New Synthetic Methods via Free Radicals. Free-Radical Generation via Photolytic Homolysis of Alkyl-Cobaloxime C-Co Bonds. Efficient Radical Trapping with Useful Functional Groups

Bruce Branchaud, Mark S. Meier, Mohammad N. Malekzadeh

Research output: Contribution to journalArticle

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Visible-light photolyses of primary and secondary (pyridine)alkylcobalt(III) cobaloximes, R-CoIII(dmgH)2py (2-7), generate free radicals that can be trapped in good to excellent yield (75% to nearly quantitative) with radical-trapping agents PhSSPh (to produce R-SPh), PhSeSePh (to produce R-SePh), or BrCCl3(to produce R-Br). Studies with CH2═CH(CH2)4-CoIII(dmgH)2py (6) demonstrate that a 5-hexenyl intramolecular radical-olefin cyclization can intervene between radical generation and radical trapping. At the dilute concentrations required to suppress premature radical trapping prior to 5-hexenyl cyclization, competing side reactions limit the yields of cyclized, trapped product to about 60%. Studies of n-decyl-CoIII(dmgH)2py (2) and n-pentyl-CoIII(dmgH)2py (9) photolyses in the presence of PhSSPh at various concentrations demonstrate that β-hydride elimination (4%) was the major side reaction at high concentrations (18-22 mM) and that at low concentrations (1 mM) β-hydride elimination (17-31%) and as yet uncharacterized radical-cobaloxime ligand reactions (14-26%) were the major side reactions.

Original languageEnglish (US)
Pages (from-to)212-217
Number of pages6
JournalJournal of Organic Chemistry
Issue number2
Publication statusPublished - Jan 1 1987
Externally publishedYes


ASJC Scopus subject areas

  • Organic Chemistry

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