Cyclization - Elimination Route to Cyclopentenyl Sulfones Using (Phenylsulfonyl)-1,2-propadiene

Article abstract of DOI:10.1021/jo00022a032

Treatment of (phenylsulfonyl)-1,2-propadiene (1) with bis(phenylsulfonyl)methane in the presence of sodium hydride affords 2,4,4-tris(phenylsulfonyl)-1-butene in 94percent yield.Similar rearranged products were obtained using other soft nucleophiles and related allenes.The formation of these products involves addition of benzenesulfinate anion onto allene 1.The initially formed carbanion undergoes proton transfer with bis(phenylsulfonyl)methane followed by a S_N2' reaction of the resulting anion with 2,3-bis(phenylsulfonyl)-1-propene.Supporting evidence for the proposed mechanism is provided by the observation that the reaction of dimethyl malonate with the activated allene in the presence of sodium benzenesulfinate gives mostly abnormal products.When allene 1 is allowed to react with olefins bearing an electron-withdrawing group in the presence of sodium benzenesulfinate, a substituted cyclopentenyl sulfone is formed.The reaction proceeds in a stepwise fashion by addition of the initially produced carbanion onto the activated ?-bond of the olefin followed by a 5-endo-trig cyclization and elimination of benzenesulfinate.This approach represents a mild and versatile anionic <3 + 2> route to five-membered unsaturated sulfones.