Spirocyclic betaines or 2-amino-Δ2-1,3,4-thiadiazoline-5-acetic acid and their rearrangement in acetic anhydride
Reaction of N-(1-pyrrolidinyl)-, N-(1-piperidinyl)-, N-(4-morpholinyl)-, and N-(1-hexahydroazepinyl)-thioureas with propiolic acid gives hetero-N-spiro-4′-(2′-amino-Δ2-1′,3′,4′-thiadizolin-4′-io-5′-acetates), which rearrange in acetic anhydride to 2-(N-heteryl)imino-2,3-dihydro-4H-1,3-thiazin-4-ones.