Palladium- and nickel-catalyzed aminations of aryl imidazolylsulfonates and sulfamates

Article abstract of DOI:10.1021/ol200267b

A nickel complex derived from dppf, along with NaOt-Bu as the base, allowed for challenging aminations of aryl sulfamates. An improved functional group tolerance is observed in novel palladium-catalyzed aminations of imidazolylsulfonates with rac-BINAP as the ligand.

Full text of DOI:10.1021/ol200267b

ORGANIC
LETTERS
2011
Vol. 13, No. 7
1784–1786
Palladium- and Nickel-Catalyzed
Aminations of Aryl Imidazolylsulfonates
and Sulfamates
ꢀ
Lutz Ackermann,* Rene Sandmann, and Weifeng Song
€
Institut fu€r Organische und Biomolekulare Chemie, Georg-August-Universitat,
€
Tammannstrasse 2, 37077 Gottingen, Germany
Lutz.Ackermann@chemie.uni-goettingen.de
Received January 27, 2011
ABSTRACT
A nickel complex derived from dppf, along with NaOt-Bu as the base, allowed for challenging aminations of aryl sulfamates. An improved
functional group tolerance is observed in novel palladium-catalyzed aminations of imidazolylsulfonates with rac-BINAP as the ligand.
Transition-metal-catalyzed arylations of amines with
aryl halides are among the most important methods for the
selective formation of C-N bonds.1 Particularly, the use of
phenol-derived electrophiles in catalyzed arylations is highly
attractive,2 since they are readily accessible and can be easily
implemented as directing groups in site-selective arene func-
tionalization strategies.2,3 However, the inherently high C-O
bond strength in phenols calls for an activation of these
precursors, which was largely achieved through the use of
rather expensive fluorine-containing reagents.4 On the con-
trary, recent progress in the use of phenol-derived electro-
philes in catalytic arylations was represented by the use of
imidazolylsulfonates and sulfamates, because of their air-
and moisture-stable nature, their attractive handling properties,
and their low costs.5,6 While these user-friendly electro-
philes were recently employed for efficient C-C bond forma-
tions, their use in transition-metal-catalyzed aminations
(5) For representative examples of catalyzed arylations with tosylates
or mesylates, see: C-N bond formation: (a) Mantel, M. L. H.; Lind-
hardt, A. T.; Lupp, D.; Skrydstrup, T. Chem.;Eur. J. 2010, 16, 5437–
5442. (b) Lundgren, R. J.; Stradiotto, M. Angew. Chem., Int. Ed. 2010,
49, 8686–8690. (c) So, C. M.; Zhou, Z.; Lau, C. P.; Kwong, F. Y. Angew.
Chem., Int. Ed. 2008, 47, 6402–6406. (d) Nguyen, H. N.; Huang, X.;
Buchwald, S. L. J. Am. Chem. Soc. 2003, 125, 11818–11819. (e) Roy,
A. H.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 8704–8705. (f) Huang,
X.; Anderson, K. W.; Zim, D.; Jiang, L.; Klapars, A.; Buchwald, S. L.
J. Am. Chem. Soc. 2003, 125, 6653–6655. (g) Bolm, C.; Hildebrand, J. P.;
Rudolph, J. Synthesis 2000, 911–913. (h) Hamann, B. C.; Hartwig, J. F.
J. Am. Chem. Soc. 1998, 120, 7369–7370 and references cited herein. See
also: (i) Ackermann, L.; Fenner, S. Chem. Commun. 2011, 47, 430–432.
(j) Yeung, P. Y.; So, C. M.; Lau, C. P.; Kwong, F. Y. Angew. Chem., Int.
Ed. 2010, 49, 8918–8922. (k) Wilson, D. A.; Wilson, C. J.; Moldoveanu,
C.; Resmerita, A.-M.; Corcoran, P.; Hoang, L. M.; Rosen, B. M.;
Percec, V. J. Am. Chem. Soc. 2010, 132, 1800–1801. (l) Chow, W. K.;
So, C. M.; Lau, C. P.; Kwong, F. Y. J. Org. Chem. 2010, 75, 5109–5112.
(m) Bhayana, B.; Fors, B. P.; Buchwald, S. L. Org. Lett. 2009, 11, 3954–
3957. (n) Ackermann, L.; Althammer, A.; Fenner, S. Angew. Chem., Int.
Ed. 2009, 48, 201–204. (o) So, C. M.; Lau, C. P.; Kwong, F. Y. Angew.
Chem., Int. Ed. 2008, 47, 8059–8063. (p) Zhang, L.; Wu, J. Adv. Synth.
Catal. 2008, 350, 2409–2413. (q) Zhang, L.; Wu, J. J. Am. Chem. Soc.
2008, 130, 12250–12251. (r) Hansen, A. L.; Ebran, J.-P.; Ahlquist, M.;
Norrby, P.-O.; Skrydstrup, T. Angew. Chem., Int. Ed. 2006, 45, 3349–
3353. (s) Ackermann, L.; Althammer, A. Org. Lett. 2006, 8, 3457–3460.
(t) Zhou, J.; Fu, G. C. J. Am. Chem. Soc. 2003, 125, 12527–12530 and
references cited therein.
(1) (a) Surry, D. S.; Buchwald, S. L. Chem. Sci. 2011, 2, 27–50. (b)
Klinkenberg, J. L.; Hartwig, J. F. Angew. Chem., Int. Ed. 2011, 50, 86–
95. (c) Monnier, F.; Taillefer, M. Angew. Chem., Int. Ed. 2009, 48, 6954–
€
6971. (d) Kruger, K.; Tillack, A.; Beller, M. Adv. Synth. Catal. 2008, 350,
2153–2167. (e) Ackermann, L. Synlett 2007, 507–526. (f) Schlummer, B.;
Scholz, U. Adv. Synth. Catal. 2004, 346, 1599–1626.
(2) (a) Rosen, B. M.; Quasdorf, K. W.; Wilson, D. A.; Zhang, N.;
Resmerita, A.-M.; Garg, N. K.; Percec, V. Chem. Rev. 2011, DOI:
10.1021/cr100259t. (b) Li, B.-J.; Yu, D.-G.; Sun, C.-L.; Shi, Z.-J.
Chem.;Eur. J. 2011, 17, 1728–1759. (c) Yu, D.-G.; Li, B.-J.; Shi, Z.-J.
Acc. Chem. Res. 2010, 43, 1486–1495. (d) Littke, A. In Modern Arylation
Methods; Ackermann, L., Ed.; Wiley-VCH: Weinheim, 2009; pp 25-67.
(3) Hartung, C. G.; Snieckus, V. In Modern Arene Chemistry; Astruc,
D., Ed.; Wiley-VCH: Weinheim, 2002; pp 330-367.
€
(4) Select reviews: (a) Hogermeier, J.; Reissig, H.-U. Adv. Synth.
Catal. 2009, 351, 2747–2763. (b) Zeni, G.; Larock, R. C. Chem. Rev.
2006, 106, 4644–4680. (c) Stang, P. J.; Hanack, M.; Subramanian, L. R.
Synthesis 1982, 85–126.
r
10.1021/ol200267b
Published on Web 02/25/2011
2011 American Chemical Society

has unfortunately thus far proven elusive. Within our
research program on the development of efficient amina-
tion reactions for modular heteroarene syntheses,7 we thus
explored various transition metal complexes for catalyzed
aminations with aryl sulfamates and imidazolylsulfonates,
on which we report herein.
Scheme 1. Nickel-Catalyzed Amination of Sulfamtes 1
At the outset, we tested various ligands and bases in the
nickel-catalyzed amination of sulfamate 1a (Table 1).
While representative monodentate phosphine ligands
provided only unsatisfactory results (entries 1-5), nickel
complexes derived from N-heterocyclic carbene (NHC)
precursors (entries 6 and 7) or bidentate phosphine ligands
(entries 8-14) displayed improved catalytic activities.
Notably, the best results were accomplished with dppf as
the ligand, along with NaOt-Bu as the base (entries
12-14).
Table 1. Optimization of Nickel-Catalyzed Aminationa
entry
L (mol %)
base
yield (%)
1
-
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
NaOt-Bu
KOt-Bu
-
-
-
-
2
PPh3 (10)
Scheme 2. Nickel-Catalyzed Arylation of Secondary Amine 2b
3
PCy3 (10)
4
S-Phos (10)
X-Phos (10)
IPrHCl (10)
SIPrHCl (10)
rac-BINAP (5.0)
1,10-phenanthroline (5.0)
dppe (5.0)
5
-
6
85
82
54
8
7
8
9
10
11
12
13
14
52
dppp (5.0)
-
65
-
dppf (5.0)
dppf (5.0)
Cs2CO3
and their functional group tolerance was significantly
restricted by the required strong base NaOt-Bu. Therefore,
we subsequently tested various palladium catalysts for the
amination of imidazolylsulfonate 4a using milder bases
(Table 2). Unfortunately, various NHC palladium com-
plexes gave only unsatisfactory yields (entries 1-4). How-
ever, among a variety of phosphine ligands (entries 5-16),
dppf (5.0)
NaOt-Bu
95
a Reaction conditions: 1a (0.50 mmol), 2a (0.75 mmol), Ni(cod)2 (5.0
mol%), L (5.0-10 mol%), base (0.75 mmol), PhMe (2.0 mL), 105°C, 16 h;
S-Phos = 2-dicyclohexylphosphino-20,60-dimethoxybiphenyl; X-Phos =
2-dicyclohexylphosphino-20,40,60-tri-iso-propylbiphenyl; (S)IPrH = N,N0-
bis-(2,6-di-iso-propylphenyl)imidazol(in)ium.
With an optimized catalytic system in hand, we explored
its scope in the nickel-catalyzed amination of differently
substituted sulfamates 1 (Scheme 1). Importantly, aniline
derivatives bearing electron-withdrawing as well as elec-
tron-donating substituents efficiently provided the desired
products 3b-3i, even when being sterically hindered.
Moreover, challenging n-alkyl amines were converted with
comparable catalytic efficacy.
For alkyl-substituted secondary amines, a nickel com-
plexgenerated insitufrom anNHC precursorconstituteda
viable alternative (Scheme 2).
While the optimized nickel complexes displayed promis-
ing catalytic activities, they relied on air-sensitive Ni(cod)2,
(6) (a) Macklin, T. K.; Snieckus, V. Org. Lett. 2005, 7, 2519–2522. (b)
When, P. M.; Du Bois, J. Org. Lett. 2005, 7, 4685–4688. (c) Albaneze-
Walker, J.; Raju, R.; Vance, J. A.; Goodman, A. J.; Reeder, M. R.; Liao,
J.; Maust, M. T.; Irish, P. A.; Espino, P.; Andrews, D. R. Org. Lett. 2009,
11, 1463–1466. (d) Goegsig, T. M.; Lindhardt, A. T.; Skrydstrup, T. Org.
€
Lett. 2009, 11, 4886–4888. (e) Ackermann, L.; Barfusser, S.; Pospech, J.
Org. Lett. 2010, 12, 724–726. (f) Luo, Y.; Wu, J. Organometallics 2009,
28, 6823–6826. (g) Shirbin, S. J.; Boughton, B. A.; Zammit, S. C.;
Zanatta, S. D.; Marcuccio, S. M.; Hutton, C. A.; Williams, S. J.
Tetrahedron Lett. 2010, 51, 2971–2974. (h) Quasdorf, K. W.; Riener,
M.; Petrova, K. V.; Garg, N. K. J. Am. Chem. Soc. 2009, 131, 17748–
17749 and references cited therein. (i) For nickel-catalyzed aminations of
aryl pivalates, see: Shimasaki, T.; Tobisu, M.; Chatani, N. Angew.
Chem., Int. Ed. 2010, 49, 2929–2932. (j) After submission of our manu-
script, a nickel-catalyzed amination of aryl sulfamates was reported by
Garg and coworkers: Ramgren, S. D.; Silberstein, A. L.; Yang, Y.; Garg,
N. K. Angew. Chem., Int. Ed. 2011, 50, DOI: 10.1002/anie.201007325.
Org. Lett., Vol. 13, No. 7, 2011
1785

Table 2. Optimization of Palladium-Catalyzed Aminationa
Scheme 3. Scope of Palladium-Catalyzed Aminations of
Imidazolylsulfonates 4
entry
L
base
solvent
PhMe
yield (%)
1
-
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K3PO4
-
2
sHIPrCl
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
THFd
5b
9b
-
3
HIPrCl
4
HIMesCl
PPh3
5
-
6
John-Phos
X-Phos
83
90
79c
-
7
8
X-Phos
9
dppe
10
11
12
13
14
15
16
dppf
8b
64
80
58
29b
-
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
rac-BINAP
1,4-dioxane
PhMe
PhMe
PhMe
PhMe
a [Pd] (5.0 mol %).
K2CO3
Na2CO3
Cs2CO3
86
a Reaction conditions: 4a (0.50 mmol), 2a (0.60-0.75 mmol),
Pd(OAc)2 (10 mol %), L (10 mol %), base (0.65-1.25 mmol), solvent
(2.0 mL), 105 °C, 17 h; John-Phos = 2-di(tert-butyl)phosphinobiphenyl.
b GC conversion. c Pd(OAc)2 (2.0 mol %), L (4.0 mol %). d 65 °C.
Scheme 4. Palladium-Catalyzed Amination of Electron-Rich
Imidazolylsulfonate 4b
particularly X-Phos8 and rac-BINAP turned out to be
superior (entries 11-16).
The optimized reaction conditions were thereafter em-
ployed for evaluating the scope of palladium-catalyzed
aminations of imidazolylsulfonates 4 (Scheme 3). Notably,
differently substituted aniline derivatives were successfully
converted, as was an alkyl-substituted amine. Contrary to
reactions with nickel complexes (vide supra), the palladium-
catalyzed amination proved tolerant of valuable electrophilic
functional groups, such as fluoro-, nitro-, or cyano-substitu-
ents, as well as ester or ketone functionalities. An additional
valuable asset of the catalytic system is inter alia represented
by its chemoselectivity in the conversion of chloro-substituted
aryl imidazolylsulfonates 4, which is complementary to the
one observed in palladium-catalyzed aminations with aryl
tosylates5d or mesylates5c as electrophiles.
In summary, we have disclosed unprecedented general
metal-catalyzed aminations of aryl sulfamates and imida-
zolylsulfonates. Hence, a nickel catalyst derived from
ligand dppf allowed for arylations with challenging sulfa-
mates as electrophiles, provided that NaOt-Bu was used as
the base. On the contrary, palladium complexes of rac-
BINAP set the stage for widely applicable aminations of
aryl imidazolylsulfonates, a notable feature of which is
constituted by their excellent functional group tolerance.
Further studies on applications of these electrophiles in
catalytic arylations are currently ongoing in our labora-
tories and will be reported in due course.
When using electron-rich aryl imidazolylsulfonates, a
palladium complex of phosphine ligand X-Phos delivered
high yields as well (Scheme 4).
Acknowledgment. Support by the DFG and the Chi-
nese Scholarship Council (fellowship to W.S.) is gratefully
acknowledged.
(7) For representative examples, see: (a) Ackermann, L.; Song, W.;
Sandmann, R. J. Organomet. Chem. 2011, 696, 195–201. (b) Ackermann,
Supporting Information Available. Experimental pro-
1
€
L.; Barfusser, S.; Potukuchi, H. K. Adv. Synth. Catal. 2009, 351, 1064–
cedures, characterization data, and H and 13C NMR
1072. (c) Ackermann, L.; Sandmann, R.; Kaspar, L. T. Org. Lett. 2009,
11, 2031–2034. (d) Ackermann, L.; Sandmann, R.; Kondrashov, M. V.
Synlett 2009, 1219–1222. (e) Ackermann, L.; Sandmann, R.; Villar, A.;
Kaspar, L. T. Tetrahedron 2008, 64, 769–777. (f) Ackermann, L.; Spatz,
J. H.; Gschrei, C. J.; Born, R.; Althammer, A. Angew. Chem., Int. Ed.
2006, 45, 7627–7630. (g) Ackermann, L.; Born, R. Angew. Chem., Int.
Ed. 2005, 44, 2444–2447 and references cited therein.
spectra for new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
(8) Surry, D. S.; Buchwald, S. L. Angew. Chem., Int. Ed. 2008, 47,
6338–6361.
1786
Org. Lett., Vol. 13, No. 7, 2011