Substituent effects on the rearrangements of cyclohexyl to cyclopentyl radicals involving avermectin-related radicals.
The rearrangement of a substituted cyclohexyl radical to a cyclopentylmethyl radical on the skeleton of avermectin B1 has been investigated using density functional (UB3LYP/6-31G(d)) and G3MP2B3 computational methods. The rearrangement is preferred when highly radical stabilizing groups are present at the 2- and 3-positions of the cyclohexyl radical. A substituent on the 3-position of the cyclohexyl radical enables ring-cleavage of the cyclohexyl radical, while a radical stabilizing substituent on the 2-position of the cyclohexyl radical stabilizes the final cyclopentylmethyl radical, enabling the overall rearrangement and reversing the normal thermodynamic preference for the hexenyl radical ring closure.
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
Jennifer A R
JA
Luft
Tammo
T
Winkler
Fiona M
FM
Kessabi
K N
KN
Houk
D003510:Cyclohexanes / Q000737:chemistry*; D003517:Cyclopentanes / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry*; D007559:Ivermectin / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D013816:Thermodynamics
D003510:Cyclohexanes; D003517:Cyclopentanes; D005609:Free Radicals; D007559:Ivermectin; C019264:avermectin