1.1- Diphenylethylene, photocycloaddition

It is conceivable that a carbonyl compound with an n,n triplet energy lower than that of benzophenone could yield the photocycloaddition product in some of these cases. A reaction which may illustrate this point is the photocycloaddition of ethyl glyoxylate to styrene and 1,1-diphenylethylene.66 Unfortunately, the triplet energy of ethyl glyoxalate has not been measured however, there is adequate reason to believe it is lower than that of benzophenone (see Table VI). 

Aoyama et al. in relation to their studies on photochemical synthesis of (3-lactams [91] reported the synthesis of 4-spirocyclopropylazetidin-2-one [92] via photocycloaddition of 4-thioxoazetidin-2-one to alkenes followed by subsequent desulfurization. A solution of 1-isopropyl-3-phenyl-4-thioxoazetidin-2-one 70 and 1,1-diphenylethylene in benzene on irradiation with a high pressure mercury lamp afforded a [2 + 2] adduct 72 (R = Ph), in 67% yield which, on desulfurization with Raney-nickel [93] in anhydrous ethanol gave two isomeric... 

Caldwell, R.A., Hrncir, D.C., Munoz, T. Jr, and Unett, D.J. (1996) Photocycloaddition of 4,4-dimethylcyclohexenone to 1,1-diphenylethylene. Evidence for a triplet exciplex intermediate. Journal of the American Chemical Society, 118, 8741-8742. 

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