A Novel Approach to Pyrrolo[2,1-b][1,3]benzothiazines

Abstract

Alkylation of (3,4-dihydro-4-oxo-2H-1,3-benzothiazin-2-ylidene)acetic acid ethyl ester and (3,4-dihydro-4-oxo-2H-1,3-benzothiazin-2-ylidene)acetonitrile with phenacyl chlorides in the presence of potassium carbonate was shown to occur at the nitrogen atom yielding the corresponding N-phenacyl derivatives. The latter, upon treatment with DMF˙POCl₃ complex, were converted into 1-aroyl-9-oxo-9H-pyrrolo[2,1-b][1,3]benzothiazine-3-carboxylic acid ethyl esters and -3-carbonitriles. The structure of the obtained pyrrolobenzothiazine derivatives was confirmed unambiguously by X-ray crystallographic study. Reaction of these pyrrolo[2,1-b][1,3]benzothiazines with aliphatic primary amines resulted in the thiazine ring cleavage and formation of 2-[(5-aroyl-3-cyano(or ethoxycarbonyl)-1H-pyrrol-2-yl)thio]-N-alkylbenzamides.

Key words

alkylations - cleavage - cyclizations - heterocycles - pyrroles

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Full crystallographic parameters have been deposited at Cambridge Crystallographic Data Center under reference number CCDC 681250. Copies of the data may be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: [phone] or e-mail: [e-mail]).