Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions

Per-Ola Norrby, Mary M. Mader, Maxime Vitale, Guillaume Prestat, Giovanni Poli

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Abstract

Computational methods were applied to the Pd-catalyzed intramolecular allylations of resonance-stabilized carbanions obtained from amide and ketone substrates, with the aim of rationalizing the endo- vs. exo-selectivity in the cyclizations. In addition, ester substrates were prepared and subjected to the Pd-catalyzed cyclization conditions, and were found to form lactones via exo attack. DFT calculations using BP86/LACVP*+level of theory with a CH2Cl2 solvation correction reproduce the relative transition state energies. The preference for exo-cyclization of the nitrogen-containing starting material appears to result from the preference for near-planarity of the amide N. Both the oxygen- and nitrogen tethers are too short to allow efficient endo-cyclization, whereas the carbon-tether is long enough to allow favorable endo-cyclization. The carbon tether also disfavors the exo-cyclization transition states slightly from eclipsing interaction, leading to almost isoenergetic exo- and endo-transition states, and thus accounting for the experimentally observed mixture of 5- and 7-membered ring products.
Original languageEnglish
JournalOrganometallics
Volume22
Issue number9
Pages (from-to)1849-1855
ISSN0276-7333
Publication statusPublished - 2003

Cite this

Norrby, P-O., Mader, M. M., Vitale, M., Prestat, G., & Poli, G. (2003). Rationalizing Ring-Size Selectivity in Intramolecular Pd-Catalyzed Allylations of Resonance-Stabilized Carbanions. Organometallics, 22(9), 1849-1855.