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■ Intramolecular Exciplex Formation and Photochemical Synthesis of 1,2,3,4-Tetrahydroisoquinolin-3-ones and Oxindoles from N-Chloroacetyl Derivatives of Benzylamines and Anilines

Tatsuo Hamada, Yohmei Okuno, Masayuki Ohmori, Takao Nishi, and Osamu Yonemitsu*

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

Abstract

On the basis of fluorescence quenching and disappearance quantum yield measurements, the efficiency of exciplex formation and photochemical reaction of N-chloroacetyl-(3,4-dimethoxyphenyl)alkylamines (1) was clarified to be dependent on the length of alkyl chain. The apparent unreactivity of benzylamine derivatives (1a, 4) for photocyclization, therefore, is attributable to the trans form of the amide groups. Since introduction of N-alkyl groups increases the stability of the cis isomers, on irradiation N-alkylbenzylamine derivatives (7, 8, 9) gave the corresponding isoquinolin-3-ones (10, 11, 12). This photocyclization was further extended to the synthesis of oxindoles (16, 17, 18) from N-alkylaniline derivatives (13, 14, 15).