Synthesis of vinyl sulfones and cis-vinyl diphosphonates

Abstract

We reported previously that benzenesulfonyl chloride, generally known as a sulfonylating reagent, could be used as a chlorenium source for lithiated phosphonates`` case. The extension of these results, we examined the reactivity of benzenesulfonyl fluoride with lithiated alkyl phosphonates, and found that benzenesulfonyl fluoride could be used as a direct sulfonylating reagent for alkyl phosphonates. Benzenesulfonyl fluoride acted as a sulfonylating reagent in α-position of lithiated alkyl phosphonate, but yields were varied with the kind and amount of base. The higher yield was obtained when α-substituted alkyl group was the smaller. LiHMDS showed the best result as the base of the reaction and stoichiometric amount of base reduced the yield which might be due to the proton exchange between lithiated alkyl phosphonate and produced a-sulfonyl phosphonate. Vinyl sulfones were obtained by one-pot synthesis through Horner-Emmons reaction via α-sulfonyl phosphonate in moderate yields. cis-vinyl diphosphonates could be obtained from monoethyl ester of 1-alkynylphosphonic acids, but it was very difficult and it need many steps. New pathway through monodealkylation using LiCl was focused in this paper. It is very easy and convenient.