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Ring opening of benzothiazole in the Pinner reaction: synthesis of 4-amidino-substituted 2- aminothiophenols

The study of benzothiazole derivatives is of great interest due to their important biological and biophysical properties. Recently, we have focused on different synthetic routes for heterocyclic molecules containing an amidino group and their biological evaluation. We have developed condensation methods for amidino-substituted 2- amino(thio)phenols with aldehydes, carboxylic acids, or carboxylic acid derivatives to prepare amidino-substituted 2-aryl or 2-heteroaryl benzazole compounds.1, 2 The Pinner reaction is the most commonly used method for the preparation of amidines in a two-step procedure. First, the formation of an imidate by acid-catalysed addition of an alcohol to a nitrile is required, and in the second step, nucleophilic addition of amines or ammonia to imidates produces the corresponding amidines. Here, we present the synthesis of novel 4-amidino-substituted 2-aminothiophenols from 5- cyanobenzothiazole by Pinner reaction. The opening of the benzothiazole ring in the Pinner reaction was achieved with ethylenediamine (EDA) and 1, 3- propylenediamine (PDA), while 6- amidinobenzothiazole was isolated with ammonia and subjected to reaction with EDA, producing the targeted 4-amidino-2-aminothiophenol. X-ray structural analysis confirmed the zwitterionic forms.

Pinner reaction, benzothiazole, amidines

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