Expected and unforeseen reactions of 2,3,3-trimethyl-1λ6- isothiazolidine-1,1,4-trione and their Spiro derivative

Herein, we present a full account of our studies with respect to the reactivity of insufficiently explored 1 lambda(6)-isothiazolidine-1,1,4-triones (so-called beta-keto-gamma-sultams). This heterocyclic system possesses two reaction centers: the EWG-activated methylene group and the carbonyl moiety which were investigated in the course of present study. 2,3,3-Trimethyl-1 lambda(6)-isothiazolidine-1,1,4-trione and 4-methyl-5 lambda(6)-thia-4-azaspiro[2.4]heptane-5,5,7-trione were chosen as representatives of the given class of substances. The former is a classical spatially uncomplicated model substance, the latter bearing a spiranic cyclopropane substituent is interesting in terms of evaluation of strain cycle effects. Indeed, the data obtained convey information about the impact of the highly strained substituent on the reaction centers of the ketosultam core. Thus, in addition to less stability of the strained spiranic ketosultam, the reactivity of its carbonyl group is suppressed whereas the activity of the methylene group is enhanced being compared with the nonspiranic substrate. Apart from the difference in the chemical character of the given fi-keto-y-sultams we faced unprecedented products (1,1-dioxo-5-[2-(triphenylphosphonio)acetyl]-2,3-dihydro-1H-1 lambda(6)-isothiazol-4-olates) formed during the course of the reaction with the Wittig reagent triphenylcarbethoxymethylenephosphorane. (C) 2019 Elsevier Ltd. All rights reserved.