Organic Chemistry: Isoxazole and Isothiazole
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Questions and Answers

What is the characteristic of an isoxazole?

  • A four-membered ring with a carbon atom
  • A five-membered ring with an oxygen atom next to the nitrogen (correct)
  • A five-membered ring with two nitrogen atoms
  • A six-membered ring with a sulfur atom

    • What is the IUPAC name of the compound with the molecular formula C3H3NO?

  • Isothiazole
  • Ibotenic acid
  • Isoxazole (correct)
  • Furoxan

    • At what temperature does isoxazole boil?

  • 100 °C
  • 85 °C
  • 95 °C (correct)
  • 90 °C

    • What is the reaction used to synthesize isoxazole?

    <p>Reaction of 1,3-dicarbonyl compounds with hydroxylamine</p> Signup and view all the answers

    What is the role of furoxan in the human body?

    <p>A nitric oxide donor</p> Signup and view all the answers

    What is the application of isoxazole in the pharmaceutical industry?

    <p>As a drug, specifically as a COX-2 inhibitor</p> Signup and view all the answers

    What is an example of a natural product that contains an isoxazole ring?

    <p>Ibotenic acid</p> Signup and view all the answers

    What determines the formation of pyrazole or isoxazole in 1,2-azoles preparation?

    <p>The type of reagent used</p> Signup and view all the answers

    What is the product of the cyclization of β-keto esters with hydroxylamine?

    <p>3-hydroxy-isoxazoles</p> Signup and view all the answers

    What is the intermediate reactant formed in the 1,3-dipolar cycloaddition reaction to produce a simple isoxazole?

    <p>Nitrile oxide</p> Signup and view all the answers

    What is the molar mass of isothiazole?

    <p>85.13 g/mol</p> Signup and view all the answers

    What is the characteristic of the ring structure of isothiazole?

    <p>It consists of three carbon atoms, one nitrogen atom, and one sulfur atom</p> Signup and view all the answers

    What is the class of compounds that isothiazole is a member of?

    <p>Azoles</p> Signup and view all the answers

    What is the characteristic of the position of the two heteroatoms in isothiazole?

    <p>They are in adjacent positions</p> Signup and view all the answers

    What is the reactant used with propiolaldehyde to prepare isothiazole?

    <p>Sodium thiosulfate</p> Signup and view all the answers

    What is the position of the main substitution in 1,2 azole?

    <p>C-4 position</p> Signup and view all the answers

    What is the result of halogenation of pyrazole?

    <p>4-Halopyrazole</p> Signup and view all the answers

    Why is the reaction of 1,2 azole different from that of furan, pyrrole, and thiophene?

    <p>Due to the presence of the =N- group in the ring</p> Signup and view all the answers

    What is the characteristic of the reactivity of isoxazole and isothiazole?

    <p>Similar to benzene</p> Signup and view all the answers

    What is the condition required for the halogenation of isoxazole or isothiazole?

    <p>Presence of an activating group</p> Signup and view all the answers

    What is the product of the cyclo-condensation of β-chloro-α,β-unsaturated aldehydes with ammonium thiocyanate?

    <p>4,5-Disubstituted isothiazoles</p> Signup and view all the answers

    What is the product of the reaction of pyrazole with acetyl nitrate?

    <p>Nitropyrazole</p> Signup and view all the answers

    What is the position of nitration in 3-methylisoxazole?

    <p>4-position</p> Signup and view all the answers

    Which type of pyrazoles can be C-acylated directly?

    <p>N-substituted pyrazoles</p> Signup and view all the answers

    What is the product of the Vilsmeier formylation of pyrazole?

    <p>4-formylpyrazole</p> Signup and view all the answers

    What is the temperature required for the metallation of N-sulfonyl 4-bromopyrazoles?

    <p>Low temperature</p> Signup and view all the answers

    What is the position of lithiation in N-sulfonyl 4-bromopyrazoles?

    <p>5-position</p> Signup and view all the answers

    What is the reaction that occurs during the metallation of 4-Bromopyrazoles by Metal-Halogen Exchange?

    <p>Metal-halogen exchange</p> Signup and view all the answers

    What is the significance of 1,2-Azoles in natural products and pharmaceutical drugs?

    <p>They are important components</p> Signup and view all the answers

    What is the difference between the nitration of pyrazoles and isothiazoles, compared to isoxazoles?

    <p>Isoxazoles undergo nitration in very low yield</p> Signup and view all the answers

    Which of the following isoxazoles is sufficiently reactive to undergo nitration at the 4-position?

    <p>3-methylisoxazole</p> Signup and view all the answers

    What is the major difference between the nitration of pyrazoles and isothiazoles, compared to isoxazoles?

    <p>Isoxazoles undergo nitration in very low yield</p> Signup and view all the answers

    What is the product of the reaction of pyrazole with acetyl nitrate?

    <p>Nitropyrazole</p> Signup and view all the answers

    What is the significance of the low temperature in the metallation of N-sulfonyl 4-bromopyrazoles?

    <p>It prevents metal-halogen exchange</p> Signup and view all the answers

    What is the characteristic of the reactivity of pyrazoles and isothiazoles?

    <p>They undergo straightforward nitration</p> Signup and view all the answers

    What is the product of the Vilsmeier formylation of pyrazole?

    <p>4-formylpyrazole</p> Signup and view all the answers

    Which type of pyrazoles can be directly C-acylated?

    <p>N-substituted pyrazoles</p> Signup and view all the answers

    What is the position of nitration in the reaction of pyrazole with acetyl nitrate?

    <p>4-position</p> Signup and view all the answers

    What is the role of acid in the rearrangement of nitropyrazole?

    <p>It promotes the reaction</p> Signup and view all the answers

    What is the significance of 1,2-Azoles in natural products and pharmaceutical drugs?

    <p>They are commonly found</p> Signup and view all the answers

    Study Notes

    Isoxazole and Isothiazole

    • Isoxazole is an azole with an oxygen atom next to the nitrogen.
    • Isoxazole rings are found in some natural products, such as ibotenic acid.
    • Isoxazoles also form the basis for a number of drugs, including the COX-2 inhibitor valdecoxib (Bextra).
    • Furoxan is a nitric oxide donor.

    Isoxazole Properties

    • Molecular formula: C3H3NO
    • Boiling point: 95 °C

    Synthesis of Isoxazole

    • Reaction of 1,3-dicarbonyl compounds with hydroxylamine under mild acidic conditions.
    • 1,2-azoles preparation depending on the reagent used.
    • Cyclization of β-keto esters with hydroxylamine to provide 3-hydroxy- isoxazoles.
    • 1,3-Dipolar Cycloaddition Formation of a Simple Isoxazole.

    Isothiazole

    • IUPAC name: Isothiazole
    • Other names: 1,2-thiazole
    • Properties: Molecular formula: C3H3NS, Molar mass: 85.13 g/mol, Boiling point: 114 °C
    • An isothiazole is a type of organic compound containing a five-membered aromatic ring that consists of three carbon atoms, one nitrogen atom, and one sulfur atom.

    Isothiazole Synthesis

    • Isothiazole can be prepared from thioamides in the following way:
    • By reaction propiolaldehyde with sod.thiosulfate in the presence of ammonia solution.
    • By cyclo-condesation of β-chloro-α,β-unsaturated aldehydes with ammonium thiocyanate will give 4,5- disubstituted isothiazoles.

    Reaction of 1,2 Azole

    • Like 1,3 azole, due to the presence of =N- group in the ring, the 1,2 azole are much less reactive towards ES reactions than furan, pyrrole and thiophene.
    • 1,2 azole undergo ES reactions under an appropriate reaction condition.
    • The main substitution takes place at the C-4 position.
    • Pyrazole reactivity like phenol, but isoxazole & isothiazole reactivity like benzene.

    Halogenation of Isoxazoles, Pyrazoles and Isothiazoles

    • Halogenation (iodination, bromination) of pyrazole leads to the 4-halopyrazole.
    • Poor yields are obtained when attempting to halogenate isoxazole or isothiazole, but bromination can be accomplished when an activating group is present as a substituent.

    Nitration of Isoxazoles, Pyrazoles and Isothiazoles

    • Pyrazoles and isothiazoles undergo straightforward nitration:
      1. Nitropyrazole is formed in good yield by treatment of pyrazole with the mild nitrating reagent, acetyl nitrate.
      1. Nitropyrazole can be rearranged to give 4-nitropyrazole by treatment with acid at low temperature.
    • Isoxazole nitrates in very low yield, but 3-methylisoxazole is sufficiently reactive to undergo nitration at the 4-position.

    Acylation of Pyrazole

    • Only N-substituted pyrazoles can be C-acylated directly.
    • Vilsmeier formylation produces the 4-formylpyrazole in modest yield.

    Metallation of Pyrazole

    • Direct Metallation of 4-Bromopyrazoles.
    • At low temperature, N-sulfonyl 4-bromopyrazoles can be lithiated at 5-position without undergoing metal-halogen exchange.
    • Metallation of 4-Bromopyrazoles by Metal-Halogen Exchange.

    1,2-Azoles in Natural Products and Pharmaceutical Drugs

    • Isoxazole rings are found in some natural products, such as ibotenic acid.
    • Isoxazoles also form the basis for a number of drugs, including the COX-2 inhibitor valdecoxib (Bextra).
    • The ring structure of isothiazole is incorporated into larger compounds with biological activity such as the pharmaceutical drugs ziprasidone and perospirone.

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