Selectivity of nitrene addition to the C[dbnd]C[sbnd]S[sbnd] fragment depends on the oxidative state of the sulfur atom as has been exemplified on various derivatives of 3,4-dihydro-2H-thiopyran under conditions of oxidative aminoaziridination. A unique structure with 2-thia-7-azabicyclo[4.1.0]heptane-2,2-dioxide core was obtained via addition of nitrene to the C[dbnd]C bond of thiopyran S,S-dioxide. For an unoxidized thiopyran, only en(phthaloyl)hydrazine resulted after cleavage of the initially formed aziridine. S-Oxide trapped the nitrene by the sulfur atom to form the sulfoximine leaving the double bond unaffected.