CYCLIZATION REACTIONS OF 2,3-BIS(PHENYLSULFONYL)-1,3-BUTADIENE WITH VARIOUS CARBANIONS - A [4+1] ANIONIC ANNULATION APPROACH TO PHENYLSULFONYL-SUBSTITUTED CYCLOPENTENES

2,3-Bis(phenylsulfonyl)-1,3-butadiene undergo es conjugate addition in the presence of carbanions giving rise to a variety of unsaturated sulfones. Reaction with lithium enolates proceeds via an allylic anionic intermediate which undergoes a subsequent elimination of phenylsulfinate anion to produce an allene. Generation of enolates from silyl enol ethers results in conjugate addition to the diene without subsequent elimination. Substituted cyclopentenyl sulfones are available via a [4 + 1] annulation reaction of the diene with various distabilized carbanions. The reaction involves a tandem addition-proton exchange-addition sequence. In the special case of 2,4-pentanedione, pyrans are formed, the isomeric identity of which depends upon the reaction conditions. 2-Alkylated 1,3-dicarbonyl compounds react with the activated diene to produce substituted allenes in high yield. Phenylsulfonyl alkenyl substituted allenes were conveniently prepared by a similar protocol and were found to serve as substrates for intramolecular [2 + 2] cycloaddition chemistry.