[Studies on antiviral agents. I. Antiviral activity of pyridobenzoazoles]

Approach to Pyrido[2,1-b][1,3]benzothiazol-1-ones via In Situ Generation of Acyl(1,3-benzothiazol-2-yl)ketenes by Thermolysis of Pyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones

Acyl(imidoyl)ketenes are highly reactive heterocumulenes that enable diversity-oriented synthesis of various drug-like heterocycles. Such ketenes, bearing heterocyclic substituents, afford angularly fused pyridin-2(1H)-ones in their [4+2]-cyclodimerization reactions. We have utilized this property for the development of a new synthetic approach to pharmaceutically interesting pyrido[2,1-b][1,3]benzothiazol-1-ones via the [4+2]-cyclodimerization of acyl(1,3-benzothiazol-2-yl)ketenes generated in situ. The thermal behaviors of 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones and 3-benzoylpyrrolo[2,1-b][1,3]benzothiazole-1,2-dione (two new types of [e]-fused 1H-pyrrole-2,3-diones reported by us recently) have been studied by thermal analysis and HPLC to elucidate their capability to be a source of acyl(1,3-benzothiazol-2-yl)ketenes. As a result, we have found that only 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones are suitable for this. The experimental results are supplemented with computational studies that demonstrate that thermolysis of 3-aroylpyrrolo[2,1-c][1,4]benzothiazine-1,2,4-triones proceeds through an unprecedented cascade of two thermal decarbonylations. Based on these studies, we discovered a novel mode of thermal transformation of [e]-fused 1H-pyrrole-2,3-diones and developed a new pot, atom, and step economic synthetic approach to pyrido[2,1-b][1,3]benzothiazol-1-ones. The synthesized drug-like pyrido[2,1-b][1,3]benzothiazol-1-ones are of interest to pharmaceutics, since their close analogs show significant antiviral activity.

Orthoamide und Iminiumsalze, CVIa. Kondensationsreaktionen von Orthoamiden der Alkincarbonsäuren mit CH-aciden Methylheterocyclen

Orthoamides of alkynecarboxylic acids 10 react with 2-thienyl-acetonitrile under condensation to give ketene aminals. In the reaction of orthoamides 10 with 2-benzimidazolyl-acetonitrile tricyclo[1,2-a]benzimidazol-4-carbonitriles are formed under similar conditions. From 2-methyl-1,3-disubstituted-triazin-2,4-diones and orthoamides 10 the ketene aminals result at room temperature.

Carbanion induced synthesis of pyrido[2,1-b] benzothiazoles through ring transformation reactions

3-Aryl-1-[(E)-cyanomethylidene]-1H-pyrido[2,1-b]benzothiazole-4-carbonitriles (3) and the polysubstituted pyrido[2,1-b]benzothiazoles (8, 9) have been prepared from the reaction of 2-benzothiazoleacetonitrile (2) with 6-aryl-4-methylsulfanyl-2-oxo-2H-pyran-3-carbonitrile (1) and the ketenedithioacetals (6, 7), respectively.