GENERATION OF BIRADICALOIDS AND BIRADICALS BY PHOTOINDUCED ELECTRON TRANSFER

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Photoinduced electron transfer reaction of methoxy-substituted benzocyclobutanes results in their electrocycloreversion to generate omicron-xylylenes, which can be trapped with dienophiles such as tetracyanoethylene to produce cycloadducts. It is found that stereochemistry for the ring opening is non-stereospecific. Accordingly, photoinduced electron transfer presents a new and remarkable method for facile disrotatory ring opening of ring fused benzocyclobutanes. These derivatives do not undergo thermal ring opening because its symmetry allowed conrotaory process is sterically constrained.Photoinduced electron transfer reactions of 1,2-bis (1-phenylvinyl) benzene and 1,2-bis (1-phenylvinyl) furan have been investigated. These compounds undergo electron-transfer induced electrocyclization to generate an omicron-xylylene derivative and dimethylenefuran derivative When photolyzed with an electron-accepting sensitizer such as 9,10-dicyanoanthracene (DCA).Biradicaloid and biradical can be observed spectroscopically and trapped by dienophiles. It is clear that photoinduced electron transfer from 1,2-bis (1-phenylvinyl) benzene or 1,2-bis (1-phenylvinyl) furan to the singlet excited DCA is an important initial step. Substrate cation radicals in photogenerated ion radical pairs, [Substrate^<・+>, DCA^<・->] may undergo electrocyclization and omicron-xylylene and dimethylenefuran derivative can be produced by back ET possibly within the resulting ion pairs. The [4+2] cycloaddition of the resulting omicron-xylylene and dimethylenefuran derivative with added dienophiles leads to adducts.