Substituent effects on the rearrangements of cyclohexyl to cyclopentyl radicals involving avermectin-related radicals |
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Authors: | Luft Jennifer A R Winkler Tammo Kessabi Fiona M Houk K N |
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Institution: | Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA. |
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Abstract: | 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. |
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