Irradiation benzene

The unexpected formation of cyclopenta[b]indole 3-339 and cyclohepta[b]indole derivatives has been observed by Bennasar and coworkers when a mixture of 2-in-dolylselenoester 3-333 and different alkene acceptors (e. g., 3-335) was subjected to nonreductive radical conditions (hexabutylditin, benzene, irradiation or TTMSS, AIBN) [132]. The process can be explained by considering the initial formation of acyl radical 3-334, which carries out an intermolecular radical addition onto the alkene 3-335, generating intermediate 3-336 (Scheme 3.81). Subsequent 5-erafo-trig cyclization leads to the formation of indoline radical 3-337, which finally is oxidized via an unknown mechanism (the involvement of AIBN with 3-338 as intermediate is proposed) to give the indole derivative 3-339. 

C02 to give adduct complexes. NMR evidence indicates that [ReH(dppe)2] undergoes rapid but reversible ortho metalation and insertion into the C-H bonds of benzene. Irradiation of the complexes [ReH5L3] (L = PMe2Ph, PMePh2, PPh3) and [ReH3 ... 

The photochemistry of borazine delineated in detail in these pages stands in sharp contrast to that of benzene. The present data on borazine photochemistry shows that similarities between the two compounds are minimal. This is due in large part to the polar nature of the BN bond in borazine relative to the non-polar CC bond in benzene. Irradiation of benzene in the gas phase produces valence isomerization to fulvene and l,3-hexadien-5-ynes Fluorescence and phosphorescence have been observed from benzene In contrast, fluorescence or phosphorescence has not been found from borazine, despite numerous attempts to observe it. Product formation results from a borazine intermediate (produced photochemically) which reacts with another borazine molecule to form borazanaphthalene and a polymer. While benzene shows polymer formation, the benzyne intermediate is not known to be formed from photolysis of benzene, but rather from photolysis of substituted derivatives such as l,2-diiodobenzene ... 

Less heavily substituted benzenes also undergo photochemical scrambling of the type observed in the vapor phase for the xylenes. Thus 1,4-difluoro benzene irradiated at 2690 A produces solely quantities of the 1,3- and 1,2-isomers.58 Upon irradiation with a less monochromatic light source, the 1,3-isomer gives 1,2 and 1,4, and the 1,2-isomer gives the 1,3 and 1,4, although in these cases there is some polymer formation.58... 

The Cundall technique shows only a small triplet state yield at 2400 A. As the wavelength decreases " an additional process comes into play. This must be a very rapid process whose rate depends on the vibrational level of the initially formed HPh. Neither this method nor the Cundall method based on cis-butene-2 shows triplet benzene molecules to be formed in benzene irradiated at 2400 A. 

Reaction with benzene. Irradiation of a solution of ethyl azidoformate (I) in benzene affords N-carboethoxyazepine (4) in about 70% yield. In a study of the flash-photolytic decomposition of ethyl azidoformate, Lwowski found spectro-... 

In the absence of catalysts and in the dark, pure benzene does not react with bromine, as is the case also with chlorine. Photochemical addition of bromine, like that of chlorine, is a radical chain reaction.130 131 Bromine has a more powerful substituting action than chlorine, and its rate of addition is slower.132 At low temperatures light and addition of peroxides favor addition of bromine. To date, two isomeric hexabromocyclohexanes have been isolated, by very slow addition of bromine to benzene irradiated at 0° 1% sodium hydroxide solution must be placed under the benzene and frequently renewed even so, yields are poor.126b 133... 

Figure 5-2. Fluorescence intensity from neat liquid benzene irradiated with 1-15 MeV protons as a function of time (left), and lifetimes for the dual exponential deconvolution (right) [41, reprinted with permission, 1996 American Chemical Society]. Solid symbols are for the slow component and open symbols are for the fast component.

Methyl-4-phenylquinazoline 3-oxide in benzene irradiated by a 200 w. high-pressure Hg-immersion lamp with Pyrex filter until the startg. m. has disappeared after 6 hrs. -> 2-phenyl-4-methylbenz[f]-l,3,5-oxadiazepine. Y 46%. C. Kaneko and S. Yamada, Tetrah. Let. 1967, 5233 s. a. G.F. Field and L. H. Sternbadi, J. Org. Chem. 33, 4438 (1968). 

A soln. of acridine and phenylacetic acid in benzene irradiated 2 hrs. under Ng in a Pyrex tube with a 200 w. high-pressure Hg-lamp -> 9-benzylacridan. Y 12% based on acridine consumed. F. e., also intramolecular ring closure, and without hydrogenation s. R. Noyori et ak, Tetrahedron 25, 1125 (1969). 

A soln, of 3-carbamoyl-2,2,5,5-tetramethylpyrroline 1-oxyl in benzene irradiated 15 hrs. with a 200 w. Hanovia high-pressure Hg-lamp with Pyrex filter -> diene. Y 95%. Limitations s. J. F. W. Keana and F. Baitis, Tetrah. Let. 1968, 365. 

A soln. of methyl l,3,3-triphenylpropen-3-yl ether in benzene irradiated 36 hrs. under argon with low-pressure Hg-lamps 1-methoxy-1,2,3-triphenylcyclo-... 

Dimerization. 4,4 -Bisdimethylaminobenzothiophenone and tributylborane in benzene irradiated 3-5 days by sunlight under Ng -> letrakis-4-dimethylamino-tetraphenylethylene. Y almost 100%. M. Inatome and L. P. Kuhn, Tetrah. Let. 1965, 73. 

A soln. of 3-diphenylhydroxymethyl-4-diphenylmethylenecyclobut-2-en-l-one in benzene irradiated 4 hrs. at room temp, under Ng with a 100 w. high-pressure Hg-lamp 5,5-diphenyl-4-diphenylvinylidene-tetrahydrofuran-2-one. Y 82%. F. e. s. F. Toda and E. Todo, Chem. Lett. 1974, 1279. 

A soln. of N,N-dibenzylbenzoylacetamide in benzene irradiated with the Pyrex-filtered light of a high-pressure Hg-lamp l-benzyl-4,5-diphenyl-4-hydroxy-2-pyrrolidinone. Y 80%. F. e. s. T. Hasegawa and H. Aoyama, Chem. Commun. 1974, 743. 

A soln. of 2,3-diphenylnaphthoquinone oxide in benzene irradiated with Pyrex-filtered light in the presence of N-phenylmaleimide -> product. Y 72%. Also in the presence of norbornadiene s. H. Kato, K. Yamagudii, and H. Tezuka, Chem. Lett. 1974, 1089. 

A soln. of 2-methoxy-3 bromo-1,4-naphthoquinone and 1,1-diphenylethylene in benzene irradiated with a 300 w. high-pressure Hg-arc lamp -> 5-phenyl-7,12-benz[a]anthraquinone. Y 61%. F. e. s. K. Maruyama and T. Otsuki, Chem. Lett. 1975,87. 

A degassed soln. of 2,2-dimethyl-l-p-tolylpentane-l-thione in benzene irradiated 26 hrs. with a 450 w. medium-pressure Hg-arc in an evacuated Pyrex tube, the solvent-free intermediate (conversion ca. 95%) dissolved in glacial acetic acid, treated with mercuric acetate, and stirred 0.5 hr. at room temp. 5,5-dimethyl-1-p-tolylcyclopentene. Y 65%. F. de Mayo and R. Suau, Soc. Perkin I 7974, 2559 cyclopropanethiols from thioketones s. A. Couture, M. Hoshino, and P. de Mayo, Chem. Commun. 1976, 131. 

A soln. of startg. pyranocarbazole in benzene irradiated at room temp, in a quartz immersion well photochemical reactor using a low- or medium-pressure Hg-vapour lamp (400 W 365 nm) under Nj for 4 h - product. Y 60%. F.e.s. A. Chakrabarti, D.P. Chakraborty, Tetrahedron Letters 29, 6625-8 (1988). 

A soln. of (E)-3-benzylideneflavanone in benzene irradiated in a quartz immersion system with a 125 W high-pressure mercury-arc with external cooling for ca. 48 h - product. Y 90%. F.e.s. V.P. Dhande et al., Tetrahedron 44, 3015-23 (1988). 

Benzylphosphonic acid esters. A soln. of benzyl diethyl phosphite (0.1-0.2 M) in deoxygenated benzene irradiated in a quartz tube with a 450 W medium-pressure Hg-lamp - diethyl benzylphosphonate. Y 85-95%. With chiral O-benzyl groups, reaction proceeds with complete retention of configuration at the chiral carbon, F.e.s. W.G. Bentrude et al., J. Am. Chem. Soc. 110, 6908-9 (1988) stereochemistry s.a. Tetrahedron Letters 30, 1025-8 (1989). 

Acetoxy-ll-oxo-5a-pregnane-20-carboxamide, Pb-tetraacetate, and iodine in benzene irradiated 5 hrs. at 15° with a 125 W high-pressure Hg-arc lamp, and the product isolated after refluxing with alc.-aq. KOH and reacetylation with acetic anhydride and pyridine y-lactone. Y ca. 55%. F. e., also with tert-butyl hypochlorite instead of Pb-tetraacetate, s. D. H. R. Barton, A. L. J. Beckwith, and A. Goosen, Soc. 1965, 181. 

Dimerization of photoreactive olefins is generally enhanced in micelles. In iso-phorone (128) dimerization, the ratio of possible photodimers is altered on micellization, and acenaphthene dimerization to (129) gives 95% of product in non-ionic or anionic surfactant solution, but 10% on irradiation in benzene solution under otherwise identical conditions. The cis.trans ratio varies from 22.3 1 in sodium lauryl sulphate micelles, but 0.06 1 at low substrate concentration in non-ionic micelles. The crossed photodimer (130) is a significant product on co-irradiation of acenaphthene and acrylonitrile in micelles, but not in benzene. Irradiation of 3-alkylcyclopentenones in micelles of potassium dodecanoate gives 98% of head-to-head dimer (131), which is never the dominant product in organic solvents. This result implies ordering of the... 

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