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15.5.1.1.1.2.3.3 Method 3: From 2-Arylethylamines, Carboxylic Acids, and Polyphosphoric Acid

DOI: 10.1055/sos-SD-015-01146

Álvarez, M.; Joule, J. A.Science of Synthesis, (200515688.

When a 2-arylethylamine and a carboxylic acid are heated together with polyphosphoric acid, a 3,4-dihydroisoquinoline 108 is produced (Scheme 46).[‌89‌] In this one-pot procedure, FriedelCrafts acylation of the activated aromatic ring to give 107 is the first step. This was illustrated by the reaction of 2-(3,4-dimethoxyphenyl)-N-(phenylsulfonyl)ethylamine with polyphosphoric acid and phenylacetic acid under controlled conditions, when only ring acylation occurred; closure to the 3,4-dihydroisoquinoline occurred, with loss of the N-substituent, on subsequent hydrolysis.

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