Oxidation with Singlet Oxygen Light and Sensitizer

167 °C and 152 C, respectively. They can be isolated in about 15% each. The higher-melting compound proved to be identical with 4-hydroxy-phoq)hinic acid 81a, previously described by Mach p. 55). In cyclohexane/methanol the methyl-ester 81b, also described by, Mach is obtained. 

The analytical and spectroscopic data of the lower-melting compound are in accord with structure 82. We therefore suppose that in the first step addition of the singlet oxygen takes place at the C, position 4, and at the phosphoms of 24, leading to the endoperoxide 80. This intermediate, which we could not isolate, is then converted by hydrolysis or alcoholysis to 81a or 81b, or it rearranges to the endoxy-X -phosphinoxide 82. Analogous processes with carbon compounds have been discussed by Schuler-Elte and others The course of this photooxidation is noteworthy since it represents the first example of 1.4 addition in which a heteroatom is involved. 

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