Z. Wang et al. / Tetrahedron Letters 46 (2005) 5313–5316
5315
The only by-products isolated from the cross-coupling
References and notes
reactions were 2,3-difluoro-1,3-dienes 8 resulting from
the oxidative homocoupling of (a-fluoro)vinyl TTMS-
germanes.15 Surprisingly, reductive homocoupling of
halide components has not been observed, although
they were often formed during attempted cross-cou-
plings with organogermanes (12–60%),2b including vinyl
TTMS-germanes (5–20%).3b It is also noteworthy that
no addition of extra ligands2e such as PhAr3,2a AsPh3,2b
(2-furyl)3P,2b,c or But2P(biphenyl)2b,2d was required for
the coupling reaction to occur with TTMS-germanes
when Pd(Ph3)4 was used as Pd source. Moreover,
coupling of 3a with iodobenzene in the presence of
Pd2(dba)3 afforded 4a(Z) in 70% yield in addition to
dimer 8a (20%). Attempted couplings of germanes
3a–c with iodobenzene and bromobenzene under oxida-
tive anhydrous conditions (tert-butylperoxide/KH/
THF)3b,16 failed to give the corresponding coupled
products 4–7.
1. (a) Metal-Catalyzed Cross-Coupling Reactions; Diederich,
F., Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998; (b)
Topics in Current Chemistry; Miyaura, N., Ed.; Springer:
Berlin, 2002; Vol. 219.
2. (a) Kosugi, M.; Tanji, T.; Tanaka, Y.; Yoshida, A.;
Fugami, K.; Kameyama, M.; Migita, T. J. Organometal.
Chem. 1996, 508, 255–257; (b) Faller, J. W.; Kultyshev, R.
G. Organometallics 2002, 21, 5911–5918; (c) Nakamura,
T.; Kinoshita, H.; Shinokubo, H.; Oshima, K. Org. Lett.
2002, 4, 3165–3167; (d) Faller, J. W.; Kultyshev, R. G.;
Parr, J. Tetrahedron Lett. 2003, 44, 451–453; (e) Enokido,
T.; Fugami, K.; Endo, M.; Kameyama, M.; Kosugi, M.
Adv. Synth. Catal. 2004, 346, 1685–1688; (f) Spivey, A. C.;
Gripton, C. J. G.; Hannah, J. P. Cur. Org. Synth. 2004, 1,
211–226 (a review on Si and Ge-based alternatives to the
Stille reaction).
3. (a) Wnuk, S. F.; Garcia, P. I., Jr.; Wang, Z. Org. Lett.
2004, 6, 2047–2049; (b) Wang, Z.; Wnuk, S. F. J. Org.
Chem. 2005, 70, 3281–3284.
´
4. (a) Lesbre, M.; Mazerolles, P.; Satge, J. The Organic Com-
It appears that hydrogen peroxide cleaves the Ge–Si
bond(s) in 3a–c [R0Ge(SiMe3)3] to generate active
germanol or germanoxane species17 of the type
R0Ge(OH)n(SiMe3)3ꢀn or R0Ge(OSiMe3)n(SiMe3)3ꢀn
(n = 1,2,or 3). Cleavage of Ge–Si bond under oxidative
conditions via oxygen insertion has been reported.18 To
obtain mechanistic insights of this process, we examined
the coupling reaction of 3a(E) with iodobenzene in
THF-d8 directly in an NMR tube. After adding H2O2,
the 19F peak of substrate 3a(E) [d: ꢀ81.93 (d,
J = 51.4 Hz)] quickly disappeared (ꢁ5min, ambient
temperature) and a new signal appeared as doublet
(J = 50.8 Hz) of multiplets at d ꢀ101.42. With the
subsequent addition of iodobenzene and Pd(0) catalyst
the peak for the fluoro stilbene 4a(Z) gradually was
formed at d ꢀ114.64 ppm (d, J = 39.5Hz). Further-
more, the TTMS peak of substrate 3a(E) [d: 0.34 (s)]
was shifted upfield (D 0.33 ppm) on the 1H NMR
spectra upon addition of H2O2. These observations indi-
cate that TTMS-germane 3a(E) reacts with H2O2
generating a new intermediate, possibly a germanol
or a germanoxane, which subsequently undergoes
coupling.
pounds of Germanium; Wiley-Interscience: London, 1971;
(b) The Chemistry of Organic Germanium, Tin and Lead
Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley &
Sons: Chichester, 1995; Vol. 1, 2002; Vol. 2.
5. (a) Percy, J. M.; Wilkes, R. D. Tetrahedron 1997, 53,
14749–14762; (b) Chen, C.; Wilcoxen, K.; Zhu, Y.-F.;
Kim, K.-I.; McCarthy, J. R. J. Org. Chem. 1999, 64, 3476–
3482; (c) Liu, Q.; Burton, D. Org. Lett. 2002, 4, 1483–
1485.
6. Hanamoto, T.; Kobayashi, T. J. Org. Chem. 2003, 68,
6354–6359.
7. Bernardoni, S.; Lucarini, M.; Pedulli, G. F.; Valgimigli,
L.; Gevorgyan, V.; Chatgilialoglu, C. J. Org. Chem. 1997,
62, 8009–8014.
8. (a) (E)-1-Fluoro-4-phenyl-1-[tris(trimethylsilyl)germyl]-1-
butene (3b): Germyldesulfonylation procedure—Argon
was bubbled through
a
solution of 2b9b (450 mg,
1.55 mmol; E/Z, 70:30) in anhydrous benzene (15mL)
for 15min. (Me 3Si)3GeH (0.485 mL, 454 mg, 1.55 mmol)
and AIBN (51 mg, 0.31 mmol) were added, and degassing
of oxygen was continued for another 10 min and then the
solution was refluxed for 6 h. The volatiles were evapo-
rated, and the residue was flash chromatographed (hex-
ane) to give 3b (342 mg, 50%; E isomer only) as a colorless
oil: 1H NMR d 0.24 (s, 27H), 2.48 (q, J = 7.5Hz, 2H),
2.69 (t, J = 7.3 Hz, 2H), 4.75(dt,
J = 48.9, 7.3 Hz,
1H), 7.18–7.30 (m, 5H); 13C NMR d 1.76 (TMS), 26.11
(d, J = 10.4 Hz, C3), 36.35(C4), 121.39 (d, J = 4.0 Hz,
C2), 126.12 (Ph), 128.62 (Ph), 128.87 (Ph), 142.24 (Ph),
166.86 (d, J = 305.2 Hz, C1); 19F NMR d ꢀ91.64 (d,
3JF-H(trans) = 48.9 Hz); GC–MS (tR 21.27 min) m/z 442 (5,
M+), 220 (100). Anal. Calcd for C19H37FGeSi3 (442.14):
C, 51.70; H, 8.45. Found: C, 51.36; H, 8.22. (b) 3c: 1H
NMR d 0.28 (s, 27H), 1.54 (br s, 6H), 1.98 (br s, 2H), 2.31
(br s, 2H); 13C NMR d 2.43 (TMS), 26.10 (d, J = 14.5Hz),
27.08, 27.61 (d, J = 1.3 Hz), 28.47 (d, J = 2.5Hz), 31.44
(d, J = 9.1 Hz), 131.37 (d, J = 5.6 Hz, C2), 157.96 (d,
J = 291.6 Hz, C1); 19F NMR d ꢀ96.38 (s); GC–MS (tR
18.14 min) m/z 406 (3, M+). Anal. Calcd for C16H37FGeSi3
(406.14): C, 47.41; H, 9.20. Found: C, 47.85; H, 9.51.
9. (a) McCarthy, J. R.; Matthews, D. P.; Stemerick, D. M.;
Bey, P.; Lippert, B. J.; Snyder, R. D.; Sunkara, P. S.
J. Am. Chem. Soc. 1991, 113, 7439–7440; (b) McCarthy, J.
R.; Huber, E. W.; Le, T.-B.; Laskovics, F. M.; Matthews,
D. P. Tetrahedron 1996, 52, 45–58.
In summary, we have demonstrated that conjugated
and nonconjugated (a-fluoro)vinyl tris(trimethylsilyl)-
germanes successfully undergo Pd-catalyzed cross-
couplings with aryl and alkenyl halides under aqueous
oxidative conditions to produce fluoroalkenes and
fluorodienes with retention of stereochemistry. Cou-
plings with the (a-fluoro)vinyl TTMS-germanes ap-
peared to more facile than with the corresponding
(a-fluoro)vinyl stannanes and silanes since neither addi-
tion of an extra ligand nor activation with CuI or
fluoride was required.
Acknowledgements
We thank NIH/NIGMS program (S06 GM08205) for
supporting this research. A.G. was a McNair Post-
Baccalaureate Achievement Program Fellow.
10. (a) Stang, P. J.; Zhdankin, V. Alkynyl Halides and
Chalcogenides. In Comprehensive Organic Functional