SYNTHESIS OF FUSED 1,2,4-THIADIAZOLINES BY INTRAMOLECULAR CYCLOADDITION-ELIMINATION REACTIONS OF 4-METHYL-5-(CYANO TETHERED)IMINO-DELTA-2-1,2,3,4-THIATRIAZOLINES

A series of 5-imino-1,2,3,4-thiatriazolines, bearing a cyano tether at the imine function, were prepared and converted into fused 1,2,4-thiadiazole derivatives by thermolysis; these are 12a --> 13, 20a --> 21, 20b --> 22 and 29 --> 30 (Schemes 2-5). In one case, the precursor thiatriazole also underwent an intramolecular cycloaddition-elimination reaction to give a fused 1,2,4-thiadiazole; namely 17a --> 18. Thiatriazoline 33, with an aryl group attached directly to the imine function, thermolyzed to the benzothiazole 34.