the Role of Silicon in Substitution of Furan

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the Role of Silicon in Substitution of Furan

• By Andy Arifin Tjeng

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Outline

• Introduction
• Role of Silicon in Furan substitution
• Conclusion

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Carbon-Silicon bond

• Bond Length 1.89 Å
• Bond strength 300 kJ/mol
• Partly polarized bond
• Carbon-Silicon bonds does not occurs naturally.
• No natural product containing silicon has been
  found.

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ß-Effects

• Stabilization of carbocation at ß-position.
• Possibility from donation of C-Si bond to empty p
  orbital.
• Maximum stabilization at 90 angle from cations
• Other possibiltiy hyperconjugation

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a-Effects

• Stabilization of carbanion at a-position.
• Possible reason backbonding interaction,
  similar to Si-O bond (full p orbital interaction
  with empty d orbital from Si)

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Arylsilanes

• Synthesis Grignard reaction
• Cycloaddition reaction
• Removal Fluoride ion

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ipso-substitution

• Ipso-Substitution with Electrophiles
• Reason stabilization from ß-effects

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Substitution of Furan

• Attack of electrophiles are C-2 or C-5 site
• Substitution at C-3 results in regioisomers of
  C-2 and C-5 position.
• Silyl group in substitution of Pyrroles

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ipso-substitution of Furan

• First reported in 1948 by Benkeser and Currie

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3,4-substituted Furan
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3,4-substituted Furan
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2,4-Substituted Furan
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Synthesis of 3,4-Furan
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3,4-substituted Furan
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2,3-substituted benzene
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2,3,4-substituted Furan
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2,3,5-substituted furan
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Conclusion

• The properties of Silyl group bulkiness, ease of
  attachment and removal, migration tendency and
  ipso-substitution has been used to control
  substitution in furan ring.

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References

• Keay, B. A. Chem. Soc. Rev., 1999, 28, 209-215