A study of atypical reaction of methyl (triphenylphosphoranylidene)-acetate with 3a-substituted bicyclic β-keto-γ-sultams

A number of 2-substituted 4–7-membered cyclic amino acid esters bearing endocyclic amino group were sequentially mesylated and cyclized via the CSIC reaction strategy to give the key precursors 3a-substituted bicyclic isothiazolidin-4-one 1,1-dioxides. Further reaction with methyl (triphenylphosphoranylidene) acetate afforded the corresponding 3a-substituted 2-[(triphenylphosphonio)acetyl]-perhydro[1,2]thiazoloazahetaryl-3-olate 1,1-dioxides. The nature of the substituent at position 3a plays a crucial role in the reaction direction with this Wittig reagent. Specifically, 3a-unsubstituted counterpart participates in the classical course of the reaction providing the expected prototropic mixture of corresponding esters.