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Ring transformation and chalcogene elimination of 1,3,4-thia- and 1,3,4-selenadiazines in trifluoroacetic acid and trifluoroacetic anhydride
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RING TRAHSFORXATION AND CBALCOGEXE ELIKINATION OF 1,3,4-TKIAAND 1,3,4-SELENADIAZIPS IN TRIFLUOROACETIC ACID AND TRIFLUOROACETIC ANBYDRIDE
U. ROTH, W.-D. FFBIFE'ER,E. BULKA Ernst-Moritz-Arndt-UniversitatGreifswald Pachbereich Chemie, Germany
1,3,4_thiadiazines and 1,3,4_selenadiazineswill be converted to pyrazoles under special conditions by chalcogene elimination. The tendency of pyrazole formation depends very strongly on the substituen-tsin 5- and &position of the 1,3,4-thia- or 1,3,4_selenadiazine. Trifluoroacetic acid has proved to be a suitable reagent for S and Se extrusions. 5-phenyl-GH-1,3,4-thiacliazines will also undergo ring transformations in the presence of trifluoroacetic acid, but the sulfur at this site persists at the molecule as a mercapto group. Under the conditions used by us I-trifluoroacetyl-4Grifluoroacetylthio-pyrazoleswill be formed. 5,6-disubstituted 1,3,4-thiadiazines and 1,3,4-selenadiazines will be transformed to S and Se free l-trifluoroacetylpyrazoles by heating with trifluoroacetic anhydride. The structures of the I-trifluoroacetgl-4-trifluoroacetylthiopyrazoles obtained will be proved by secondary reactions.
P42
RING TRAHSFORXATION AND CBALCOGEXE ELIKINATION OF 1,3,4-TKIAAND 1,3,4-SELENADIAZIPS IN TRIFLUOROACETIC ACID AND TRIFLUOROACETIC ANBYDRIDE
U. ROTH, W.-D. FFBIFE'ER,E. BULKA Ernst-Moritz-Arndt-UniversitatGreifswald Pachbereich Chemie, Germany
1,3,4_thiadiazines and 1,3,4_selenadiazineswill be converted to pyrazoles under special conditions by chalcogene elimination. The tendency of pyrazole formation depends very strongly on the substituen-tsin 5- and &position of the 1,3,4-thia- or 1,3,4_selenadiazine. Trifluoroacetic acid has proved to be a suitable reagent for S and Se extrusions. 5-phenyl-GH-1,3,4-thiacliazines will also undergo ring transformations in the presence of trifluoroacetic acid, but the sulfur at this site persists at the molecule as a mercapto group. Under the conditions used by us I-trifluoroacetyl-4Grifluoroacetylthio-pyrazoleswill be formed. 5,6-disubstituted 1,3,4-thiadiazines and 1,3,4-selenadiazines will be transformed to S and Se free l-trifluoroacetylpyrazoles by heating with trifluoroacetic anhydride. The structures of the I-trifluoroacetgl-4-trifluoroacetylthiopyrazoles obtained will be proved by secondary reactions.
P42