Novel Synthesis of 1,3,4‐Thiadiazine Derivatives and Their Cycloaddition Reactions

4‐Phenyl‐3‐thiosemicarbazide 1 reacted with the α‐halocarbonyl compounds 2a, b to give the thiosemicarbazone derivatives 3a, b . The latter compounds underwent cyclization to the 1,3,4‐thiadiazine derivatives 4a, b which underwent [2 + 4] cycloaddition reactions to give the 4 H ‐thiopyran derivatives 7a, b . The chemistry of these thiopyrans was studied. Some of the fused derivatives among them compounds 20a , 20b , 21a , 21b allowed good mycelial growth and sporulation by the two fungi. This indicates that the two fungi can use the N‐containing heterocyclic ring as a nitrogen source.