Vinylphosphonium salt mediated preparation of substituted imides and furans from benzoic acid, 1,1,3,3-tetramethylbutyl isocyanide, and acetylenic esters

Article abstract of DOI:10.1080/10426500802081202

Protonation of the reactive intermediates produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by benzoic acid leads to vinyltriphenylphosphonium salts, which undergo complex reactions with 1,1,3,3-tetramethylbutyl isocy

Full text of DOI:10.1080/10426500802081202

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Vinylphosphonium Salt
Mediated Preparation of
Substituted Imides and Furans
from Benzoic Acid, 1,1,3,3-
Tetramethylbutyl Isocyanide,
and Acetylenic Esters
Ali Ramazani a & Mohsen Valizadeh Holagh b
a Chemistry Department , Islamic Azad University ,
Zanjan Branch, Zanjan , Iran
b Chemistry Department , Zanjan University ,
Zanjan , Iran
Published online: 19 Dec 2008.
To cite this article: Ali Ramazani & Mohsen Valizadeh Holagh (2008)
Vinylphosphonium Salt Mediated Preparation of Substituted Imides and Furans
from Benzoic Acid, 1,1,3,3-Tetramethylbutyl Isocyanide, and Acetylenic Esters,
Phosphorus, Sulfur, and Silicon and the Related Elements, 184:1, 171-178, DOI:
10.1080/10426500802081202
To link to this article: http://dx.doi.org/10.1080/10426500802081202
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Phosphorus, Sulfur, and Silicon, 184:171–178, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802081202
Vinylphosphonium Salt Mediated Preparation of
Substituted Imides and Furans from Benzoic Acid,
1,1,3,3-Tetramethylbutyl Isocyanide,
and Acetylenic Esters
Ali Ramazani1 and Mohsen Valizadeh Holagh2
1Chemistry Department, Islamic Azad University–Zanjan Branch,
Zanjan, Iran
2Chemistry Department, Zanjan University, Zanjan, Iran
Protonation of the reactive intermediates produced in the reaction between
triphenylphosphine and dialkyl acetylenedicarboxylates by benzoic acid leads to
vinyltriphenylphosphonium salts, which undergo complex reactions with 1,1,3,3-
tetramethylbutyl isocyanide to produce corresponding substituted furans and
imides in fairly good yields in a stereoselective manner.
Keywords Acetylenic ester; densely functionalized furan; electron-poor imide; phospho-
rus ylide; triphenylphosphine
INTRODUCTION
Organophosphorus compounds1,2 have been extensively employed in
organic synthesis as useful reagents as well as ligands in a number of
transition metal catalysts.3 Phosphorus ylides are a class of a special
type of zwitterions, which bear strongly nucleophilic electron-rich car-
–
banions. The electron distribution around the P+ –C bond and its con-
sequent chemical implications has been probed and assessed through
theoretical, spectroscopic, and crystallographic investigations.4 They
are excellent ligands and excel in their ligating functions with the
unstabilized ylides because of their ambidentate and chemically dif-
ferentiating character. Proton affinity of these ylides can be used as a
molecular guide to assess their utility as synthetic reagents and their
function as ligands in coordination and organometallic chemistry.3,5
Received 4 November 2007; accepted 30 December 2007.
This work was supported by the Zanjan University.
Address correspondence to Ali Ramazani, Chemistry Department, Islamic Azad
University–Zanjan Branch, P.O. Box 49195-467, Zanjan, Iran. E-mail: aliramazani@
gmail.com
171

172
A. Ramazani and M. V. Holagh
The nucleophilicity at the ylidic carbon is a factor of essential mechanis-
tic importance in the use of these ylides as Wittig reagents. Phosphorus
ylides are important reagents in synthetic organic chemistry, especially
in the synthesis of naturally occurring products, and compounds with
biological and pharmacological activity.1,2 In recent years, we have es-
tablished a one-pot method for the synthesis of stabilized ylides.6–15
For several years acetylenic esters have attracted the attention of
organic chemists and are reactive systems that can take part in many
chemical syntheses,16–18 almost as a Michael acceptor in the organic
reactions.16 In recent years, there has been increasing interest in the
applications of acetylenic esters in the multicomponent19–21 synthesis.
Due to the atom economy, convergent character, and simplicity of one-
pot procedures, multicomponent condensation reactions (MCRs) have
an advantageous position among other reactions. The development of
novel MCRs is receiving growing interest from industrial chemistry re-
search groups and represents a challenge for organic chemists.22–26 As
part of our ongoing program to develop efficient and robust methods for
the preparation of heterocyclic compounds,27–37 we sought to develop a
convenient preparation of densely functionalized furans 5 and imides
4 in fairly good yields in neutral conditions.
RESULTS AND DISCUSSION
Protonation of the reactive intermediates produced in the reaction be-
tween triphenylphosphine and dialkyl acetylenedicarboxylates 2 by
benzoic acid 3 leads to vinyltriphenylphosphonium salts 7, which un-
dergo complex reactions with 1,1,3,3-tetramethylbutyl isocyanide 1 to
produce corresponding densely functionalized furans 5 and imides 4 in
fairly good yields in neutral conditions (Schemes 1 and 2). The reac-
tion proceeds smoothly and cleanly under reaction conditions, and no
side reactions were observed. The reactions were completed in 48 h,
and densely functionalized furans 5 were observed as major products
(Table I). In this reaction, triphenylphosphine acts as a catalyst. In the
absence of the triphenylphosphine,25,26 the reactions were completed
after 72 h in CH2Cl2 at room temperature with imides 4 observed as
major products (Table I).25,26 The 1H NMR (CDCl3) spectra of com-
pounds 4 show the presence of one estereoisomer (E) for each imides 4.
Z isomers of the imides 4 were not isolated. It seems that Z isomers 12
are more reactive than E isomers toward formation of adduct 13 with
1,1,3,3-tetramethylbutyl isocyanide 1 and act as intermediate in the
formation of furans 5 (Scheme 2). The reaction is stereoselective.

Benzoic Acid, 1,1,3,3-Tetramethylbutyl Isocyanide
173
TABLE I Synthesis of Imides 4 and Furans 5 (see Scheme 1)
In the presence of PPh3
( r. t., 48 h.): Total isolated
Entry Products yield % (4 + 5); Ratio of 4:5
In the absence of PPh3 ( r. t., 72 h.):
Total isolated yield % (4 + 5);
Ratio of 4:5
1
2
4a/5a
4b/5b
91;
85;
31:69
30:70
80;
75;
90:10
83;17
_
C
PPh 3
CO 2R
CH2Cl2
+
2
N
2
+
+
3
r. t., 48 h.
O
HO
CO 2R
3
2
1
RO
O
O
O
N
O
RO
H
N
+
N
CO 2R
O
Ph
O
RO 2C
5
4
5a : R=Me
5b : R=Et
4a : R=Me
4b : R=Et
SCHEME 1
The mechanism of the reaction between the triphenylphosphine,
1,1,3,3-tetramethylbutyl isocyanide (1) dialkyl acetylenedicarboxylates
(2), and benzoic acid (3) has not been established experimentally.
However, a possible explanation is proposed in Scheme 2. The struc-
1
tures of the products were deduced from their IR, H NMR, and 13C
NMR spectra (see the Experimental section).
CONCLUSIONS
In summary, we have found a new and efficient method for prepar-
ing electron-poor imides (4) and fully substituted furans (5) from

174
A. Ramazani and M. V. Holagh
Ph 3P
RO 2
Ph 3
C
P
O
CO 2
R
RO 2
C
CO 2R
Ph
R
OH
3
2
6
RO 2C
Ph 3P
CO 2R
RO 2C
CO 2
C
NR'
1
C
NR'
O
H
O
Ph 3
P
H
7
8
Ph
O
Ph
O
RO2C
Ph3P
CO2R
C
RO2C
Ph3P
NR'
CO2R
O
C
H
O
H
NR'
O
O
9
O
10
Ph
Ph
H
RO2C
Ph3P
CO2R
CO2R
RO2C
H
_
C
-PPh3
C
O
4
+
NR'
NR'
11
12
O
O
Ph
Ph
CO2R
RO2C
CO2R
C
RO2C
H
1
H
C
C
12
NR'
C
_
R'N
NR'
5
O
+
R'N
O
Ph
O
Ph
O
14
13
R = Me, Et
;
R' = 1,1,3,3-tetramethylbutyl
SCHEME 2
triphenylphosphine, 1,1,3,3-tetramethylbutyl isocyanide (1) dialkyl
acetylenedicarboxylates (2), and benzoic acid (3) in neutral conditions
(Scheme 1, Scheme 2, and Table I). We believe the reported method
offers a simple and efficient route for the preparation of electron-poor

Benzoic Acid, 1,1,3,3-Tetramethylbutyl Isocyanide
175
imides (4) and fully substituted furans (5) (Scheme 1). Its ease of work-
up and fairly good yields make it a useful addition to modern synthetic
methodologies.Other aspects of this process are under investigation.
EXPERIMENTAL
1H (250.13 MHz) and 13C (62.90 MHz) NMR measurements were
recorded on a Brucker 250 spectrometer in CDCl3 with tetramethyl-
silane as internal standard. IR spectra were measured on a Mattson-
1000 FTIR spectrophotometer. Starting materials and solvents were
obtained from Merck (Germany) and Fluka (Switzerland) and were
used without further purification. Flash chromatography columns were
prepared from Merck silica gel powder.
General Procedure for the Preparation of Compounds 4a–b
and 5a–b
To a magnetically stirred solution of triphenylphosphine (0.262 g,
1 mmol) and benzoic acid 3 (0.28 g, 2 mmol) in dry CH2Cl2 (1 ml) was
added dropwise a solution of 2 (2 mmol) in CH2Cl2 (2 mL) at −10◦C over
15 min. The mixture was allowed to warm to room temperature and to
it was added dropwise a solution of 1,1,3,3-tetramethylbutyl isocyanide
1 (3 mmol) in CH2Cl2 (1 mL) over 10 min. The mixture was stirred for
48 h. The solvent was removed under reduced pressure, and the viscous
residue was purified by flash column chromatography (silica gel; light
petroleum ether-ethyl acetate). Characterization data are given in the
next section.
Dimethyl (E)-2-{[benzoyl(1,1,3,3-tetramethylbutyl)-
amino]carbonyl}-2-butenedioate 4a
Viscous yellow oil, IR (KBr) (υmax, cm−1): 1738 (OCNCO), 1669
(CO2Me), 1600 (C C), 1546 and 1454 (Ph), 1369, 1253, 1200 and 1123
(C O).1H NMR (250.13 MHz, CDCl3): δH 0.99 (9 H, s, CMe3), 1.55 (6 H,
s, CMe2), 2.30 (2 H, s, CH2), 3.54 (3 H, OMe), 3.70 (3 H, s, OMe), 6.28
(1 H, NH), 7.30 (2 H, dd, 3JHH = 7.5 Hz, 3JHH = 7.5 Hz, 2 CHmeta of C6H5),
7.45 (1 H, t, 3JHH = 7.7 Hz, CHpara of C6H5), 7.68 (2 H, d, 3JHH = 7.7 Hz,
2 CHortho of C6H5). 13C NMR (62.90 MHz, CDCl3): δC 22.59 (CMe3),
28.23 (CH3 of CMe2), 31.66 (CH3 of CMe3), 50.44 (CH2), 52.21 (OMe),
52.53 (OMe), 64.91 (C of CMe2), 128.15 (2 CHmeta of C6H5), 128.43 (2
CHortho of C6H5), 130.38 (C CH), 134.03 (CHpara of C6H5), 136.04 (Cipso
of C6H5), 140.99 (C CH), 161.68 (PhCONCO), 162.77 (CO2Me), 163.53
(CO2Me), 175.11 (PhCON).

176
A. Ramazani and M. V. Holagh
Diethyl (E)-2-{[benzoyl(1,1,3,3-tetramethylbutyl)-
amino]carbonyl}-2-butenedioate 4b
Viscous yellow oil, IR (KBr) (υmax, cm−1): 1730 (OCNCO), 1676
(CO2Me), 1610 (C C), 1553 and 1469 (Ph), 1376, 1261, 1200 and 1161
(C O).1H NMR (250.13 MHz, CDCl3): δH 1.07 (9 H, s, CMe3), 1.25 (3
H, t,3JHH = 7.2 Hz, CH3), 1.28 (3 H, t,3JHH = 7.2 Hz, CH3), 1.65 (6 H,
s, CMe2), 2.38 (2 H, s, CH2), 4.11 (2 H, q,3JHH = 7.2 Hz, OCH2CH3),
4.22 (2 H, q,3JHH = 7.2 Hz, OCH2CH3), 6.33 (1 H, s, NH), 7.40 (2 H, dd,
3JHH = 7.5 Hz, 3JHH = 7.5 Hz, 2CHmeta of C6H5), 7.54 (1 H, t, 3JHH = 7.4
Hz, CHpara of C6H5), 7.78 (2 H, d, 3JHH = 7.4 Hz, 2 CHortho of C6H5).13C
NMR (62.90 MHz, CDCl3): δC 13.76 (CH3CH2), 14.08 (CH3CH2), 28.59
(CMe3), 31.58 (CH3 of CMe2), 31.77 (CH3 of CMe3), 50.41(CH2), 61.49
(OCH2), 62.18 (OCH2), 65.12 (C of CMe2), 128.45 (2 CHmeta of C6H5),
128.77 (2 CHortho of C6H5), 130.41 (C CH), 134.00 (CHpara of C6H5),
136.40 (Cipso of C6H5), 141.74 (C CH), 162.15 (PhCONCO), 162.63
(CO2Me), 163.41 (CO2Me), 175.39 (PhCON).
Dimethyl 2-[Benzoyl(1,1,3,3-tetramethylbutyl)amino]-5-
(1,1,3,3-tetramethylbutylamino)-3,4-furandicarboxylate 5a
Viscous yellow oil, IR (KBr) (υmax, cm−1): 3485 (NH), 1730 (CO2Me),
1669 (CO2Me), 1576 CON), 1215 (C O).1H NMR (250.13 MHz, CDCl3):
δH 1.04 (9 H, s, CMe3), 1.11 (9 H, s, CMe3), 1.40 (3 H, s, CMe2), 1.50 (3
H, s, CMe2), 1.52 (3 H, s, CMe2), 1.54 (3 H, s, CMe2), 1.60 (2 H, s, CH2),
1.90 (1 H, d, 2 JHH = 15.0 Hz, CH2), 1.75 (1 H, d, 2JHH = 15.0 Hz, CH2),
3.63 (3 H, s, OMe), 3.75 (3 H, s, OMe), 7.07 (1 H, s, NH), 7.22 (2 H, d,
3JHH = 7.0 Hz, 2 CHortho of C6H5), 7.27 (1 H, t, 3JHH = 7.0 Hz, CHpara of
3
C6H5), 7.44 (2 H, t, JHH = 7.5 Hz, 2 CHmeta of C6H5).13C NMR (62.90
MHz, CDCl3): δC 28.11 (CMe3), 28.79 (CMe3), 30.01 (CH3 of CMe2),
30.18 (CH3 of CMe2), 31.44 (CH3 of CMe3), 31.66 (CH3 of CMe3), 31.73
(CH2), 49.33 (CMe2), 50.90 (CMe2), 51.80 (OMe), 53.01 (OMe), 56.18
(CH2), 65.69 (CH2), 85.59 (C4 of furan), 114.76 (C3 of furan), 127.28
(CHpara of C6H5), 127.62 (2 CHortho of C6H5), 129.83 (2 CHmeta of C6H5),
138.32 (Cipso of C6H5), 139.89 (C5 of furan), 159.02 (C2 of furan), 163.62
(CO2Me), 165.13 (CO2Me), 172.20 (NCO).
Diethyl 2-[Benzoyl(1,1,3,3-tetramethylbutyl)amino]-5-(1,1,3,3-
tetramethylbutylamino)-3,4-furandicarboxylate 5b
Viscous yellow oil, IR (KBr) (υmax, cm−1): 3492 (NH), 1746 (CO2Me),
1684 (CO2Me), 1569 (CON), 1230 (C O).1H NMR (250.13 MHz, CDCl3):
δH 1.03 (9 H, s, CMe3), 1.10 (9 H, s, CMe3), 1.18 (3 H, t, 3JHH = 7.0 Hz,
CH3), 1.29 (3 H, t, 3JHH = 7.0 Hz, CH3), 1.40 (3 H, s, CMe2), 1.51 (3 H,
s, CMe2), 1.55 (6 H, s, CMe2), 1.60 (2 H, m, CH2), 1.71 (2 H, d, 1J= 15.0

Benzoic Acid, 1,1,3,3-Tetramethylbutyl Isocyanide
177
Hz, CH2), 1.86 (2 H, d, 1J= 15.0 Hz, CH2), 4.11 (3 H, m, OEt), 4.32 (3 H,
m, OEt), 7.02 (1 H, s, NH), 7.12 (2 H, d, 3JHH = 7 Hz, 2 CHortho of C6H5),
7.26 (1 H, t, 3JHH = 7 Hz , CHpara of C6H5), 7.46 (2 H, t, 3JHH = 7.5 Hz ,
2 CHmeta of C6H5).13C NMR (62.90 MHz, CDCl3): δC 14.04 (CH3), 14.17
(CH3), 28.12 (CMe3), 28.94 (CMe3), 30.03 (CH3 of CMe2), 30.20 (CH3 of
CMe2), 31.45 (CH3 of CMe3), 31.62 (CH3 of CMe3), 31.65 (CH2), 49.35
(CMe2), 52.98 (CMe2), 56.11 (OEt), 59.57 (OEt), 61.17 (CH2), 65.67
(CH2), 85.91 (C4 of furan), 115.2 (C3 of furan), 127.42 (CHpara of C6H5),
127.59 (2 CHortho of C6H5), 129.77 (2 CHmeta of C6H5), 138.22 (Cipso
of C6H5), 139.07 (C5 of furan), 158.88 (C2 of furan), 164.75 (CO2Me),
165.13 (CO2Me), 172.13 (NCO).
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