On the 6-endo selectivity in 4-penten-1-oxyl radical cyclizations

Journal of the American Chemical Society
Jens HartungGerhard Bringmann

Abstract

Regioselectivities in cyclizations of 4-substituted 4-penten-1-oxyl radicals have been investigated in a combined experimental and computational study (density functional theory). The progressive increase of the 6-endo-trig selectivity along the series of 4-substituents H < CH(3) < C(CH(3))(3) < C(6)H(5) has been interpreted to originate from a balance between strain and FMO interactions. Torsional strain, which is associated with geometrical changes upon an approach of the reacting entities, is relevant for the 6-endo-trig but not for the 5-exo-trig reactions, as seen, for instance, in selective tetrahydrofuran formation from the 4-penten-1-oxyl radical and its 4-methyl derivative. The preference for tetrahydropyran formation in cyclizations of the 4-tert-butyl and the 4-phenyl-4-penten-1-oxyl radical has been attributed to FMO interactions between the terminal carbon atom of the pi bond and the O-radical center thus favoring the 6-endo-trig reaction on the basis of lower transition state energies.

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Citations

Feb 23, 2007·Organic & Biomolecular Chemistry·Jens HartungGerhard Bringmann
Sep 12, 2014·Organic & Biomolecular Chemistry·Christine SchurJens Hartung
Oct 16, 2008·Organic Letters·Maria ZlotorzynskaGlenn M Sammis
Sep 25, 2007·The Journal of Organic Chemistry·Yi-Yun YuQing-Xiang Guo
Aug 25, 2011·Chemical Reviews·Kerry Gilmore, Igor V Alabugin
Oct 7, 2021·Chemical Reviews·Liang ChangZhiwei Zuo

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