Vyacheslav Diev - Cyclopropenes in the 1,3-Dipolar Cycloaddition with Carbonyl Ylides: an Experimental and Theoretical Evidence for the Enhancement of sigma-Withdrawal in 3-Substituted-Cyclopropenes

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      Publication Details (including relevant citation   information):

      J.   Org. Chem.   2006, 71, 4066-4077


      The carbonyl ylide dipoles generated by the dirhodium   tetra-acetate-catalyzed decomposition of diazocarbonyl precursors   1, 5, and 8  cycloadd to 3-substituted 1,2-diphenylcyclopropenes   3ae and 3,3-disubstituted   cyclopropenes 13, 14,   19, and 20 to give polycyclic   compounds with 8-oxatricyclo[,4]octane and   9-oxatricyclo[,4]nonane frameworks. Generally,   reactions proceed stereoselectively to give adducts of exo   stereochemistry with the approach of the carbonyl ylide dipoles   from the less-hindered face of cyclopropenes. The electronic   properties of the substituent at the C3 position of   cyclopropenes play an important role in governing the reactivity   of cyclopropenes:  when the C3 position is substituted   by electron-acceptors such as the methoxycarbonyl or cyano   groups, the yields of adducts are decreased significantly or no   adducts can be detected at all. Relative reactivities of   cyclopropenes were quantified by competition experiments to give   the best correlation with σF-Taft constants. Both   measured photoelectron spectra and ground-state calculations of a   series of 1,2-diphenylcyclopropenes indicate considerable   lowering of cyclopropene π-**** energies by substitution with an   acceptor group. Such changes in electronic structures of   cyclopropenes may cause the inversion of frontier molecular   orbital (FMO) interactions from   ****cyclopropene−LUMOylide to   LUMOcyclopropene−****ylide type. In terms   of philicity, nucleophilic properties of acceptor-substituted   cyclopropenes are diminished to such an extent that these species   are no longer good nucleophiles in the reaction with carbonyl   ylides, and neither are they good electrophiles, being   unreactive. This was shown by the B3LYP calculations of addends.

      Address (URL): http://pubs.acs.org/doi/abs/10.1021/jo0600656