The reaction of N -isocyaniminotriphenylphosphorane with biacetyl in the presence of (E) -cinnamic acids: Synthesis of fully substituted 1,3,4-oxadiazole derivatives via intramolecular aza -wittig reactions of in situ generated iminophosphoranes

Article abstract of DOI:10.1080/10426507.2012.700351

Reaction of N-isocyaniminotriphenylphosphorane with biacetyl in the presence of (E)-cinnamic acids proceeds smoothly at room temperature and under neutral conditions to afford sterically congested 1,3,4-oxadiazole derivatives in high yields. The reaction

Full text of DOI:10.1080/10426507.2012.700351

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Phosphorus, Sulfur, and Silicon and the
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The Reaction of N-
Isocyaniminotriphenylphosphorane
With Biacetyl in the Presence of (E)-
Cinnamic Acids: Synthesis of Fully
Substituted 1,3,4-Oxadiazole Derivatives
via Intramolecular AZA-Wittig Reactions
of in Situ Generated Iminophosphoranes
Ali Ramazani a , Behnaz Abdian a , Fatemeh Zeinali Nasrabadi a &
Morteza Rouhani b
a Department of Chemistry , University of Zanjan , Zanjan , Iran
b Young Researchers Club, Zanjan Branch , Islamic Azad University ,
Zanjan , Iran
Accepted author version posted online: 22 Jun 2012.Published
online: 31 May 2013.
To cite this article: Ali Ramazani , Behnaz Abdian , Fatemeh Zeinali Nasrabadi & Morteza Rouhani
(2013) The Reaction of N-Isocyaniminotriphenylphosphorane With Biacetyl in the Presence of (E)-
Cinnamic Acids: Synthesis of Fully Substituted 1,3,4-Oxadiazole Derivatives via Intramolecular AZA-
Wittig Reactions of in Situ Generated Iminophosphoranes, Phosphorus, Sulfur, and Silicon and the
Related Elements, 188:5, 642-648, DOI: 10.1080/10426507.2012.700351
To link to this article: http://dx.doi.org/10.1080/10426507.2012.700351
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Phosphorus, Sulfur, and Silicon, 188:642–648, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.700351
THE REACTION OF
N-ISOCYANIMINOTRIPHENYLPHOSPHORANE WITH
BIACETYL IN THE PRESENCE OF (E)-CINNAMIC ACIDS:
SYNTHESIS OF FULLY SUBSTITUTED 1,3,4-OXADIAZOLE
DERIVATIVES VIA INTRAMOLECULAR AZA-WITTIG
REACTIONS OF IN SITU GENERATED
IMINOPHOSPHORANES
Ali Ramazani,1 Behnaz Abdian,1 Fatemeh Zeinali Nasrabadi,1
and Morteza Rouhani2
1Department of Chemistry, University of Zanjan, Zanjan, Iran
2Young Researchers Club, Zanjan Branch, Islamic Azad University, Zanjan, Iran
GRAPHICAL ABSTRACT
Abstract Reaction of N-isocyaniminotriphenylphosphorane with biacetyl in the presence of
(E)-cinnamic acids proceeds smoothly at room temperature and under neutral conditions to
afford sterically congested 1,3,4-oxadiazole derivatives in high yields. The reaction proceeds
smoothly and straightforward under mild conditions and no side reactions are observed.
Keywords
N-isocyaniminotriphenylphosphorane; biacetyl; (E)-cinnamic acid; 1,3,4-
oxadiazole; aza-Wittig reaction
INTRODUCTION
In recent years, multicomponent reactions (MCRs) have become important tools in
modern preparative chemistry because these reactions increase the efficiency by combining
several operational steps without any isolation of intermediates or changes of the condi-
tions.1–9 Hence, this principle is highly efficient in terms of time as well as resources.10
Among the MCRs, the most valuable reactions are those based on isocyanides. Isocyanide-
based multicomponent reactions (abbreviated to IMCRs by Ugi and Do¨mling) due to their
synthetic potential, their inherent atom efficiency, convergent nature, ease of implementa-
tion, and molecular diversity, have attracted much attention because of the advantages that
they offer to the field of combinatorial chemistry.11–13
Recently, the intramolecular version of the aza-Wittig-type reaction has attracted
much attention because it has exhibited high potential for the synthesis of a wide variety of
Received 8 February 2012; accepted 28 May 2012.
This research was supported by the “Iran National Science Foundation: INSF.”
Address correspondence to Ali Ramazani, Department of Chemistry, University of Zanjan, PO Box 45195-
313, Zanjan, Iran. E-mail: aliramazani@gmail.com
642

REACTION OF N-ISOCYANIMINOTRIPHENYLPHOSPHORANE
643
nitrogen heterocycles. This can be attributed to the rapid progress in the preparation of func-
tionalized iminophosphoranes.14 Existence of the nucleophilicity at the nitrogen is a factor
of essential mechanistic importance by applying these iminophosphoranes as aza-Wittig
reagents. Iminophosphoranes are important reagents in synthetic organic chemistry, espe-
cially in the synthesis of naturally occurring products and compounds with biological and
pharmacological activity.14–16 In recent years, several synthetic methods have been reported
for the preparation of N-isocyaniminotriphenylphosphorane (3).17,18 There are several re-
ports on the use of 3 in the synthesis of metal complexes.17,18 Nevertheless, the organic
chemistry of N-isocyaniminotriphenylphosphorane 3 remains almost unexplored.17,18 N-
isocyaniminotriphenylphosphorane 3 is expected to have a huge synthetic potential because
it represents a reagent, in which the iminophosphoranyl group can react with a compound
having a carbonyl functionality.17,18 Recently, we have established a one-pot method for
the synthesis of organophosphorus compounds.19–23
1,3,4-Oxadiazoles have attracted interest in medicinal chemistry as surrogates of car-
boxylic acids, esters, and carboxamides.24–26 They are an important class of heterocyclic
compounds that have a wide range of pharmaceutical and biological activities, including
antimicrobial, anti-fungal, anti-inflammatory, antihypertensive, analgesic, antibacterial, hy-
poglycemic, antimalarial, antitubercular, and antidepressant activity.24–26 Several methods
have been reported in the literature for the synthesis of 1,3,4-oxadiazoles. These protocols
are multi-step in nature.27–30 As part of our ongoing program to develop efficient and robust
methods for the synthesis of heterocyclic compounds,31–40 we report the preparation of
a new class of 1,3,4-oxadiazole derivatives 4a–g by a novel three-component condensa-
tion reaction of biacetyl 1, N-isocyaniminotriphenylphosphorane 3, and the corresponding
(E)-cinnamic acid 2 in excellent yields under neutral conditions (Scheme 1).
RESULTS AND DISCUSSION
The (E)-cinnamic acid derivatives 2 with biacetyl 1 and N-isocyaniminotriphenyl-
phosphorane 3 in CH2Cl2 react in a 1:1:1 molar ratio at room temperature to produce steri-
cally congested 1,3,4-oxadiazole derivatives 4 and triphenylphosphine oxide 5 (Scheme 1).
The reaction proceeds smoothly and straightforward under mild conditions and no side re-
actions were observed. Other aspects of these types MCRs are currently under investigation
in our laboratory.
C
N
N
O
O
N
O
N
CH2Cl2
r.t. 12 h
CH3
Ar
+
+
+
Ph3P
O
H3C
Ar
OH
H3C
O
R
O
R
HO CH3
5
Ph3P
1
2
3
4
R
Ar
a
b
c
d
e
f
H
H
H
H
4-MeC6H4
4-FC6H4
4-ClC6H4
Ph
Me Ph
H
H
3-ClC6H4
3-MeOC6H4
g
Scheme 1

644
A. RAMAZANI ET AL.
The structures of the products were deduced from their H NMR, 3C NMR, IR, and
mass spectra (MS). The H NMR spectrum of 4a consists of two singlets for the two methyl
groups of biacetyl (δ = 1.92 and 2.37 ppm), a singlet for the methyl group from (E)-
cinnamic acid (δ = 2.35 ppm), a singlet for the OH proton (δ = 4.70 ppm, exchangeable by
D2O), an AAꢁXXꢁ pattern for the aromatic protons (δ = 7.21 and 7.43 ppm, 3JHH = 7.5 Hz),
and two doublets for the HC CH protons (δ = 6.95 and 7.53 ppm, 3JHH = 16.5 Hz). The
1H decoupled 13C NMR spectrum of 4a shows 13 distinct resonances; partial assignment
of these resonances is given in the experimental section. The 1H and 13C NMR spectra of
compounds 4b–g are similar to those of 4a, except for the aromatic moieties, which exhibit
characteristic signals with appropriate chemical shifts.
The suggested mechanism for the formation of products 4a–g is depicted in Scheme 2.
On the basis of the chemistry of isocyanides,11 it is reasonable to assume that the first step
may involve nucleophilic addition of the N-isocyaniminotriphenylphosphorane 3 to biacetyl
1, which facilitates its protonation with the acid 2 leading to nitrilium intermediate 6. This
intermediate may be attacked by the conjugate base of the acid 2 to form the 1:1:1 adduct
7. This adduct may undergo intramolecular aza-Wittig reaction31–40 of iminophosphorane
moiety with the ester carbonyl group to afford the isolated sterically congested 1,3,4-
oxadiazole derivatives 4 by removal of triphenylphosphine oxide 5 from intermediate 8.
Scheme 2
In summary, we think that the reported method offers a mild, simple, and efficient
route for the preparation of sterically congested 1,3,4-oxadiazole derivatives 4 from biacetyl,
N-isocyaniminotriphenylphosphorane 3 and (E)-cinnamic acids. Its ease of workup, high
yields, and fairly mild reaction conditions make it a useful addition to modern synthetic
methodologies.
EXPERIMENTAL
General
N-isocyaniminotriphenylphosphorane 3 was prepared on the basis of reported pro-
cedures.17 Other starting materials and solvents were obtained from Merck and Fluka and

REACTION OF N-ISOCYANIMINOTRIPHENYLPHOSPHORANE
645
were used without further purification. The methods used to follow the course of the reac-
tions are TLC and NMR. TLC and NMR indicated that there were no side products. Melting
points (mp) were measured with an Electrothermal 9100 apparatus and are uncorrected.
The IR spectra were measured with a Jasco 6300 FTIR spectrophotometer. The 1H and 13
C
NMR spectra (CDCl3) were recorded with a BRUKER DRX-250 AVANCE spectrometer
at 250.0 and 62.5 MHz, respectively. Elemental analyses were performed using a Heraeus
CHN-O-Rapid analyzer. The MS were recorded with a Finnigan MAT 8430 mass spec-
trometer operating at an ionization potential of 70 eV. Preparative layer chromatography
(PLC) plates were prepared from Merck silica gel (F254) powder.
Synthesis of Compounds 4a–g: General Procedure
A mixture of N-isocyaniminotriphenylphosphorane (1.0 mmol, 0.300 g), biacetyl
(1.0 mmol, 0.10 mL), and the corresponding (E)-cinnamic acid (1.0 mmol; 0.16 g for 4a,
0.166 g for 4b, 0.18 g for 4c, 0.15 g for 4d, 0.16 g for 4e, 0.18 g for 4f, and 0.175 g for 4g)
in CH2Cl2 (5 mL) was stirred at room temperature for 12 h. The solvent was removed under
reduced pressure and the viscous residue was purified by PLC [silica gel (F254) powder;
petroleum ether-ethyl acetate 4:1]. The characterization data of the compounds are given
below.
3-Hydroxy-3-{5-[(E)-2-(4-methylphenyl)-1-ethenyl]-1,3,4-oxadiazol-2-
yl}-2-butanone (4a)
◦
1
White powder (276 mg, yield 92%); mp 125–127 C; H NMR (CDCl3): δ = 1.92
3
(s, 3H, CH3), 2.35 (s, 3H, CH3), 2.38 (s, 3H, CH3), 4.70 (s, 1H, OH), 6.95 (d, JHH
=
3
3
16.5 Hz, 1H, CH), 7.21 (d, JHH = 7.5 Hz, 2H, arom-H), 7.43 (d, JHH = 7.5 Hz, 2H,
arom-H), 7.53 (d, 3JHH = 16.5 Hz, 1H, CH). 13C NMR (CDCl3): δ = 21.5 (CH3), 23.2
(CH3), 23.8 (CH3), 75.7 (C–OH), 108.2 (CH ), 140.2 (CH ), 127.6 (CH), 129.8 (CH),
131.7 (C),140.7 (C), 164.7 (C N), 165.6 (C N), 204.7 (C O). IR (neat): υmax = 3298,
2998, 2918, 1723, 1644, 1532, 1363, 1180, 833 cm−1. MS: m/z (%) = 272 (M+, 20), 229
(100), 187 (72), 160 (32), 143 (68), 115 (52), 91 (24), 43 (96). Anal. calcd. for C15H16N2O3
(272.12): C, 66.16; H, 5.92; N, 10.29. Found: C, 66.24; H, 5.97; N, 10.24%.
3-{5-[(E)-2-(4-Fluorophenyl)-1-ethenyl]-1,3,4-oxadiazol-2-yl}-3-hydroxy-
2-butanone (4b)
◦
1
White powder (270 mg, yield 90%); mp 84–86 C; H NMR (CDCl3): δ = 1.87
3
(s, 3H, CH3), 2.35 (s, 3H, CH3), 4.70 (s, 1H, OH), 6.92 (d, JHH = 16.5 Hz, 1H, =CH),
7.01–7.55 (m, 5H, arom-H and =CH); 13C NMR (CDCl3): δ = 23.3 (CH3), 23.7 (CH3),
2
75.7 (C–OH), 109.0 (CH=), 138.9 (CH=), 116.2 (d, JCF = 28.3 Hz, arom-CH), 129.4
3
1
(d, JCF = 8.2 Hz, arom-CH), 130.7 (C), 162.5 (d, JCF = 440.3 Hz, C), 164.9 (C=N),
165.2 (C=N), 204.6 (C=O). IR (neat): υmax = 3372, 2923, 1731, 1670, 1529, 1505, 1163,
818 cm−1. MS: m/z (%) = 276 (M+, 12), 234 (100), 191 (56), 164 (32), 147 (60), 121 (20),
101 (24), 43 (68). Anal. calcd. for C14H13FN2O3 (276.09): C, 60.87; H, 4.74; N, 10.14.
Found: C, 60.81; H, 4.80; N, 10.08%.

646
A. RAMAZANI ET AL.
3-{5-[(E)-2-(4-Chlorophenyl)-1-ethenyl]-1,3,4-oxadiazol-2-yl}-3-hydroxy-
2-butanone (4c)
◦
1
White powder (264 mg, yield 88%); mp 148–150 C; H NMR (CDCl3): δ = 1.92
3
(s, 3H, CH3), 2.35 (s, 3H, CH3), 4.67 (s, 1H, OH), 6.97 (d, JHH = 16.8 Hz, 1H, CH),
7.25–7.54 (m, 5H, arom-H and CH). 13C NMR (CDCl3): δ = 23.3 (CH3), 23.7 (CH3),
75.7 (C–OH), 109.8 (CH ), 138.8 (CH ), 128.7 (CH), 129.3 (CH), 132.9 (C), 136.2 (C),
164.9 (C N), 165.1 (C N), 204.5 (C O). IR (neat): υmax = 3363, 2921, 1726, 1648,
1523, 1406, 1152, 815 cm−1. Anal. calcd. for C14H13ClN2O3 (292.06): C, 57.44; H, 4.48;
N, 9.57. Found: C, 57.39; H, 4.53; N, 9.52%.
3-Hydroxy-3-{5-[(E)-2-phenyl-1-ethenyl]-1,3,4-oxadiazol-2-yl}-2-
butanone (4d)
◦
1
White powder (255 mg, yield 85%); mp 79–81 C; H NMR (CDCl3): δ = 1.93
3
(s, 3H, CH3), 2.36 (s, 3H, CH3), 4.69 (s, 1H, OH), 7.01 (d, JHH = 16.5 Hz, 1H, CH),
7.40–7.60 (m, 6H, arom-H and CH); 13C NMR (CDCl3): δ = 23.3 (CH3), 23.7 (CH3),
75.7 (C–OH), 109.3 (CH ), 140.2 (CH ), 127.6 (CH), 129.1 (CH), 130.2 (CH), 134.4
(C), 165.0 (C N), 165.4 (C N), 202.6 (C O). IR (neat): υmax = 3311, 2923, 1726, 1649,
1528, 1449, 1150, 759, 693 cm−1. Anal. calcd. for C14H14N2O3 (258.10): C, 65.11; H,
5.46; N, 10.85. Found: C, 65.05; H, 5.40; N, 10.91%.
3-Hydroxy-3-{5-[(E)-1-methyl-2-phenyl-1-ethenyl]-1,3,4-oxadiazol-2-yl}-
2-butanone (4e)
Yellow viscous oil (255 mg, yield 85%); 1H NMR (CDCl3): δ = 1.93 (s, 3H, CH3),
2.36 (s, 3H, CH3), 2.39 (s, 3H, CH3), 4.66 (s, 1H, OH), 7.36–7.51 (m, 6H, arom-H and
CH). 13C NMR (CDCl3): δ = 14.6 (CH3), 23.3 (CH3), 23.8 (CH3), 75.8 (C–OH), 128.5
(CH), 129.6 (CH), 135.3 (CH), 135.4 (CH), 120.9 (C), 167.8 (C N), 170.0 (C N), 204.7
(C O). IR (neat): υmax = 3298, 2994, 2926, 1720, 1601, 1526, 1447, 1093, 713, 695 cm−1
.
Anal. calcd. for C15H16N2O3 (272.12): C, 66.16; H, 5.92; N, 10.29. Found: C, 66.24; H,
5.84; N, 10.37%.
3-{5-[(E)-2-(3-Chlorophenyl)-1-ethenyl]-1,3,4-oxadiazol-2-yl}-3-hydroxy-
2-butanone (4f)
White powder (258 mg, yield 86%); mp 62–64 ◦C; 1H NMR (CDCl3): δ = 1.93 (s, 3H,
CH3), 2.36 (s, 3H, CH3), 4.69 (s, 1H, OH), 7.01 (d, 3JHH = 16.5 Hz, 1H, CH), 7.36–7.52
(m, 5H, arom-H and CH); 13C NMR (CDCl3): δ = 23.3 (CH3), 23.7 (CH3), 75.7 (C–OH),
110.7 (CH ), 135.1 (CH ), 125.7 (CH), 127.4 (CH), 130.1 (CH), 130.3 (CH), 136.2 (C),
138.6 (C), 162.8 (C N), 165.0 (C N), 204.9 (C O). IR (neat): υmax = 3274, 2923, 1728,
1650, 1528, 1426, 1110, 840, 789, 691 cm−1. Anal. calcd. for C14H13ClN2O3 (292.06): C,
57.44; H, 4.48; N, 9.57. Found: C, 57.49; H, 4.53; N, 9.52%.

REACTION OF N-ISOCYANIMINOTRIPHENYLPHOSPHORANE
647
3-Hydroxy-3-{5-[(E)-2-(3-methoxyphenyl)-1-ethenyl]-1,3,4-oxadiazol-2-
yl}-2-butanone (4g)
White powder (261 mg, yield 87%); mp 70–72 ◦C; 1H NMR (CDCl3): δ = 1.93 (s,
3H, CH3), 2.35 (s, 3H, CH3), 3.83 (s, 3H, OCH3), 4.73 (s, 1H, OH), 6.91–7.35 (m, 5H,
3
arom-H and CH), 7.52 (d, JHH = 16.5 Hz, 1H, CH); 13C NMR (CDCl3): δ = 23.3
(CH3), 23.8 (CH3), 55.3 (s, 3H, OCH3), 75.8 (C–OH), 109.6 (CH ), 140.1 (CH ), 112.5
(CH), 116.1 (CH), 120.3 (CH), 130.0 (CH), 135.8 (C), 160.0 (C), 164.9 (C N), 165.3
(C N), 204.6 (C O). IR (neat): υmax = 3236, 3004, 2922, 1730, 1650, 1580, 1466, 1108,
876, 795, 687 cm−1. Anal. calcd. for C15H16N2O4 (288.11): C, 62.49; H, 5.59; N, 9.72.
Found: C, 62.44; H, 5.64; N, 9.67%.
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