Reaction between triphenylphosphine, diaroylacetylenes and arylidenemalononitriles: a novel and simple synthesis of 3-aroyl-2,5-diaryl-2,4-cyclopentadiene-1,1-dicarbonitriles

Article abstract of DOI:10.1016/j.tetlet.2007.12.018

A novel and simple synthesis of 3-aroyl-2,5-diaryl-2,4-cyclopentadiene-1,1-dicarbonitriles is described. The reactive 1:1 zwitterionic intermediate, formed by the addition of triphenylphosphine to diaroylacetylenes, was trapped by arylidenemalononitriles

Full text of DOI:10.1016/j.tetlet.2007.12.018

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 945–947
Reaction between triphenylphosphine, diaroylacetylenes
and arylidenemalononitriles: a novel and simple synthesis
of 3-aroyl-2,5-diaryl-2,4-cyclopentadiene-1,1-dicarbonitriles
a,
a
a
b
*
Mehdi Adib , Mohammad Hosein Sayahi , Shabnam Mahernia , Long-Guan Zhu
a School of Chemistry, University College of Science, University of Tehran, PO Box 14155-6455, Tehran, Iran
b Chemistry Department, Zhejiang University, Hangzhou 310027, PR China
Received 12 October 2007; revised 27 November 2007; accepted 5 December 2007
Available online 8 December 2007
Abstract
A novel and simple synthesis of 3-aroyl-2,5-diaryl-2,4-cyclopentadiene-1,1-dicarbonitriles is described. The reactive 1:1 zwitterionic
intermediate, formed by the addition of triphenylphosphine to diaroylacetylenes, was trapped by arylidenemalononitriles to produce
the title compounds under mild reaction conditions in fairly good yields.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: Triphenylphosphine; Diaroylacetylenes; Arylidenemalononitriles; 3-Aroyl-2,5-diaryl-2,4-cyclopentadiene-1,1-dicarbonitriles
Cyclopentadienes (Cps) are highly useful synthetic inter-
mediates. Considerable attention has been focused on the
synthesis of substituted Cps as units for the construction
of fused ring systems via inter- and intramolecular Diels–
Alder reactions, as ligands in coordination chemistry and
as homogeneous catalysis for olefin polymerization.1
Several methods have been reported for the direct prep-
aration of substituted Cps including [3+2] annulation of
allylidenetriphenylphosphoranes with 1,2-diacylethylenes,2
reaction between isocyanides, dimethyl acetylenedicarbox-
ylate, and electrophilic styrenes,3 Pt(II)- or Au(I)-catalyzed
cyclization of 1,2,4-trienes,4 acid catalyzed cyclization of
1,4-pentadien-3-ols,5 Pd-mediated cyclization of 1,5-hexa-
dien-3-ols,6 reaction of 1,1-dibromo-2-vinylcyclopropanes
with methyllithium,7 cycloaddition of a,b-unsaturated
Fisher carbene complexes with alkynes or alkenes,8 electro-
philic allylation of enolizable 1,3-dicarbonyl compounds
and successive acid catalyzed cyclizations,9 insertion of
aroyl cyanides or acid chlorides with zirconacyclo-
pentenes,10 reaction of zirconacyclopentadienes with a
one-carbon unit building block such as aldehydes, propy-
noates, acyl halides or 1,1-dihalides,11 and reaction of
1,4-dilithio-1,3-dienes with carboxylic acid derivatives,
aldehydes, or ketones.12
As part of our current studies on the design of new routes
for the preparation of interesting organic compounds,13 we
report herein a novel synthesis of polysubstituted Cps using
simple starting materials. Thus, a mixture of triphenylphos-
phine, a diaroylacetylene 1, and an arylidenemalononitrile 2
underwent a smooth reaction in dry dichloromethane at
ambient temperature to afford 3-aroyl-2,5-diaryl-2,4-cyclo-
pentadiene-1,1-dicarbonitriles 3a–h in 60–72% yields
(Scheme 1).
The reactions were carried out by first mixing triphenyl-
phosphine and arylidenemalononitrile 2 in dry CH2Cl2.
Then, a solution of the acetylenic compound 1 in dry
CH2Cl2 was added to the reaction mixture. The reaction
proceeded spontaneously at ambient temperature and
was completed within an hour. TLC and 1H NMR analysis
of the reaction mixtures clearly indicated the formation of
the functionalized Cps 3 in fairly good yields.14
*
Corresponding author. Tel./fax: +98 21 66495291.
E-mail address: madib@khayam.ut.ac.ir (M. Adib).
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.12.018

946
M. Adib et al. / Tetrahedron Letters 49 (2008) 945–947
COAr
O
C
O
C
CN
CN
CH2Cl2
r.t., 1 h
Ar
Ar
+
C
(C6H5)3P=O
+
(C6H5)3P +
C
'
Ar
Ar
Ar'
NC CN
3
1
2
'
3
Ar
Ar
% Yield
71
a
b
c
d
e
C6H5
C6H5
4-CH3C6H4 72
4-CH3OC6H4 70
4-ClC6H4
4-FC6H4
4-CH3C6H4 66
C6H5
C6H5
C6H5
C6H5
C6H5
65
69
f
g
h
2,5-(CH3)2C6H3 C6H5
4-CH3C6H4 C6H5
62
60
Scheme 1.
The structures of the isolated Cps 3a–h were confirmed
spectrum of 3a exhibited a single sharp resonance (d
7.23 ppm) arising from the CH of the Cp ring, along with
characteristic signals with appropriate chemical shifts and
coupling constants for the 15 H atoms of the three phenyl
by IR, 1H, and 13C NMR spectroscopy, mass spectro-
metry, and elemental analysis. The IR spectrum of 3a
showed absorptions at 2249 and 1647 cmꢀ1 indicating the
presence of a nitrile and a conjugated ketone, respectively.
The mass spectrum of 3a displayed the molecular ion (M+)
peak at m/z 372. The fragmentation pattern exhibited char-
acteristic peaks with the appropriate m/z values consistent
1
substituents. The H decoupled 13C NMR spectrum of 3a
showed three signals readily recognized as arising from
the 1,1-disubstituted quaternary carbon atom of the Cp
ring (d 45.79 ppm), 2 equiv nitrile substituents (d 111.55
ppm) and a carbonyl group (d 192.05 ppm) as well as 16
distinct resonances in agreement with the proposed struc-
ture.14 Single-crystal X-ray analysis conclusively confirmed
the structure of these compounds. An ORTEP diagram of
3a is shown in Figure 1.15
1
with the structure of the isolated product. The H NMR
A mechanistic rationalization for this reaction is pro-
vided in Scheme 2. On the basis of the well-established
chemistry of trivalent phosphorus nucleophiles,16–19 it is
reasonable to assume that zwitterion 4 formed from the
initial addition of triphenylphosphine to the electron-defi-
cient acetylenic compound 1 is trapped by the electrophilic
styrene 2 leading to 1:1:1 adduct 5, which undergoes intra-
molecular cyclization to betaine 6. This betaine can undergo
a [1,3]-proton shift to form a new betaine 7 from which
triphenylphosphine oxide is removed to afford the product
3-aroyl-2,5-diaryl-2,4-cyclopentadiene-1,1-dicarbonitriles 3.
Fig. 1. X-ray structure of 3a, with 50% probability displacement
ellipsoids, H atoms with arbitrary radii.
+
CN
Ph3P
COAr
Ar'
CN
+
O
C
O
C
Ph3P
_
CN
Ar'
CCOAr
Ar
Ar
(C6H5)3P +
C
C
Ar
2
_
O
NC
ArOC
1
5
4
+
+
Ph3P
_
O
Ph3P
_
O
COAr
Ar'
COAr
COAr
Ar'
[1,3]-proton shift
+ (C6H5)3P=O
Ar'
Ar
Ar
Ar
NC CN
NC CN
NC CN
6
7
3
Scheme 2.

M. Adib et al. / Tetrahedron Letters 49 (2008) 945–947
947
Sayahi, M. H.; Ziyadi, H.; Bijanzadeh, H. R.; Zhu, L.-G. Tetrahedron
2007, 63, 11135–11140; Adib, M.; Mahdavi, M.; Alizadeh Noghani,
M.; Bijanzadeh, H. R. Tetrahedron Lett. 2007, 48, 8056–8059; Adib,
M.; Sheibani, E.; Mostofi, M.; Ghanbary, K.; Bijanzadeh, H. R.
Tetrahedron 2006, 62, 3435–3438; Adib, M.; Mahdavi, M.; Mah-
moodi, N.; Pirelahi, H.; Bijanzadeh, H. R. Synlett 2006, 1765–1767;
Adib, M.; Ghanbary, K.; Mostofi, M.; Bijanzadeh, H. R. Tetrahedron
2005, 61, 2645–2648.
In summary, we have succeeded in synthesizing
1,1,2,3,5-pentasubstituted cyclopentadienes of potential
synthetic interest via a novel reaction between diaroylacetyl-
enes and arylidenemalononitriles in the presence of tri-
phenylphosphine. Good yields of the products, relatively
short reaction times, and use of simple starting materials
are the main advantages of this method. The reactions were
performed under neutral and mild conditions, and the
starting materials and reagents can be mixed without any
activation or modification. The highly substituted Cps pre-
pared in the present study may find useful applications in
synthetic organic chemistry.
14. The procedure for the preparation of 3-benzoyl-2,5-diphenyl-2,4-
cyclopentadiene-1,1-dicarbonitrile 3a is described as an example. To
a
magnetically stirred solution of triphenylphosphine (0.262 g,
1 mmol) and benzylidenemalononitrile (0.154 g, 1 mmol) in dry
CH2Cl2 (6 mL) was added dropwise a solution of dibenzoylacetylene
(0.234 g, 1 mmol) in dry CH2Cl2 (2 mL) at ꢀ5 °C over 4 min. The
reaction mixture was then allowed to warm to room temperature and
stirred for 1 h. The solvent was removed and the solid residue was
purified by column chromatography using n-hexane–EtOAc (3:1) as
eluent. The solvent was removed and the residue was recrystallized
from 1:1 n-hexane–EtOAc to afford 3a as pale yellow crystals, mp
153 °C, yield 0.26 g, 71%. IR (KBr) (mmax/cmꢀ1): 2249 (CN), 1647
(C@O), 1620, 1600, 1564, 1491, 1443, 1358, 1240, 1076, 982, 868,
766, 734, 692. EI-MS, m/z (%): 372 (M+, 70), 345 (M-HCN, 54), 277
(9), 240 (10), 172 (7), 159 (8), 105 (C6H5CO+, 100), 77 (C6H5þ, 61),
51 (9). Anal. Calcd for C26H16N2O (372.43): C, 83.85; H, 4.33; N,
7.52. Found: C, 83.7; H, 4.3; N, 7.4. 1H NMR (500.1 MHz, CDCl3):
Acknowledgment
This research was supported by the Research Council of
the University of Tehran as research project 6102036/1/02.
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˚
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