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

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.

Tverdokhlebov A. V.; Andrushko A. P.; Tolmachev A. A.; Shishkina S. V.; Shishkin O. V.
Synthesis 2008, 17, 2701-2706
DOI: 10.1055/s-2008-1067214