5204
M. Al-Masum, S. Alam / Tetrahedron Letters 50 (2009) 5201–5204
Method C
+
I
Z
BF3K
+
Z
5
Z
γ-product 7
α-product 6
Z = Cl, Br, CH3
Z = Cl, 6a + 7a; Yield 54 %
Z = Br, 6b + 7b; Yield 41 %
Z = CH3, 6c + 7c; Yield 77 %
Scheme 4.
5. (a) Vedejs, E.; Chapman, R. W.; Fields, S. C.; Lin, S.; Schrimpf, M. R. J. Org. Chem.
1995, 60, 3024; (b) Batey, R. A.; Thadani, A. N.; Smil, D. V. Tetrahedron Lett. 1999,
40, 4289.
6. The ratio of the central carbon selectivity with endo-products ArCH@CHCH3 3a–
3j, and exo-products ArC(CH3)@CH2 4a–4j was 5:1. In case of 4-
methyliodobenzene, 2j, the ratio was 3:2 (Table 1, entry 10). The endo- and
exo-products were unable to be separated by chromatography. For
simplification, exo-products were not shown.
the central carbon of the
p-allyl system to form palladacyclobu-
tane, followed by reductive elimination to produce the cyclopro-
pane which presumably isomerizes to trans-b-methylstyrene
(Scheme 3).8,9
Interestingly, when same reaction condition (method C) was
applied to potassium crotyltrifluoroborates and aryl halides, cou-
7. Hegedus, L. S.; Darlington, W. H.; Russell, C. E. J. Org. Chem. 1980, 45, 5193.
8. The following procedure is representative: Potassium allyltrifluoroborate
pling products with
a-selectivity were predominated along with
1
trace amount of -adduct (Scheme 4).
c
(93.0 mg, 0.625 mmol), 4-bromoiodobenzene 2d (71.0 mg, 0.25 mmol), K2CO3
(104.0 mg, 0.75 mmol), and PdCl2(dtbpf) (0.0075 mmol, 3 mol %) were placed in
an argon-flushed pyrex tube. The pyrex tube was capped with a rubber septum,
flushed with argon, and was added 2.5 mL of isopropanol/water (2:1). The
resulting mixture in pyrex tube was placed in a CEM microwave unit and
allowed to irradiate at 120 °C for 30 min. After standard work-up by adding
ammonium chloride and ethyl ether, the ether layer was separated. The reaction
mixture was adsorbed in silica gel and transferred into the column and was
subjected to silica gel chromatography using hexane as an eluent. The pure
product 4-bromo-trans-b-methylstyrene, 3d was isolated in 95% yield (Table 1,
In conclusion, our efforts demonstrate a facile and simplified
coupling reaction of potassium allyltrifluoroborates and aryl
halides with remarkable regioselectivity. Further use of these
developments in synthetic organic chemistry is in progress.
Acknowledgments
entry 4) 1H NMR (CDCl3, 300 MHz):
d 7.22(m, 4H, –4-Br–C6H4), 6.26(d,
Financial support from US department of education Title III
grant, Tennessee State University is acknowledged. Johnson Mat-
they, Inc. is also acknowledged for providing PdCl2(dtbpf) catalyst.
J = 16.8 Hz, 1H), 6.24(dq, J = 15.8 Hz, 6.3 Hz, 1H) 1.80(d, J = 5.7 Hz, 3H). LRMS
Calcd for C9H9Br M+ 197. Found: 197.
9. Analytical data for b-methylstyrenes: Compound 3a 1H NMR (CDCl3, 300 MHz): d
7.30 (m, 4H, –C6H5), 6.42 (d, J = 15.9 Hz, 1H), 6.25 (dq, J = 15.9 Hz, 6.3 Hz, 1H)
1.89 (d, J = 6.3 Hz, 3H). LRMS: Calcd for C9H10 M+ 118. Found: 118; Compound
3b 1H NMR (CDCl3, 300 MHz): d 7.48 (m, 4H, –4-I–C6H4), 6.32 (d, J = 15.9 Hz,
1H), 6.24 (m, 1H) 1.86 (d, J = 4.8 Hz, 3H). LRMS: Calcd for C9H9I M+ 244. Found:
244; Compound 3c 1H NMR (CDCl3, 300 MHz): d 7.24 (m, 4H, –4-Cl–C6H4), 6.27
(d, J = 15.3 Hz, 1H), 6.14 (dq, J = 15.3 Hz, 6.3 Hz, 1H) 1.81 (d, J = 6.3 Hz, 3H).
LRMS: Calcd for C9H9Cl (M+2)+ 154. Found: 154; Compound 3e 1H NMR (CDCl3,
References and notes
1. (a) Molander, G. A.; Ham, J. Org. Lett. 2006, 8, 2031; (b) Molander, G. A.; Figueroa,
R. Aldrichchim. Acta 2005, 38, 49; (c) Molander, G. A.; Felix, L. A. J. Org. Chem.
2005, 70, 3950; (d) Tremblay-Morin, J.-P.; Raeppel, S.; Gaudette, F. Tetrahedron
Lett. 2004, 45, 3471; (e) Molander, G. A.; Ribagorda, M. J. Am. Chem. Soc. 2003,
125, 11148; (f) Quach, T. D.; Batey, R. A. Org. Lett. 2003, 5, 1381; (g) Molander, G.
A.; Bernardi, C. R. J. Org. Chem. 2002, 67, 8424; (h) Molander, G. A.; Katona, B. W.;
Machrouhi, F. J. Org. Chem. 2002, 67, 8416; (i) Pucheault, M.; Darses, S.; Genet, J.-
P. Eur. J. Org. Chem. 2002, 3552; (j) Molander, G. A.; Rivero, M. R. Org. Lett. 2002,
4, 107; (k) Batey, R. A.; Thadani, A. N.; Smil, D. V.; Lough, A. Synthesis 2000, 990;
(l) Darses, S.; Michauld, G.; Genet, J.-P. Eur. J. Org. Chem. 1999, 1875; (m) Darses,
S.; Genet, J.-P. Chem. Rev. 2008, 108, 288.
2. For recent reviews: (a) Godleski, S. A.. In Comprehensive Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 4, p 585; (b)
Hegedus, L. In Organometallics in Synthesis; Schlosser, M., Ed.; Wiley: New
York, 1994; pp 385–459; (c) Palladium Reagents and Catalysis; Tsuji, J., Ed.;
Wiley: New York, 1995.
3. (a) Kabalka, G. W.; Al-Masum, M. Org. Lett. 2006, 8, 11; (b) Kabalka, G. W.;
Dadush, E.; Al-Masum, M. Tetrahedron Lett. 2006, 47, 7459; (c) Kabalka, G. W.;
Al-Masum, M.; Mereddy, A. R.; Dadush, E. Tetrahedron Lett. 2006, 47, 1133; (d)
Arvela, R. K.; Leadbeater, N. E.; Mack, T. L.; Kormos, C. M. Tetrahedron Lett. 2006,
47, 217; (e) Kabalka, G. W.; Al-Masum, M. Tetrahedron Lett. 2005, 46, 6329.
4. (a) Sebelius, S.; Olsson, V. J.; Wallner, O. A.; Szabo, K. J. J. Am. Chem. Soc. 2006,
128, 8150; (b) Yamamoto, Y.; Takada, S.; Miyaura, N. Chem. Lett. 2006, 35, 704.
300 MHz):
d 7.20 (m, 4H, –4-F–C6H4), 6.37 (d, J = 15.6 Hz, 1H), 6.15 (dq,
J = 16.2 Hz, 6.9 Hz, 1H) 1.87 (d, J = 6.3 Hz, 3H). LRMS: Calcd for C9H9F M+ 136.
Found: 136; Compound 3f 1H NMR (CDCl3, 300 MHz): d 7.42 (m, 4H, –4-CF3–
C6H4), 6.44 (d, J = 15.9 Hz, 1H), 6.36 (m, 1H) 1.93 (d, J = 5.4 Hz, 3H). 19F NMR
(CDCl3, 282.3 MHz): d ꢀ62.786. LRMS: Calcd for C10H9F3 M+ 186. Found: 186;
Compound 3g 1H NMR (CDCl3, 300 MHz): d 7.36 (m, 4H, –4-CN–C6H4), 6.3 (m,
1H), 6.32 (m, 1H) 1.85(d, J = 3.6 Hz, 3H. Calcd for C10H9N M+ 143. Found: 143;
Compound 3h 1H NMR (CDCl3, 300 MHz): d 7.24 (m, 4H, –3-Cl–C6H4), 6.35 (d,
J = 16.8 Hz, 1H), 6.25 (m, 1H) 1.89 (d, J = 5.4 Hz, 3H). Calcd for C9H9Cl M+ 152.
Found: 152; Compound 3i 1H NMR (CDCl3, 300 MHz): d 7.37 (m, 4H, –3-Br–
C6H4), 6.33(d, J = 15.9 Hz, 1H), 6.24 (dq, J = 15.9 Hz, 6.0 Hz, 1H), 1.89 (d,
J = 5.1 Hz, 3H). Calcd for C9H9Br M+ 198. Found: 198; Compound 3j 1H NMR
(CDCl3, 300 MHz): d 7.10 (m, 4H, –4-Me–C6H4), 6.29 (d, J = 5.6 Hz, 1H), 6.10 (dq,
J = 14.1 Hz, 6.6 Hz, 1H) 1.81 (d, J = 6.6 Hz, 3H). Calcd for C10H12 M+ 132. Found:
132; Compound 3k 1H NMR (CDCl3, 300 MHz): d 7.20 (m, 4H, –4-Cl–C6H4), 6.31
(d, J = 15.9 Hz, 1H), 5.84 (m, 1H) 1.81 (d, J = 6.3 Hz, 3H). Calcd for C9H9Cl M+ 152.
Found: 152; Compound 3l 1H NMR (CDCl3, 300 MHz): d 7.26 (m, 4H, –3-Cl–
C6H4), 6.35 (d, J = 17.0 Hz, 1H), 6.29 (m, 1H) 1.81 (d, J = 6.3 Hz, 3H). Calcd for
C9H9Cl M+ 152. Found: 152.