1,2 – Disubstituted Aromatics:
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1,2 – Disubstituted Aromatics: Directed Ortho Metalation. Dennis Hoffart. Nov. 17, 2003 59-636. Outline. Mechanism of DoM Reaction Evidence for Proposed Mechanism Properties and Hierarchy of DMGs Relative Competition of DMGs

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1,2 – Disubstituted Aromatics: Directed Ortho Metalation

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1,2 – Disubstituted Aromatics:

Directed Ortho Metalation

Dennis Hoffart

Nov. 17, 2003

59-636


Outline

  • Mechanism of DoM Reaction

  • Evidence for Proposed Mechanism

  • Properties and Hierarchy of DMGs

  • Relative Competition of DMGs

  • Cooperative Metalation of meta-Substituted Aromatics

  • Electrophilic substitution of Lithiated Aromatics


Outline

  • Successive DoM as a Route to Poly-Substituted Aromatics

  • Synthetic Consequences of ortho-Lithiation

    • Synthesis of Boronic Acids: Reagents for Suzuki Coupling

    • Synthesis of Stannyl Compounds: Reagents for Stille Coupling

  • Further Functionalisation of DoM Products: Towards Liquid Crystals

  • Potential Synthesis of Liquid Crystals


Mechanism


Mechanism


Mechanism


Mechanism


Mechanism


Directed Metalation Groups (DMGs)

Strong

Moderate

Weak


Relative Competition of DMGs

DMG1 > DMG2

a >>> b


Cooperative Metalation Effects

  • Deprotonation at ‘a’ will be favoured over deprotonation at ‘b’.

  • This can be used to our advantage in designing synthetic pathways.


Electrophilic Substitution of Ortho-Lithiated Aromatics

E+

E+

E


Successive DoM Reactions for Poly-Substituted Aromatics


Successive DoM Reactions


Synthetic Potential 1: Suzuki Reagents


Suzuki Coupling


Synthetic Potential 2: Stille Reagents


Stille Coupling


Further Functionalisation of Aromatics: Towards Liquid Crystals


Possible Synthetic Route to a Discotic Liquid Crystal


Possible Synthetic Route to a Discotic Liquid Crystal


Possible Synthetic Route to a Discotic Liquid Crystal


Possible Synthetic Route to a Calamitic Liquid Crystal


Possible Synthetic Route to a Calamitic Liquid Crystal


Possible Synthetic Route to a Calamitic Liquid Crystal


Possible Synthetic Route to a Calamitic Liquid Crystal


Conclusions and References

  • DoM reaction is an excellent strategy for the (poly-)substitution of aromatic systems.

  • Straight forward mechanism with a wide scope.

  • Excellent method for the generation of coupling precursors, such as boronic acids and stannyl reagents.

Snieckus, V. Chem. Rev.1990, 90, 879.

Queguiner, G.; Marsais, F.; Snieckus, V.; Epsztajn, J. Adv. Heterocycl. Chem. 1991, 52, 187.


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