Reaction of functionalized carbodiimide with α-amino ester: A selective synthesis of 2,3,5-trisubstituted imidazol-4-ones

Article abstract of DOI:10.1080/00397910802326562

3-(Ethoxycarbonylmethylene)-2-(arylimino)-imidazol-4-ones 5 were synthesized selectively by reaction of α-amino ester with carbodiimides 4, which were obtained from aza-Wittig reaction of iminophosphoranes 2 with aromatic isocyanates. Copyright Taylor & F

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Reaction of Functionalized
Carbodiimide with α-Amino
Ester: A Selective Synthesis
of 2,3,5-Trisubstituted
Imidazol-4-ones
Hong-Xia Li a , Yong Sun b & Ming-Wu Ding b
a College of Science, Naval University of
Engineering, Wuhan, China
b Key Laboratory of Pesticide and Chemical Biology
of Ministry of Education, Central China Normal
University, Wuhan, China
Published online: 07 Nov 2008.
To cite this article: Hong-Xia Li , Yong Sun & Ming-Wu Ding (2008) Reaction of
Functionalized Carbodiimide with α-Amino Ester: A Selective Synthesis of 2,3,5-
Trisubstituted Imidazol-4-ones, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 38:24, 4328-4336, DOI:
10.1080/00397910802326562
To link to this article: http://dx.doi.org/10.1080/00397910802326562
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Synthetic Communications1, 38: 4328–4336, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802326562
Reaction of Functionalized Carbodiimide with
a-Amino Ester: A Selective Synthesis of
2,3,5-Trisubstituted Imidazol-4-ones
Hong-Xia Li,1 Yong Sun,2 and Ming-Wu Ding2
1College of Science, Naval University of Engineering, Wuhan, China
2Key Laboratory of Pesticide and Chemical Biology of Ministry of
Education, Central China Normal University, Wuhan, China
Abstract: 3-(Ethoxycarbonylmethylene)-2-(arylimino)-imidazol-4-ones
5
were
synthesized selectively by reaction of a-amino ester with carbodiimides 4, which
were obtained from aza-Wittig reaction of iminophosphoranes 2 with aromatic
isocyanates.
Keywords: a-Amino ester, aza-Wittig reaction, carbodiimide, imidazolin-4-one,
ylides
Imidazolin-4-ones have received considerable attention over the past few
years because of their interesting biological activities. Some of them have
exhibited good antibacterial or antifungal activities or are used as leuko-
triene B4 receptor antagonist and potassium channel openers[1–5]; others
have shown high herbicidal activities, such as imazamethabez and ima-
zethapyr.[6] They are also involved in some alkloids. Examples of these
include the discapamides or mauritiamines, isolated from Caribbean Age-
las sponges or marine sponges Agelas mauritiana, which show potential
antihistamine or antifouling activities.[7,8] Hence these heterocycles, in
particular 2,3,5-trisubstituted imidazolin-4-ones, have become attractive
targets involved in drug discovery and crop protection, because of
Received May 9, 2008.
Address correspondence to Ming-Wu Ding, Key Laboratory of Pesticide and
Chemical Biology of Ministry of Education, Central China Normal University,
Wuhan 430079, China. E-mail: mwding@mail.ccnu.edu.cn
4328

Reaction of Functionalized Carbodiimide
4329
their large number of possible substitution patterns and interesting
combination of potential hydrogen bond donors and acceptors on a small
five-membered ring system.
Recently we have been interested in the synthesis of imidazolinones,
quinazolinones, and thienopyrimidinones via an aza-Wittig reaction of a-
or b-ethoxycarbonyl iminophosphorane with aromatic isocyanate and sub-
sequent reaction with various nucleophiles under mild conditions.[9–14]
However, the reaction of a-amino ester with a-ethoxycarbonyl carbodiimde
was not investigated. Here we report first an efficient and selective synthesis
of 3-(ethoxycarbonylmethylene)- 2-(arylimino)-imidazol-4-ones 5 from
iminophosphorane 2.
As shown in Scheme 1, the easily accessible azide 1 reacted with tri-
phenylphosphine to create the iminophosphorane 2, which was allowed
to react with aromatic isocyanates to produce carbodiimides 3 via inter-
molecular aza-Wittig reaction. Further reaction of the carbodiimides 3
with a-amino ester at room temperature gave selectively 3-(ethoxycarbo-
nyl-methylene)-2-(arylimino)-imidazol-4-ones 5. A variety of a-amino
esters and isocyanates could be used for this synthetic strategy, and the
products 5 were obtained in good yields (Table 1). Presumably the reac-
tion of carbodiimides 3 with a-amino ester should afford primarily gua-
nidine intermediates of type 4. From these intermediates 4, the formation
of two regioisomers 5 (via path a) and 6 (via path b) could in principle
Scheme 1. Selective synthesis of imidazol-4-ones 5.

4330
H.-X. Li, Y. Sun, and M.-W. Ding
Table 1. Selective synthesis of imidazolin-4-ones 5 by aza-Wittig reaction
Entry Product
Ar
R
Conditions Yielda (%) eeb (%)
1
2
3
4
5a
5b
5c
5d
Ph
Ph
Ph
Ph
Me
i-Pr
(CH2)2CO2Et
rt=1 h
rt=2 h
rt=1 h
rt=2 h
91
77
84
81
48
64
81
77
5
6
7
8
5e
5f
Ph
Ph
PhCH2
i-Bu
Me
rt=1 h
rt=2 h
rt=1 h
rt=2 h
87
88
92
85
54
62
58
71
5g
5h
3-Me–C6H4
3-Me–C6H4
9
10
11
5i
5j
3-Me–C6H4 (CH2)2CO2Et
3-Me–C6H4
3-Me–C6H4
rt=1 h
rt=2 h
rt=2 h
80
86
78
79
62
54
PhCH2
i-Bu
5k
aIsolated yields based on carbodiimide 3.
bThe ee was determined by HPLC.
take place. However, only regioisomer 5 was obtained from the reaction
mixture. This is probably due to the easier cyclization between the less
steric amino group and ester group in path a. Unfortunately partial race-
mization of the product 5 took place under the reaction condition, and
the ee of 5 was between 48% and 81% (Table 1).
The structures of the target compounds 5 have been confirmed by spec-
troscopic data. Furthermore, a single crystal of 5f was obtained from a
CH2Cl2 solution of 5f, and an X-ray structure analysis verified the proposed
structure (Fig. 1). The N1ꢀC7, N2ꢀC7, and N3ꢀC7 bond lengths of 5f are
˚
1.263(3), 1.364(3), and 1.401(3) A, respectively, indicating a degree of
electron delocalizition. The N3–C7–N1–C1 torsion angle ofꢀ174.1(2)ꢁ
indicates an E configuration of the molecule about the C7 ¼ N1 bond.
In conclusion, we have developed a selective synthesis of 3-(ethoxycar-
bonylmethylene)-2-(arylimino)-imidazol-4-ones by reaction of a-amino
ester with carbodiimides in good yield. Because of the mild reaction

Reaction of Functionalized Carbodiimide
4331
Figure 1. X-ray structure of compound 5f (50% thermal ellipsoids).
condition, good yields, and easily accessible starting material, we think that
the versatile approach discussed here has the potential to synthesize many
biologically and pharmaceutically active imidazolones.
EXPERIMENTAL
Melting points are uncorrected. MS were measured on a Finnigan Trace
MS spectrometer. NMR were recorded in CDCl3 on a Varian Mercury
400 spectrometer, and resonances are given in ppm (d) relative to
TMS. Elementary analyses were taken on a Vario EL III elementary
analysis instrument. The ee of the product was determined by HPLC
(chiralpak AD-H column, hexane=i-PrOH, flow rate 1 ml=min,
k ¼ 254 nm).
Preparation of Carbodiimide 3
A solution of triphenylphosphine (2.62 g, 10 mmol) in dry methylene
dichloride (15 mL) was added dropwise under nitrogen at room tempera-
ture to a well-stirred solution of azide 1 (1.29 g, 10 mmol) in dry methy-
lene dichloride (15 mL). The reaction mixture was stirred at room
temperature for 2 h; then phenyl isocyanate (1.19 g, 10 mmol) was added
at 0 ꢁC. After the reaction mixture was stirred at 0 ꢁC for 2 h, the solvent
was removed under reduced pressure. The crude carbodiimides 3 were
then purified by column chromatography on silica gel, with petroleum
ether=diethyl ether (10:1, v=v) as eluent.

4332
H.-X. Li, Y. Sun, and M.-W. Ding
Preparation of 3-(Ethoxycarbonylmethylene)-2-(arylimino)-
imidazol-4-ones 5
Carbodiimide 3 (0.41 g, 2 mmol) in CH3 CN (10 mL) was added to a
stirred solution of (L)-a-amino ester hydrogen chloride (2 mmol) and
NEt3 (0.3 g, 3 mmol) in CH3CN (5 mL). The mixture was stirred at room
temperature for the time shown in Table 1, and the solvent was removed
under reduced pressure. The 3-(ethoxycarbonylmethylene)-2-(arylimino)-
imidazol-4-ones 5 were obtained by recrystallization from a mixed sol-
vent of hexane and dichloromethane (1:1–1:3) or by column chromato-
graphy on silica gel (EtOAc–petroleum ether, 1:3–1:1). Spectral data
for compound 5 are as follows.
Data
Compound 5a
White solid, mp 76–77 ꢁC. 1H NMR (CDCl3, 400 MHz): d ¼ 1.30 (t,
J ¼ 7.2 Hz, 3H, CH3), 1.44 (d, 3H, J ¼ 6.8 Hz, CH3), 4.15 (q, 1H,
J ¼ 6.8 Hz, CH), 4.24 (q, 2H, J ¼ 7.2 Hz, OCH2), 4.43 (s, 2H, NCH2),
4.80 (s, 1H, NH), 6.96–7.34 (m, 5H, Ar-H). MS (m=z, %): 275 (Mþ,
69), 202 (52), 174 (68), 145 (66), 131 (100). Anal. calcd. for C14 H17 N3
O3: C, 61.08; H, 6.22; N, 15.26. Found: C, 61.27; H, 6.28; N, 15.19.
Compound 5b
1
White solid, mp 117–118 ꢁC. H NMR (CDCl3, 400 MHz): d ¼ 0.96 (dd,
J ¼ 6.8 Hz, 6H, 2CH3), 1.29 (t, J ¼ 7.2 Hz, 3H, CH3), 2.18–2.25 (m, 1H,
CH), 3.93 (d, J ¼ 3.2 Hz, 1H, CH), 4.22 (q, J ¼ 7.2 Hz, 2H, OCH2),
4.42 (s, 2H, NCH2), 4.75 (s, 1H, NH), 6.95–7.34 (m, 5H, Ar-H). MS
(m=z, %): 303 (Mþ, 100), 260 (25), 230 (62), 186 (75), 131 (94). Anal.
calcd. for C16H21N3O3: C, 63.35; H, 6.98; N, 13.85. Found: C, 63.21;
H, 6.88; N, 13.92.
Compund 5c
Light yellow solid, mp 52–54 ꢁC. 1H NMR (CDCl3, 400 MHz): 1.22
(t, J ¼ 7.2 Hz, 3H, CH3), 1.30 (t, J ¼ 7.2 Hz, 3H, CH3), 2.05–2.19 (m,
2H, CH2), 2.45 (t, J ¼ 7.6 Hz, 2H, CH2), 4.07 (q, J ¼ 7.2 Hz, 2H,
OCH2), 4.15 (t, J ¼ 5.2 Hz, 1H, CH), 4.22 (q, J ¼ 7.2 Hz, 2H, OCH2),
4.40 (s, 2H, NCH2), 5.15 (s, 1H, NH), 6.93–7.31 (m, 5H, Ar-H). MS

Reaction of Functionalized Carbodiimide
4333
(m=z, %): 361 (Mþ, 55), 316 (20), 274 (100), 200 (22), 186 (8), 131 (20).
Anal. calcd. for C18H23N3O5: C, 59.82; H, 6.41; N, 11.63. Found: C,
59.58; H, 6.53; N, 11.48.
Compound 5d
Light yellow solid, mp 72–74 ꢁC. 1H NMR (CDCl3, 400 MHz): 1.29
(t, J ¼ 7.2 Hz, 3H, CH3), 3.05–3.47 (m, 2H, CH2), 4.23 (q, J ¼ 7.2 Hz,
2H, OCH2), 4.31 (dd, J ¼ 3.6, 9.2 Hz, 1H, CH), 4.40 (s, 2H, NCH2),
4.74 (s, 1H, NH), 6.76–7.57 (m, 9H, Ar-H), 8.13 (s, 1H, NH). MS
(m=z, %): 390 (Mþ, 50), 275 (74), 246 (24), 186 (58), 174 (30), 145
(100). Anal. calcd. for C22H22N4O3: C, 67.68; H, 5.68; N, 14.35. Found:
C, 67.42; H, 5.56; N, 14.22.
Compund 5e
White solid, mp 101–103 ꢁC. 1H NMR (CDCl3, 400 MHz): 1.29
(t, J ¼ 7.2 Hz, 3H, CH3), 2.84–3.29 (m, 2H, CH2), 4.20–4.26 (m, 3H,
OCH2 and CH), 4.38 (s, 2H, NCH2), 4.71 (s, 1H, NH), 6.86–7.32 (m,
10H, Ar-H). MS (m=z, %): 351 (Mþ, 42), 260 (41), 186 (90), 131 (100),
91 (39). Anal. calcd. for C20H21N3O3: C, 68.36; H, 6.02; N, 11.96. Found:
C, 68.25; H, 6.19; N, 11.84.
Compound 5f
White solid, mp 140–142 ꢁC. 1H NMR (CDCl3, 400 MHz): 0.94 (dd,
J ¼ 6.8 Hz, 6H, 2CH3), 1.29 (t, J ¼ 7.2 Hz, 3H, CH3), 1.54–1.60 (m, 1H,
CH), 1.70–1.80 (m, 2H, CH2), 4.08 (dd, J ¼ 4.4, 9.2 Hz, 1H, CH), 4.23
(q, J ¼ 7.2 Hz, 2H, OCH2), 4.44 (s, 2H, CH2), 4.82 (s, 1H, NH),
6.95–7.33 (m, 5H, Ar-H). MS (m=z, %): 317 (Mþ, 82), 244 (44), 216
(28), 174 (30), 131 (100). Anal. calcd. for C17H23N3O3: C, 64.33; H,
7.30; N, 13.24. Found: C, 64.37; H, 7.43; N, 13.06.
Compound 5g
Light yellow solid, mp 54–55 ꢁC. 1H NMR (CDCl3, 400 MHz): 1.29
(t, J ¼ 7.2 Hz, 3H, CH3), 1.40 (d, 3H, J ¼ 6.8 Hz, CH3), 2.34 (s, 3H,
CH3), 4.10 (q, J ¼ 6.8 Hz, 1H, CH), 4.22 (q, J ¼ 7.2 Hz, 2H, OCH2),
4.38 (s, 2H, NCH2), 4.95 (s, 1H, NH), 6.74–7.20 (m, 4H, Ar-H). MS
(m=z, %): 289 (Mþ, 41), 244 (9), 216 (23), 188 (45), 159 (56), 145 (100).
Anal. calcd. for C15H19N3O3: C, 62.27; H, 6.62; N, 14.52. Found: C,
62.25; H, 6.57; N, 14.60.

4334
H.-X. Li, Y. Sun, and M.-W. Ding
Compound 5h
Light yellow solid, mp 59–60 ꢁC. 1H NMR (CDCl3, 400 MHz): 1.30
(t, J ¼ 6.8 Hz, 3H, CH3), 2.24 (s, 3H, CH3), 3.01–3.46 (m, 2H, CH2),
4.22 (q, J ¼ 7.2 Hz, 2H, OCH2), 4.28 (dd, J ¼ 3.6, 9.2 Hz, 1H, CH),
4.39 (s, 2H, NCH2), 4.78 (s, 1H, NH), 6.56–7.57 (m, 8H, Ar-H), 8.22
(s, 1H, NH). MS (m=z, %): 404 (Mþ, 1), 275 (74), 200 (8), 145 (17),
130 (100). Anal. calcd. for C23H24N4O3: C, 68.30; H, 5.98; N, 13.85.
Found: C, 68.31; H, 5.79; N, 13.66.
Compound 5i
1
Light yellow solid, mp 45–46 ꢁC. H NMR (CDCl3, 400 MHz): 1.23
(t, J ¼ 6.8 Hz, 3H, CH3), 1.30 (t, J ¼ 6.8 Hz, 3H, CH3), 2.08–2.20
(m, 2H, CH2), 2.33 (s, 3H, CH3), 2.47 (t, J ¼ 6.8 Hz, 2H, CH2), 4.10
(q, J ¼ 7.2 Hz, 2H, OCH2), 4.18 (t, J ¼ 5.6 Hz, 1H, CH), 4.24
(q, J ¼ 7.2 Hz, 2H, OCH2), 4.43 (s, 2H, NCH2), 5.05 (s, 1H, NH),
6.75–7.22 (m, 4H, Ar-H). MS (m=z, %): 375 (Mþ, 16), 288 (100), 214
(27), 171 (30), 145 (42). Anal. calcd. for C19H25N3O5 C, 60.79; H, 6.71;
N, 11.19. Found: C, 60.91; H, 6.59; N, 11.02.
Compound 5j
White solid, mp 88–90 ꢁC. 1H NMR (CDCl3, 400 MHz): 1.29
(t, J ¼ 7.2 Hz, 3H, CH3), 2.30 (s, 3H, CH3), 2.85–3.31 (m, 2H, CH2),
4.21–4.26 (m, 3H, OCH2 and CH), 4.39 (s, 2H, NCH2), 4.73 (s, 1H,
NH), 6.68–7.34 (m, 9H, Ar-H). MS (m=z, %): 365 (Mþ, 100), 274 (36),
200 (27), 145 (13). Anal. calcd. for C21H23N3O3: C, 69.02; H, 6.34; N,
11.50. Found: C, 69.21; H, 6.52; N, 11.46.
Compound 5k
White solid, mp 110–112 ꢁC. 1H NMR (CDCl3, 400 MHz): 0.94 (dd,
J ¼ 6.4 Hz, 6H, 2CH3), 1.29 (t, J ¼ 7.2 Hz, 3H, CH3), 1.56–1.60 (m, 1H,
CH), 1.72–1.81 (m, 2H, CH2), 2.33 (s, 3H, CH3), 4.08–4.11 (m, 1H,
CH), 4.23 (q, J ¼ 7.2 Hz, 2H, OCH2), 4.41 (s, 2H, NCH2), 4.78 (s, 1H,
NH), 6.79–7.22 (m, 4H, Ar-H). MS (m=z, %): 331 (Mþ, 75), 258 (35),
230 (37), 200 (23), 188 (28), 145 (100). Anal. calcd. for C18H25N3O3: C,
65.23; H, 7.60; N, 12.68. Found: C, 65.13; H, 7.59; N, 12.53.

Reaction of Functionalized Carbodiimide
Crystal Structure of 5f
4335
Crystal data for 5f: C17H23N3O3, Mr ¼ 317.38, orthorhombic, space
˚
˚
˚
group Pbca, a ¼ 16.059 (2) A, b ¼ 10.6310 (16) A, c ¼ 20.690 (3) A,
V ¼ 3532.2 (9) A ; Z ¼ 8; d ¼ 1.374 Mg=m3; (MoKa) ¼ 0.08 mmꢀ1
;
3
˚
26,346
reflections
collected,
3,097
independent
reflections,
wR(F2) ¼ 0.195. Crystallographic data for the structure analysis have
been deposited with the Cambridge Crystallographic Data Centre,
CCDC No. 672985, for compound 5f. Copies of this information may
be obtained free of charge from the director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [e-mail: deposit@ccdc.cam.ac.uk, fax: 44
(1223) 336033].
ACKNOWLEDGMENT
We gratefully acknowledge financial support of this work by the
National Natural Science Foundation of China (No. 20772041) and
Hubei Province (No. 2006ABB016) and the Key Project of Chinese Min-
istry of Education (No. 107082).
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