Poly photocycloaddition reactions

There are few reports of photocycloaddition reactions of di- and poly-ynes which involve more than one of the alkyne groups, but the production of toluene or other alkylbenzenes in the irradiation of butadiyne with propene or other terminal alkenes (equation 60) is one such process. ... 

Me and co-workers studied the intramolecular photocycloaddition of naphthyl groups in poly(l-vinylnaphthalene) (335) in cyclohexane, benzene, and dichloromethane [338], In cyclohexane, the reaction proceeds via first-order kinetics to a high conversion of 70%, whereas in dichloromethane, the reaction levels off at a very low conversion of 20%. Quenching and sensitizing experiments proved that the Mplet mechanism is predominant in cyclohexane, whereas in dichloromethane, a singlet mechanism is predominant. The addition of trifluo-roacetic acid to the illuminated sample restores the initial absorbance. 

Mizuno et al. demonstrated an intramolecular version of [2 + 2] photocycloaddition using a microreactor made of PDMS [poly(dimethoxysilane)] (channel dimensions 300 pm wide, 50 pm deep and 45 or 202 mm long) [40], Because one of the products photochemically reverts to the starting material, while the other does not, a much shorter residence time, that is, 3.4 min (batch reaction time = 3 h), inside the microchannel reduces the possibility of the reverse reaction. The difference in residence times explains the slight difference in regioselectivity between the microflow and batch systems (Scheme 4.27). 

Diastereoselective [2+2] photocycloaddition of a polymer-supported cyclic chiral enone with ethylene has been reported (Scheme 12.33) [43]. The auxiliary was derived from (-)-8-(p-methoxyphenyl) menthol (87). Protection of the secondary alcohol and demethylation were carried out to give (-)-8-(p-hydroxyphenyl)menthyl acetate (88). An alkyl linker was introduced and finally loaded to poly (ethylene glycol) grafted Wang resin. Deprotection of the alcohol functionality was followed by esterification with cyclohexen-3-one-l-carboxylic acid to provide the chiral enone 89. The photochemical reaction with ethylene was performed by irradiating with light (k > 280 nm). Trifluoroacetic acid (TFA) or aqueous hydrolysis with... 

Anthracene and its derivatives undergo a [4-F4] photocycloaddition to cyclooctane-containing dimers. This reaction can be reversed with mechanical forces, 3delding fluorescent anthracenes. Poly(vinyl alcohol) was crosslinked with anthracene dimers to give polymers that could report microcracks in a similar way as the tricinnamate-containing polymers described above (Figure 11.3). 

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