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1,2 – Disubstituted Aromatics: Directed Ortho Metalation

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. 1,2 – Disubstituted Aromatics: Directed Ortho Metalation Dennis Hoffart Nov. 17, 2003 59-636

  2. 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

  3. 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

  4. Mechanism

  5. Mechanism

  6. Mechanism

  7. Mechanism

  8. Mechanism

  9. Directed Metalation Groups (DMGs) Strong Moderate Weak

  10. Relative Competition of DMGs DMG1 > DMG2 a >>> b

  11. Cooperative Metalation Effects • Deprotonation at ‘a’ will be favoured over deprotonation at ‘b’. • This can be used to our advantage in designing synthetic pathways.

  12. Electrophilic Substitution of Ortho-Lithiated Aromatics E+ E+ E

  13. Successive DoM Reactions for Poly-Substituted Aromatics

  14. Successive DoM Reactions

  15. Synthetic Potential 1: Suzuki Reagents

  16. Suzuki Coupling

  17. Synthetic Potential 2: Stille Reagents

  18. Stille Coupling

  19. Further Functionalisation of Aromatics: Towards Liquid Crystals

  20. Possible Synthetic Route to a Discotic Liquid Crystal

  21. Possible Synthetic Route to a Discotic Liquid Crystal

  22. Possible Synthetic Route to a Discotic Liquid Crystal

  23. Possible Synthetic Route to a Calamitic Liquid Crystal

  24. Possible Synthetic Route to a Calamitic Liquid Crystal

  25. Possible Synthetic Route to a Calamitic Liquid Crystal

  26. Possible Synthetic Route to a Calamitic Liquid Crystal

  27. 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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