An unusual reaction of phenacylsulfonylacetic acid methyl ester and styrylsulfonylacetic acid methyl ester with hydrazine hydrate

The reaction of phenacylsulfonylacetic acid methyl ester and styrylsulfonylacetic acid methyl ester with hydrazine hydrate gives unusual products, 1,1-dioxo-6-phenyl-1,2,4,7-tetrahydro-1λ 6 - [1,4,5]thiadiazepin-3-one and 1,1-dioxo-6-phenyl-1λ 6 -[1,4,5]thiadiazepan-3-one instead of the expected acid hydrazide.