Exploratory and mechanistic phenylallene photochemistry: protic solvent additions, isomerizations, and reactions of photogenerated radical cations

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1986
Authors
Klett, Michael
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Altmetrics
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Chemistry
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Chemistry
Abstract

Exploratory and mechanistic photochemistry of tetraphenyl-, triphenyl-, diphenyl- and phenyl-allene are described in alcohol and hydrocarbon solvents. Phenylallene singlet excited states yield predominantly allylic methyl ethers in methanol. A high stereoselectivity and deuterium isotope effect observed for product formation strongly argue for a rate determining protonation and fast methoxide trapping in an effectively concerted manner. By contrast, phenylallenes undergo photoisomerization to cyclopropenes, indenes and propynes in hydrocarbon solvents. The common, but not exclusive, intermediacy of vinyl-carbenes in allene and cyclopropene photochemistry is strongly indicated by product studies, independent generation and deuterium isotope effects. Reactions of photogenerated radical cations of tetraphenyl- and triphenyl-allene and triphenylpropyne in methanol are described. Allene radical cations yield vinyl methyl ethers as the major products whereas the predominant pathway for the propyne radical cations is efficient deprotonation-reprotonation to allene.

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