Photoaddition of ethylene

Photoaddition of acetylene, 349 Photoaddition of allene, 349 Photoaddition of dichloroethylene, 349 Photoaddition of ethylene, 348 Photoaddition of hexafluoroacetone, 345 Photoaddition of maleic anhydride, 348 Photochemical addition of ethylenes and acetylenes to steroidal enones and dienones, 343... 

High diastereofacial selectivity (84% de) was obtained in the photoaddition of ethylene to the chiral bicyclic lactam 188 with preferential approach from the expected convex side96. The photoproduct was used as the key step in the synthesis of enantiomerically... 

The use of these cyclobutano sugars has been developed for the synthesis of natural products such as grandisol [47]. Both enantiomers of this pheromone are available by 2 + 2 photoaddition of ethylene to methyl hex-2-enopyranosid-4 ulose 44. After further manipulations, ( + ) and (—) grandisol (45, 46) are synthesized following Scheme 21. 

Photoadditions of ethylene and of cyclopentene to the A" -olefinic bond in steroidal 4-en-3-ones, or 4,6-dien-3-ones (Scheme 23), is reported to give cis-4a,5a-and/or frans-4a,5/i-adducts. Configurations are assigned from consideration... 

The defined geometry of these steps has permitted the synthesis of some cycloheptane acids related to terpenoid natural products. The key reaction was the rearrangement of a suitably substituted bicy-clo[4.2.0]octane. Thus the photoaddition of ethylene to 3-methylcyclohexenone gave the ketone (42), which was converted to the alcohol (43). On treatment with HgO and HBF4 this gave the unstable hydroxy aldehyde (44), which was readily oxidized to the dicarboxylic acid (45 Scheme 17).- Ring expansion methodology was also used in an approach to the synthesis of the trichothecenes (see Scheme 18).32... 

The acetone-sensitized photoaddition of ethylene to the imidazolinone (78) yields the adduct (79). Other adducts can also be obtained by the use of different... 

Photoaddition of ethylene to the bicyclo[3,3,0]octenone (11 R = H) gave mainly the cis,anti,cis-adduct (12 R = H) which was converted into 7a-protoil-ludanol (13)." Similarly the adduct (12 R = OAc) was converted in eleven steps into compound (14) which has the carbon skeleton of the biologically active metabolite fomannosin." Illudol (16) has been obtained from the diethoxyethy-lene photoadduct (15) (Scheme 3). ... 

Reports of [ 2 + 2] cycloaddition of nitrogen containing heterocycles to alkenes are so numerous that attention can be drawn here to only a few. Recent examples include the acetone-sensitized photoaddition of 4-oxazolin-2-one (248) to ethylene to give the cis-adduct 249,203 the photocycloadditions of N-substituted imidazoles to acrylonitrile204 and of N-methyl-4-hydroxy-quinol-2-one to cyclohexene,205 and the photoaddition of pentafluoro-pyridine to ethylene to give the 1 1- and 1 2-adducts 250 and 251,... 

The prototype of the present surface photografting is the surface photoreaction of maleic anhydride(MAH) onto poly(butadiene) film(15). Although fair improvement of surface wettability was achieved, photoaddition of MAH cannot be applied to other polymers having no ethylenic double bonds. The present process is applicable to almost all polymers except for poly(tetrafluoroethy-lene) and its analogues. 

The photoaddition of the pyran-2-one (330) to ethylene to give the adduct (331) has been employed in a synthesis of grandisol,274 and the cyclobutane derivatives (332 and 333) were obtained on irradiation of the pyran-4-one (334) in 2-methylpropene.275 Photocycloadditions of dehydroacetic acid276 and 2,4-dioxo-3,3-dimethyl-2,3-dihydropyran277 have also been described, and the synthetically useful addition of 2,2,6-trimethyl-1,3-dioxolenone (335) to 2,3-dimethylbut-2-ene has been reported.278... 

Wiesner and coworkers have emphasized that while the equilibrium constants between the two diastereomeric photoexcited states and anionic intermediates respectively should be similar, there is no reason to expect that they must be numerically identical. Small differences in equilibrium constants could in some cases reverse the stereoselectivity of photocycloaddition with respect to metal reduction. The group of Cargill94 examined the validity of Wiesner s models by the photoaddition of tert-butylcyclohexenone 178 with ethylene. Irradiation at low temperature (—78 °C) afforded a mixture of three isomers 179-181, in which the photoproduct 179 is the major product while isomer 180, expected to be the major one based on the first model, was obtained as the minor isomer. This result seems to rule out the first model (it does not take into consideration the reversibility of the first bond formation in the intermolecular photoadditions), however, it is consistent with the second model (Scheme 39). 

Fig. 2. Stern-Volmer plot for the quenching of (+) cycloadduct 56, ( ) ene product 5 7, and (0) azepinone 58 formation from photoaddition of 3-ethoxy isoindolenone (50) to tetramethyl-ethylene by di-f- butyl nitroxide (DTBN)...

However, no catalytic turnover could be achieved with this capsule because the product is bound more tightly than the starting materials. Replacing the ethylene diamine end-cap on each palladium center with chiral diamines resulted in a chiral derivative of the metallocage with the electronic nature and size of the aromatic cavity being maintained. Fujita and coworkers (61) reported that such a simple modification is sufficient to effect the previously unknown [2 - - 2] cross photoaddition of fluoranthene and maleimide derivatives with enantiomeric excesses of up to 50%. 

Photoinduced reactions of ethylenes and acetylenes with five-membered heteroarenes continues to be of interest to a number of groups. Mukai and co-workers have shown that 3-aryl-2-isoxazolines (65) undergo [2 r + 2 r] photoaddition to furan and thiophene to give the novel adducts (66) and (67), respectively. The reaction provides a further example of the rarely observed... 

In some systems an alcohol gives rise to photoreduction products of the alkyne rather than to products by photoaddition of the whole alcohol molecule. The acetylenic ester 13 gives the corresponding ethylenic ester on irradiation in methanol (equation 24). Under the same conditions the ketone (CH3)3C—C=C—COMe... 

A second piece of experimental evidence to be considered at this point is the photoaddition of I to a substrate that is sensitive to the appearance of a free radical in its vicinity, that is, the cyclopropyl ethylene derivative X. This sensitivity is expressed by its fast fragmentation to a pentenyl derivative XIII that would give rise to coupling compound XIV. 

Figure 7.39. Photoaddition of formaldehyde and ethylene. Schematic representation of the carbon-oxygen attack as a function of the C,C distance Rcc and the dihedral angle q> between the formaldehyde and ethylene fragments (by permission from Palmer et al., 1994).

Tedder and co-workers [154] have examined the kinetics of the photoaddition of SFsCl to several olefins. SF5CI photolyses readily, and the kinetics suggest a moderately complex series of reactions with both chlorine atoms and SFj radicals being engaged in chain propagation, e.g. for ethylene... 

The photochemical addition of 9,10-phenanthraquinone, tetrachloro-1,2-benzoquinone (and benzil) to alkenynes (285) has been reported.167 The addition of the quinones takes place to the ethylenic bond of the alkenyne to yield alkynyl dioxins (286) and (287). The reaction is not stereospecific and a biradical intermediate is proposed to account for the loss of the stereochemical integrity of the olefin. Ishibe et a/.168 have published the results of an investigation of the photoaddition of p-benzoquinone, 1,4-naphthoquinone, 2-methyl-1,4-benzoquinone,... 

Some examples of photoadditions of carbonyl groups to ethylenic systems in solution are shown in Eqs. (64)-(66). In Reaction (65) the absence of quenching by oxygen in the vapor phase was taken to imply that this cycloaddition occurs from a singlet excited state. The stereospecificity of the reaction [Eejs. (64) and (66)] indicates that addition of excited ketone to the olefins occur s with formation of the most stable diradical (Hammond and Turro, 1963). If a triplet state were involved, cyclization would follow spin-flipping. 

Another variant of the photochemical reaction between A-hetero-cyclic o-quinones and olefins has been described by Mustafa et al.196 200 Stilbene reacts with CXLIX and with CL to give the photoproducts CLVIII and CLIX, respectively. Similar photoaddition products were obtained by the interaction of phenanthraquinone with a-stilbazole245 and with l,2-di-(4 -pyridyl)ethylene.241 Although the process has been suggested as involving diradicals, it is not clear whether the quinone or the olefin undergoes photoexcitation. 

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