Ring closure reactions of β-nitroso-, β-acyl-, and β-thiocarbamoyl-α,β-unsaturated sulfilimines. Synthesis of [1,2,5]oxadiazolo[3,4-d]-, isoxazolo[3,4-d]-, and isothiazolo[3,4-d]pyrimidine derivatives from uracils

1,3-Dialkyl-6-chlorouracils were treated with S,S-diphenylsulfilimine to give N-(1,3-dialkyluracil-6-yl)-S,S-diphenylsulfilimines. The uracilylsulfilimines were nitrosated, acylated, or thiocarbamoylated to give N-(5-nitroso-, 5-acyl-, or 5-thiocarbamoyluracil-6-yl)sulfilimines, respectively. These conjugated sulfilimines were cyclized by thermolysis or photolysis to [1,2,5]oxadiazolo[3,4-d], isoxazolo[3,4-d], or isothiazolo[3,4-d]pyrimidine derivatives.