Exploratory studies on reactions of cobaloxime π-cations with C-nucleophiles: Irreversible alkene decomplexation versus nucleophilic capture

Jennifer L. Gage, Bruce Branchaud

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18 Citations (Scopus)

Abstract

(β-Hydroxyalkyl)- and (β-acetoxyalkyl)cobaloximes can undergo facile acid-catalyzed β-heteroatom exchange with oxygen and nitrogen nucleophiles in an SN1-like mechanism via cationic metal-alkene π-complex intermediates (cobaloxime π-cations). The reaction of cobaloxime π-cations with carbon nucleophiles has not been previously reported. The results reported in this paper demonstrate that cobaloxime π-cations are reasonably good electrophiles. They are sufficiently reactive to add to the electron-rich sp2 centers in allyltrimethylsilane and pyrrole. A major side reaction for intermolecular reactions is irreversible alkene decomplexation. An intramolecular pyrrole cyclization (22 to 23, 83% yield) significantly raised the yield for nucleophilic addition compared to that of the analogous intermolecular couplings (12b tb 13b, 32% yield and 17 to 18, 29% yield). The results of these studies provide a foundation for the design and evaluation of modified cobalt ligands with the goal of suppressing alkene decomplexation and enhancing reaction of cobaloxime π-cations with C-nucleophiles.

Original languageEnglish (US)
Pages (from-to)831-837
Number of pages7
JournalJournal of Organic Chemistry
Volume61
Issue number3
DOIs
StatePublished - Feb 9 1996
Externally publishedYes

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Nucleophiles
Alkenes
Cations
Pyrroles
Cyclization
Cobalt
Nitrogen
Carbon
Metals
cobaloxime
Oxygen
Ligands
Acids
Electrons

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

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title = "Exploratory studies on reactions of cobaloxime π-cations with C-nucleophiles: Irreversible alkene decomplexation versus nucleophilic capture",
abstract = "(β-Hydroxyalkyl)- and (β-acetoxyalkyl)cobaloximes can undergo facile acid-catalyzed β-heteroatom exchange with oxygen and nitrogen nucleophiles in an SN1-like mechanism via cationic metal-alkene π-complex intermediates (cobaloxime π-cations). The reaction of cobaloxime π-cations with carbon nucleophiles has not been previously reported. The results reported in this paper demonstrate that cobaloxime π-cations are reasonably good electrophiles. They are sufficiently reactive to add to the electron-rich sp2 centers in allyltrimethylsilane and pyrrole. A major side reaction for intermolecular reactions is irreversible alkene decomplexation. An intramolecular pyrrole cyclization (22 to 23, 83{\%} yield) significantly raised the yield for nucleophilic addition compared to that of the analogous intermolecular couplings (12b tb 13b, 32{\%} yield and 17 to 18, 29{\%} yield). The results of these studies provide a foundation for the design and evaluation of modified cobalt ligands with the goal of suppressing alkene decomplexation and enhancing reaction of cobaloxime π-cations with C-nucleophiles.",
author = "Gage, {Jennifer L.} and Bruce Branchaud",
year = "1996",
month = "2",
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doi = "10.1021/jo951319i",
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volume = "61",
pages = "831--837",
journal = "Journal of Organic Chemistry",
issn = "0022-3263",
publisher = "American Chemical Society",
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TY - JOUR

T1 - Exploratory studies on reactions of cobaloxime π-cations with C-nucleophiles

T2 - Irreversible alkene decomplexation versus nucleophilic capture

AU - Gage, Jennifer L.

AU - Branchaud, Bruce

PY - 1996/2/9

Y1 - 1996/2/9

N2 - (β-Hydroxyalkyl)- and (β-acetoxyalkyl)cobaloximes can undergo facile acid-catalyzed β-heteroatom exchange with oxygen and nitrogen nucleophiles in an SN1-like mechanism via cationic metal-alkene π-complex intermediates (cobaloxime π-cations). The reaction of cobaloxime π-cations with carbon nucleophiles has not been previously reported. The results reported in this paper demonstrate that cobaloxime π-cations are reasonably good electrophiles. They are sufficiently reactive to add to the electron-rich sp2 centers in allyltrimethylsilane and pyrrole. A major side reaction for intermolecular reactions is irreversible alkene decomplexation. An intramolecular pyrrole cyclization (22 to 23, 83% yield) significantly raised the yield for nucleophilic addition compared to that of the analogous intermolecular couplings (12b tb 13b, 32% yield and 17 to 18, 29% yield). The results of these studies provide a foundation for the design and evaluation of modified cobalt ligands with the goal of suppressing alkene decomplexation and enhancing reaction of cobaloxime π-cations with C-nucleophiles.

AB - (β-Hydroxyalkyl)- and (β-acetoxyalkyl)cobaloximes can undergo facile acid-catalyzed β-heteroatom exchange with oxygen and nitrogen nucleophiles in an SN1-like mechanism via cationic metal-alkene π-complex intermediates (cobaloxime π-cations). The reaction of cobaloxime π-cations with carbon nucleophiles has not been previously reported. The results reported in this paper demonstrate that cobaloxime π-cations are reasonably good electrophiles. They are sufficiently reactive to add to the electron-rich sp2 centers in allyltrimethylsilane and pyrrole. A major side reaction for intermolecular reactions is irreversible alkene decomplexation. An intramolecular pyrrole cyclization (22 to 23, 83% yield) significantly raised the yield for nucleophilic addition compared to that of the analogous intermolecular couplings (12b tb 13b, 32% yield and 17 to 18, 29% yield). The results of these studies provide a foundation for the design and evaluation of modified cobalt ligands with the goal of suppressing alkene decomplexation and enhancing reaction of cobaloxime π-cations with C-nucleophiles.

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