Cycloaddition of N‐(2,2,2‐trichloroethylidene)‐substituted carboxamides and carbamates to 1,2,4‐thiadiazol‐5(2H)‐imines

1,2,4‐Thiadiazol‐5(2H)‐imines 4 react with N‐(2,2,2‐trichloroethylidene)‐substituted amides 5 to form [3 + 2]‐cycloaddition products 6 featured by an extra coordination of the ring sulfur atom to the terminal nitrogen atom of the side 1,3‐diazapropenylidene group, as established by X‐ray diffraction investigation. This coordination evidently plays an important role in the alkylation of compounds 6 into 8 at the oxygen atom under mild conditions. The S N bond “switch‐over” restoring the original 1,2,4‐thiadiazole ring occurs therewith. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:474–480, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10182