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Paper | Special issue | Vol 84, No. 2, 2012, pp.1057-1065
Published online, 6th September, 2011
DOI: 10.3987/COM-11-S(P)83
Versatile Photorearrangement of Photocycloadducts from 5-Fluoro-1,3-dimethyluracil and Naphthalene

Kazue Ohkura,* Hiromichi Akizawa, Mikiko Kudo, Tetsuya Ishihara, Nobuhiro Oshima, and Koh-ichi Seki*

*Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido 061-0293, Japan


Direct UV-irradiation of 5-fluoro-1,3-dimethyluracil (5-FDMU) and naphthalene (1) with a 500 W high-pressure mercury lamp in a degassed Pyrex tube (λ > 300 nm) predominantly afforded benzopyrimidobarrelene derivative (2) through 1,4-addition, while irradiation in the presence of piperylene in singlet excited states preferentially afforded naphthocyclobuta- pyrimidine derivative (3) via 1,2-addition. Upon 254 nm light-irradiation of 2 gave rise to the formation of benzopyrimidosemibullvalene (4) in fair yields. The reaction pathway for the formation of 4 is reasonably explained in the terms of di-π-methane rearrangement. Adduct 3 was newly converted to the corresponding barrelene derivative (2) by long-wave-length irradiation in the presence of a triplet sensitizer.