Cycloaddition of Azosulfones and Sulfonylimines

Ketene N,N-acetals ( I ) and ketene 0,N-acetals (2) containing hydrogen in the 2-position afford P-substitution products when treated with compounds such as isocyanates and isothiocyanates that contain an electrophilic double bond system[l~zl. However, azosulfones (3) [31 and N-sulfonylimines (7) [41 react with ketene N,N-acetals ( I ) by cycloaddition, affording the hitherto unknown 1,2-dihydro-1,2-diazetes (5) (Table 1) and 1,2-dihydroazetes ( 9 ) (Table 2), respectively. Ketene 0,N-acetals (2) and azosulfones (3), under comparable conditions, also give 1,2-dihydro-1,2-diazetes (5).