ELECTRON-TRANSFER REACTIONS OF 1-PHENYL-4-VINYLPYRAZOLE MEDIATED BY CERIUM(IV) AMMONIUM-NITRATE

The title compound is converted into the cyclic ethers 5 and the alcoh ol 6 upon treatment with ceric ammonium nitrate in acetone. Using meth anol as a solvent the dimethoxy derivative 9 and the nitrate ester 10 are formed. No cross cycloaddition is observed in the presence of olef ins such as ethyl vinyl ether, DMAD, or indene, however, with cyclopen tadiene as co-reagent a mixture of the exo-endo Diels-Alder adducts 14 involving the vinylic system of 1 as 2pi component is obtained. The r esults are rationalized through the intermediacy of the radical cation 1.+, generated by single electron transfer (SET) from the neutral pre cursor 1 to Ce(IV).