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

Yoshiyuki Nishikubo, Bruce Branchaud

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10 Citations (Scopus)

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
Externally publishedYes

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Cations
Positive ions
Acids
Nucleophiles
Alkenes
isofenphos
cobaloxime
Olefins
Conformations

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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title = "Cobaloxime π-cation steric and stereoelectronic effects: The amazing effect of a single methyl group adjacent to the site of reaction",
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.",
author = "Yoshiyuki Nishikubo and Bruce Branchaud",
year = "1999",
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T1 - Cobaloxime π-cation steric and stereoelectronic effects

T2 - The amazing effect of a single methyl group adjacent to the site of reaction

AU - Nishikubo, Yoshiyuki

AU - Branchaud, Bruce

PY - 1999/12/1

Y1 - 1999/12/1

N2 - 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.

AB - 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.

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