Photosensitive irradiation

A recent report by Kropp(85) indicates that whereas 2-norbomene undergoes radical reactions when irradiated in alcohol solution in the presence of a sensitizer, 2-phenyl-2-norbomene and related analogs undergo polar addition of methanol when irradiated directly (photosensitized irradiation led to no products) ... 

Direct or mercury photosensitized irradiation of cyclodctatetraene, (Formula 402) gives primarily acetylene, and benzene with a trace of... 

Achiral cis-1,2-diphenylcyclopropane photoisomerizes to the chiral trans isomer upon singlet- or triplet-photosensitized irradiation [64-67], It is expected that the reactant and chiral inductor immobilized in a zeolite supercage interact intimately with each other to afford more efficient photochirogenesis. Ramamurthy and coworkers reported that the enantio- and diastereodifferentiating photoisomeriza-tions of ris-2p,3p-diphenyl-la-cyclopropanecarboxylates 20 (Scheme 7) in chirally modified zeolite supercages lead to the corresponding chiral trans isomer 21 [68]. 

Dias and co-workers 48, 48a) investigated the photochemistry of the complexes MoCp2(CH3)2 48) and [MCp2(CH3)2]PF6 (M = Mo or W) 48, 48a) and found that only the cationic complexes were photosensitive. Irradiation of MoCp2(CH3)2 with pyrex-filtered light (A > 310 nm) led to no detectable reaction. However, irradiation of the complexes [MCp2(CH3)2] in the presence of added donor ligands led to photopro-... 

Photosensitized irradiation of (6) in the presence of isobutylene gave (7) as the major product, but only in 33 % yield. 

Then, treatment of this benzoannulated bicyclic lactam 5 with trimethyloxonium tetrafluoro-borate gave, in 96% yield, a crystalline imino methyl ether 6, which on direct irradiation in diethyl ether gave a benzoazabullvalene 7 in only 20% yield, together with minor products. However, photolysis of 6 with acetone sensitization afforded in 93% yield predominately benzoazabullvalene 7 (> 95%), and benzoisobullvalene 8 (< 5%). In contrast, photosensitized irradiation of bicyclobenzolactam 5 in acetone solution produced in quantitative yield a mixture of amides 9 and 10 which without purification were treated directly with trimethyloxonium tetrafluoroborate to give the benzoazabullvalene 7 and benzoisobullvalene 8 in 17 and 50% yields, respectively. 

Acetone- or acetophenone-sensitized irradiation of the enones yields the reeurranged ketones (213, 214) which are described as useful substrates for the synthesis of polyquinane natural products. The enones (215) can be converted by photosensitized irradiation into the diquinanediones (216). Irradiation of (215) in acetone gives a low yield of the tricyclic ketone (217). This ketone, while stable in the dark, is photochemically converted into the diquinanedione (215). The authors present evidence that this conversion results from fission of the cyclopropyl bond to yield the biradical (218). Demuth and Hinsken have reported the use of the oxardi-ir-methane rearrangement in the synthesis of annelated triquinanes. Thus the photo conversion of the enone (219) affords the tetracyclic ketone (220,72%). In an analogous reaction the enone (221) is converted into the isomeric ketone (222,70%). ... 

The dimer (h -C5HjNi(CO)]2 is photosensitive irradiation in pentane with SjRj (R = CFj or CjF,) in a closed system leads to h -C5HjNi(CO)SR. In an open system [h -CjHjNiSR] forms via carbonyl loss. With alkynes, e.g., PhC=CPh, irradiation of the Ni dimer yields a dinickelatetrahedrane, e.g., (h -C5H5Ni)2C2Phj. 

The dimer (h -CjH5Ni(CO)]2 is photosensitive irradiation in pentane with SjR ... 

Sonawane s group, meanwhile, disclosed the photosensitized irradiation of carene-derived VCPs to [4,5]-ring-fused cyclopentenes using toluene as a photosensitizer. A variety of VCPs... 

Photosensitized irradiation of myrcene. Which possesses a sweet balsamic-resinous odor of poor tenacity, gives a bicyclic isomer as shown in Scheme 9 (Liu and Hammond, 1967 White and Grpta, 1969). The biradical mechanism could be used to elucidate this reaction. 

The naphthalene-photosensitized irradiation of a-phellandrene (Scheme 10), which has a peppery odor, gives the dimmers (Baldwin and Nelson, 1966). The sensitized irradiation is more complex than direct irradiation since the dimer can be converted photo-chemically into the other isomers. Dimerization reaction is readily achieved when the conjugation is increased in diene system which results in more accessible energy levels (Horspool, 1976). 

The two examples discussed above show that, at least in certain cases, direct or photosensitized irradiation of solutions containing a receptor (in this case, E. coli ribosomes) and a radioactive but not especially photolabile native ligand can yield true affinity labeling results. Several of the problems that arise in the course of utilizing this approach are discussed below. 

Beukers, R. and Berends, W, Effects of ultraviolet irradiation on nucleic acid and their components, Biochem. Biophys. Acta, 41, 550,1960 49, 181,1961 Leonard, N.J., Me Credie, R.S., Logne, M.W., and Cundall, R., Synthetic spectroscopic models related to coenzymes and base pairs. XI. SoHd state ultraviolet irradiation of l,l -trimethylenebisthymine and photosensitized irradiation of 1,1 -polymethylenebisthymines, /. Am. Chem. Soc., 95, 2320,1973. 

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