Photoisomerization of Cyclic Phosphinic Esters

6-Trisubstituted X -phosphorins or X -phosphorins can be isolated unchanged even after long periods of irradiation when oxygen is excluded. Stade discovered that cyclic phosphinic acid esters 208 a-c which contain a cyclic butadiene (1.3)-moiety, photochemically rearrange smoothly to the tricyclic compounds 214 a-c. 

All analytical and spectroscopic data are in full agreement with the tricyclic structure. 

Treatment of 214 a with trifluoroacetic acid and water causes take-up of one mole H2O. The new compounds have not yet been identified. 

Hettche ) investigated irradiation of compounds of type 215a and b. He isolated the crystalline photoproducts 276a and b which are isomers of 215a and b. 

The exact structure is still under discussion and seems to be analogous to the structure of 214. 

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