engleski

Polysulfones as "green" organic catalyst for selective alkene isomerization and hole catalyzed reactions

When dissolved in S02 methylidenecyclopentane undergoes two reactions: (l) formation of poly(1nethylidenecyclopentanesulfone), (2) isomerization into l-n1ethylcyclopent-l-ene. Mechanistical studies shows that sulfonyl radicals trapped in the polysulfone catalyze the isomerization. It occurs via the intermediary of methylidenecyclopent-2-yl radical (radical chain process), as demonstrated by deuteriun1 labelling experiments. This is not the mechanism proposed earlier.2 The rate of the polysulfone catalyzed alkeue isomerization depends strongly upon its ionization potential. This fact has been used to invent a new strategy for alcohol protection. While allyl ethers are not isomerized with polysulfones, ethers are isomerized into the corresponding enol ethers (and then hydrolyzed) on heating with polysulfone catalysts. Prenyl ethers and methylprenyl ethers are isomerized much faster. Accordingly, a polyol protet:ted as allyl, methallyl and methylprenyl ethers will be deprotected selectivly under neutral conditions by the polysulfone with the reaction sequence methylpreny > prenyl >> methallyl > allyl. Polysulfones catalyze also the cycloreversion of quadricyclane into norbomadiene. As Ar3N'+SbC16-, they are catalysts for the hole-catalyzed reactions.

polysulfone, izomerisation, SO2, radicals

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