Facile synthesis of highly substituted iminocyclopentenes: A novel isocyanide-based three-component condensation reaction

Article abstract of DOI:10.1055/s-0030-1261219

The reaction of alkoxymethylenemalononitrile with dialkyl acetylenedicarboxylates (DAAD) and cyclohexylisocyanide results in a three-component condensation reaction in which the alkoxymethylenemalononitrile group acts as a dipolarophile, producing highly functionalized iminocyclopentenes under mild conditions in high yields. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0030-1261219

LETTER
2307
Facile Synthesis of Highly Substituted Iminocyclopentenes:
A Novel Isocyanide-Based Three-Component Condensation Reaction
Isocyanide-Based
b
T
hree-Comp
b
onent Conde
a
nsationRea
s
c
tion Ali Esmaeili,*a Abbas Moradi,a Azizollah Habibib
a
Department of Chemistry, University of Birjand, P.O. Box 97175/615, Birjand, Iran
Fax +98(561)2230009; E-mail: aa_esmaeili@yahoo.com
b
Faculty of Chemistry, University of Tarbiatmoallem, 15719-14911 Tehran, Iran
Received 16 May 2011
activated alkenes, leading to highly substituted cyclopen-
tadienes (Scheme 1).18 However, a literature survey re-
vealed that the reaction of isocyanide and dialkyl
acetylenedicarboxylate (DAAD) in the presence of
Abstract: The reaction of alkoxymethylenemalononitrile with di-
alkyl acetylenedicarboxylates (DAAD) and cyclohexylisocyanide
results in a three-component condensation reaction in which the
alkoxymethylenemalononitrile group acts as a dipolarophile, pro-
ducing highly functionalized iminocyclopentenes under mild condi- alkoxymethylenemalononitrile has not been investigated.
tions in high yields.
–
C
Key words: alkoxymethylenemalononitrile, dialkyl acetylenedi-
carboxylates, isocyanides, iminocyclopentenes
+
N
R1
Ph
R2O2C
R2O2C
+
CN
CN
THF, 65 °C
24 h
R2O2C
CO2R2
+
The development of new multicomponent reactions
(MCR) offers efficient and convenient entries into inter-
esting structures.1 Devising such types of reactions that
form several bonds in one-step is one of the main goal
in modern organic synthesis.2 Isocyanide-based MCR
(IMCR), leading to novel heterocyclic scaffolds, are par-
ticularly useful for the construction of diverse chemical li-
braries of ‘drug-like’ molecules.3
NH
CN
R1
Ph
CN
Scheme 1
In the light of our interest in IMCR involving zwitterionic
species19–21 and impressed by the success of the above-
mentioned reaction, cyclohexylisocyanide 1 was treated
with DAAD and alkoxymethylenemalononitrile 3. Struc-
tural characterization of the isolated product supported
that the products obtained here should be 4 rather than 5
(Scheme 2). It should be pointed out that even under pro-
longed reaction times and high temperatures, product 4
failed to isomerize to 5 via a [1,5]-H shift.
Owing to their chemical and biological properties, five-
membered carbocycles such as cyclopentenes have at-
tracted much attention. They are frequently encountered
components in natural products, and they are also valu-
able intermediates in organic synthesis.4–6 As examples,
cyclopentene-1,2-dicarboxylic acids have been incorpo-
rated in ACE inhibitors,7 and Samuelsson et al. have re-
ported the use of a trisubstituted cyclopentene moiety in
VCH NS3 protease inhibitors.8
–
C
+
N
Consequently, a wide range of approaches has been de-
vised for the synthesis of cyclopentene derivatives. One of
these employs a classical intramolecular Michael-type
conjugate addition to activated alkenes, alkynes,9 and al-
lenyl solfones.10 Other approaches to cyclopentene deriv-
atives include Ramberg–Bäcklund rearrangement of
thiosugar-drived sulfones11 and rearrangement of vinyl
cyclopropanes.12 Recent methods for the synthesis of cy-
clopentenes include the intramolecular Morita–Baylis–
Hillman reaction,13 ring-closing metathesis,14 intramolec-
ular Wittig reaction,15,16 and an isocyanide-based three-
component reaction.17
R3
1
O
N
R2O2C
R2O2C
+
CN
toluene
reflux
R2O2C
CO2R2
CN
2
+
CN
4
O
R3
CN
3
X
R3
[1,5]-H shift
O
R2O2C
R2O2C
CN
CN
In 2004, Nair envisaged the possibility of intermolecular
trapping of the zwitterionic intermediates generated from
isocyanides and DMAD with arylidenemalononitriles as
HN
5
Scheme 2
SYNLETT 2011, No. 16, pp 2307–2310
x
x
.x
x
.2
0
1
1
Advanced online publication: 08.09.2011
DOI: 10.1055/s-0030-1261219; Art ID: D14911ST
© Georg Thieme Verlag Stuttgart · New York

2308
A. A. Esmaeili et al.
LETTER
In a pilot experiment, cyclohexylisocyanide, DMAD, and CN triple-bond stretching did not appear in IR spectrum
methoxymethylenemalononitrile were refluxed in tolu- of 4 owing to being attached to a carbon-bearing electron-
ene. After 0.5 hours, the solvent was removed under vac- accepting cyanide and imine groups.22 Nevertheless, the
uum. The residue was crystallized from n-hexane, to appearance of a moderately strong band at 2200 cm–1 in
afford the highly substituted iminocyclopentene deriva- the FT-Raman spectrum of 4e, clearly confirmed the pres-
tive 4a in 93% yield. To explore the scope of this reaction ence of a nitrile group in the products. The proton-decou-
further, other acetylenic esters and alkoxymethylenema- pled 13C NMR spectrum of 4a showed 18 distinct
lononitriles were used in a series of reactions and the out- resonances. Two characteristic 13C NMR signals due to
comes are shown in Table 1. Two other isocyanides, tert- the cyanide carbons appeared at d = 108.83 and 111.70
butylisocyanide and 1,1,3,3-tetramethylbutylisocyanide ppm and those of the two ester carbonyls at d = 161.27
were also examined, but no conversion occurred. Further- and 161.92 ppm. The 1H NMR and 13C NMR of 4b–h are
more use of unsymmetrical alkynes such as methyl acety- comparable to those of 4a except for the R1 and R2 groups,
lenecarboxylate and ethyl acetylenecarboxylate as which exhibit characteristic signals with appropriate
1
reactants afforded a complex mixture of products. H chemical shifts (see Supplementary Information).
NMR analysis indicated the formation of desired product
Although the mechanism of the reaction between the iso-
in the crude reaction mixture, but all attempts to purify the
cyanide and dialkyl acetylenedicarboxylate in the pres-
product failed.
ence of arylidenemalononitrile has not yet been
established experimentally, a possible explanation is pro-
posed in Scheme 3. The initial event is the formation of
the zwitterion 6 from the isocyanide 1 and DAAD 2. The
zwitterion can add to the electrophilic carbon–carbon
double bond of 3 resulting in the formation of 7, which
then undergoes cyclization to product 4.
Table 1 Synthesis of Highly Fuctionalized Iminocyclopentenes
–
+
N
C
R3
1
O
N
R2O2C
R2O2C
+
CN
toluene
reflux
R2O2C
CO2R2
CN
2
+
CO2R2
CN
N+
4
3
O
–
C
+
N
R3
CN
3
–
CO2R2
R2O2C
CH2O2R2
4
R2
R3
Time (min) Yield (%)a
1
2
6
4a
4b
4c
4d
4e
4f
Me
Et
Me
30
60
93
82
84
75
90
86
60
82
R3
O
R3
CO2R2
O
R2O2C
R2O2C
Me
Me
Me
Et
CN
CN
CO2R2
NC
NC
i-Pr
N-Pb
Me
Et
120
120
25
–
+N
N
4
7
Et
60
Scheme 3
4j
i-Pr
N-Pb
Et
120
120
4h
Et
In conclusion, we have devised a novel three-component,
one-pot reaction for the synthesis of highly substituted im-
inocyclopentene derivatives. The simple and readily
available starting materials, lack of need for catalysts,
neutral reaction conditions, and good to high yields of the
products are the main advantages of our method.
a Isolated yield.
b N-P = neopentyl.
The structures of the products were deduced from their IR,
1H NMR, 13C NMR and mass spectral data. The mass
spectra of these compounds displayed molecular ion
peaks at the appropriate m/z values. For example, the 1H
NMR spectrum of 4a contained multiplet signals for a cy-
clohexyl ring (d = 1.12–1.85 ppm), a singlet for the meth-
oxy group (d = 3.73 ppm), two singlets for the two ester
General Procedure for the Synthesis of Dimethyl-4,4-dicyano-
3-(cyclohexylimino)-5-methoxycyclopent-1-ene-1,2-dicarboxy-
late (4a)
To a stirred solution of methoxymethylenemalononitrile 3a (1.0
methoxy groups (d = 3.86 and 3.89 ppm), a multiplet for mmol) and dimethyl acetylenedicarboxylate (1.0 mmol) in toluene
(5 mL) was added dropwise a solution of cyclohexyl isocyanide (1.0
NCH of the cyclohexyl ring (d = 3.97 ppm), and a singlet
mmol) over 10 min by syringe, and the reaction mixture was stirred
and refluxed for about 0.5 h. On completion of the reaction, as mon-
itored by TLC, solvent was removed under vacuum. The residue
for the ring methine proton (d = 5. 98 ppm). The assign-
ment was supported by IR absorptions at 1741, 1725 (2
C=O), and 1656 (C=N) cm–1. The vibration band for the
Synlett 2011, No. 16, 2307–2310 © Thieme Stuttgart · New York

LETTER
Isocyanide-Based Three-Component Condensation Reaction
2309
was then crystallized from n-hexane to yield the fully substituted
cyclopentene 4a in 93% yield.
(C), 53.19 (OCH3), 64.81 (CHN), 70.06 (OCH2), 85.34 (HCOEt),
109.15, 111.76 (2 CN), 141.00, 143.48 (2 C), 150.21 (C=N),
161.29, 162.07 (2 C=O). MS: m/z (%) = 374 (93) [MH+], 341 (19)
[M+ – OMe – H], 327 (19) [M+ – OEt – H], 314 (18) [M+ – CO2Me],
291 (20) [M+ –C6H11], 83 (100) [C6H11].
Compound 4a
White solid; yield 93%; mp 112–114 °C. IR (KBr): 2916 and 2843
1
(CH), 1741 and 1725 (2 C=O), 1664 (C=N), 1436, 1270 cm–1. H
NMR (300 MHz, CDCl3): d = 1.27–1.85 (m, 10 H), 3.73 (s, 3 H),
3.86 (s, 3 H), 3.89 (s, 3 H), 3.97 (m, 1 H), 5.98 (s, 1 H). 13C NMR
(75.46 MHz, CDCl3): d = 23.62, 23.69, 25.25, 32.10, 32.13 (5 CH2),
37.41 (C), 53.16, 53.21 (2 OMe), 61.50 (CHN), 64.78 (OMe), 86.96
(CHOMe), 108.83, 111.70 (2 CN), 140.80, 143.61 (2 C), 150.12
(C=N), 161.27, 161.92 (2 C=O). MS: m/z (%) = 359 (4) [M+], 327
(17) [M+ – H – OMe], 300 (8) [M+ – CO2Me], 245 (33) [M+ – C6H11
– OMe], 83 (100) [C6H11].
Diethyl-4,4-dicyano-3-(cyclohexylimino)-5-ethoxycyclopent-1-
ene-1,2-dicarboxylate (4f)
White solid; yield 86%; mp 115–116 °C. IR (KBr): 2972 and 2919
(CH), 1737 and 1718 (C=O), 1658 (C=N), 1633, 1328, 1252 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.24–1.35 (m, 12 H), 1.39–1.50
(m, 2 H), 1.54–1.63 (m, 2 H), 1.65–1.70 (m, 1 H), 1.78–1.89 (m, 4
H), 3.84–4.04 (m, 3 H), 4.21–4.39 (m, 4 H), 5.18 (s, 1 H). 13C NMR
(75.46 MHz, CDCl3): d = 13.88, 13.99, 14.74 (3 CH3), 23.55, 23.61,
25.29, 32.13 (5 CH2), 37.75 (C), 62.28, 62.33 (2 OCH2), 64.48
(CHN), 70.00 (OCH2), 85.48 (HCOEt), 109.22, 111.86 (2 CN),
140.97, 143.41 (2 =C), 150.29 (C=N), 160.82, 161.58 (2 C=O). MS:
m/z (%) = 402 (51) [MH+], 401 (6) [M+], 355 (19) [M+ – OEt – H],
328 (12) [M+ – CO2Me], 273 (15) [M+ – OEt – C6H11], 83 (97)
[C6H11].
Diethyl-4,4-dicyano-3-(cyclohexylimino)-5-methoxycyclopent-
1-ene-1,2-dicarboxylate (4b)
White solid; yield 82%; mp 104–106 °C. IR (KBr): 2923 (CH),
1739 and 1720 (2 C=O), 1656 (C=N), 1629, 1332, 1253, 11.96 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.28–1.39 (m, 9 H), 1.43–1.64 (m,
3 H), 1.78–1.84 (m, 3 H), 3.73 (s, 3 H), 3.97 (m, 1 H), 4.32 (m, 4 H),
5.09 (s, 1H). 13C NMR (75.46 MHz, CDCl3): d = 13.88, 13.98 (2
CH3), 23.54, 23.61, 25.27, 32.10, 32.13 (5 CH2), 37.37 (C), 61.47
(CHN), 62.36 (OCH2Me), 64.50 (OMe), 87.01 (CHOMe), 108.92,
111.77 (2 CN), 140.77, 143.49 (2 C), 150.15 (C=N), 160.81, 161.48
(2 C=O). MS: m/z (%) = 387 (7) [M+], 355 (8) [M+ – H – OMe], 341
(17) [M+ – H – OEt], 314 (15) [M+ – CO2Et], 259 (51) [M+ – C6H11
– OEt], 231 (50) [M+ – CO2Et – C6H13], 82 (100) [C6H10].
Diisopropyl-4,4-dicyano-3-(cyclohexylimino)-5-ethoxycyclo-
pent-1-ene-1,2-dicarboxylate (4g)
White solid; yield 60%; mp 77–79 °C. IR (KBr): 2937, 2924 and
2848 (CH), 1733 and 1716 (C=O), 1655 (C=N), 1628, 1446, 1365,
1257 cm–1. 1H NMR (300 MHz, CDCl3): d = 1.31 (m, 18 H), 1.45–
1.63 (m, 4 H), 1.78–1.84 (m, 4 H), 3.84–4.01 (m, 3 H), 5.12–5.28
(m, 3 H). 13C NMR (75.46 MHz, CDCl3): d = 14.78, 21.55, 21.63 (3
CH3), 23.44, 23.51, 25.34, 32.16 (5 CH2), 37.68 (C), 64.14 (CHN),
69.97 [OCH(Me)2], 70.38 (OCH2), 85.65 (HCOEt), 109.27, 111.96
(2 CN), 140.86, 143.46 (2 C), 150.30 (C=N), 160.36, 161.23 (2
C=O). MS: m/z (%) = 430 (24) [MH+], 429 (4) [M+], 383 (5) [M+ –
Diisopropyl-4,4-dicyano-3-(cyclohexylimino)-5-methoxycyclo-
pent-1-ene-1,2-dicarboxylate (4c)
White solid; yield 84%; mp 82–83 °C. IR (KBr): 2926 (CH), 1730,
1725 (2 C=O), 1659 (C=N), 1642, 1448, 1442, 1367, 1285 cm–1. 1H
NMR (300 MHz, CDCl3): d = 1.25–1.41 (m, 16 H), 1.45–1.63 (m,
4 H), 1.79–1.85 (m, 4 H), 3.75 (s, 3 H), 3.98 (m, 1 H), 5.11 (s, 1 H),
5.13–5.32 (m, 2 H). 13C NMR (75.46 MHz, CDCl3): d = 21.58
21.65 (2 CH3), 23.46, 23.52, 25.34, 32.18 (5 CH2), 37.31 (C), 61.41
(CHN), 64.23 (OMe), 70.47, 70.56 [2 OCH (Me)2], 87.24
(CHOMe), 108.98, 111.89 (2 CN), 140.61, 143.55 (2 C), 150.12
(C=N), 160.38, 161.17 (2 C=O). MS: m/z (%) = 415 (5) [MH+], 383
(5) [M+ – CO2Me], 356 (4) [M+ – OCH(CH3)2], 328 (10) [M+ + 1 –
CO2CH(CH3)2], 314 (15) [M+ – CN – OMe – CH(CH3)2], 83 (89)
[C6H13].
OEt – H], 370 (4) [M+ – OCH (CH3)2], 342 (13) [M+
O2CH(CH3)2], 83 (97) [C6H11].
–
Dineopentyl-4,4-dicyano-3-(cyclohexylimino)-5-ethoxycyclo-
pent-1-ene-1,2-dicarboxylate (4h)
White solid; yield (82%); mp 122–124 °C. IR (KBr): 2919, 2844
(CH), 1738 and 1720 (C=O), 1657 (C=N), 1637, 1473, 1366, 1271
cm–1. 1H NMR (300 MHz,CDCl3): d = 0.96 (s, 18 H), 1.26–1.60 (m,
8 H), 1.68–1.72 (m, 1 H), 1.80–1.90 (m, 4 H), 3.88–4.11 (m, 4 H),
5.22 (s, 1 H). 13C NMR (75.46 MHz, CDCl3): d = 14.74 (CH3),
23.68, 23.76, 25.24 (3 CH2), 26.3 (CH3), 31.43, 31.70 (2 C), 32.24
(2 CH2), 37.56 (C), 64.76 (CHN), 70.03, 75.54, 75.54 (3 CH2),
85.75 (HCOEt), 109.26, 111.91 (2 CN), 140.90, 143.20 (2 C),
150.55 (C=N), 161.13, 161.77 (C=O). MS: m/z (%) = 486 (30)
[MH+], 485 (3) [M+], 470 (6) [M+ – Me], 439 (5) [M+ – OEt – H],
370 (6) [M+ – O2CH2C(CH3)3], 83 (25) [C6H11], 71 (100) [M+ –
CH2C(CH3)3].
Dineopentyl-4,4-dicyano-3-(cyclohexylimino)-5-methoxycyclo-
pent-1-ene-1,2-dicarboxylate (4d)
White solid; yield 75%; mp 131–133 °C. IR (KBr): 2918 (CH),
1740 and 1720 (C=O), 1642 (C=N), 1638, 1365, 1362, 1278 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.96 (s, 18 H), 1.26–1.57 (m, 5 H),
1.57–1.60 (m, 2 H), 1.61–1.9 (m, 4 H), 3.76 (s, 3 H), 3.90–4.1 (m,
5 H), 5.11 (s, 1 H), 5.13–5.32 (m, 2 H). 13C NMR (75.46 MHz,
CDCl3): d = 23.67, 23.75, 25.23 (3 CH2), 26.31 (CH3), 31.41, 31.69
(2 C), 32.24 (2 CH2), 37.21 (C), 61.39 (CHN), 64.78 (OMe), 75.55,
75.76 [2 OCH2C(Me)3], 87.31 (CHOMe), 108.96, 111.82 (2 CN),
140.66, 143.40 (2 C), 150.39 (C=N), 161.09, 161.66 (2 C=O). MS:
m/z (%) = 472 (47) [MH+], 456 (7) [M+ – Me], 439 (6) [M+ – OMe],
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett. Copies of
the IR, mass, 1H NMR, and 13C NMR spectra for products are avail-
able.
356 (7) [M+
[CH2C(CH3)3].
– CH2C(CH3)3], 83 (27) [C6H11], 71 (100)
Acknowledgment
We gratefully acknowledge financial support from the Research
Council of University of Birjand.
Dimethyl-4,4-dicyano-3-(cyclohexylimino)-5-ethoxycyclopent-
1-ene-1,2-dicarboxylate (4e)
White solid; yield 90%; mp 92–94 °C. IR (KBr): 2928 and 2849
(CH), 1747 and 1727 (C=O), 1660 (C=N), 1637, 1270, 1428, 1272
cm–1. 1H NMR (300 MHz, CDCl3): d = 1.22–1.77 (m, 13 H), 3.78–
4.10 (m, 9 H), 5.12 (s, 1 H), 13C NMR (75.46 MHz, CDCl3):
d = 14.77 (CH3), 23.65, 23.72, 25.25, 32.10, 32.13 (5 CH2), 37.77
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