ORGANIC
LETTERS
2
003
Vol. 5, No. 6
15-818
P[N(i-Bu)CH CH ] N: A Versatile Ligand
for the Pd-Catalyzed Amination of Aryl
Chlorides
2
2 3
8
Sameer Urgaonkar, M. Nagarajan, and John G. Verkade*
Department of Chemistry, Gilman Hall, Iowa State UniVersity, Ames, Iowa 50011
Received December 11, 2002
ABSTRACT
Palladium-catalyzed amination reactions of aryl chlorides with amines proceeded in the presence of the bicyclic triaminophosphine
P[N(i-Bu)CH CH N to afford the corresponding arylamines in good to excellent yields. Electron-poor, electron-neutral, and electron-rich aryl
2
2 3
]
chlorides all participated with equal ease.
The Pd-catalyzed amination of aryl halides (or halide
equivalents) has emerged as a powerful tool for the synthesis
of substituted anilines in recent years. Though less reactive,
benes as ligands, presumably facilitating the oxidative
addition of otherwise unreactive aryl chlorides.
1
Although triaminophosphines (e.g., P[NMe
2 3
] ) are well-
aryl chloride substrates are highly desirable compared with
their bromide and iodide counterparts in terms of cost and
availability. The relatively low reactivity of aryl chlorides
has been attributed to their aversion to oxidatively adding
to Pd(0) species because of the large dissociation energy (402
known, they have not been studied (prior to our previous
studies ) in these cross-coupling reactions. This may be
partly due to the diminished electron-donating capability of
4
,5
acyclic triaminophosphines (associated with their pseudo C
2
symmetry) compared with trialkylphosphines, as has been
2
6
kJ/mol at 298 K) of the C-Cl bond. Recently, much
rationalized by Woollins recently. We reasoned, however,
progress has been made in the development of catalysts
that triaminophosphines could function as ligands if their
framework were made fairly rigid but strain-free in a bicyclic
(approximately C3V) structure, thus enhancing the lone pair
capable of utilizing aryl chlorides as substrates in aryl
3
amination processes. Most of these catalyst systems employ
7
bulky electron-rich alkylphosphines or N-heterocyclic car-
electron density at phosphorus. In accordance with this
(
1) For reviews, see: (a) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem.
002, 219, 131. (b) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S.
L. Acc. Chem. Res. 1998, 31, 805. (c) Hartwig, J. F. Acc. Chem. Res. 1998,
1, 852. (d) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046.
Organometallics 1999, 18, 1840. (g) Hartwig, J. F.; Kawatsura, M.; Hauck,
S. I.; Shaughnessy, K, H.; Alcazar-Roman, L. M. J. Org. Chem. 1999, 64,
5575. (h) Huang, J.; Grasa, G. A.; Nolan, S. P. Org. Lett. 1999, 1, 1307. (i)
Nishiyama, M.; Yamamoto, T.; Koie, Y. Tetrahedron Lett. 1998, 39, 617.
(j) Reddy, N. P.; Tanaka, M. Tetrahedron Lett. 1997, 38, 4807. (k) Wolfe,
J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 39, 22367.
(4) Urgaonkar, S.; Nagarajan, M.; Verkade, J. G. J. Org. Chem. 2003,
68, 452.
2
3
(
(
2) Grushin, V. V.; Alper, H. Chem. ReV. 1994, 94, 1047.
3) For representative examples of aryl chloride aminations, see: (a)
Ehrentraut, A.; Zapf, A.; Beller, M. J. Mol. Catal. A: Chem. 2002, 3494,
. (b) Grasa, G. A.; Viciu, M. S.; Huang, J.; Nolan, S. P. J. Org. Chem.
1
2
001, 66, 7729. (c) Stauffer, S. R.; Lee, S.; Stambuli, J. P.; Hauck, S. I.;
(5) Urgaonkar, S.; Nagarajan, M.; Verkade, J. G. Tetrahedron Lett. 2002,
43, 8921.
(6) (a) Clarke, M. L.; Cole-Hamilton, D. J.; Slawin, A. M. Z.; Woollins,
J. D. Chem. Commun. 2000, 2065. (b) Clarke, M. L.; Cole-Hamilton, D.
J.; Woollins, J. D. J. Chem. Soc., Dalton Trans. 2001, 2721.
Hartwig, J. F. Org. Lett. 2000, 2, 1423. (d) Wolfe, J. P.; Tomori, H.; Sadighi,
J. P.; Yin, J.; Buchwald, S. L. J. Org. Chem. 2000, 65, 1158. (e) Wolfe, J.
P.; Buchwald, S. L. Angew. Chem., Int. Ed. 1999, 38, 2413. (f) Bei, X.;
Uno, T.; Norris, J.; Turner, H. W.; Weinberg, W. H.; Guram, A. S.
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0.1021/ol027450b CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/27/2003