROCH2NpCH2*(D(n))] using the third 355-nm laser during the three-color three-laser flash photolysis at room temperature. It was revealed that acenaphthene was produced as the final product during the stepwise C-O bond cleavages of 1,8-(BPOCH2)2Np and 1,8-(PhOCH2)2Np. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using the three-color three-laser photolysis method.

Photosensitized oxygenation of diaryl tellurides to telluroxides and their oxidizing properties.

Photosensitized oxidation of tellurides carrying bulky aromatic substituents afforded the corresponding telluroxides which were found to react with simple alcohols to give the corresponding carbonyl compounds in excellent yields along with the starting tellurides.

Stepwise photocleavage of two C-O bonds of 1,8-bis[(4-benzoylphenoxy)-methyl]naphthalene with three-step excitation using three-color, three-laser flash photolysis.

Stepwise photocleavage of two naphthylmethyl-oxygen bonds of 1,8-bis[(4-benzoylphenoxy)methyl]naphthalene (1,8-(BPO-CH2)2Np, 1) was observed during three-color, three-laser flash photolysis at room temperature. The mechanism from 1 to the final product, acenaphthene (2), was clearly elucidated. The first (308 nm, 5 mJ pulse-1) XeCl laser excited 1 to the lowest triplet excited state 1(T1), in which the excited energy was localized in the naphthalene moiety, but the C-O bond cleavage did not occur. The second (430 nm, 7 mJ pulse-1) OPO laser excited 1(T1) to the higher triplet excited states 1(Tn) in which the excited energy is delocalized in the naphthalene moiety and C-O bonds, and one C-O bond cleavage occurred. The third (355 nm, 10 mJ pulse-1) YAG laser excited the carbon-centered radical in the ground state 1-(BPO-CH2)NpCH2*(D0) to its excited states 1-(BPO-CH2)NpCH2*(Dn), from which the second C-O bond cleavage occurred to give 2 as the final product. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using three-color three-laser photolysis method.

Rapid cleavage of the naphthylmethyl-oxygen bond in higher triplet excited states.

Rapid cleavage of the naphthylmethyl-oxygen bond of 1- and 2-[(4-benzoylphenoxy)methyl]naphthalenes in higher triplet excited states occurred within a laser flash of 5 ns to give 1- and 2-naphthylmethyl radicals with formation quantum yields of 0.042 +/- 0.004 and 0.020 +/- 0.002, respectively, during two-colour two-laser flash photolysis.

A two-color laser photolysis method for determining reaction rates of short-lived intermediates by product analysis: application to the o-quinodimethane problem.

A time-delayed, two-color pulse laser photolysis technique was used for a kinetic study of short-lived transient species through product analysis, the determination of the rate constant of the cycloaddition of o-quinodimethane (1) and maleic anhydride (2) in room-temperature solutions. o-Quinodimethane (1) was generated from 1,2-bis[(phenylseleno)methyl]benzene (3) by the irradiation of a pulse of a KrF excimer laser (248 nm) in the presence of excess 2, and a successive pulse of a XeCl excimer laser (308 nm) was irradiated to the reaction mixture after varied delay times from 0 to 0.1 s for the decomposition of the remaining 1 to quench the cycloaddition reaction. The rate constant of the cycloaddition of 1 and 2 was 2.1 x 10(5) M(-1) s(-1), which was obtained by the analysis of the delay-time dependence of the product yields.

Large substituent effect on the photochemical rearrangement of 1,6-(N-Aryl)aza-[60]fulleroids to 1,2-(N-Arylaziridino)-[60]fullerenes.

Large substituent effects were observed in the rates and reaction mechanisms of the photochemical rearrangement of N-arylaza-[60]fulleroid 1 to N-arylaziridino-[60]fullerene 2, in which the difference of the rates between the fastest and the slowest (>2160-fold) was attained only by changing the aryl group from 1-naphthyl to 2-naphthyl. The decreasing order of the reaction rates in relation to the substituents was 1-naphthyl (1b) > 1-pyrenyl (1d) > phenyl (1a) > 2-naphthyl (1c). The reactions proceeded via triplet states of the fulleroids and a triplet sensitization of the reaction by rearranged product 2b was observed in the case of 1b. The slow reactions of 1a,c were interpretated by the participation of charge-separated species in the excited triplet states, which was supported by nanosecond transient absorption spectra.

Complexation with albumins of chiral aromatic substrates and their chemistry in ground and excited states. Catalytic and chirality recognition properties of the protein in the cases of binaphthol, its photoisomers, and ketoprofen.

The reactivity of organic molecules can be modified upon complexation with proteins: these changes can be different and more significant when the substrate is in an electronically excited state. Here we review UV, CD, and fluorescence spectroscopy studies on the photochemistry and on the chemistry of atropisomeric binaphthols and of ketoprofen, complexed to serum albumins. The chemical and photochemical properties of the organic substrates, complexed to the albumins or free in common solvents, are different. The role of the protein complexation is also evidenced in photoresolution processes of racemate-protein complexes. Catalytic effects due to serum albumins are also reported. In particular, the Arrhenius parameters for the rate of thermal isomerization of a metastable photoproduct of binaphthol in common solvents are compared with those of the bovine serum albumin catalyzed isomerization.

A Facile Synthesis of Tetra- and Dihydronaphthalene Derivatives by Excimer Laser Photolysis of 1,2-Bis(substituted-methyl)benzenes in the Presence of Olefins and Acetylene.

o-Quinodimethane (3A) was generated effectively by excimer laser photolyses of 1,2-bis(phenoxymethyl)benzene (1-O), 1,2-bis[(phenylthio)methyl]benzene (1-S), and 1,2-bis[(phenylseleno)methyl]benzene (1-Se) in acetonitrile solutions via a two-photon process, which was followed by cycloaddition of 3A with several dienophiles-maleic anhydride (4a), dimethyl maleate (4b), dimethyl fumarate (4c), fumaronitrile (4d), and dimethyl acetylenedicarboxylate (4e)-to give corresponding cycloadducts 5. Three kinds of excimer lasers, namely, KrF (248 nm), XeCl (308 nm), and XeF (351 nm) excimer lasers were used for the reaction. The KrF excimer laser was found to be most effective for obtaining high consumption of 1-(O, S, Se) and yield of 5; the maximum yield of the cycloadduct obtained was 48%.