Benzene, photoreaction with 1,3 dienes

In a detailed report of the photoreactions of dienes with benzene, it is shown... 

Upon UV irradiation of dicyanofpyridinio- or pyridazinio )methanide, dicyanocarbene was generated, which then reacted with benzene to give bicyclo[4.1.0]hepta-2,4-diene-7,7-dicarboni-trile (2) or with (Z)-4-methylpent-2-ene nonstereospecifically to give cis- and trans-2-iso-propyl-3-methylcyclopropane-l,l-dicarbonitrile. However, due to competing photoreactions of the ylide, the carbene-transfer reaction is not efficient and the cyclopropanes were obtained in poor yield only. ... 

The photoreactions of acyclic and cyclic alkenes with benzene depend on the ionization potential of the alkene relative to that of benzene, In general meta cycloaddition to give tricyclo[3.3.0.0 ]oct-3-ene derivatives occurs to some degree in every case and often predominates. ortho Cycloaddition tends mostly to occur with alkenes of lower ionization potential than benzene and gives bicyclo[4.2.0]octa-2,4-diene derivatives para cycloaddition gives bi-cyclo[2.2.2]octa-2,5-diene derivatives to a smaller extent. 

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