SYNTHESIS OF PGB(1) ANALOGS BY RADICAL-CHAIN SUBSTITUTION-REACTION

PGB1 analogues with functionalized or sulfur atom-containing alpha-sid e chains have been synthesized in several steps from 1,3-cyclopentaned ione. Introduction of alpha- and omega-side chains into the PGB1 cyclo pentenone skeleton has been accomplished by replacement of an allylic sulfonyl group in 3-substituted 2-[(phenylsulfonyl)methyl]-2-cyclopent en-1-one by stabilized carbanions or thiolate ions and Pd(0)-catalyzed cross-coupling reaction between the vinylic iodide moiety in 2-substi tuted 3-iodo-2-cyclopenten-1-ones and a vinyltin reagent or an alkyne, respectively. The former substitution reaction with stabilized carban ions has been confirmed to proceed via a radical chain mechanism of S( RN)1 type by investigating the effects of a radical scavenger and by t he ESR studies. Further, comparison of the reduction potentials of sub strates with those of products supports a single electron transfer mec hanism.