Cycloadditions to pyrrolo[1,2-c]thiazoles and pyrazolo[1,5-c]thiazoles

Sutcliffe, O B and Storr, R C and Gilchrist, T L and Rafferty, P (2000) Cycloadditions to pyrrolo[1,2-c]thiazoles and pyrazolo[1,5-c]thiazoles. Tetrahedron, 56 (51). pp. 10011-10021. ISSN 0040-4020 (https://doi.org/10.1016/S0040-4020(00)00956-X)

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Abstract

The pyrrolo[1,2-c]thiazole generated by dehydration of dimethyl 5-methyl-1H,3H-pyrrolo[1,2-c]thiazole-6,7-dicarboxylate 2-oxide acts as a thiocarbonyl ylide in its cycloaddition to electron deficient alkenes but as an azomethine ylide with electron deficient alkynes. The analogous pyrazolo[1,5-c]thiazole, generated similarly, acts as a thiocarbonyl ylide with both types of dipolarophile. This behaviour is partially explained by Frontier MO theory.