Triphenylphosphine-catalyzed nucleophilic α-addition to alkyl propiolates synthesis of α-substituted alkyl acrylates

Article abstract of DOI:10.1080/10426500210225

The α-addition of NH-acids such as pyrrole, indole, imidazole, or benzimidazole to methyl or ethyl propiolate proceeds under neutral conditions in the presence of a catalytic amount of triphenylphosphine to give the corresponding α-substituted alkyl acryl

Full text of DOI:10.1080/10426500210225

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Phosphorus, Sulfur, and Silicon and the Related
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Triphenylphosphine-Catalyzed Nucleophilic α-Addition
to Alkyl Propiolates Synthesis of α-Substituted Alkyl
Acrylates
Issa Yavari a & Hassan Norouzi-Arasi b
a Department of Chemistry , University of Tarbiat Modarres , PO Box 14155-4838, Tehran,
Iran
b Department of Chemistry , Islamic Azad University , Tehran North Campus, Tehran, Iran
Published online: 27 Oct 2010.
To cite this article: Issa Yavari & Hassan Norouzi-Arasi (2002) Triphenylphosphine-Catalyzed Nucleophilic α-Addition to Alkyl
Propiolates Synthesis of α-Substituted Alkyl Acrylates, Phosphorus, Sulfur, and Silicon and the Related Elements, 177:1, 87-92,
DOI: 10.1080/10426500210225
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Phosphorus, Sulfur and Silicon, 2002, 177:87–92
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Copyright 2002 Taylor & Francis
1042-6507/02 $12.00 + .00
TRIPHENYLPHOSPHINE-CATALYZED
NUCLEOPHILIC -ADDITION TO ALKYL
PROPIOLATES SYNTHESIS OF -SUBSTITUTED
ALKYL ACRYLATES
Issa Yavaria and Hassan Norouzi-Arasib
Department of Chemistry, University of Tarbiat Modarres,
PO Box 14155-4838, Tehran, Irana and Department of
Chemistry, Islamic Azad University, Tehran North Campus,
Tehran, Iranb
(Received July 10 2001.)
The -addition of NH-acids such as pyrrole, indole, imidazole, or ben-
zimidazole to methyl or ethyl propiolate proceeds under neutral con-
ditions in the presence of a catalytic amount of triphenylphosphine to
give the corresponding -substituted alkyl acrylates.
Keywords: Alkyl acrylates; alkyl propiolates; NH-acids; nitrogen het-
erocycles; triphenylphosphine
Organophosphorus compounds have been extensively used in organic
synthesis as useful reagents as well as ligands of a number of tran-
4
sition metal catalysts.1 However, there are few reactions in which
organophosphorous (III) species work as catalysts.5,6 The phosphine-
induced isomerization of alkynoates to 2,4-dienoates7 and addition of
pronucleophiles to the 4-position of these substrates indicated the pos-
sibility of a new reactivity pattern for alkynoates-nucleophilic addition
at the -position as shown in Scheme 1 as a new source of -substituted
alkyl acrylates.
An important point is the ability of the nucleophile to undergo simple
Michael addition in preference to the -attack since phosphines could
also serve as general base catalysts for conjugate additions1,4 Alkyl
propiolates should be particularly prone to undergo such Michael addi-
tions. Although the proposed route of Scheme 1 requires both general
acid and base catalysis, the nucleophilic -addition of NH-acids such
as pyrrole, indole, imidazole, or benzimidazole to alkyl propiolates was
Address correspondence to Issa Yavari, Department of Chemistry, University of
Tarbiat Modarres, PO Box 14155-4838, Tehran, Iran. E-mail: isayavar@yahoo.com
87

88
I. Yavari and H. Norouzi-Arasi
SCHEME 1
carried out under neutral conditions. Thus, methyl or ethyl propiolate
undergo a smooth -addition reaction with the NH-acids in the presence
of a catalytic amount of triphenyphosphine to produce -substituted
alkyl acrylates in 80–90% yield (see Scheme 2).
SCHEME 2
The structures of compounds 3a–h were deduced from their elemen-
tal analysis and their IR, 1H, and 13C NMR spectra. The mass spectra
of these -substituted alkyl acrylates are fairly similar and exhibit
molecular ion peaks.
The 1H NMR spectra of compounds 3a–h exhibited two slightly broad
single peaks at = 5.7–6.0 and = 6.1–6.6 for the two diastereotopic
protons of the methylene group. The alkoxy groups and the hetero-
cyclic moieties give characteristic signals at appropriate chemical shifts
(see Experimental section). Further evidence was obtained from the 13
C
NMR spectra which displayed a methylene carbon resonance at about
= 115–123.

Alkyl Acrylates
89
The structural assignments of compounds 3a–h made on the basis of
their NMR spectra are supported by their IR spectra. Of special interest
1
are the strong carbonyl absorption bands at 1733–1728 cm for all
compounds. The characteristic C H out-of-plane bending absorption
of the 1,1-disubstituted alkene (RR0C CH2) appears as an intense band
1
at about 859-887 cm (see Experimental section).
In summary, the reaction of NH-acids such as pyrrole, indole,
imidazole, or benzimidazole with alkyl propiolates in the presence
of triphenyphosphine provides a simple one-pot entry into the
synthesis of -substituted alkyl acrylates of potential synthetic
interest.
EXPERIMENTAL
Alkyl propiolates were obtained from Fluka (Buchs, Switzerland). Pyr-
role, indole, imidazole, and triphenylphosphine were obtained from
1
Merck (Germany) and were used without further purification. H and
13C NMR spectra were measured with a BRUKER DRX-300 AVANCE
spectrometer at 300 and 75 MHz respectively. Mass spectra were
recorded on a Hewlett-Packard MSD 5973 mass spectrometer operat-
ing at an ionization potential of 70 eV. FT-IR spectra were recorded on
a Bomem spectrometer. Elemental analyses were performed using a
Heraeus CHN O Rapid analyzer.
The typical procedure for the preparation of 2-prrrol-l-yl-acrylic acid
methyl ester (3a) is described as an example. To a magnetically stirred
solution of 0.13 mL pyrrole (2 mmol) and 0.17 mL methyl propiolate
(2 mmol) in 5 mL of dichloromethane was added dropwise a mixture
of 0.52 g of triphenylphosphine (2 mmol) in 2 mL of dichloromethane
at 0 C. The reaction mixture was then allowed to warm up to room
temperature. After 24 h the solvent was removed under reduced pres-
sure and the residue was purified by column chromatography. The sol-
vent was removed and the product was obtained as a light-yellow oil,
0.24 g, 80%; IR (neat) ( max, cm 1) 1733 (C O), 1629 (C C), 1235 and
1
1127 (C O), 887 ( CH2 bending); H NMR (300 MHz, , CDCl3): 3.89
(3 H, s, OCH3), 5.70 (1 H, s, CH), 6.11 (1 H, s, CH), 6.28 (2 H, m,
-CH of pyrrole) and 6.93 (2 H, m, -CH of pyrrole), 13C NMR (75
MHz, , CDCl3): 53.08 (OCH3), 110.27 ( -CH), 116.24 (CH2), 121.65
( -CH), 137.65 (C), 164.07 (C O). MS, m/z (%): 152 (M+ + 1, 5), 147
(24), 135 (3), 121 (6), 119 (8), 81 (17), 57 (100). Analysis: Cal. for
C8H9NO2 (151.16): C, 63.56; H, 6.00; N, 9.27. Found: C, 63.7; H, 6.2;
N, 9.1.

90
I. Yavari and H. Norouzi-Arasi
Selected Data for 2-Prrrol-1-yl-Acrylic Acid Ethyl
Ester (3b)
Light-yellow oil, 0.27 g, 82%; IR (neat) ( max , cm 1) 1729 (C O),
1629 (C C), 1234 and 1125 (C O), 864 ( CH2 bending); 1H NMR
3
3
(300 MHz, , CDCl3): 1.39 (3 H, t, JHH, 7.1 CH3), 4.38 (2 H, q, JHH
7.1, CH2), 5.69 (1 H, s, CH), 6.10 (1 H, s, CH), 6.29 (2 H, m, -CH
of pyrrole); and 6.96 (2 H, m, -Ch of pyrrole); 13C NMR (75 MHz,
, CDCl3):14.53 (CH3), 62.26 (OCH2), 110.21 ( -CH), 115.73 (CH2),
121.64, ( -CH), 137.90 (C), 163.57 (C O). MS, m/z (%): 165 (M+, 18),
152 (25), 121 (18), 19 (16), 95 (44), 67 (83), 55 (100). Analysis: Cal. for
C9H11NO2 (165.19): C, 65.44; H, 6.71; N, 8.48. Found: C, 65.2; H, 6.6;
N, 8.3.
Selected Data for 2-Indol-1-yl-Acrylic Acid Methyl
Ester (3c)
Colorless oil; 0.35 g, 88%; IR (neat) ( max, cm 1) 1732 (C O), 1632 (C C),
1216 and 1115 (C O), 859 ( CH2 bending); 1H NMR (300 MHz,
,
CDCl3): 3.88 (3 H, s, OCH3), 5.97 (1 H, s, CH), 6.57 (1 H, s, CH), 6.66
(1 H, m, CH), 7.18–7.35 (4 H, m, CH), 7.66 (1 H, m, CH); 13C NMR
(75 MHz, , CDCl3): 53.17 (OCH3), 104.06, 110.98, 120.97, 121.50,
122.85 and 128.80 (CH), 121.76 (CH2), 129.41, 136.35 and 136.80
(C), 164.49 (C O). MS, m/z (%): 201 (M+, 90), 185 (13), 142 (84),
115 (97), 83 (40), 69 (51), 55 (100). Analysis: Cal. for C12H11NO2
(201.15): C, 71.62; H, 5.51; N, 6.96. Found: C, 71.7; H, 5.6; N,
6.9.
Selected Data for 2-Indol-1-yl-Acrylic Acid Ethyl
Ester (3d)
Colorless oil; 0.39 g, 90%; IR (neat) ( max, cm 1) 1728 (C O), 1629 (C C),
1200 and 1114 (C O), 863 ( CH2 bending); 1H NMR (300 MHz,
,
3
3
CDCl3):1.34 (3 H, t, JHH 7.1, CH3), 4.35 (2 H, q, JHH 7.1, OCH2),
5.95 (1 H, s, CH), 6.55 (1 H, S, CH), 6.64 (1 H, br d, CH), 7.15–7.36
(4 H, m, CH); 7.66 (1 H, br d, CH); 13C NMR (75 MHz, , CDCl3): 14.52
(CH3), 62.35 (OCH2), 103.97, 111.07, 120.90, 121.20, 122.74 and 128.85
(CH), 121.44 (CH2), 129.42, 136.63 and 136.79 (C), 163.95 (C O). MS,
m/z (%): 215 (M+, 15), 142 (13), 109 (35), 95 (65), 81 (84), 67 (81), 55
(100). Analysis: Cal. for C13H13NO2 (215.16):C, 72.54; H, 6.09; N, 6.51.
Found: C, 72.6; H, 5.9; N, 6.4.

Alkyl Acrylates
91
Selected Data for 2-Imidazol-1-yl-Acrylic Acid Methyl
Ester (3e)
Light-yellow oil; 0.27 g, 88%; IR (neat) ( max, cm 1) 1733 (C O),
1653 (C C), 1221 and 1100 (C O), 877 ( CH2 bending); 1H NMR
(300 MHz,
,
CDCl3): 3.90 (3 H, s, OCH3), 5.86 (1 H,
br s, CH), 6.30 (1 H, br s, CH), 7.12 (1 H, br s, CH), 7.15 (1 H,
m, CH) and 7.76 (1 H, br s, CH); 13C NMR (75 MHz, , CDCl3):
53.45 (OCH3), 119.63 (CH2), 119.80, 129.95 and 137.55 (CH),
134.69 (C), 163.03 (C O). MS, m/z (%): 152 (M+, 27), 137 (14), 121
(18), 97 (56), 93 (21), 83 (67), 68 (32), 55 (100). Analysis: Cal. for
C7H2O2 (152.08): C, 55.26; H, 5.3; N, 18.41. Found: C, 55.4; H, 5.4;
N, 18.3.
Selected Data for 2-Imidazol-1-yl-Acrylic Acid Ethyl
Ester (3f)
Light-yellow oil; 0.29 g, 87%; IR (neat) ( max , cm 1) 1728 (C O),
1634 (C C), 1221 and 1125 (C O), 878 ( CH2 bending); 1H NMR
3
(300 MHz, , CDCl3):1.36 (3 H, t,3JHH 7.1, CH3), 4.33 (2 H, q, JHH
7.1 OCH2), 5.82 (1 H, br s, CH), 6.28 (1 H, br s, CH), 7.10 (1 H, br s,
CH), 7.14 (1 H, m, CH) and 7.75 (1H, br s, CH; 13C NMR (75 MHz, ,
CDCl3): 14.47 (CH3), 62.73 (OCH2), 119.24 (CH2), 119.81, 129.85 and
137.54 (CH), 134.93 (C) and 162.52 (C O). MS, m/z (%): 167 (M++, 1,
15), 166 (M+, 18), 152 (21), 121 (22), 95 (59), 81 (75), 69 (78). Analysis:
Cal. for C8H10N2O2 (166.09):C, 57.82; H, 6.07; N, 16.86. Found: C, 57.9;
H, 6.2; N, 16.7.
Selected Data for 2-Benzoimidazol-1-yl-Acrylic Acid
Methyl Ester (3g)
Light-yellow oil; 0.36 g, 88%; IR (neat) ( max , cm 1) 1732 (C O),
1636 (C C), 1271 and 1215 (C O), 882 ( CH2 bending); 1H NMR
(300 MHz, , CDCl3): 3.85 (3 H, s, OCH3), 6.04 (1 H, s, CH), 6.63 (1
H, s, CH), 7.31 (3 H, m, CH benzimidazole ring), 7.82 (1 H, m, CH ben-
zimidazole ring) 8.04 (1 H, s, CH); 13C NMR (75 MHz, , CDCl3): 53.51
(OCH3), 110.89, 120.89, 123.31 (CH), 123.47 (CH2), 124.20 and 143.28
(CH), 133.52, 134.05 and 143.66 (C), 163.03 (C O). MS, m/z (%): 202
(M+, 75), 187 (8), 142 (100), 117 (10), 102 (66), 89 (35). 76 (30). Analy-
sis: Cal. for C11H10N2O2 (202.14): C, 65.33; H, 4.99; N, 13.86. Found: C,
65.5; H, 5.1; N, 13.7.

92
I. Yavari and H. Norouzi-Arasi
Selected Data for 2-Benzoimidazol-1-yl-Acrylic Acid
Ethyl Ester (3h)
Light-yellow oil; 0.37 g, 85%; IR (neat) ( max , cm 1) 1728 (C O), 1633
(C C), 1269 and 1204 (C O), 864 ( CH2 bending); 1H NMR (300 MHz,
, CDCl3):1.31 (3 H, t,3JHH 7.1, CH3), 4.33 (2 H, q, 3JHH 7.1, OCH2), 6.04
(1 H, s, CH), 6.63 (1 H, s, CH), 7.31 (H, m, CH), 7.83 (H, m, CH) and
8.06 (1H, s, CH);
14.48 (CH3), 62.84 (OCH2), 110.97, 120.85 (CH),
C
123.02 (CH2), 123.29, 124.14, 143.31 (CH), 133.82, 134.04, 143.61 (C)
and 162.75 (C O). MS, m/z (%): 217 (M++, 1, 88), 216 (M+, 100), 187
(6), 144 (15), 117 (6). Analysis: Cal. for C12H12N2O2 (216.15):C, 66.65;
H, 5.59; N, 12.96. Found: C, 66.8; H, 5.7; N, 12.8.
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