Protonation of the electron adducts of pyrimidine derivatives

Article abstract of DOI:10.1248/cpb.43.1024

Photolyses of 5-substituted 1,3-dimethyluracils (1a-e: a, R = F; b, R = Cl; c, R = H; d, R = CH₃; e, R = p-xylyl) in p-xylene in the presence of trifluoroacetic acid (TFA) afforded 5,6-dihydro-1,3-dimethyl-6-p-methylbenzyluracils (3a-d), 5,6-dihydro-1,3-dimethyl-5-p-methylbenzyluracils (4a-e), and 5,6-dihydro-1,3-dimethyluracils (5a-e) in varying ratios. It is suggested that the 6-isomers (3) are derived from the O(4)-protonated electron adducts of 1, while 4 and 5 are the products from the C(6)-protonated electron adducts. The ratio of (4 + 5) vs. 3 depends on the ionization potentials of the O(4)-protonated intermediates. The formation of 4 + 5 increases with increasing concentration of TFA.

Full text of DOI:10.1248/cpb.43.1024

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