Diphenylacetylene photoaddition

Oxets have similarly been proposed as intermediates in the photoaddition of carbonyl-containing compounds to alkynes.372 The addition of the esters (424) to diphenylacetylene to give the a,/(-unsaturated ketones (425) has been rationalized in this way.373 In contrast, no evidence was found for the... 

Using the temperature effect, it was proven that non-emitting exciplex intermediates were also involved in the cycloaddition. For example, in the reaction of naphthalene with diphenylacetylene, with increasing temperature both the quantum yields of photoaddition and the quenching of the naphthalene fluorescence by acetylene decrease by the same magnitude [65],... 

Photoaddition of carboxylate esters to diphenylacetylene has also been reported. For example, irradiation of methyl p-cyanobenzoate and diphenylacetylene gave in 86% overall yield the enol ether (71), presumably a result of carbonyl n,tt triplet addition to the alkyne to form the unstable oxetene, which r idly ring opens. This complements the utility of aromatic esters in the Paterno-Biichi reaction with al-kenes as discussed by Cantrell. - ... 

Amines, too, undergo photoaddition to alkynes. From diphenylacetylene and a secondary amine are obtained an enamine (which is hydrolysed during work-up) and products which arise by further reaction of stilbene, the photoreduction product of diphenylacetylene (equation 28). The products can be rationalized in terms of an initial hydrogen transfer to the excited state of the alkyne the fact that the N—H... 

Thiets have been proposed as intermediates in the corresponding photoaddition of thiones to alkynes. The stable spirothiet (421) was obtained in this way along with the 1,2-dithiole (422) on irradiation of l,3-dimethyl-2-thioparabanic acid (423) with diphenylacetylene the proposed pathway is outlined in Scheme 28. Stable thiets have also been detected in the photoaddition of xanthenethione to bis(tcrf-butylthio)ethynes. ... 

The regiospecific formation of the cyclobutene-type adduct (261) has been reported as a result of the photoaddition of diphenylacetylene to the cyanouracil (262). The cycloaddition of 1-phenylprop-l-yne to the same substrate is reported to yield the cyclobutene (263) as the main product when Pyrex-filtered irradiation is used. The irradiation of the same compounds using 254 nm light afforded the novel adduct (264), presumably formed by the secondary cyclization of the initially produced adduct (265). Indeed the sensitized irradiation of the uracil (262) and the propyne yields this adduct (265) as a Z- -mixture as well as the cyclobutene (263). Direct irradiation of (265) affords the cyclized compound... 

All the previously reported examples of photoaddition of acetylenes to benzene involve 1,2-cycloaddition and subsequent formation of cyclo-octatetraenes10 (but see ref. 43 for a discussion of the addition of perfluorobut-2-yne to benzene). The report of 1,3-cycloaddition of diphenylacetylene to the trimethyl ester of trimesic acid, is, therefore, of interest as this leads directly to the semibullvalene system.44 The reaction apparently requires 6 days, the yield of the product is low, and the adduct (28) is not isolable in the pure state. The triethyl ester and the acetylene also yield (29) via a stilbene-phenanthrene cyclization of the primary... 

It is interesting to note that unlike this rearrangement, similar bicyclo[4.2.0]octa-dienediones, obtained by photoaddition of diphenylacetylene to benzo- and naphthoquinones, upon alcoholysis, rearrange with splitting of the cyclobutene ring [530]. 

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