Reactions of cyclohexyl isocyanide, dialkyl acetylenedicarboxylates and 1-aryl-2-ene-3-acetyl-1,4-diketones: One-pot synthesis of highly functionalized 5-cyclohexylimino-2,5-dihydrofurans

Article abstract of DOI:10.24820/ark.5550190.p010.628

Dihydrofurans are important intermediates in organic synthesis, and are also important starting materials used in syntheses of a number of natural products. A facile synthesis of highly functionalized 5- cyclohexylimino-2,5-dihydrofuran derivatives by the multi-component reaction of cyclohexyl isocyanide, dialkyl acetylenedicarboxylates and 1-aryl-2-ene-3-acetyl-1,4-diketones is described.

Full text of DOI:10.24820/ark.5550190.p010.628

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Arkivoc 2018, part vii, 0-0
Reactions of cyclohexyl isocyanide, dialkyl acetylenedicarboxylates and 1-aryl-2-
ene-3-acetyl-1,4-diketones: one-pot synthesis of highly functionalized 5-
cyclohexylimino-2,5-dihydrofurans
Mahsa Latifi, Mahdiyeh Talebdizaeh, and Mohammad Anary-Abbasinejad*
Department of Chemistry, Faculty of Science, Vali-e-Asr University of Rafsanjan, Rafsanjan 77176, Iran
E-mail: m.anary@vru.ac.ir
Received 05-19-2018
Accepted 07-27-2018
Published on line 09-02-2018
Abstract
Dihydrofurans are important intermediates in organic synthesis, and are also important starting materials
used in syntheses of a number of natural products. A facile synthesis of highly functionalized 5-
cyclohexylimino-2,5-dihydrofuran derivatives by the multi-component reaction of cyclohexyl isocyanide,
dialkyl acetylenedicarboxylates and 1-aryl-2-ene-3-acetyl-1,4-diketones is described.
Keywords: Isocyanide, multi-component reactions, dialkyl acetylenedicarboxylates, arylglyoxal, 5-imino-2,5-
dihydrofuran
DOI: https://doi.org/10.24820/ark.5550190.p010.628
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Introduction
The Michael addition of isocyanides to activated carbon-carbon multiple bonds produces reactive zwitterionic
intermediates which may be trapped by carbon or hydrogen proton electrophiles to afford a wide range of
carbocyclic or heterocyclic organic compounds. It has been reported that isocyanides attack dialkyl
acetylenedicarboxylates (DAADs), yielding zwitterionic species which could be trapped by the carbonyl group
of aldehydes,1 ketones,2 esters,3 isocyanates,4 acyl chlorides5, and even carbon dioxide6, to afford five- to
seven-membered oxygen and nitrogen heterocyclic compounds.
Multi-component reactions of arylglyoxals have recently attracted much attention for the synthesis of a
wide range of important heterocyclic compounds. The application of arylglyoxals for the preparation of three-
to six-membered heterocyclic compounds has been recently reviewed.7
Dihydrofurans are important intermediates in organic synthesis and have been attracting much attention
in synthetic studies8,9. Several methods have been developed for their preparation.10-17 2,5-Disubstituted
dihydrofuran-3,4-dicarboxylates are important starting materials which have been used for the synthesis of
some natural products.18 Thus, developing new, simple and efficient syntheses of dihydrofuran derivatives
have been an area of interest.
In recent years, we have been focusing our attention on the applicability of multi-component reactions of
isocyanides19,20 and arylglyoxals21,22 for the synthesis of heterocyclic compounds. In continuation of our
studies in this area, we wish to report, herein, the reaction of 1-aryl-2-ene-3-acetyl-1,4-diketone derivatives,
prepared by Knoevenagel condensation of arylglyoxals with acetylacetone,22 with isocyanides and DAADs to
produce 5-imino-2,5-dihydrofuran derivatives in good yields.
Results and Discussion
To investigate the reactions of cyclohexyl isocyanide, DAADs and 1-aryl-2-ene-3-acetyl-1,4-diketone
derivatives, dimethyl acetylenedicarboxylate (DMAD) was added to a mixture of cyclohexyl isocyanide and 3-
acetyl-1-p-tolyl-2-ene-1,4-dione (1, Ar = p-tolyl) in CH2Cl2 as solvent at room temperature. Progress of the
reaction was monitored by TLC. After 10 h, TLC analysis of the reaction mixture showed the presence of only
dimethyl
(E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-5-(cyclohexylimino)-2-(4-methylphenyl)-2,5-dihydrofuran-3,4-
dicarboxylate (4a). Silica-gel chromatography afforded 4a in 80% yield.
To investigate the scope of the reaction, different DAADs were treated with cyclohexyl isocyanide and
different 1-aryl-2-ene-3-acetyl-1,4-diketones. The corresponding 5-cyclohexylimino-2,5-dihydrofuran
derivatives 4a-i were obtained in good yields (Scheme 1).
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Latifi, M. et al.
O
O
O
CO2R
O
O
N
CH2Cl2
r.t .10 h
O
N C
+
+
Ar
Ar
RO2C
CO2R
CO2R
2
1
3
4
R
Yield%*
Ar
4
80
4a
MeC6H4
Me
4b
4c
MeC6H4
BrC6H4
Et
78
80
Me
4d
4e
4f
75
80
75
80
BrC6H4
ClC6H4
ClC6H4
C6H5
Et
Me
Et
4g
Me
78
80
4h
4i
Et
Et
C6H5
MeOC6H4
*Isolated yields
Scheme 1. Three-component reaction of cyclohexyl isocyanide, dialkyl acetylenedicarboxylates and 1-aryl-2-
ene-3-acetyl-1,4-diketones.
1
The structures of compounds 4a–i were deduced from their elemental analyses and their infrared (IR), H
NMR, and 13C NMR spectral data. The 400-MHz 1H NMR spectrum of 4a exhibited five sharp signals at δ 2.34,
2.39, 2.42, 3.80 and 3.96 ppm for the three methyl and two methoxy groups. The cyclohexyl protons
resonated as multiplets at 1.22-1.85 (5 CH2) and at 3.51 (CH) ppm. The aromatic protons resonated as a
multiplet at 7.25 ppm and the olefinic CH was observed at 7.44 ppm as a singlet. The 13C NMR spectrum of
compound 4a showed twenty-five distinct resonances in agreement with the proposed structure. The
structural assignment for compound 4a, made on the basis of the NMR spectra, were supported by its IR
spectrum as the ester carbonyl groups exhibited strong absorption bands at about 1755 and 1724cm-1,
respectively. The ketone carbonyls were observed as strong absorptions at 1684 and 1669 cm-1, respectively.
The suggested mechanism for formation of the 5-cyclohexylimino-2,5-dihydrofuran derivatives 4a-i by the
reaction of cyclohexyl isocyanide, DAAD and 1-aryl-2-ene-3-acetyl-1,4-diketone derivatives is shown in Scheme
2. Michael addition of cyclohexyl isocyanide to DAAD produces the reactive zwitterionic species (5). The
formal [3+2] type cycloaddition of this reactive intermediate with the carbonyl group of 1-aryl-2-ene-3-acetyl-
1,4-diketone (1) affords the 5-cyclohexylimino-2,5-dihydrofuran product series 4.
RO2C
RO2C
Ar
O
CO2R
O
1
O
4
N C
+
N
CO2R
5
3
2
Scheme 2. Suggested mechanism for formation of 5-cyclohexylimino-2,5-dihydrofuran derivatives 4a-i.
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Conclusions
In conclusion, we have developed a simple and efficient method for preparation of functionalized 5-
cyclohexylimino-2,5-dihydrofuran derivatives by a three-component reaction of cyclohexyl isocyanide, dialkyl
acetylenedicarboxylates and 1-aryl-2-ene-3-acetyl-1,4-diketone derivatives. This method has the advantages
that the reactions can be performed under neutral conditions with readily available starting materials which
require no modification or preparation.
Experimental Section
General. All of the utilized arylglyoxals were prepared by the SeO2-oxidation of the related aryl methyl ketones
on the basis of the reported procedure and used as their monohydrates.24 Elemental analyses were performed
1
using a Heraeus CHN-O-Rapidanalyzer. IR spectra were recorded on a Shimadzu IR-470 spectrometer. H and
13C NMR spectra were recorded on a Bruker DRX-400 Avance spectrometer at 400 and 100 MHZ, respectively.
The chemicals used in this work were purchased from Merck and used without further purification.
General procedure. To a magnetically-stirred solution of dialkyl acetylenedicarboxylate (2 mmol) and 1-aryl-2-
ene-3-acetyl-1,4-diketone derivative (2 mmol) in CH2Cl2 (10 mL) was added a solution of cyclohexyl isocyanide
(2 mmol) in CH2Cl2 (5 mL) dropwise at room temperature over 10 min. The mixture was then allowed to stir for
10 h. The solvent was removed under reduced pressure, and the residue was separated by column
chromatography (silica gel, hexane–EtOAc, 5:1) to afford the pure title compounds.
Dimethyl (E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-5-(cyclohexylimino)-2-(4-methylphenyl)-2,5-dihydrofuran-3,4-
dicarboxylate (4a). Yellow solid, (770 mg, 80%). mp 169-172˚C. IR (solid, KBr, νmax cm-1): 1755, 1724, 1684,
1669 (4C=O).1H NMR (400 MHz, CDCl3): δH 1.22 -1.85 (10H, m, 5CH2 of cyclohexyl), 2.34, 2.39, 2.42 (9H, 3s,
3CH3), 3.51(1H, m, CH of cyclohexyl), 3.80, 3.96 (6H, 2s, 2OMe), 7.25 (4H, m, 4CH, HAr), 7.44 (1H, s, CH
olefinic). 13C NMR (100 MHz, CDCl3) δC 21.2, 24.5, 24.7, 25.6, 26.6, 32.3, 33.0, 33.8 (5CH2 of cyclohexyl and
3CH3), 53.1, 53.2 (2OMe), 57.0 (CH of cyclohexyl), 90.1 (C of dihydrofuran), 125.9, 129.9, 133.9, 136.4, 137.1,
139.7, 142.6, 143.7 (aromatic and olefinic carbons), 152.4 (C=N), 160.8, 161.9 (2C=O of esters), 196.3, 202.0
(2C=O of ketones). Calcd. for (C27H31NO7): C, 67.35; H, 6.49; N, 2.91. Found: C, 67.33; H, 6.42; N, 2.95.
Diethyl
(E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-5-(cyclohexylimino)-2-(4-methylphenyl)-2,5-dihydrofuran-3,4-
dicarboxylate (4b). Yellow oil, (794 mg, 78%). IR (neat, νmax cm-1): 1724, 1675 (4C=O).1H NMR (400 MHz,
DMSO-d6) δH 1.17 (3H, t, 3JHH 8.0 Hz,CH3), 1.30 (3H, t, 3JHH 8.0 Hz, CH3), 1.21-1.75 (10H, m, 5CH2 of cyclohexyl),
2.23, 2.34, 2.44 (9H, 3s, 3CH3), 3.35 (1H, m, CH of cyclohexyl), 4.22 (2H, m, CH2), 4.36 (2H, m, CH2), 7.26 (2H, d,
3JHH 9.0 Hz, 2CH, HAr), 7.31 (2H, d,3JHH 9.0 Hz, 2CH, HAr), 7.36 (1H, s, CH olefinic). 13C NMR (100 MHz, DMSO-
d6) δC 14.0, 14.3, 21.3, 24.5, 24.6, 25.6, 26.9, 32.4, 33.1, 34.0 (5CH2 of cyclohexyl and 5CH3), 55.3 (CH of
cyclohexyl) 62.6, 62.7 (2OCH2), 90.4 (C of dihydrofuran), 126.2, 130.31, 134.3, 135.9, 136.9, 139.8, 143.2, 143.6
(aromatic and olefinic carbons), 153.0 (C=N), 159.9, 161.4 (2C=O of esters), 197.4, 202.4 (2C=O of ketones).
Calcd. for (C29H35NO7): C, 68.35; H, 6.92; N, 2.75. Found: C, 68.33; H, 6.85; N, 2.85.
Dimethyl (E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-2-(4-bromophenyl)-5-(cyclohexylimino)-2,5-dihydrofuran-3,4-
dicarboxylate (4c). White solid, (874 mg, 80%). mp 137-140 ˚C. IR (solid, KBr, νmax cm-1): 1752, 1731, 1688,
1674 (4C=O).1H NMR (400 MHz, CDCl3) δH 1.22-1.83 (10H, m, 5CH2 of cyclohexyl), 2.33, 2.41 (6H, 2s, 2CH3),
3
3.51 (1H, m, CH of cyclohexyl), 3.82, 3.96 (6H, 2s, 2OMe),7.26 (2H, d, JHH 9.0 Hz, 2CH, HAr), 7.38 (1H, s, CH
3
olefinic), 7.57 (2H, d, JHH 9.0 Hz, 2CH, HAr). 13C NMR (100 MHz, CDCl3) δC 24.5, 24.7, 25.5, 26.7, 32.2, 33.0,
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33.8 (5CH2 of cyclohexyl and 2CH3), 53.2, 53.3 (2OMe), 57.1 (CH of cyclohexyl), 89.5 (C of dihydrofuran), 124.0,
127.7, 132.4, 136.1, 136.2, 136.7, 142.0, 144.2 (aromatic and olefinic carbons), 152.0 (C=N), 160.7, 161.7
(2C=O of esters), 196.1, 202.1 (2C=O of ketones). Calcd. for (C26H28BrNO7): C, 57.15; H, 5.17; N, 2.56. Found: C,
57.18; H, 5.12; N, 2.50.
Diethyl (E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-2-(4-bromophenyl)-5-(cyclohexylimino) -2,5-dihydrofuran-3,4-
dicarboxylate (4d). Yellow oil (861 mg, 75%). IR (neat, νmax cm-1):1724, 1676 (4C=O). 1H NMR (400 MHz, CDCl3):
δH 1.25 (3H, t, 3JHH 7.0 Hz, CH3), 1.36 (3H, t, 3JHH 7.0 Hz,CH3), 1.23 - 1.80 (10H, m, 5CH2 of cyclohexyl), 2.28, 2.37
(6H, 2s, 2CH3), 3.48 (1H, m, CH of cyclohexyl), 4.22 (2H, m, CH2), 4.38 (2H, q, 3JHH 7.0 HZ, CH2), 7.24 (2H, d, 3JHH
3
9.0 Hz, 2CH, HAr), 7.38 (1H, s, CH olefinic), 7.53 (2H, d, JHH 9.0 Hz, 2CH, HAr). 13C NMR (100 MHz, CDCl3) δC
13.8, 14.0, 24.4, 24.6, 25.6, 26.6, 32.2, 33.0, 33.8 (5CH2 of cyclohexyl and 4CH3), 56.9 (CH of cyclohexyl), 62.4,
62.5 (2OCH2), 89.5 (C of dihydrofuran), 123.8, 127.8, 132.3, 136.3, 136.4, 136.6, 141.8, 143.9 (aromatic and
olefinic carbons), 152.1 (C=N), 160.3, 161.3 (2C=O of esters), 196.2, 201.8 (2C=O of ketones). Calcd. for
(C28H32BrNO7): C, 58.54; H, 5.61; N, 2.44. Found: C, 58.28; H, 5.82; N, 2.50.
Dimethyl (E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-2-(4-chlorophenyl)-5-(cyclohexylimino)-2,5-dihydrofuran-3,4-
dicarboxylate (4e). White solid (803 mg, 80%). mp 170-173˚C. IR (solid, KBr, νmax cm-1): 1754, 1723, 1683
(4C=O). 1H NMR (400 MHz, CDCl3): δH 1.18 -1.77 (10H, m, 5CH2 of cyclohexyl), 2.29, 2.37 (6H, 2s, 2CH3), 3.47
3
(1H, m, CH of cyclohexyl), 3.77, 3.92 (6H, 2s, 2OMe), 7.28 (2H, d, JHH 8.0 Hz, 2CH, HAr), 7.35 (1H, s, CH
3
olefinic), 7.37 (2H, d, JHH 8.0Hz, 2CH, HAr). 13C NMR (100 MHz, CDCl3) δC 24.4, 24.6, 26.6, 32.2, 33.0, 33.8
(5CH2 of cyclohexyl and 2CH3), 53.2 (2OMe), 57.1 (CH of cyclohexyl), 89.5 (C of dihydrofuran), 127.4, 129.4,
135.6, 135.7, 136.2, 136.7, 142.0, 144.1 (aromatic and olefinic carbons), 152.0 (C=N), 160.7, 161.7 (2C=O of
esters), 196.0, 201.7 (2C=O of ketones). Calcd. for (C26H28ClNO7): C, 62.21; H, 5.62; N, 2.79. Found: C, 62.19; H,
5.59; N, 2.77.
Diethyl
(E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-2-(4-chlorophenyl)-5-(cyclohexylimino)-2,5-dihydrofuran-3,4-
dicarboxylate (4f). White solid (795 mg, 75%). mp 155-158˚C IR (solid, KBr, ν max cm-1): 1724, 1676 (4C=O).1H
NMR (400 MHz, CDCl3): δH 1.23 (3H, t, 3JHH 7.1Hz, CH3), 1.34 (3H, t, 3JHH 7.1Hz, CH3), 1.21-1.76 (10H, m, 5CH2 of
cyclohexyl), 2.27, 2.35 (6H, 2s, 2CH3), 3.47 (1H, m, CH of cyclohexyl), 4.20 (2H, m, CH2), 4.36 (2H, q, 3JHH 7.0Hz,
CH2), 7.27-7.36 (5H, m, CH aromatic and olefinic). 13C NMR (100 MHz, CDCl3) δC 13.7, 14.0, 24.3, 24.5, 25.5,
26.5, 32.1, 33.0, 33.8 (5CH2 of cyclohexyl and 4CH3), 56.9 (CH of cyclohexyl), 62.4 (2OCH2), 89.4 (C of
dihydrofuran), 127.5, 129.3, 135.5, 135.8, 136.4, 136.6, 141.9, 144.0 (aromatic and olefinic carbons), 152.0
(C=N), 160.3, 161.3 (2C=O of esters), 196.0, 201.7 (2C=O of ketones). Calcd. for (C28H32ClNO7): C, 63.45; H,
6.09; N, 2.64. Found: C, 63.40; H, 6.03; N, 2.60.
Dimethyl
(E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-5-(cyclohexylimino)-2-phenyl-2,5-dihydrofuran-3,4-dicarboxylate
(4g). Yellow solid (748 mg, 80%), mp 178-180˚C. IR (solid, KBr, νmax cm-1): 1754, 1719, 1681, 1669 (4C=O).1H
NMR (400 MHz, CDCl3): δH 1.19-1.82 (10H, m, 5CH2 of cyclohexyl), 2.30, 2.38 (6H, 2s, 2CH3), 3.50 (1H, m, CH of
cyclohexyl), 3.77, 3.92 (6H, 2s, 2OMe), 7.34-7.42 (6H, m, CH aromatic and olefinic). 13C NMR (100 MHz, CDCl3)
δC 24.5, 24.7, 25.6, 26.5, 32.2, 33.0, 33.8 (5CH2 of cyclohexyl and 2CH3), 53.0, 53.1 (2OMe), 57.0 (CH of
cyclohexyl), 90.0 (C of dihydrofuran), 125.9, 129.1, 129.5, 136.5, 136.9, 137.0, 142.5, 143.8 (aromatic and
olefinic carbons), 152.2 (C=N), 160.8, 161.8 (2C=O of esters), 196.1, 201.8 (2C=O of ketones). Calcd. for
(C26H29NO7): C, 66.80; H, 6.25; N, 3.00. Found: C, 66.78; H, 6.20; N, 3.07.
Diethyl (E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-5-(cyclohexylimino)-2-phenyl-2,5-dihydrofuran-3,4-dicarboxylate
(4h). White solid (773 mg, 78%) mp 150-153˚C. IR (solid, KBr, νmax cm-1): 1747, 1717, 1673 (4C=O). 1H NMR (400
3
3
MHz CDCl3): δH 1.24 (3H, t, JHH 7.0 Hz, CH3), 1.36 (3H, t, JHH 7.0 Hz, CH3), 1.22-1.79 (10H, m, 5CH2 of
cyclohexyl), 2.30, 2.38 (6H, 2s, 2CH3), 3.50 (1H, m, CH of cyclohexyl), 4.22 (2H, m, CH2), 4.38 (2H, q, 3JHH 8.0 Hz,
CH2), 7.35 -7.42 (5H, m, 5CH, HAr), 7.45(1H, s, CH olefinic). 13C NMR (100 MHz, CDCl3) δC 13.7, 14.0, 24.4, 24.6,
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25.6, 26.5, 32.2, 33.0, 33.8 (5CH2 of cyclohexyl and 4CH3), 56.8 (CH of cyclohexyl), 62.2, 62.3 (2OCH2), 90.0 (C
of dihydrofuran), 126.0, 129.1, 129.4, 136.4, 137.1, 137.2, 142.3, 143.7 (aromatic and olefinic carbons), 152.3
(C=N), 160.4, 161.4 (2C=O of esters), 196.2, 201.8 (2C=O of ketones). Calcd. for (C28H33NO7): C, 67.86; H, 6.71;
N, 2.83. Found: C, 67.86; H, 6.71; N, 2.83.
Diethyl (E)-2-(2-acetyl-3-oxobut-1-en-1-yl)-5-(cyclohexylimino)-2-(4-methoxyphenyl)-2,5-dihydrofuran-3,4-
dicarboxylate (4i). Yellow oil (841 mg, 80%). IR (neat, νmax cm-1): 1720 (4C=O). 1H NMR (400 MHz, CDCl3): δH
3
3
1.24 (3H, t, JHH 7.1 Hz, CH3), 1.34 (3H, t, JHH 7.1 Hz, CH3), 1.23-1.77 (10H, m, 5CH2 of cyclohexyl), 2.29, 2.37
(6H, 2s, 2CH3), 3.48 (1H, m, CH of cyclohexyl), 3.80 (3H, s, OMe), 4.21 (2H, m, CH2), 4.37 (2H, m, CH2), 7.27 (4H,
m, 4CH aromatic), 7.41(1H, s, CH olefinic). 13C NMR (100 MHz, CDCl3) δC 13.8, 14.2, 24.3, 24.6, 25.7, 26.2, 32.2,
33.1, 33.8 (5CH2 of cyclohexyl and 4CH3), 53.2 (OCH3), 56.7 (CH of cyclohexyl), 62.3, 62.5 (2OCH2), 90.0 (C of
dihydrofuran), 123.0, 125.1, 126.4, 137.1, 137.2, 142.3, 143.7, 151.3 (aromatic and olefinic carbons), 152.3
(C=N), 160.2, 161.5 (2C=O of esters), 196.0, 201.2 (2C=O of ketones). Calcd. for (C29H35NO8): C, 66.27; H, 6.71;
N, 2.66. Found: C, 66.36; H, 6.78; N, 2.83.
Acknowledgements
We gratefully acknowledge the Vail-e-Asr University of Rafsanjan Faculty Research Grant for financial support
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