CYCLIZATION REACTIONS OF 2,3-BIS(PHENYLSULFONYL)-1,3-BUTADIENE WITH VARIOUS CARBANIONS - A [4-SUBSTITUTED CYCLOPENTENES(1] ANIONIC ANNULATION APPROACH TO PHENYLSULFONYL)
A. Padwa et al., CYCLIZATION REACTIONS OF 2,3-BIS(PHENYLSULFONYL)-1,3-BUTADIENE WITH VARIOUS CARBANIONS - A [4-SUBSTITUTED CYCLOPENTENES(1] ANIONIC ANNULATION APPROACH TO PHENYLSULFONYL), Journal of organic chemistry, 59(3), 1994, pp. 588-596
2,3-Bis(phenylsulfonyl)-1,3-butadiene undergo es conjugate addition in
the presence of carbanions giving rise to a variety of unsaturated su
lfones. Reaction with lithium enolates proceeds via an allylic anionic
intermediate which undergoes a subsequent elimination of phenylsulfin
ate 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 carba
nions. The reaction involves a tandem addition-proton exchange-additio
n 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 t
o produce substituted allenes in high yield. Phenylsulfonyl alkenyl su
bstituted allenes were conveniently prepared by a similar protocol and
were found to serve as substrates for intramolecular [2 + 2] cycloadd
ition chemistry.