2,3-Bis(phenylsulfonyl)-1,3-butadiene: substrate for Michael donor/acceptors in a novel synthesis of fused cyclopentenes

Article abstract of DOI:10.1021/jo960064l

The reaction of 2,3-bis(phenylsulfonyl)-1,3-butadiene with the anion of various 1-substituted dimethyl 1-pentenedioates has been investigated with the purpose of devising a tandem conjugate addition - <3+2>-anionic cyclization route for the synthesis of bicyclo<3.3.0>octanes.The reaction proceeds with complete stereospecificity as was evidenced by treating (E)- and (Z)-dimethyl (3-cyano-2-propenyl)propanedioate with NaH in the presence of the bis(phenylsulfonyl)diene.In both cases only a single cycloadduct was obtained with no detectable signs of the other diastereomer.The overall process involves a series of three sequential conjugate additions followed by benzenesulfinate ion ejection.The success of the method is dependent on the electrophilicity of the proximal ?-bond.When 2-((5-oxo-2,5-dihydrofuranyl)methyl)malonic acid dimethyl ester was used, a mixture of the tricyclic adduct as well as an allene was obtained.In this case, elimination of the benzenesulfinate group from the initially formed sulfone-stabilized carbanion is competitive with the intramolecular <3+2>-annulation process.The base-induced reaction of dimethyl 2-(methoxycarbonyl)-2-pentenedioate with the bis(phenylsulfonyl)diene was also studied.Even though the position of the acceptor moiety on the ?-bond was altered, the tandem Michael reaction sequence still occurs.The course of the reaction is dependent upon the length of the tether as well as the relative placement of the electron-withdrawing group on the olefin.Reaction with γ-substituted β,γ-alkenyl derivatives leads to bicyclo<3.3.0> octenes, whereas β-substituted β,γ-alkenyl reagents provide bicyclo<3.3.0>octenes derived from a novel α-elimination reaction.