Polyphosphoric Acid Induced Construction of Quinazolinone Skeleton from 1‐(3,4‐Dimethoxyphenyl)‐3‐phenylurea and Carboxylic Acids.

Abstract

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Synthesis and Contractile Activity of Substituted 1,2,3,4-Tetrahydroisoquinolines

“…We report herein an alternative of the classical methods which includes ortho -acylation of 2-phenethylamines in polyphosphoric acid and following cyclization. In our previous reports we applied this protocol for the synthesis of variety O - and N -heterocycles and alkaloids [ 43 , 44 , 45 , 46 , 47 ]. Our synthetic approach to 1- and 1,1-disubstituted 1,2,3,4-tetrahydroisoquinolines is depicted in the Scheme 1 , which shows the key steps as well as the main starting material.…”

“…Starting ketoamides of homoveratrylamine 3 were obtained by Friedel-Crafts-type acylation. The Friedel-Crafts acylation of activated benzene rings in the presence of polyphosphoric acid (PPA) is a very convenient method for direct synthesis of aromatic ketones [ 43 ], 1-substituted 3,4-dihydroisoquinolines [ 44 ], 1-substituted 3,4-dihydro-b-carbolines [ 45 ], quinazolinones [ 46 ], isochromanes [ 47 ], etc . The reaction of amides of homoveratrylamine 1 with acetic anhydride, benzoic or phenylacetic acid 2 in PPA gave the expected ketoamides 3 in high yield ( Scheme 2 , Table 1 ).…”