A Novel "Double-Coupling" Strategy for Iterative Oligothiophene Synthesis Using Orthogonal Si/Ge Protection

Organic Letters

Volumn 4, Issue 11, 2002, Pages 1899-1902

  Spivey, Alan C ^a   Turner, David J ^a   Turner, Michael L ^a   Yeates, Stephen ^b  

^a UNIVERSITY OF SHEFFIELD   (United Kingdom)

^b Avecia Biologics Limited   (United Kingdom)

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ARTICLE;

EID: 0013017424     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol025879x     Document Type: Article

References (26)

1. Reviews: (a) Katz, H. E.; Bao Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34, 359-369. (b) Dimitrakopoulos, C. D.; Mascaro, D. J. IBM J. Res. Dev. 2001, 45, 11-27.
2. Reviews: (a) Katz, H. E.; Bao Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34, 359-369. (b) Dimitrakopoulos, C. D.; Mascaro, D. J. IBM J. Res. Dev. 2001, 45, 11-27.
3. (a) Bao, Z.; Dodabalpur, A.; Lovinger, A. Appl. Phys. Lett. 1996, 69, 4108-4110.
4. (b) Bao, Z.; Lovinger, A. J. Chem. Mater. 1999, 11, 2607-2612.
5. (c) Sirringhaus, H.; Tessler, N.; Friend, R. H. Science 1998, 280, 1741-1744.
6. Bäuerle, P. In Handbook of Oligo-Polythiophenes; Fichou, D., Ed.; Wiley-VCH: Weinheim, 1999; 89-181.
7. (a) Malenfrant, P. R. L.; Fréchet, J. M. J. Chem. Commun. 1998, 2657-2658.
8. (b) Huang, H.; Tour, J. M. J. Org. Chem. 1999, 64, 8898-8906.
9. (c) Briehn, C. A.; Kirschbaum, T.; Bäuerle, P. J. Org. Chem. 2000, 65, 352-359.
10. (d) Kirschbaum, T.; Briehn, C. A.; Bäuerle, P. J. Chem. Soc., Perkin Trans. 1 2000, 1211-1216.
11. (e) Kirschbaum, T.; Bäuerle, P. Synth. Mer. 2001, 119, 127-128.
12. (f) Briehn, C. A.; Schiedel, M.-S.; Bonsen, E. M.; Schuhmann, W.; Bäuerle, P. Angew. Chem., Int. Ed. 2001, 40, 4680-4683.
13. The term "double-coupling" is used in the context of solid-phase peptide synthesis for the process whereby a coupling protocol is repeated to drive up the yield of a "difficult" peptide coupling step. Our use of the term is by analogy with this usage. See: Dettin, M.; Pegoraro, S.; Rovero, P.; Bicciato, S.; Bagno, A.; Di Bello, C. J. Pept. Res. 1997, 49, 103-111.
14. (a) Spivey, A. C.; Diaper, C. M.; Rudge, A. J. Chem. Commun. 1999, 835-836.
15. (b) Spivey, A. C.; Diaper, C. M.; Adams, H.; Rudge, A. J. Org. Chem. 2000, 65, 5253-5263.
16. The term "orthogonal" is used in the context of peptide synthesis to refer to protecting groups (or families thereof) that can be deprotected in the presence of each other. Our use of the term is by analogy with this usage. See: Barany, G.; Merrifield, R. B. J. Am. Chem. Soc. 1977, 99, 7363-7365.
17. Li; W.; Maddux, T.; Yu, L. Macromolecules 1996, 29, 7329-7334.
18. The trimethylgermyl precursor to chlorogermane 1 (see Supporting Information) is commercially available from AFChemPharm Ltd. See: http://www.afchempharm.co.uk.
19. Germyl-vs silylalkynes also display orthogonal stability towards nucleophiles; see: Vasella, A.; Cai, C. Helv. Chim. Acta 1996, 79, 255-268 and references therein.
20. Tour, J. M.; Wu, R. Macromolecules 1992, 25, 1901-1907.
21. Eaborn, C. J. Organomet. Chem. 1975, 100, 43-57.
22. See, e.g., ref 4c and references therein.
23. Boronic ester 8 was prepared by lithiation/transmetalation of thiophene 3 with 2,6-(4-isopropyliden-cyclopentadithiophenyl)-4,4,5,5-tetramethyl-(1,3,2) dioxadiborolane in 52% yield (see Supporting Information). The corresponding boronic acid was unstable in our hands.
24. We have not rigorously characterized salt 9, and its structure must therefore be regarded as tentative. For an example of the use of a furan-derived trimethylborate salt in "base-free" cross-coupling, see: Cristofoli, W. A.; Keay, B. A. Tetrahedron Lett. 1991, 32, 5881-5884.
25. 2, eluting with 9:1 petrol (bp 40-60 °C)/EtOAc. This process removes the "baseline" Pd and excess triethylborate salt 9.
26. This feature of germanium-based linker systems has not previously been exploited. Attention has focused on the opportunities that arylgermane-based linkers provide relative to their arylsilane counterparts for more facile electrophilic ipso-demetalative cleavage and for employing a wider range of electrophiles for diversity enhancement. See ref 6 and Plunkett M. J.; Ellman, J. A. J. Org. Chem. 1997, 62, 2885-2893.