Irradiation cyclooctadiene

The irradiation of 1,5-cyclooctadienes can lead to either linear 437) (4.34) or crossed 438) (4.35) adducts as demonstrated in the examples below. 

Another unique example was observed for the recently isolated marine natural product, alteramide A (209), isolated from a symbiotic bacteria (Alteromonas sp.) found on the sponge Halichondria okaclai96. It was found that the tetraene core of this compound underwent intramolecular [4 + 4]-photocycloaddition upon exposure to sunlight (equation 9). Deliberate irradiation led to a quantitative conversion to cyclooctadiene 210. 

Ketone rac-13 was transformed into the corresponding silylenolether and by Pd(II)-mediated Saegusa oxidation [14] into a, -unsaturated ketone rac-14. By alkylative enone transposition comprising methyl lithium addition and pyridinium chlorochromate (PCC) oxidation [15], rac-14 was finally converted into the racemic photo cycloaddition precursor rac-6. In conclusion, the bicyclic irradiation precursor rac-6 was synthesized in a straightforward manner from simple 1,5-cyclooctadiene (11) in nine steps and with an overall yield of 21%. 

With electron-rich olefins, the rate of addition to a second thione is faster than that of the combination of the intermediate diradical to thietane. By substituting these olefins, however, with groups that provide steric hindrance, the reaction of the diradical with another thione molecule can be inhibited. Irradiation of thiobenzophenone and 1,3-cyclooctadiene, propenylbenzene. 

Irradiation of 109 in the presence of 110 results in the [4+4] cycloaddition to give the cyclooctadienes 111 and 112 with the side product 113 product formation is highly dependent on the reaction stoichiometry (Equation 58 Table 9) <1996TL1141, 2001TL5155>. 

The ( ),( )-isomer 35 331 of 1,5-cyclooctadiene was reported to be formed (1.5% yield) when a solid residue, obtained from an UV irradiation product of bis[chloro-((Z),(Z)-l,5-cyclooctadiene)Copper(I)], was decomposed with NaCN solution. It has been claimed that the same compound 35 was also formed (2.4% yield) by the double Hofmann elimination of (Z)- or ( )-l,5-bis-(dimethylamino)cyclooctane dimetho-... 

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

Irradiation of 1,3-cyclooctadiene (Formula 378) which could, in principle, give acyclic products gives the bicyclic valence tautomer, (Formula 379) (167-169). 1,3,5-Cyclooctatriene gives Formula 381 among other products (170). 

Ultraviolet photolysis of Os3(CO)12 in the presence of dienes such as butadiene (291), cyclooctatetraene (291), or cyclooctadienes (412) leads to mononuclear species of type Os(CO)3 (diene). Irradiation of methylacrylate... 

Cyclic conjugated earbanions have also been studied and rarely found to give an electron transfer photochemistry in the absence of an electron acceptor. One example was however found in the case of cyclooctadienyl carbanion irradiated in THF and in the presence of chlorobenzene or rrans-stilbene. Dimeric radical products and phenylated cyclooctadiene were formed in the first case while trans-cis isomerization of stilbene was observed in the second one... 

Interestingly, irradiation of 20 with a low-pressure mercury lamp in the presence of 1,3-cyclooctadiene yields 9-phenyl-9-trimethylsilyl-9-silabi-cyclo[6.1.0]nona-2-ene as the sole silylene insertion product. This compound readily isomerizes to give two isomers of 9-phenyl-9-trimethylsilyl-9-silabicyclo[4.2.1]nona-7-ene (30a and 30b) when irradiated with a high-pressure mercury lamp. On the other hand, similar photolysis of 20 using a high-pressure mercury lamp affords 9-silabicyclo[4.2. l]nona-7-enes, 30a and 30b, as the sole volatile products as shown in Scheme 8 (54). 

However, when a 1 1 mixture of cyclohexadiene and cyclooctadiene was irradiated in the presence of 2 p2Ph2, a catalytic hydrogen transfer reaction occurred to give benzene and cyclooctene [Eq. (32)]. 

Irradiation of the title complex in the presence of excess cyclooctadiene (COD) has been reported to yield Pt(cod)2 but no further details have been given 154). TMs reaction may proceed via photoinduced /3-hydride elimination as in Eq. (122). 

The dimerization of vinyl acetylene presented by H. Hopf requires the presence of benzophenone as triplet sensitizer. Either by irradiation in sealed glass tubes or by using a low temperature immersion well apparatus 1,2-diethynylcyclobutane is formed in good yields. Note that the analogous dimerization of 1,3-butadiene yields similar products beside vinylcyclohexane and cyclooctadiene depending on the triplet energy of the sensitizer. 

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