Palladium-catalyzed three-component reaction of 2,3-allenyl amines, isocyanates, and organic halides: A diversified assembly of imidazolidinones

Article abstract of DOI:10.1002/chem.201003611

A three-component reaction of 2,3-allenyl amines with isocyanates and organic halides has been developed. Two carbon-nitrogen bonds as well as a carbon-carbon bond were sequentially formed to construct imidazolidinone derivatives in good to excellent yiel

Full text of DOI:10.1002/chem.201003611

DOI: 10.1002/chem.201003611
Palladium-Catalyzed Three-Component Reaction of 2,3-Allenyl Amines,
Isocyanates, and Organic Halides: A Diversified Assembly of
Imidazolidinones
Wei Shu,[a] Qiong Yu,[b] Guochen Jia,*[c] and Shengming Ma*[a, b]
Imidazolidinones are important moieties that are present
in various biologically active compounds,[1] such as 5-HT2C
receptor antagonist[2] and NK1 antagonists[3] (Scheme 1). In
general, imidazolidinones can be prepared by cyclization of
a-amino derivatives of ketones, aldehydes, and related com-
pounds,[4] or by derivatization of imidazolidinones.[5] Recent-
ly, Shi and co-workers have reported the copper(I)-catalyzed
a-amination of aryl ketones and diamination of disubstitut-
ed terminal olefins to afford substituted imidazolidinones.[6]
allows the formation of several bonds in just one single syn-
thetic operation. Furthermore, in this way complex molecu-
lar architectures can be built from simple precursors without
the need for the isolation of intermediates.
During the past decades, palladium-catalyzed two-compo-
nent cyclization reactions of functionalized allenes with or-
ganic halides represented one of the most powerful and ver-
satile tools to construct cyclic compounds.[8] As we know,
isocyanates have found a wide range of applications in or-
ganic synthesis, particularly in the synthesis of heterocy-
cles.[9] Based on the analysis of the structures of biologically
active compounds shown in Scheme 1, we envisioned that
these potentially important imidazolidinones may be pre-
pared in a three-component reaction of 2,3-allenyl amines[10]
with organic halides in the presence of isocyanates. In this
process, the p-allylic palladium moiety would be formed by
carbometalation[11] of 2,3-allenyl amines and the urea anion
would be formed from the reaction of amines with isocya-
nates.[12] The C=C bond adds the opportunity to convert it
into the required ether functionality through the intermedia-
cies of ketones and alcohols; R1, R2, and R3 from the three
starting compounds would provide the diversity required by
the bio-screening. The challenge would be the premature
cyclization of intermediate syn-M1 forming vinylic azacyclo-
propanes or anti-M1 forming 2,5-dihydroprroles and the for-
mation of the seven-membered three-component products
from anti-M2 (Scheme 2).[8] Herein, we report the realiza-
tion of such a diversified protocol for the efficient synthesis
of imidazolidinones with an excellent selectivity.
Scheme 1. Some biologically active compounds containing imidazolidi-
nones.
On the other hand, the design of multicomponent reac-
tions[7] for the construction of organic molecules has attract-
ed more and more attention. This strategy offers significant
advantages over the classical step-by-step approaches, as it
We started our effort by reacting 2,3-allenyl amine 1a
with phenyl isocyanate 2a and iodobenzene 3a in the pres-
ence of K2CO3 (2 equiv) catalyzed by [PdACHTNUTGRNEUGN(PPh3)4] (5 mol%)
in THF at 708C. To our delight, the desired product 4a was
obtained in 72% yield after 22 h in this first try. After
screening of the solvent effect, we found that the reaction
proceeded smoothly in all the solvents tested, and afforded
4a in moderate to good yields (Table 1), and CH3CN gave
the best result, thus affording 4a in 96% yield (Table 1,
entry 6). The reaction with [Pd2ACHTNUTRGNEUNG(dba)3]·CHCl3 (2.5 mol%;
dba=dibenzylideneacetone) and PPh3 (10 mol%) gave the
product 4a in a slightly lower yield (Table 1, entry 7)
Next we examined the base effect on this reaction.
Among the bases tested, potassium carbonate, which was
the first to be tested (Table 1), resulted to be the best one
(Table 2, entries 1–4). Reducing the amount of potassium
[a] W. Shu, Prof. Dr. S. Ma
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
354 Fenglin Lu, Shanghai 200032 (P. R. China)
Fax : (+86)21-62609305
E-mail: masm@sioc.ac.cn
[b] Q. Yu, Prof. Dr. S. Ma
Shanghai Key Laboratory of Green Chemistry and Chemical Process
Department of Chemistry, East China Normal University
3663 North Zhongshan Road, Shanghai 200062 (P. R. China)
[c] Prof. Dr. G. Jia
Department of Chemistry
The Hong Kong University of Science and Technology
Clear Water Bay, Kowloon, Hong Kong (P.R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201003611.
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Chem. Eur. J. 2011, 17, 4720 – 4723

COMMUNICATION
Table 2. Further optimization on the palladium-catalyzed reaction of 2,3-
allenyl amine 1a with isocyanate 2a and iodobenzene (3a).[a]
Entry
Base (n [equiv])
n1:n2:n3
t [h]
Yield of 4a [%][b]
1
2
3
4
5
6
7
8
9
Cs2CO3 (2)
Na2CO3 (2)
K3PO4·3H2O (2)
K2CO3 (2)
K2CO3 (1.5)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
K2CO3 (2)
1:1.5:1.5
1:1.5:1.5
1:1.5:1.5
1:1.5:1.5
1:1.5:1.5
1:1.2:1.5
1:2:1.5
11
11
11
26.5
12
10
10
16
16
82
57
75
96
83
83
61
73
75
1:1.5:1.2
1:1.5:2
[a] The reaction was carried out using 1a (0.2 mmol), phenyl isocyanate
2a (n2 equiv), PhI 3a (n3 equiv), [Pd(PPh3)4] (5 mol%) and base
AHCTUNGTRENNUNG
(n equiv) in CH3CN (4 mL) in a Schlenk tube. [b] Yield of isolated prod-
uct.
Scheme 2. Reaction scheme.
As listed in Table 3, phenyl iodides substituted with
phenyl, electron-donating, and electron-withdrawing groups
are all suitable for this reaction, thus affording correspond-
ing imidazolidinones in good to excellent yields (Table 3, en-
tries 1–10).
Table 1. Solvent effect on the palladium-catalyzed reaction of 2,3-allenyl
amine 1a with isocyanate 2a and iodobenzene (3a).[a]
À
This chemistry shows excellent selectivity of the C I bond
À
over the C Br bond (Table 3, entry 9). Polysubstituted
phenyl iodides also worked smoothly (Table 3, entries 12–
Entry
Solvent
t [h]
Yield of 4a [%][b]
Table 3. Palladium-catalyzed reaction of 2,3-allenyl amine 1a and 2a
with various organic halides 3.[a]
1
2
3
4
5
6
THF
DME
DMF
DMSO
DCE
CH3CN
CH3CN
anisole
toluene
22
11
13
13
26.5
26.5
12
11
13
72
70
87
76
77
96
92
83
54
7[c]
8
9
Entry
R (3)
t [h]
Yield of 4 [%][b]
[a] The reaction was carried out using 1a (0.2 mmol), phenyl isocyanate
2a (0.3 mmol), PhI 3a (0.3 mmol), [Pd(PPh3)4] (5 mol%), and K2CO3
(2 equiv) in the indicated solvent (4 mL) in a Schlenk tube. [b] Yield of
isolated product. [c] [Pd2A(dba)3]·CHCl3 (2.5 mol%) and PPh3 (10 mol%)
were used. DCE=dichloroethane, DME=1,2-dimethoxyethane, DMF=
N,N-dimethylformamide, DMSO=dimethyl sulfoxide.
1
2
3
4
5
6
7
8
C6H5 (3a)
26.5
16
16
12
10
16
16
12
16
17
17
17
15.5
15.5
15.5
16
96 (4a)
90 (4b)
93 (4c)
83 (4d)
90 (4e)
74 (4 f)
92 (4g)
75 (4h)
86 (4i)
87 (4j)
64 (4k)
81 (4l)
84 (4m)
82 (4n)
70 (4o)
77 (4p)
63 (4q)
AHCTUNGTRENNUNG
4-MeO2CC6H4 (3b)
4-MeOCC6H4 (3c)
3-MeC6H4 (3d)
4-MeC6H4 (3e)
4-MeOC6H4 (3 f)
4-PhC6H4 (3g)
4-CNC6H4 (3h)
4-(4-BrC6H4)C6H4 (3i)
4-iPrC6H4 (3j)
CTHUNGTRENNUNG
9
carbonate (1.5 equiv), the yield dropped from 96% to 83%
(Table 2, entries 4 and 5). By varying the ratio of the starting
materials, we found that 1a/2a/3a (1:1.5:1.5) gave the best
results. Thus, we defined the reaction of 1a (1 equiv), 2a
10
11
12
13
14
15
16
17
3-thienyl (3k)
3,5-Me2C6H3 (3l)
3,4-Me2C6H3 (3m)
3,4-(OCH2)2C6H3 (3n)
(E)-C6H13CH=CH (3o)
(E)-MeO2CCH=CH (3p)
4-NH2C6H4 (3q)
(1.5 equiv), and 3a (1.5 equiv) catalyzed by [PdACHTNUTRGNE(UNG PPh3)4]
(5 mol%) and K2CO3 (2 equiv) in CH3CN at 708C as the
standard for further study. With the optimized protocol in
hand, we turned to demonstrate the generality of this reac-
tion with a broad range of 2,3-allenyl amines 1, isocyanates
2, and organic halides 3.
11
[a] The reaction was carried out using 1a (0.2 mmol), 2a (0.3 mmol), and
3 (0.3 mmol) in CH3CN (4 mL) and catalyzed by [Pd
[b] Yield of isolated product.
AHCTUNGTRENNUNG
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S. Ma, G. Jia et al.
14). Furthermore, the reaction of 1-alkenyl iodides also pro-
ceeded smoothly to afford the corresponding products in
good yields (Table 3, entries 15 and 16). In the case of heter-
ocyclic aromatic iodide 3k, 4k was obtained in 64% yield
(Table 3, entry 11). It is noteworthy that even 4-iodoaniline
with a free amine group is compatible in this process, and
gave the substituted 4q in 63% yield with the aniline func-
tionality untouched for further elaboration (Table 3,
entry 17).
In addition to 1a and 2a, N-benzyl or n-butyl-protected
2,3-allenyl amines and even free 2,3-allenyl amine 1d can be
used for this process (Scheme 3 and Equation (1)): Various
Figure 1. ORTEP representation of 4r. Ellipsoids set at 30% probability,
hydrogen atoms omitted for clarity.
cated to study the potential applications of these products as
well as the development of asymmetric version of this reac-
tion.
Experimental Section
Typical procedure for the synthesis of 1-(4-methoxybenzyl)-3-phenyl-4-
(1-phenylvinyl)imidazolidin-2-one (4a): Once the Schlenk tube contain-
ing K2CO3 (55 mg, 0.40 mmol) was flamed, dried, and filled with argon,
Scheme 3. The effect of different protecting groups on the nitrogen
atoms.
[PdACHTUNGRTNEUNG(PPh3)4] (12 mg, 0.010 mmol), 1a (37 mg, 0.20 mmol), 3a (58 mg,
0.28 mmol), 2a (36 mg, 0.30 mmol), and CH3CN (4 mL) were added se-
quentially. The resulting solution was heated to and stirred at 708C.
When the reaction was completed as monitored by TLC, the solvent was
evaporated under reduced pressure, and the residue was purified by chro-
matography on silica gel (eluent: petroleum ether/ethyl acetate=7:1) to
afford 72 mg (96%) of 4a as an oil: 1H NMR (400 MHz, CDCl3) d=
7.64–7.60 (m, 2H), 7.36–7.29 (m, 7H), 7.18–7.15 (m, 2H), 7.07–7.02 (m,
1H), 6.86–6.82 (m, 2H), 5.44 (s, 1H), 5.26 (s, 1H), 5.09 (dd, J=9.6,
4.4 Hz, 1H), 4.45 (d, J=15.0 Hz, 1H), 4.39 (d, J=15.0 Hz, 1H), 3.79 (s,
3H), 3.60 (dd, J=9.2, 8.8 Hz, 1H), 3.06 ppm (dd, J=8.8, 4.4 Hz, 1H);
13C NMR (100.5 MHz, CDCl3) d=158.9, 157.6, 145.0, 139.5, 138.0, 129.3,
128.62, 128.55, 128.1, 126.4, 122.5, 118.7, 114.4, 113.9, 56.3, 55.2, 48.0,
47.0 ppm; IR (neat): n˜ =1704, 1610, 1599, 1512, 1502, 1456, 1437, 1417,
1348, 1247, 1205, 1175, 1151, 1112, 1033 cmÀ1; MS (EI): m/z (%): 385
([M+ +1], 7.88), 384 ([M+], 27.11), 121 (100); HRMS calcd for
C25H24N2O2 [M+]: 384.1838; found: 384.1837.
isocyanates (2) containing phenyl groups with electron-do-
nating or electron-withdrawing substituent are all suitable
substrates for this transformation. The structure of 4 was
further confirmed by X-ray diffraction analysis of 4r
(Figure 1).[13]
In conclusion, we have demonstrated a novel three-com-
ponent cascade reaction of 2,3-allenyl amines with isocya-
nates and organic halides, which provide an efficient route
for the diversified synthesis of polysubstituted imidazolidi-
nones with biological potentials. This method offers several
advantages such as good functional-group tolerance, mild re-
action conditions, high yields, and easily accessible starting
materials (diversity), which will be of board interest for me-
dicinal chemistry. In this transformation, simultaneously,
Acknowledgements
Financial support from the National Natural Science Foundation of
China (20732005), the State Basic and Research Development Program
(Grant No. 2011CB808700), and the Chinese Academy of Sciences is
greatly appreciated. We thank Qiankun Li from our group for reproduc-
ing the results presented in entries 6 and 15 in Table 3 and the formation
of 4s in Scheme 3.
À
À
one C C bond and two C N bonds are efficiently formed
with the breaking of two p bonds. Further work will be dedi-
Keywords: allenes · amines · cyclization · heterocycles ·
isocyanates · palladium
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Chem. Eur. J. 2011, 17, 4720 – 4723

Palladium-Catalyzed Synthesis of Imidazolidinone Derivatives
COMMUNICATION
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indices (all data): R1=0.0689, wR2=0.1305; a=6.1299(3), b=
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T=296 (2) K, wavelength: 0.71073 ꢄ, Z=4, reflections collected/
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Received: December 14, 2010
Published online: March 24, 2011
Chem. Eur. J. 2011, 17, 4720 – 4723
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4723