Journal of the American Chemical Society
ARTICLE
(9) For a review of ligand-accelerated catalysis, see: Berrisford, D. J.;
Bolm, C.; Sharpless, K. B. Angew. Chem., Int. Ed. 1995, 34, 1059–1070.
(10) For the initial reports of Pd(II)-mediated C(aryl)ꢀH
olefination, see: (a) Moritani, I.; Fujiwara, Y. Tetrahedron Lett. 1967,
8, 1119–1122. (b) Fujiwara, Y.; Moritani, I.; Matsuda, M.; Teranishi, S.
Tetrahedron Lett. 1968, 9, 3863–3865.
(20) Examples of Ru(0)-catalyzed CꢀH/RꢀM cross-coupling:
(a) Kakiuchi, F.; Kan, S.; Igi, K.; Chatani, N.; Murai, S. J. Am. Chem.
Soc. 2003, 125, 1698–1699. (b) Pastine, S. J.; Gribkov, D. V.; Sames, D. J.
Am. Chem. Soc. 2006, 128, 14220–14221. For Ru(II)-catalyzed CꢀH/
RꢀM cross-coupling, see:(c) Li, H.; Wei, W.; Xu, Y.; Zhang, C.; Wan, X.
Chem. Commun. 2011, 47, 1497–1499.
(11) Examples of Pd-catalyzed CꢀH arylation using other modes of
catalysis: (a) Campeau, L.-C.; Rousseaux, S.; Fagnou, K. J. Am. Chem.
Soc. 2005, 127, 18020–18021. (b) Daugulis, O.; Zaitsev, V. G. Angew.
Chem., Int. Ed. 2005, 44, 4046–4048. (c) Kalyani, D.; Deprez, N. R.;
Desai, L. V.; Sanford, M. S. J. Am. Chem. Soc. 2005, 127, 7330–7331.
(12) For the first reports of Pd(II)-catalyzed CꢀH/RꢀM cross-
coupling, see: (a) Chen, X.; Li, J.-J.; Hao, X.-S.; Goodhue, C. E.; Yu, J.-Q.
J. Am. Chem. Soc. 2006, 128, 78–79. (b) Chen, X.; Goodhue, C. E.; Yu,
J.-Q. J. Am. Chem. Soc. 2006, 128, 12634–12635.
(13) Wang, D.-H.; Mei, T.-S.; Yu, J.-Q. J. Am. Chem. Soc. 2008,
130, 17676–17677.
(14) (a) Giri, R.; Maugel, N.; Li, J.-J.; Wang, D.-H.; Breazzano, S. P.;
Saunders, L. B.; Yu, J.-Q. J. Am. Chem. Soc. 2007, 129, 3510–3511.
(b) Wang, D.-H.; Wasa, M.; Giri, R.; Yu, J.-Q. J. Am. Chem. Soc. 2008,
130, 7190–7191.
(21) In an intriguing recent report, it was found that nucleophilic
aryl-centered radicals, generated from arylboronic acids in the presence
of catalytic Ag(I), could add to electron-poor heterocycles: Seiple, I. B.;
Shun, S.; Rodriguez, R. A.; Gianatassio, R.; Fujiwara, Y.; Sobel, A. L.;
Baran, P. S. J. Am. Chem. Soc. 2010, 132, 13194–13196.
(22) In ref 13 the substrate scope was largely limited to α-substituted
and α,α,-disubstiuted phenylacetic acids, in which palladation is more
favorable owing to the ThorpeꢀIngold effect. The reaction conditions
reported in that reference were as follows: ArBF3K (1.2 equiv), Pd-
(OAc)2 (10 mol %), BQ (0.5 equiv), K2HPO4 (1.5 equiv), t-BuOH
(solvent), 110 °C, O2 (20 atm), 48 h. Under those conditions, many
substrates gave unsatisfactory product conversions. Representative ex-
amples include 3a (44%), 3d (56%), and 3h (17%). (See SI for further
details.) It is important tonote that, thoughout this work, weused 5 mol %
Pd(OAc)2.
(15) Examples of Pd(II)-catalyzed CꢀH/RꢀM cross-coupling from
other groups: (a) Yang, S.; Li, B.; Wan, X.; Shi, Z. J. Am. Chem. Soc. 2007,
129, 6066–6067. (b) Kawai, H.; Kobayashi, Y.; Oi, S.; Inoue, Y. Chem.
Commun. 2008, 1464–1466. (c) Ge, H.; Niphakis, M. J.; Georg, G. I.
J. Am. Chem. Soc. 2008, 130, 3708–3709. (d) Yang, S.-D.; Sun, C.-L.;
Fang, Z.; Li, B.-J.; Li, Y.-Z.; Shi, Z.-J. Angew. Chem., Int. Ed. 2008,
47, 1473–1476. (e) Zhao, J.; Zhang, Y.; Cheng, K. J. Org. Chem. 2008,
73, 7428–7431. (f) Kirchberg, S.; Fr€ohlich, R.; Studer, A. Angew. Chem.,
Int. Ed. 2009, 48, 4235–4238. (g) Zhou, H.; Xu, Y.-H.; Chung, W.-J.;
Loh, T.-P. Angew. Chem., Int. Ed. 2009, 48, 5355–5357. (h) Wei, Y.; Kan,
J.; Wang, M.; Su, W.; Hong, M. Org. Lett. 2009, 11, 3346–3349.
(i) Liang, Z.; Yao, B.; Zhang, Y. Org. Lett. 2010, 12, 3185–3187.
(j) Tredwell, M. J.; Gulias, M.; Bremeyer, N. G.; Johansson, C. C. C.;
Collins, B. S. L.; Gaunt, M. J. Angew. Chem., Int. Ed. 2011,
50, 1076–1079. (k) Kirchberg, S.; Tani, S.; Ueda, K.; Yamaguchi, J.;
Studer, A.; Itami, K. Angew. Chem., Int. Ed. 2011, 50, 2387–2391.
(l) Schnapperelle, I.; Breitenlechner, S.; Bach, T. Org. Lett. 2011, 13,
3640–3643. (m) Mochida, K.; Kawasumi, K.; Segawa, Y.; Itami, K. J. Am.
Chem. Soc. 2011, 133, 10716–10719.
(16) One elegant approach to improve reactivity with electron-rich
substrates has been the use of more electrophilic Pd(II) catalysts:
Nishikata, T.; Abela, A. R.; Huang, S.; Lipshutz, B. H. J. Am. Chem. Soc.
2010, 132, 4978–4979.
(17) Aryl carboxylic acid derivatives have been found to be effective
organometallic reagent surrogates (via decarboxlation) in Pd(II)-cata-
lyzed RꢀH/RꢀCO2H cross-coupling. For leading references, see:
(a) Voutchkova, A.; Coplin, A.; Leadbeater, N. E.; Crabtree, R. H.
Chem. Commun. 2008, 6312–6314. (b) Wang, C.; Piel, I.; Glorius, F.
J. Am. Chem. Soc. 2009, 131, 4194–4195. (c) Li, M; Ge, H. Org. Lett.
2010, 12, 3464–3467.
(23) In ref 13 it was stated that Ag(I) salts completely inhibited the
transformation under the reported reaction conditions (given above).
That claim does not seem to be true across all reaction conditions.
(24) For an example of olefin-promoted reductive elimination from
Pd(II), see: (a) Kurosawa, H.; Emoto, M.; Ohnishi, H.; Miki, K.; Kasai,
N.; Tatsumi, K.; Nakamura, A. J. Am. Chem. Soc. 1987, 109, 6333–6340.
BQ has previously been found to promote reductive elimination in a
Stille coupling reaction involving allyl halides: (b) Albꢀeniz, A. C.;
Espinet, P.; Martín-Ruiz, B. Chem.—Eur. J. 2001, 7, 2481–2489. For
the effects of BQ as a ligand in Pd-catalyzed CꢀH cleavage/CꢀC
bondꢀforming reactions, see: (c) Boele, M. D. K.; van Strijdonck,
G. P. F.; de Vries, A. H. M.; Kamer, P. C. J.; de Vries, J. G.; van Leeuwen,
P. W. N. M. J. Am. Chem. Soc. 2002, 124, 1586–1587. (d) Hull, K. L.;
Sanford, M. S. J. Am. Chem. Soc. 2007, 129, 11904–11905.
(25) For an elegant study of reductive elimination of C2H6 from a
[Pd(II)Me2] complex using different methods, including treatment with
BQ or Ag(I) salts, see: Lanci, M. P.; Remy, M. S.; Kaminsky, W.; Mayer,
J. M.; Sanford, M. S. J. Am. Chem. Soc. 2009, 131, 15618–15620.
(26) Engle, K. M.; Mei, T.-S.; Wang, X.; Yu, J.-Q. Angew. Chem., Int.
Ed. 2011, 50, 1478–1491.
(27) For perspectives on the use of RBF3K reagents, see: (a) Darses,
S.; Genet, J.-P. Chem. Rev. 2007, 108, 288–325. (b) Molander, G. A.;
Ellis, N. Acc. Chem. Res. 2007, 40, 275–286. (c) Vedejs, E.; Chapman,
R. W.; Fields, S. C.; Lin, S.; Schrimpf, M. R. J. Org. Chem. 1995,
60, 3020–3027. (d) Butters, M.; Harvey, J. N.; Jover, J.; Lennox, A. J. J.;
Lloyd-Jones, G. C.; Murray, P. M. Angew. Chem., Int. Ed. 2010,
49, 5156–5160. For the use of MIDA-boronates, see: (e) Gillis, E. P.;
Burke, M. D. J. Am. Chem. Soc. 2007, 129, 6716–6717.
(28) For detailed data concerning the effects of PhBF3K/Ag2CO3
loading, see SI.
(18) Examples of stoichiometric palladacycle/RꢀM coupling:
(a) Murahashi, S.-I.; Tanba, Y.; Yamamura, M.; Moritani, I. Tetrahedron
Lett. 1974, 15, 3749–3752. (b) Yamamura, M.; Moritani, I.; Murahashi,
S.-I. Chem. Lett. 1974, 3, 1423–1424. (c) Kasahara, A.; Izumi, T.;
Maemura, M. Bull. Chem. Soc. Jpn. 1977, 50, 1878–1880. (d) Murahashi,
S.-I.; Tamba, Y.; Yamamura, M.; Yoshimura, N. J. Org. Chem. 1978,
43, 4099–4106. (e) Louie, J.; Hartwig, J. F. Angew. Chem., Int. Ed. 1996,
35, 2359–2361. (f) Dangel, B. D.; Godula, K.; Youn, S. W.; Sezen, B.;
Sames, D. J. Am. Chem. Soc. 2002, 124, 11856–11857. In one case, Pd(0)
was found to catalyze the intermolecular cross-coupling of 2,4,6-tri-tert-
butylbromobenzene with arylboronic acids via an unusual intervening
C(sp3)ꢀH cleavage step following oxidative addition: (g) Barder, T. E.;
Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J. Am. Chem. Soc. 2005,
127, 4685–4696.
(29) Due to averaging effects, in Figure 1 it appears as if the reaction
in the presence of Ac-Ile-OH decelerates after 20 min. However, in
individual trials the rate appears to be nearly constant for time points
from 20 min until the reactions proceed to completion.
(30) High conversion with α,α,-disubstituted phenylacetic acids can
be obtained using the conditions reported in ref 13. With these
substrates, the use of mono-N-protected amino acid ligands does not
seem to improve the reactivity.
(31) Reviews of aerobic Pd(II)-catalyzed oxidation chemistry:
(a) Stahl, S. S. Angew. Chem., Int. Ed. 2004, 43, 3400–3420. (b) Stoltz,
B. M. Chem. Lett. 2004, 33, 362–367. (c) Gligorich, K. M.; Sigman, M. S.
Chem. Commun. 2009, 3854–3867.
(32) Although at the present time high pressure O2 poses a safety
risk when used at elevated termperatures, the advent of flow technology
may soon render this approach more tenable. For leading references, see:
(a) Ye, X.; Johnson, M. D.; Diao, T.; Yates, M. H.; Stahl, S. S. Green
Chem. 2010, 12, 1180–1186. (b) Murphy, E. R.; Martinelli, J. R.;
(19) Examples of Rh(I)-catalyzed CꢀH/RꢀM cross-coupling:
(a) Oi, S.; Fukita, S.; Inoue, Y. Chem. Commun. 1998, 2439–2440.
(b) Vogler, T.; Studer, A. Org. Lett. 2007, 10, 129–131.
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