Cycloaddition reactions of 5H,7H-thiazolo[3,4-c]oxazolium-1-oxides with imines

The behaviour of mesoionic 5H,7H-thiazolo [3,4-c] oxazol-1-ones (α) towards imines (2) and (3) was studied. The cycloaddition reaction affords 7-thia-2,5-diazaspiro [3,4] octan-1-one (4-7) and lH,3H-imidazo [1,5-c] thiazole (8) derivatives. The possible mechanism involved in the formation of products as well as the unusual rearrangement showed by spirocyclic β-lactams (6,7) are discussed.