Cyclooctene photocycloaddition reactions

The first investigations by Bryce-Smith et al. [46,67,153] on ortho photocycloaddition of an alkene to hexafluorobenzene have revealed yet another secondary reaction of ortho photocycloadducts. Irradiation of a solution of hexafluorobenzene in r/.v-cyclooctene leads to the rapid formation of seven adducts of which six were identified (i) the exo-meta adduct, (ii) a product that can be formed from the meta adduct by a thermal 1,5 H-shift but which apparently is also a primary product, (iii) an ortho adduct of which the configuration could not be established, (iv) a cyclooctatriene derivative formed by thermal ring opening of the ortho adduct, and (v) and (vi) two stereoisomers of 2,3,4,5,6,7-hexaflu-orotetracyclo[6.6.0.02,7.03,6]tetradec-4-ene. The experiment was repeated 9 years later by Sket et al. [151] with the important difference that cyclohexane was used as a diluent. The meta adduct (i) and its formal rearrangement product (ii) were not found. One ortho adduct (iii), the cyclooctatriene (iv), and the two tetracyclic products (v) and (vi) could be identified and their stereochemistry determined. From their results, the authors concluded that a second ortho adduct with the alternative stereochemistry must also have been formed. They also performed experiments in which the influence of the solvent on the course of the reaction was studied and found that the difference between their results and those of Bryce-... 

The meta photocycloaddition of cis-cyclooctene to benzene was one of the first examples of this reaction reported, and the addition of this cycloalkene to low molecular weight polystyrene and mono- and di-aromatic model-compounds has now been described. The results were analysed by mass spectroscopy, and it was reptorted that for polymers having up to six styrene units, more than one phenyl group in each chain had reacted. In the 2 1... 

Irradiation of cyclohexene in the presence of CuOTf produces the dimers 14 (49%) and 15 (8%), along with the cyclohexylcyclohexene 16 (24%) (Scheme 5)T The stereochemical outcome in Cu(I)-catalyzed dimerization of cyclohexene may be the result of cis-tram isomerization on irradiation of the initially formed Cu(I)-cyclohexene complex to the trans-cyclohexene-CuOTf complex 13, followed by a concerted ground state 2 + 2 cycloaddition of the highly strained tram-cyclohexene to another cyclohexene. Cycloheptene, on the other hand, produces the aU tra s-fused trimer 17 (Scheme 6) as the sole product. A 1 3 CuOTf-trans-cycloheptene complex has been proposed to be the precursor of this product. No dimerization reaction has been observed for cyclooctene and acychc olefins.However, mixed photocycloaddition occurs with cyclooctene if the other olefin is sufficiently reactive. Thus, cyclooctene adds to norbornene to produce the cyclobutane derivative 18 in 40% yield. GDdimerization was also observed when a mixture of cyclohexene and cycloheptene was irradiated in the presence of CuOTf to yield the adduct 19 (Scheme 6). ... 

The concentration dependence of the photocycloaddition of cis- and tra 5-cyclooctene 48 with ah-phatic aldehydes was studied in order to test the spin selectivity with respect to the cisitrans oxetane ratio and/or the endolexo selectivity relevant for the cis-photoadduct. The results depicted in Figure 59.2 indicate a moderate but stiU significant spin correlation effect in the Paterno-Biichi reaction of cyclooctene with ahphatic aldehydes. The exo-diastereoisomers tc-74 were formed with similar probability as the e do-diastereoisomers cc-74 in the singlet carbonyl manifold, whereas the triplet excited aldehydes preferred the formation of the e do-diastereoisomer and trans-fused products tt-74. 

Adam, W., Stegmann, V. R., and Weinkoetz, S., Unusual temperature-dependent diastereoselectivity in the [2-1-2]-photocycloaddition (Paterno-Biichi reaction) of benzophenone to ds- and trans-cyclooctene through conformational control, /. Am. Chem. Soc., 123, 2452, 2001. 

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