956
E. Le Gall et al.
LETTER
(6) Fillon, H.; Gosmini, C.; Périchon, J. J. Am. Chem. Soc. 2003,
125, 3867.
totally oxidized using H2O2 before work up. It should be
mentioned that symmetrical diarylphenylphosphines were
detected only as traces in the reaction mixture. In order to
improve products recovery, a protection of diarylphen-
ylphosphines as phosphine–borane complexes would also
be appropriate and perhaps even more efficient since
deprotection steps are clearly easier than reduction steps.
Nevertheless, we found rather difficult to realize the
protection on crude mixtures without losing a part of the
product under the oxide form.
(7) In a typical procedure, about 10–12 mmol of the organozinc
reagent were prepared from 15 mmol of an aryl bromide
according to the method described in ref. 6. To the filtered
solution containing the organozinc reagent was added
chlorodiphenylphosphine (10 mmol) at r.t. Stirring was
continued for additional 2 h at r.t. The reaction was
quenched using a 5% HCl solution and the resulting mixture
was extracted with CH2Cl2. After evaporation to dryness, the
chromatographic purification of the crude oil over silica gel
using a pentane–Et2O mixture as an eluent afforded the
analytically pure phosphine derivative.
In conclusion, the results reported in this paper show that
aromatic organozinc reagents constitute valuable nucleo-
philes in the synthesis of functionalized symmetrical
arylphosphines11 starting from chlorophosphines. Cou-
plings are achieved in very mild conditions compared to
those commonly used with organolithium or Grignard re-
agents and selectivities are satisfactory. Unsymmetrical
diarylphenylphosphines11 can also be obtained using a se-
quential coupling between two different organozinc re-
agents and dichlorophenylphosphine. These preliminary
results are encouraging and prompt us to optimize reac-
tions and work-up conditions. In addition, sustained ef-
forts are in progress to realize the synthesis of
unsymmetrical triarylphosphines starting from trichloro-
phosphine.
(8) The protection of phosphines could be verified using 31
P
NMR (80 MHz, CDCl3). Indeed, the d value shifts from ca.
–12 ppm (R3P) to ca. 13 ppm (R3PBH3).
(9) The original procedure: Imamoto, T.; Kusumoto, T.; Suzuki,
N.; Sato, K. J. Am. Chem. Soc. 1985, 107, 5301.
This procedure, which reported the concomitant reduction–
protection of phosphine oxides, was simplified according to
the fact that no reduction was necessary. Consequently
LiAlH4 has been removed from the procedure.
(10) In order to add exactly the required amount of the
organozinc compound, a titration was realized as follows:
aliquots of the solution were exposed to iodine and analyzed
using GC. The amount of aryl iodide so obtained was
compared to the amount of the starting aryl bromide using
dodecane as internal standard.
(11) Coupling products were characterized using 1H NMR (200
MHz, CDCl3), 13C NMR (50 MHz, CDCl3) when required,
31P NMR (80 MHz, CDCl3), mass spectroscopy and, when
useful, 19F NMR (188 MHz, CDCl3) and FT-IR
References and Notes
spectroscopy.
Some Data for Selected Compounds.
(1) (a) Mann, F. G.; Chaplin, E. J. J. Chem. Soc. 1937, 527.
(b) Hart, F. A.; Mann, F. G. J. Chem. Soc. 1955, 4107.
(c) Russell, M. G.; Warren, S. Tetrahedron Lett. 1998, 39,
7995. (d) Whitaker, C. M.; Kott, K. L.; McMahon, R. J. J.
Org. Chem. 1995, 60, 3499. (e) Caron, L.; Canipelle, M.;
Tilloy, S.; Bricout, H.; Monflier, E. Tetrahedron Lett. 2001,
42, 8837. (f) Brune, H. A.; Falck, M.; Hemmer, R.;
Schmidtberg, G.; Alt, H. G. Chem. Ber. 1984, 117, 2791.
(2) (a) Letsinger, R. L.; Nazy, J. R.; Hussey, A. S. J. Org. Chem.
1958, 23, 1806. (b) Ravindar, V.; Hemling, H.; Schumann,
H.; Blum, J. Synth. Commun. 1992, 22, 841.
(3) (a) Knochel, P.; Singer, R. D. Chem. Rev. 1993, 93, 2117.
(b) Knochel, P.; Jones, P. In Organozinc Reagents, A
Practical Approach; Harwood, L. M.; Moody, C. J., Eds.;
Oxford University Press: Oxford, 1999.
(4) Langer, F.; Knochel, P. Tetrahedron Lett. 1995, 36, 4591.
(5) Le Gall, E.; Troupel, M.; Nédélec, J. Y. Tetrahedron 2003,
59, 7497.
Diphenyl[3-(trifluoromethyl)phenyl]phosphine (1d): 1H
NMR: d = 7.80–7.10 (m, 14 H) ppm. 31P NMR: d = –9.99
ppm. 19F NMR: d = –62.38 ppm. MS: m/z (rel. intensity) =
330 (100) [M], 251 (19) [M – 79], 203 (18) [M – 127], 183
(48) [M – 147], 108 (22) [M – 222].
Phenylbis[3-(trifluoromethyl)phenyl]phosphine (2c): 1H
NMR: d = 7.84–7.23 (m, 13 H) ppm. 31P NMR: d = –9.97
ppm. 19F NMR: d = –62.71 ppm. MS: m/z (rel. intensity) =
399 (24) [M + 1], 398 (100) [M], 397 (21) 9M – 1], 251 (40)
[M – 147], 203 (44) [M – 195], 183 (22) [M – 215].
Tris(3-methylphenyl)phosphine (3g): 1H NMR: d = 7.15–
6.94 (m, 12 H), 2.19 (s, 9 H) ppm. 31P NMR: d = –10.22 ppm.
MS: m/z (rel. intensity) = 304 (100) [M], 303 (37) [M – 1],
211 (36) [M – 93], 197 (20) [M – 107].
(4-Methoxyphenyl)(phenyl)(o-tolyl)phosphine oxide (4c):
1H NMR: d = 7.83–6.92 (m, 13 H), 3.81 (s, 3 H), 2.43 (s, 3
H) ppm. 31P NMR: d = 29.08 ppm. MS: m/z (rel. intensity) =
322 (40) [M], 321 (100) [M – 1], 213 (21) [M – 109].
Synlett 2006, No. 6, 954–956 © Thieme Stuttgart · New York