Sonogashira Coupling and Application in LC Synthesis

1. Sonogashira Coupling and Application in LC Synthesis 59-636 Nov.21,2003 Weijuan Jia

2. Outline • 1. Sonogashira Coupling • 1.1 Introduction to Sonogashira Coupling • 1.2 Sonogashira coupling reaction protocol • 1.3 The affection of various conditions to Sonogashira coupling • 1.4 Synthesis examples of Sonogashira coupling • 2. Application in LC Synthesis • 2.1 A calamitic LC synthesis • 2.2 A discotic LC synthesis and physical properties • 3. Summary

3. 1.1 Introduction to Sonogashira Coupling Sonogashira coupling is one of straightforward methods for the preparation of aryl alkynes and conjugated enynes. It is attractive from a synthetic point of view because mild reaction conditions and simplicity of the procedure. Sonogashira coupling is the Pd-catalyzed cross-coupling of aryl or alkenyl halides with terminal alkynes under mild conditions in the presence of cocatalyst of cuprous iodide in amine solvents.

4. 1.2 Sonogashira coupling reaction protocol

5. 1.3 The affection of various conditions to Sonogashira coupling • 1.3.1 Catalyst: • Common used catalyst: PdCl2(PPh3)2;Pd(PPh3)4;Pd(OAc)2;Pd2(dba)3;PdCl2(PhCN)2

6. 1.3 The affection of various conditions to Sonogashira coupling • 1.3.2 The reactivity order of coupling for organic halides: Vinyl iodide≈ vinyl bromide > aryl iodide> vinyl chloride>>aryl bromide • 1.3.3 Solvent: Common used amine: BuNH2, Et3N;Pr2NH; Et2NH;piperidine;pyrrolidine

7. 1.3 The affection of various conditions to Sonogashira coupling • 1.3.3 The affection of Solvent:

8. 1.4 Synthesis examples of Sonogashira coupling • 1.4.1 Synthesis of terminal acetylenes

9. 1.4 Synthesis examples of Sonogashira coupling • 1.4.2 Stereospecific synthesis

10. 1.4.2 Stereospecific synthesis

11. 2 Sonogashira Coupling Application in LC Synthesis • 2.1 A calamitic LC synthesis:

12. 2.2.1 A discotic LC Synthesis routine • (i)THF,triethylamine,0°C with compound 2 (ii)triethlamine, CuI, PdCl2(PPh)3,PPh3;(iii) K2CO3, methanol, rt

13. 2.2.2 Light properties of the discotic LC In the LC state, Schlieren texture, typical of nematic phase, was observed between the crossed polarizer.

14. 2.2.3 Thermal properties of the discotic LC

15. 2.2.4 The XRD of the discotic LC • The X-ray diffractogram of the LC taken at 140°C showed two diffuse haloes corresponding to spacing of 44-35Å and 6.3-5.0Å, attributable to the lateral and vertical disk-to-disk distances of discotic nematic phase, respectively. • The lateral disk-to-disk distance in the nematic phase(44-35Å) is much smaller than the fully extended disk diameter(46Å). This result suggests that the hexyloxy groups attached to the end of rigid arms would be interdigitated to some extent.

16. 3 Summary • Sonogashira Coupling that Pd-Cu-catalyzed cross-coupling of terminal acetylenes with sp2-C halides is a broadly useful method for conjugated acetylenes. • Select appropriate starting materials, calamitic LCs and discotic LCs can be synthesized by Sonogashira coupling.

17. Reference • Kenkichi Sonogashira, Journal of Organometallic Chemistry 653 (2002),46-49 • Bong Gi Kim et al, Tetrahedron Letters, 43 (2001) 2697-2699 • Stephan Thorand and Norbert Krause, Journal of Organic Chemistry, 1998,63, 8551-8553 • Peter J. Collings and Michael Hird, Introduction to Liquid Crystals, 1997