Effects of substituents on the acid-catalyzed photoreaction of pyrimidine derivatives in p-xylene.
In order to obtain insight into the protonation of the electron adducts of pyrimidine bases (I) and the chemical behavior of the resulting radicals under an acidic condition, the photoreaction of 5-substituted 1,3-dimethyluracil (1) (substituents; p-xylyl, methyl, H, Cl, and F) was performed in p-xylene (2) in the presence of a large amount of trifluoroacetic acid (TFA). 5, 6-dihydrouracil derivatives (3), 5-p-methylbenzyluracils (4) and the 6-isomers (5) were yielded as the major products. Substitution of an electron-releasing group (p-xylyl) at C-5 raises the ratio of the products from the C6-protonated pyrimidine electron adduct (III) (3, 4) vs. the adduct from the O4-protonated isomer (II) (5), while the electron-withdrawing substituents (F > Cl) suppress the ratios.
Seki
K
K
Faculty of Pharmaceutical Sciences, Higashi-Nippon-Gakuen University, Hokkaido, Japan.
Ohkura
K
K
D000143:Acids; D002384:Catalysis; D005609:Free Radicals; D010777:Photochemistry; D011743:Pyrimidines / Q000737:chemistry*; D014269:Trifluoroacetic Acid / Q000737:chemistry; D014466:Ultraviolet Rays; D014498:Uracil / Q000031:analogs & derivatives / Q000737:chemistry; D014992:Xylenes / Q000737:chemistry*
D000143:Acids; D005609:Free Radicals; D011743:Pyrimidines; D014992:Xylenes; D014498:Uracil; C031286:4-xylene; C002451:1,3-dimethyluracil; D014269:Trifluoroacetic Acid