CAN Mediated Reaction of Aryl Sulfinates with Alkenes and Alkynes: Synthesis of Vinyl Sulfones, β-Iodovinyl Sulfones and Acetylenic Sulfones

Abstract

Cerium(IV) ammonium nitrate (CAN) mediated reaction of aryl sulfinates and sodium iodide with alkenes afforded vinyl sulfones in very good yields. Alkynes underwent similar reaction to give b-iodovinyl sulfones, which on treatment with potassium carbonate afforded the corresponding acetylenic sulfones in high yields.Although cerium(IV) ammonium nitrate(CAN) has found much use in carbon-carbon bond forming reactions 1,2 the use of this reagent in carbon-heteroatom bond formation has not been studied extensively. The first report on CAN mediated carbon-heteroatom bond formation was by Trahanovsky who in 1971 observed the addition of azide to alkenes resulting in azidonitrates. 3 This reaction has been subsequently exploited in the synthesis of azidosugars which are key intermediates for aminosugars, by Lemieux et al. 4 Recently we have reported a facile CAN mediated addition of thiocyanate to styrenes 5 and indoles. 6 We have also reported the synthesis of azidocinnamates, 7 phenacylazides and phenacylthiocyanates 8 from the corresponding cinnamates and styrenes respectively. Very recently, we have observed similar CAN mediated addition of selenocyanate to styrenes. 9 In view of the success of these reactions and in the context of our recent observation of a very efficient azidoiodination, 10 we attempted the CAN mediated addition of sulfinate and iodide to alkenes with the anticipation that the reaction would lead to iodosulfones efficiently and the latter can serve as excellent precursors for vinyl sulfones. The reaction, however, proceeded to afford vinyl sulfones directly; a preliminary report of this work has been published. 11 It is noteworthy that the available methodology for vinyl sulfone synthesis mainly consists of the Horner-Emmons 12 reaction of carbonyl compounds and sulfonyl phosphoranes, the Peterson reaction, 13 and b-elimination of selenosulfones 14 or halosulfones. 15 In view of the importance of vinyl sulfones 16 as versatile intermediates in organic synthesis, the known limitations of the existing methods, and the novelty of the present work it was of interest to examine the viability of CAN mediated addition of sulfinate and iodide to alkenes as a convenient alternative to conventional vinyl sulfone syntheses. We have carried out a detailed investigation in this area and the results are presented here.As previously reported, 11 our initial experiments involved the reaction of styrene, sodium p-toluenesulfinate, and sodium iodide in anhydrous acetonitrile with a solution of CAN in the same solvent under a deoxygenated atmosphere. A facile reaction occurred, but instead of the expected b-iodo sulfone, the vinyl sulfone 2a was formed in 82% yield (Scheme 1).Scheme 1 i. p-TolSO 2 Na, NaI, CAN, anhyd CH 3 CN, argon, r.t., 45 min.Impressed by the efficiency of the reaction, we extended it to a number of styrenes. The reaction was found to be general and the results are summarized in Table 1. b-Methylstyrene also showed similar reactivity as shown in Scheme 2. Scheme 2 i. RSO 2 Na, NaI, CAN, anhyd...

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