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Communication | Regular issue | Vol 12, No. 5, 1979, pp.647-652
Published online, 1st January, 1970
DOI: 10.3987/R-1979-05-0647
Mechanism of Photodetosylation of N-Tosyl-1,2,3,4-tetrahydroisoquinolines Involving Electron Transfer in the Excited State

Tatsuo Hamada, Atsushi Nishida, and Osamu Yonemitsu*

*Faculty of Pharmaceutical Sciences, Hokkaido University, Kita 12 Nishi 6, Kita-ku, Sapporo, Hokkaido 060-0812, Japan


Umezawa and Hoshino reported that on irradiation N-tosyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines (1) gave the detosylated, 3,4-dihydroisoquinolines (2) accompanied by the corresponding 1,2,3,4-tetrahydroisoquinolines (3) and aromatized isoquinolines (4), while in the presence of NaBH4 only 3 was isolated in high yield. The mechanism of this photodetosylation has now been elucidated. Thus, the reaction was initiated by the formation of exciplex or the electron transfer between the excited dimethoxybenzene group and the tosyl group followed by the formation of a biradical (7) and an N-radical (9), which readily changed to 2. Oxidation-reduction of 7 and 9 probably gave 3 and 4. In the presence of NaBH4, both 7 and 9 were reduced to 3. Experiments using deuterated compounds revealed that the routes via 7 and 9 acted almost equally in the photodetosylation.