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Report | Regular issue | Vol 14, No. 8, 1980, pp.1151-1154
Published online, 1st January, 1970
DOI: 10.3987/R-1980-08-1151
A One-pot Isoquinoline Synthesis by Cyclodehydrogenation of Benzylaminoacetals with Chlorosulfonic Acid

Kazuko Kido and Yasuo Watanabe*

*Daiichi College of Pharmaceutical Sciences, 22-1 Tamagawa-cho, Minami-ku, Fukuoka 815-0037

Abstract

A direct preparation of the fully aromatized isoquinolines (3a-l) by the cyclodehydrogenation of benzylaminoacetals (2a-l) with chlorosulfonic acid is described.
Comparing the behavior of chlorosulfonic acid with that of sulfuric acid toward 1,2-dihydroisoquinoline, it is able to be suggested that benzylaminoacetals were cyclized first to 1,2-dihydroisoquinolines, subsequently, dehydrogenated to the fully aromatized isoquinolines by the hydride abstraction with ClSO3H. Substitution by a larger R3 group than isopropyl in the acetal ArCH(R3)NHCH2CH(OEt)2, interfered this second step, so the corresponding isoquinolines could not be obtained.