Cobaloxime π-cation steric and stereoelectronic effects: The amazing effect of a single methyl group adjacent to the site of reaction

Yoshiyuki Nishikubo, Bruce P. Branchaud

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Typically, β-hydroxylalkylcobaloximes are very sensitive to acid, readily forming transient cobaloxime π-cations which can either be trapped with nucleophiles or undergo irreversible alkene loss. Surprisingly, 2,3- dihydroxy-3,7-dimethyl-6-octenyl cobaloxime (1) was found to be stable to acid treatment, including that by the strong acid camphorsulfonic acid. A comparative study of the acid stability of 2,3-dihydroxypropyl cobaloxime (8), 2,3-dihydroxylbutyl cobaloxime (9), and 2,3-dihydroxy-3-methylbutyl cobaloxime (10) was done, showing that 8 and 9 exhibit normal acid sensitivity whereas 10 is stable to acid. The inclusion of an additional methyl group in going from 9 to 10 completely turns off an otherwise very facile reaction, presumably due to severe steric effects of the py(dmgH)2Co moiety of the cobaloxime which forces the acyclic chain of 10 to adopt a conformation which is stereoelectronically nonproductive for cobaloxime π- cation formation.

Original languageEnglish (US)
Pages (from-to)10924-10927
Number of pages4
JournalJournal of the American Chemical Society
Volume121
Issue number47
DOIs
StatePublished - Dec 1 1999

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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