D -glucosamine as a green ligand for palladium-catalyzed cross-coupling of aryl and heteroaryl halides

Article abstract of DOI:10.1055/s-0034-1379612

Naturally occurring d-glucosamine works as an efficient green alternative to phosphines in palladium-catalyzed Heck coupling of aryl and heteroaryl halides. An array of trans-stilbene derivatives, aryl naphthyl alkenes, heteroaryl olefins, and β-aryl-substituted acrylates has been synthesized in short reaction times in moderate to high yields.

Full text of DOI:10.1055/s-0034-1379612

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
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Georg Thieme Verlag Stuttgart · New York
2015, 26, 259–264
259
letter
Synlett
A. K. Jha et al.
Letter
D-Glucosamine as a Green Ligand for Palladium-Catalyzed Cross-
Coupling of Aryl and Heteroaryl Halides
Abadh Kishor Jha
OH
O
Rahul Kumar Shahni
HO
HO
OH
Nidhi Jain*
X
Ar
Ar
HN
Pd(0)
Ar
+
or
Department of Chemistry, Indian Institute of Technology,
Hauz Khas, Delhi-110016, India
njain@chemistry.iitd.ac.in
O
COOBu
+
9
1
1
(
1
2
)
6
5
8
1
1
0
2
or
base
DMF–H2O, MW
X = I, Br
OBu
25 examples
Received: 03.10.2014
Accepted after revision: 30.10.2014
Published online: 02.12.2014
DOI: 10.1055/s-0034-1379612; Art ID: st-2014-d0835-l
developing phosphine-free ligands such as N-heterocyclic
carbenes,5 oxazolines, amines, Schiff bases, pyridines,
6
7
8
9
1
0
11
12
13
hydrazones, guanidines, pyrazoles, tetrazoles, quino-
lones, carbazones,15 imidazoles, thioureas, amino ac-
ids, and 1,3-dicarbonyl compounds.
14
16
17
Abstract Naturally occurring D-glucosamine works as an efficient
green alternative to phosphines in palladium-catalyzed Heck coupling
of aryl and heteroaryl halides. An array of trans-stilbene derivatives, aryl
naphthyl alkenes, heteroaryl olefins, and β-aryl-substituted acrylates
has been synthesized in short reaction times in moderate to high yields.
18
19
It is well documented that carbohydrates which occur as
one of the most naturally abundant organic molecules
serve as precursors to many natural products as well as
molecules of high biological, medicinal, and material im-
Key words green chemistry, cross-coupling, carbohydrates, palladi-
um, transition metals
20
portance. Not only have they been used as chiral auxilia-
ries in asymmetric induction but development of phospho-
rus, nitrogen, oxygen, and sulfur-based ligands with carbo-
hydrate backbones have also been successfully utilized in a
variety of asymmetric reactions.21 Furthermore, the use of
chiral diphosphites derived from D-glucose as ligands in
Palladium-catalyzed carbon–carbon and carbon–het-
eroatom bond formations have revolutionized the art and
concept of organic synthesis in the last two decades.1
Among the many different palladium-catalyzed coupling
protocols such as Suzuki, Kumada, Negishi, Sonogashira,
Stille, and Hiyama reactions, Heck coupling of aryl halides
with alkenes is one of the most prominent representations.
The classical Heck reaction involves the palladium-cata-
lyzed substitution of the vinylic hydrogen with a vinyl, aryl,
22
coupling reactions has recently been reported by Beller. In
spite of carbohydrates being widely available and economi-
cal to work with, there are very few reports that actually
demonstrate the direct use of monosaccharides as ligands
in metal-catalyzed reactions. While there are reports on the
use of D-glucosamine as a ligand in copper-catalyzed syn-
thesis of aryl amines, its application as a ligand for palladi-
um-catalyzed coupling reactions is limited.23 In our attempt
towards developing greener and economical chemical pro-
tocols,24 herein we explored the possibility of replacing or-
ganophosphines with cheap and environmental friendly
monosaccharide molecules in palladium-catalyzed cou-
pling reactions (Scheme 1).
2
or benzyl group. Since iodo derivatives are quite reactive,
use of auxiliary ligands can be avoided when they are used
as the coupling partners to olefins. However, with cheaper
and less reactive bromo and chloro derivatives, coupling is
relatively difficult; and noteworthy advances in the area
have been described by Milstein, Herrmann, Reetz, Beller,
3
and Fu. A variety of catalytic systems based on the use of
sterically hindered and electron-rich phosphines as ligands
has been developed. Since organophosphines tend to be
toxic and air-sensitive, efforts have been directed towards
For an initial evaluation, we chose glucosamine as a new
type of ligand for palladium-catalyzed Heck phenylation of
styrene. The reaction was carried out between iodobenzene
4
Pd(OAc)2
glucosamine
X
Ar/COOEt
R
+
Ar/COOEt
R
base
DMF–H2O (1:1)
1
2
3
X = I, Br
Scheme 1 Glucosamine as a ligand for palladium-catalyzed Heck arylation of styrene
©
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A. K. Jha et al.
Letter
(
1a, 1.0 equiv) and styrene (2a, 1.0 equiv) in DMF–H O (1:1)
Next, to establish the role of sugars in promoting palla-
dium-catalyzed coupling, a variety of monosaccharides
such as glucose, galactose, fructose, arabinose, ribose, and
glucosamine (L1–6) and disaccharide sucrose (L7) was ex-
amined. The results as shown in Figure 2 indicated that the
amino sugar, D-glucosamine (L3) gave the highest yield of
3a compared to other sugars. Further, comparison of the ef-
ficiency of glucosamine with phosphines and amines as li-
gands for palladium-catalyzed coupling revealed that with
3.0 equivalents of L8 compound 3a was not formed at all,
with 20 mol% compound 3a was obtained in 76% yield.
However, with BINAP, phenanthroline, and 1-methyl imid-
azole as ligands, lower yields of 3a (28–68%) were obtained
in all the cases. The results gave a clear indication that glu-
cosamine can serve as a potential green replacement for
phosphines in palladium-catalyzed Heck coupling reac-
tions.
2
using Pd(OAc)2 (5 mol%), and glucosamine (3.0 equiv) at
20 °C.
We were delighted to find that the reaction showed
1
complete conversion in 12 hours giving trans-stilbene (3a)
in 72% isolated yield. Changing from conventional to micro-
wave (MW) heating drastically reduced the reaction time
from 12 hours to one hour giving trans-stilbene (3a) in 83%
yield. In addition, fewer side products were seen under mi-
crowave conditions, and it allowed easy workup of the reac-
tion mixture compared to conventional heating where the
contents formed a thick slurry after 12 hours. Encouraged
by these results, we decided to extend the work further un-
der microwave conditions.
A series of organic solvent–H O (1:1) mixtures was
2
screened as shown in Figure 1. Amongst all the organic sol-
vents, it was found that the highest yield of 3a was obtained
in DMF–H O (1:1). In DMF or water alone as solvent, yields
dropped to 54% and 5%, respectively. The results indicated
that solvent affected the activity of the process, and DMF–
Next, the effect of base on the reaction was investigated.
Optimization of the reaction with respect to the nature of
base, amount of base, temperature, time, amount of glucos-
2
H O (1:1) was the optimum solvent for this reaction.
amine, as well as Pd(OAc) was carried out, and the results
2
2
are summarized in Table 1. Different bases such as KOH,
Et N, Cs CO , and K CO were tested, and it was found that,
3
2
3
2
3
under a constant set of other reaction conditions, the high-
est yield was obtained with K CO (Table 1, entry 4). Varia-
2
3
tion of temperature in the range 80–140 °C revealed that
the optimum temperature for the reaction was 120 °C.
Raising temperature to 140 °C or lowering to 100 °C and
80 °C reduced the yield (Table 1, entries 5–7) of 3a. The ide-
al time for the reaction thus was found to be 60 minutes as
decreasing or increasing the time to 45 and 75 minutes
lowered the product yield (Table 1, entries 8 and 9).
Further, optimization of the amount of D-glucosamine
in the range 0.0–3.0 equivalents was carried out. In the ab-
sence of glucosamine, reaction of 1a and 2a gave 3a in 57%
yield (Table 1, entry 10). On addition of glucosamine (0.8
Figure 1 Optimization of solvent system. Reaction conditions: iodo-
benzene (1a, 1.0 equiv), styrene (2a, 1.0 equiv), glucosamine (3.0
equiv), Pd(OAc) (5 mol%, 0.05 equiv), 60 min, MW, 120 °C.
2
OH
HO
OH
OH
O
O
O
OH HO
OH
O
OH
HO
HO
OH
O
O
HO
HO
OH
HO
HO
OH
HO
HO
OH
OH
NH2
OH
HO
OH
HO
OH
L6
L1
L2
L3
L5
L4
D-glucose (74%)
D-galactose (65%)
D-glucosamine (83%)
D-arabinose (70%)
D-ribose (54%)
D-fructose (62%)
OH
Me
N
OH
O
PPh2
N
HO
HO
OH
Ph
Ph
O
P
PPh2
L9
N
N
HO
L7
sucrose (37%)
Ph
L8
TPP (76%)
O
L11
L10
HO
HO
(±)-ꢀBNꢁP (28%)
phenanthroline (37%)
1-methylimidazole (68%)
Figure 2 Optimization and comparison of reactivity between monosaccharide ligands and conventional ligands. Reaction conditions: DMF–H O (1:1),
2
iodobenzene 1a (1.0 equiv), styrene 2a (1.0 equiv), L1–7 and L10, L11 (3.0 equiv), Pd(OAc) (5 mol%, 0.05 equiv), MW, 100 W, 60 min, 120 °C, L8 and
2
L9 (20 mol%). With 3.0 equiv of L8, 3a was not obtained.
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A. K. Jha et al.
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Table 1 Optimization of the Reactiona
Table 2 Palladium–Glucosamine-Catalyzed Heck Reaction between
Aryl or Heteroaryl Halides and Styrenea
Entry
Base
Temp Time Glucosamine Pd(OAc)
2
Yield (%)b
(
°C)
(min) (equiv)
(mol%)
X
Pd(OAc)2
glucosamine
1
2
3
4
5
6
7
8
9
KOH
Et
Cs
120
120
120
120
80
60
60
60
60
60
60
60
45
75
60
60
60
60
60
60
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
–
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
1.0
0.5
56
90
73
91
20
58
74
65
82
57
76
93
90
Ar
a–o
Entry
+
Ar
3
N
DMF–H O (1:1)
2
1
2a
MW, 120 °C, 60 min
3a–j
2
CO
3
K
K
K
K
K
K
K
K
K
K
K
K
2
2
2
2
2
2
2
2
2
2
2
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
3
3
3
3
Aryl halide
Product
Yield
b
(
%)
100
140
120
120
120
120
120
120
120
120
Ph
I
1
2
86
1a
3
a
Ph
1
1
1
1
1
0
1
2
3
4
5
NC
I
94
92
82
0.8
1.0
2.0
1.0
3.0
NC
1
b
3
b
Ph
O2N
I
c
d
3
4
96, 74, 69
O2N
1
c
1
76
3
c
a
Reaction conditions: iodobenzene (1a, 1.0 equiv), styrene (2a, 1.0 equiv),
Ph
Ph
base (3.0 equiv), MW.
b
Yield of 3a based on HPLC analysis using gradient system of MeCN and
F3C
I
4
NH OAc buffer.
F3C
3d
c
Base (2.0 equiv).
Base (1.0 equiv).
1d
d
equiv), the yield increased to 76% (Table 1, entry 11) and
with 1.0 equivalents, it increased further to 93% (Table 1,
entry 12).
O
I
5
83
77
1
e
O
3e
Further increase in glucosamine to 2.0 and 3.0 equiva-
lents did not have much influence on the product yield (Ta-
ble 1, entries 4 and 13). Thus, it was concluded that 1.0
equivalent of glucosamine was optimal for the reaction. Op-
timization of catalyst revealed that lowering the catalyst
loading to 1.0 mol% led to slight increase in the yield of 3a
Ph
I
6
7
1
f
3
f
Ph
(Table 1, entry 14). However, lowering it further to 0.5 mol%
MeO
I
73
78
led to substantial decrease in product yield (76%, Table 1,
entry 15).
MeO
1
g
3
g
After optimization of reaction conditions, a variety of
aryl and hetero aryl iodides and bromides was reacted with
styrene to yield substituted trans-stilbenoids and het-
eroaryl olefins (Table 2). As expected, activated aryl iodides
with electron-withdrawing substituents gave higher yields
of products (Table 2, entries 2–5) compared to those with
electron-donating substituents at the para position (Table
Ph
8
9
1
I
S
S
1h
3
h
Br
3a
3b
3c
84
89
82
1
i
2, entries 6 and 7). A similar trend in terms of electronic in-
NC
Br
0
fluence was observed with aryl bromides as well. The yield
of trans-stilbenoids in general was lower with aryl bro-
mides compared to aryl iodides (Table 2, entries 9–13).
Under the same reaction conditions, heterocyclic aromatic
halides also reacted with 2a giving moderate yields of
heteroaryl olefins (Table 2, entries 8, 14, and 15).
1
j
O2N
Br
11
1k
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Table 2 (continued)
the bulkier olefins such as vinyl naphthalene (4a) and deac-
tivated olefins such as butyl acrylate (4a′), high yields of
corresponding Heck-coupled products were obtained.
The mechanism of the reaction is outlined in Scheme 2.
The active catalytic species is palladium(0) I, which is stabi-
lized by glucosamine through coordination from the amino
and the anomeric hydroxyl sites. The reaction follows the
usual Heck pathway involving activation of aryl halide
through oxidative addition onto the palladium(0) species I
yield complex II. This is followed by olefin co-ordination to
form a π-complex III, migratory insertion of olefin to yield
IV and β-hydride elimination to form the π-complex. There-
after, base-promoted reductive elimination of the palladi-
um(II) complex VI regenerates the active palladium(0) cata-
lyst.
Entry
Aryl halide
Product
Yield
b
(
%)
O
Br
1
2
3
3e
74
1
1
l
Br
1
3f
72
62
m
Ph
14
N
Br
N
N
1
n
3
i
Br
Ph
15
74
To conclude, D-glucosamine has been demonstrated as
an efficient green replacement for phosphine ligands in pal-
ladium-catalyzed Heck coupling of aryl and heteroaryl ha-
lides. The protocol is mild, efficient, and versatile. The gen-
erality of the method has been exemplified through the
N
1
o
3j
a
Reaction conditions: DMF–H
2
O (1:1), aryl halide (1.0 equiv), 2a (1.0
equiv), glucosamine (1.0 equiv), Pd(OAc)
3.0 equiv), MW, 100 W, 60 min, 120 °C.
2
(1.0 mol%, 0.01 equiv), K CO
3
2
(
b
Isolated yield.
25
synthesis of a wide variety of trans-stilbene derivatives,
aryl naphthyl alkenes, heteroaryl olefins, and β-aryl-substi-
tuted acrylates in moderate to high yields. The use of micro-
wave conditions is beneficial as it helps in accelerating the
reaction, thus bringing down the reaction time from 12
hours to 1 hour. Future studies directed towards extending
the scope of palladium–glucosamine system to other cou-
pling reactions are under way.
The scope and versatility of the reaction was explored
further by synthesizing substituted aryl naphthyl olefins25
and substituted cinnamic acid esters (Table 3). In general,
yields with aryl iodides (Table 3, entries 1–5) were higher
than with aryl bromides (Table 3, entries 6–10). With both
OH
O
ArX
HX
HO
HO
OH
H2N
Pd(0)
oxidative addition
OH
reductive elimination
OH
I
O
HO
OH
H
VI
X
O
HO
HO
HO
OH
H2N
X
Pd(OAc)2 + K2CO3
D-glucosamine
2
H N
Ar
(II)
+
R
II
Ar
R
OH
O
OH
π-complex
O
HO
HO
OH
OH
Pd
HO
π-complex
X
HO
H2N
Ar
H2N
X
V
H
R
III
Ar
OH
R
O
HO
HO
OH
migratory insertion
β-hydride elimination
2
H N
Pd
X
Ar
IV
R
H
H
H
Scheme 2 Proposed mechanism
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Table 3 Palladium–Glucosamine-Catalyzed Heck Reaction between Aryl Halides and Vinyl Naphthalene or Butyl Acrylatea
X
Pd(OAc)2
glucosamine
4
or
a
R
R
5a–c
+
or
DMF–H2O (1:1)
MW, 120 °C, 60 min
O
R
COOBu
4
a'
OBu
X = I, Br
6a'–b'
Entry
1
Aryl halide
Product
Yield (%)b
1a
84
5
a
NC
2
3
1b
86
80
5
b
I
1
p
5
6
6
c
OBu
O
4
5
1a
1p
96
92
a′
b′
O
OBu
6
7
1i
1j
5a
5b
78
64
8
9
5c
62
Br
1
q
1i
6a′
6b′
66
62
10
1q
a
Reaction conditions: DMF–H
2
O (1:1), aryl halide (1.0 equiv), vinyl naphthalene or butyl acrylate (1.0 equiv), glucosamine (1.0 equiv), Pd(OAc)
2
(1.0 mol%, 0.01
equiv), K
Isolated yield.
2
CO (3.0 equiv), MW, 100 W, 60 min, 120 °C.
3
b
Acknowledgment
the Council of Scientific and Industrial Research, India for a Graduate
Fellowship. The authors thank DST-FIST for funding the ESI-HRMS fa-
cility at IIT Delhi.
This work has been financially supported by the Department of Sci-
ence and Technology, India under the project RP02555. A.K.J. thanks
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8) (a) Grasa, G. A.; Hillier, A. C.; Nolan, S. P. Org. Lett. 2001, 3, 1077.
(
(
24) Jha, A. K.; Jain, N. Tetrahedron Lett. 2013, 54, 4738.
25) General Experimental Procedure and Characterization Data
for Representative Compounds
D-glucosamine (428 mg, 2.0 mmol) was dissolved in DMF–H O
2
(1:1, 2 mL). Styrene (0.214 mL, 2.0 mmol), aryl halide (2.0
(b) Solinas, M.; Sechi, B.; Chelucci, G.; Baldino, S.; Pedro, J. R.;
mmol), K CO (3 equiv) and Pd(OAc) (1 mol%) were added to it,
2
3
2
Blay, G. J. Mol. Catal. A: Chem. 2014, 385, 73.
and the contents sealed in a vial were irradiated under micro-
wave irradiation at an output power of 100 W for 1 h at 120 °C.
The reaction mixture was extracted with hexane (3 × 25mL).
9) (a) Nájera, C.; Gil-Moltó, J.; Karlström, S.; Falvello, L. R. Org. Lett.
2
003, 5, 1451. (b) Wang, T.; Hao, X.-Q.; Huang, J.-J.; Wang, K.;
Gong, J.-F.; Song, M.-P. Organometallics 2014, 33, 194.
c) Jindabot, S.; Teerachanan, K.; Thongkam, P.; Kiatisevi, S.;
The combined organic layers were washed with H O, dried over
2
(
Na SO , filtered, and concentrated under reduced pressure.
2
4
Khamnaen, T.; Phiriyawirut, P.; Charoenchaidet, S.;
Sooksimuang, T.; Kongsaeree, P.; Sangtrirutnugul, P.
J. Organomet. Chem. 2014, 750, 35.
Column chromatography on silica gel afforded pure products.
(
E)-4-(2-Naphthalen-2-ylvinyl)benzonitrile (5b)
1
White crystalline solid. H NMR (300 MHz, CDCl ): δ = 7.75–780
3
(
10) (a) Mino, T.; Watanabe, K.; Abe, T.; Kogure, T.; Sakamoto, M.
Heterocycles 2013, 87, 2015. (b) Mino, T.; Yoshizawa, E.;
Watanabe, K.; Abe, T.; Hirai, K.; Sakamoto, M. Tetrahedron Lett.
(m, 4 H), 7.64 (d, J = 8.4 Hz, 1 H), 7.51–7.55 (m, 3 H), 7.41 (t, J =
3
.9 Hz, 2 H), 7.28 (d, J = 16.2 Hz, 1 H), 7.08–7.17 (m, 1 H) ppm.
1
3
C NMR (75 MHz, CDCl ): δ = 141.9, 133.8, 133.6, 133.5, 132.54,
3
2
014, 55, 3184.
11) (a) Li, S.; Lin, Y.; Cao, J.; Zhang, S. J. Org. Chem. 2007, 72, 4067.
b) Li, Y.-c.; Lin, Y.-j.; Zhang, S.-b.; Li, S.-h.; Duan, H.-f.; Li, Y.-c.
132.50, 128.6, 128.2, 127.8, 127.7, 126.99, 126.9, 126.6, 126.5,
(
123.3, 119.1, 110.6 ppm. MS (EI): m/z = 256 [M + 1].
(
(
E)-2-(2-o-Tolylvinyl)naphthalene (5c)
Chem. Res. Chin. Univ. 2012, 28, 242.
1
White crystalline solid. H NMR (300 MHz, CDCl ): δ = 7.731 (s,
3
(
12) (a) Chou, C.-C.; Yang, C.-C.; Syu, H.-B.; Kuo, T.-S. J. Organomet.
Chem. 2013, 745-746, 387. (b) Peral, D.; Gómez-Villarraga, F.;
Sala, X.; Pons, J.; Carles Bayón, J.; Ros, J.; Guerrero, M.; Vendier,
L.; Lecante, P.; García-Antón, J.; Philippot, K. Catal. Sci. Technol.
2
H), 7.68–7.71 (m, 2 H), 7.64 (d, J = 8.7 Hz, 1 H), 7.54 (d, J = 6.9
Hz, 1 H), 7.34–7.38 (m, 2 H), 7.31–7.33 (m, 1 H), 7.12–7.16 (m, 1
13
H), 7.02–7.11 (m, 3 H), 2.36 (s, 3 H). C NMR (75 MHz, CDCl ): δ
3
= 136.5, 135.9, 135.2, 133.8, 133.1, 130.6, 130.1, 128.4, 128.1,
127.8, 127.7, 126.9, 126.7, 126.4, 126.3, 125.9, 125.4, 123.7,
20.1. MS (EI): m/z = 244.
2013, 3, 475.
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Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 259–264

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