Acetophenone as sensitizer

Two interesting variations on the role of pyran-2-one as a synthon are worthy of mention. Irradiation of the compound in methanol containing acetophenone as sensitizer gives equal amounts of the photostable dimers (311) and (312). In this reaction the pyranone acts as both diene and dienophile and the dimers are believed to be formed via triplet excited states of the pyranone (68TL5279). 

Only with compounds (20o-q) are bicyclooctenones found which are unreactive either on direct excitation ( irr = 300 lun) or by triplet sensitization (acetone or acetophenone as sensitizer). On comparison of these exceptional cases with the substrates in Schemes S and 11, it becomes apparent that ODPM reactivity vs. inertness is influenced by very subtle differences in the substitution pattern. For example, shortening of the acetal chain of (20d) to R = Me for (24k>) renders a photoreactive substrate (20d 21d 90% yield) photochemically inert. ... 

Photoisomcrization of bicyclo[2.2.1jhepta-2,5-diene (I) in the presence of acetophenone as sensitizer provides a method for the preparation of quadricyclane (2). The... 

S-azidobenzo[b]thiophens in secondary amines unexpectedly gave a 4-aminor5-NN-dialkylaminobenzo[ b ]thiophen, whereas 4-azidpbenzo[b ]-thiophen gave no rearranged products/ Photochemical as well as thermal and silver-promoted reactions of (304) lead to (305), which was also prepared by photochemical addition of cis-dichloroethylene to benzo[b]thiophen using acetophenone as sensitizer followed by dechlorination of the adduct with sodium-phenanthrene in THF/ ... 

The overall sensitivity of the sampling and concentrating system was examined using acetophenone as the solute. Purified water (water that had been passed through a reversed-phase column) was used to make... 

The yields of cyclopropanes in this case are low in relation to the amount of acetophenone formed. However, similar cyclopropane product ratios are obtained when photolysis is carried out in the presence of Michler s ketone as sensitizer. Thus the carbene intermediate produced in the direct irradiation is thought to be a triplet, as suggested by the nonstereospecificity of its addition. Whether this intermediate arose from singlet diazoacetophenone (via singlet decomposition and intersystem crossing of the singlet carbene) or by decomposition of the triplet molecule was not determined. 

Acetic anhydride, with 2-hep-tanone to give 3-n-butyl-2, 4-pentanedione, 51, 90 ACETIC FORMIC ANHYDRIDE, 50, 1 Acetone azine, 50, 2 ACETONE HYDRAZONE, 50, 2, 28 Acetophenone, 54, 93 as sensitizer for irradiation of bicyclo[2.2.1]hepta-2,5-diene to give quadricyclane,... 

The photodimerization of coumarin has been studied in several solvents and their nature has an effect on this rather complex reaction. In a polar medium such as methanol, the only product is the cis head-to-head isomer (244) but in acetonitrile, this is accompanied by the trans head-to-head dimer (245), which becomes the main product of the reaction in non-polar solvents like benzene or dioxan. Small amounts of the head-to-tail isomers (246) are also formed in non-polar solvents (66JA5415). In some solvents, the presence of benzophenone as sensitizer is essential and it also alters the relative proportion of dimeric isomers (64JA3103, 66CB625). Photolysis of osthole (247) in the presence of acetophenone gives a mixture of two quite different dimers (248) and (249) (80MI22302), representing addition at the exocyclic and endocyclic double bond respectively. 

Boese and Goldman investigated the photocarbonylation of cyclohexane 105 cocatalyzed by d8 metal complexes, such as 106, and aromatic ketones, like acetophenone 107 or benzophenone, as sensitizers (Fig. 27) [170]. The transformation furnished cyclohexanecarbaldehyde 108. The formation of 108 was... 

Since most simple alkenes have a high triplet energy ( t = 75-78 kcal/ mol), triplet sensitizers have to be chosen accordingly to prevent oxetane formation (see Section 7.4.4), as shown in Scheme 14 for norbornene with acetophenone (E = 75 kcal/mol) and benzophenone ( t = 69 kcal/mol), respectively, as sensitizers (Arnold et al., 1965) ... 

Method B A solution of 1.2.1c (5.0 g, 41 mmol) and acetophenone (1 g) as sensitizer in acetone (200 mL) (note acetone can be replaced in this procedure by any other solvent which is light resistant and transparent > 340 nm, e.g., benzene or cyclohexane) is purged with argon for 15 min prior to irradiation in a water-cooled pyrex vessel placed in a... 

Photosensitized crosslinking of polymers has been the subject of numerous publications [l - 30], concerned mainly with poly(ethylene), poly(vinyl alcohol), various vinyl copolymers, copolymers of maleic anhydride and/or phtalic anhydride with styrene and some polymers derivated from cinnamic acid. The following compounds were used as sensitizers benzophenone, 4-chloro- and 4,4-dimethylbenzophenone [l, 3-6, 8, 9l, oC -and -derivatives of anthraquinone [3, 23] acetophenone, hydroquinone, triphenylmethane and pyridine li.] chlorobenzene and no less than trichlorinated n-paraffins [6], a complex of zink chloride with o-dia-nizidine fill potassium bichromate [l2j, anthracene fl3, 14] 2,5-methoxy-4-amino-trans-stilbene [l5], benzyl ideneacetophenone fl6-l8] -thiophenylacetophenone,... 

BenzolMfurans yielded (2 + 2)-cycloadducts (191) with dimethyl-maleic anhydride, via excitation of an initially formed charge-transfer complex, together with oxetans.218 Similar (2 + 2)-cycloadducts (192) were obtained from quinones and benzoU>] furan and some of its derivatives.143,200 Irradiation of W-acyl-l//-indoles in the presence of olefins, either with or without acetophenone as a sensitizer, produced a series of (2 + 2)-cycloadducts 193, usually as a mixture of exo- and endoisomers.219 The olefins that give a (2 + 2)-cycloadduct are either electron-rich olefms, such as ethyl vinyl ether and vinyl acetate, or... 

Ionol undergoes only trans - cis isomerization on sensitization with sensitizers of low triplet energies such as 1-acetylnaphthalene, while with sensitizers of higher triplet energies such as acetophenone, isomerization occurs in both directions [85]. This is because acetophenone can sensitize both trans and cis isomers however, 2-acetylnaphthaIene sensitizes mostly trans isomers. 

A mixture of tcirahydrofuran, diethyl maleate, and acetophenone exposed to UV-light or a few days to sunlight crude diethyl a-tetrahydrofurylsuccinale. Y 80%. F. e., also with benzophenone or acetone as sensitizers in lower yield, s. I. Rosenthal and D. Elad, Tetrahedron 23, 3193 (1967) addition of f. O-hetero-cyclics cf. J. Org. Ghem. 33, 805 (1968). 

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