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| - Mechanism of the Cyclopropenone Decarbonylation Reaction. A Density Functional Theoryand Transient Spectroscopy Study
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| - The density functional theory analysis predicts that the thermal decarbonylation of cyclopropenones proceedsby the sequential and regioselective cleavage of both single bonds in a three-membered ring. The initialring-opening process results in the formation of a reactive zwitterionic intermediate 6, which is separatedfrom the free alkyne and carbon monoxide by a very low energy barrier. Femtosecond pump−probe transientabsorption spectroscopy experiments showed that light-induced decarbonylation is also a stepwise processbut apparently proceeds on the excited-state surface. The lifetime of the intermediate in the photodecarbonylationreaction is very short and is dependent on substitution and solvent polarity. Thus, bis-p-anisyl-substitutedspecies decays with τ = 0.6 ps, bis-α-naphthyl-substituted intermediate has a lifetime of τ = 11 ps, while thebis(2-methoxy-1-naphthyl)-substituted analogue survives for 83 ps in chloroform and for 168 ps in argon-saturated methanol. The loss of carbon monoxide from these intermediates results in the formation ofcorresponding acetylenes in an electronically ground state. The addition of triplet quenchers does not affectthe dynamics or outcome of the reaction.
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