Efficient synthesis of 1-(2-propynyl)pyrrole

Full text of DOI:10.1023/A:1020886503782

Russian Journal of Organic Chemistry, Vol. 38, No. 7, 2002, pp. 1073 1075. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 7, 2002,
pp. 1115 1117.
Original Russian Text Copyright
2002 by Brandsma, Tarasova, Kalinina, Albanov, Klyba, Trofimov.
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Efficient Synthesis of 1-(2-Propynyl)pyrrole
L. Brandsma1, O. A. Tarasova2, N. A. Kalinina2, A. I. Albanov2,
L. V. Klyba2, and B. A. Trofimov2
1
Utrecht University, Utrecht, The Netherlands
2
Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
Received January 25, 2002
Recent interest in 1-(2-propynyl)pyrrole (I) is
system sodium amide liquid ammonia [4], the yield
of pyrrole I was as low as 30 and 15%, respectively,
and the reaction time was more than 12 h.
explained by wide synthetic application of diacetylene
pyrrole derivatives which are promising for prepara-
tion of highly ordered polymeric structures possessing
specific optical, electronic, and magnetic properties
[1, 2]. Nevertheless, no efficient and selective proce-
dure for synthesizing 1-(2-propynyl)pyrrole (I) was
so far reported. We were interested in this compound
as a model of heteroaromatic alkyne. Carbanions
derived therefrom were not studied in heterocycliza-
tions with isothiocyanates [3], which stimulated the
present work.
The known procedures for preparation of pyrrole I
[1, 2, 4] are based on the reaction of potassium or
sodium pyrrolate with 2-propynyl bromide and are
characterized by different modes of generation of
pyrrolate anion. The largest yield of the product
(57%) containing 10% of the allene isomer was
obtained by treatment of pyrrole with potassium
hydroxide in toluene in the presence of 18-crown-6
[1]. In the other cases, when pyrrole was treated with
metallic potassium in diethyl ether [2] or with the
Taking into acount that pyrrolate ion is capable of
undergoing alkylation at both nitrogen and carbon
atoms [5, 6] and that N-(2-propynyl) group is readily
converted into allenyl moiety (for example, 1-allenyl-
pyrrole can be synthesized in 68% yield from pyrrole
and 2-propynyl bromide in the superbasic KOH
DMSO system [7]), we have found that the best
results are obtained using the system KNH2 liquid
ammonia. In order to avoid formation of 2-, 3-, and
poly(2-propynyl)pyrroles and also the transformation
of 2-propynyl bromide into 2-propynylamine [8], the
reaction of potassium pyyrolate with 2-propynyl
bromide was carried out at 60 to 50 C, and the
reaction time was shortened to 20 min (Scheme 1).
Under these conditions we obtained 1-(2-propynyl)-
pyrrole in 70% yield, and its purity (after distillation)
was 99%. The overall concentration of by-products
did not exceed 12.2%. By preparative gas liquid
chromatography we isolated and identified previously
Scheme 1.
1070-4280/02/3807-1073$27.00 2002 MAIK Nauka/Interperiodica

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BRANDSMA et al.
unknown 2-(2-propynyl)pyrrole (II), 1,2-bis(2-pro-
pynyl)pyrrole (III), and 1,3-bis(2-propynyl)pyrrole
(IV). When lithium amide was used instead of potas-
sium amide, other conditions being equal, the yield
of pyrrole I was only 48% (purity of the crude product
82%), whereas with sodium amide (reaction time 1 h)
we obtained 43% of a mixture of 1-(2-propynyl)pyr-
role (I) and its allene isomer at a ratio of 10:1.
2-(2-Propynyl)pyrrole (II). Yield 2.1%, purity
90%. H NMR spectrum, , ppm: 8.28 br.s (1H, NH),
6.70 d.t (1H, 5-H), 6.15 q (1H, 4-H), 6.02 m (1H,
1
3
3
4
3-H, J3, 4 = 3.0, J4, 5 = 2.7, J3, 5 = 1.6 Hz), 3.61 d.d
(2H, CH2), 2.17 t [1H, CH, 4J(CH2C CH) =
4
2.74 Hz, J(CH CCH2) = 0.73 Hz]. Mass spectrum,
m/z (Irel, %): 105 M+ (93), 104 (100), 79 (22), 78
(40), 77 (37), 52 (25), 51 (42), 50 (20), 43 (5), 39
(19), 28 (14).
Synthesis of 1-(2-propynyl)pyrrole (I) from pyr-
role and 2-propynyl bromide in the system potas-
sium amide liquid ammonia. To 300 ml of
liquid ammonia (containing less than 0.1% of water)
we added 19.5 g (0.5 mol) of metallic potassium cut
in 0.5-g pieces and 0.1 g of Fe(NO3)3. After 10 min,
the solution turned grey, and 35.1 g (0.52 mol) of
pyrrole was added under stirring in a stream of nitro-
gen at 60 to 40 C over a period of 1 2 min, and
60 g (0.53 mol) of 2-propynyl bromide was then
added at 60 to 50 C over a period of 5 min. The
mixture was stirred for 5 min at 50 to 35 C, the
ammonia was evaporated on a water bath in 20 min,
and the liquid organic phase was separated using
a glass filter. The solid residue which contained KBr
and unreacted potassium was washed with ether in
a continuous stream of nitrogen. The ether washings
were combined with the organic phase. According to
the GLC data, there were 87.8% of 1-(2-propynyl)-
pyrrole (I), 2.6% of 2-(2-propynyl)pyrrole (II), 6.0
and 2.7%, respectively, of isomeric bis(2-propynyl)-
pyrroles III and IV, and 0.9% of unidentified com-
pounds. The solvent was removed in a slight vacuum,
and the residue was subjected to fractional distillation
under reduced pressure in the presence of hydro-
quinone to isolate 36.8 g of pyrrole I (yield 70% with
respect to potassium), purity 99%, bp 60 C (15 mm),
1,2-Bis(2-propynyl)pyrrole (III). Yield 3.5%,
purity 92%, n2D5 = 1.5302. H NMR spectrum, , ppm:
1
6.70 d.d (1H, 5-H), 6.06 t (1H, 4-H), 6.04 m (1H,
3
3
3-H, J3, 4 = 3.0, J5, 4 = 2.3 Hz), 4.64 d (2H, NCH2),
2.34 t [1H, NCH2C CH, 4J(NCH2C CH) = 2.65 Hz],
3.56 d.d (2H, CCH2), 2.09 t [1H, CCH2C CH,
4
4J(CCH2C CH) = 2.65, J(CH CCH2) = 0.64 Hz].
13C NMR spectrum, C, ppm: 126.31 (C2), 121.30
(C5), 108.28 and 107.75 (C4, C3), 80.30 (NCH2C ),
78.13 (CCH2C ), 73.50 (NCH2C CH), 69.90
(CCH2C CH), 36.30 (NCH2), 16.76 (CCH2). IR
1
spectrum, , cm : 646 s, 716 s, 778, 884 w, 934,
1020, 1072 s, 1119, 1206 w, 1287 s, 1312, 1344,
1424, 1484 s, 1549 w, 1670 w, 1710 w, 2122 (C C),
2827 w, 2909, 2951 w, 3095, 3110 w, 3292 s ( CH),
3405 3439. Mass spectrum, m/z (Irel, %): 143 M+
(100), 142 (98), 141 (42), 117 (26), 105 (26), 104
(77), 89 (16), 78 (24), 77 (40), 70 (16), 63 (16), 51
(55), 50 (22), 43 (5), 39 (63), 38 (9), 28 (5).
1,3-Bis(2-propynyl)pyrrole (IV). Yield 1.6%,
purity 95%, n2D5 = 1.5327. H NMR spectrum, , ppm:
1
6.69 m (1H, 2-H), 6.67 t (1H, 5-H), 6.11 t (1H, 4-H,
3J4, 5 = 2.52 Hz), 4.60 d (2H, NCH2), 2.41 t [1H,
4
NCH2C CH, J(NCH2C CH) = 2.58 Hz], 3.42 d
(2H, CCH2), 2.08 t [1H, CCH2C CH, 4J(CCH2-
n2D3 = 1.5122. H NMR spectrum, , ppm: 6.71 t (2H,
1
C CH) = 2.72 Hz]. 13C NMR spectrum, C, ppm:
3
2-H, 5-H), 6.15 t (2H, 3-H, 4-H, JH, H = 2.15 Hz),
120.76 (C2), 119.23 (C3), 118.39 (C5), 108.82 (C4),
83.29 (NCH2C ), 78.13 (CCH2C ), 73.63 (NCH2-
C CH), 68.47 (CCH2C CH), 38.60 (NCH2), 16.82
4
4.59 d (2H, CH2), 2.35 t (1H, CH, J(CH2C CH) =
2.56 Hz). 13C NMR spectrum, C, ppm: 120.44 (C2,
C5), 108.95 (C3, C4), 78.18 ( C ), 73.61 ( CH),
1
1
38.54 (CH2). The H and 13C NMR spectra of product
(CCH2). IR spectrum, , cm : 601, 644 s, 712, 749,
775, 933, 985 w, 1002 w, 1071, 1155 s, 1187 w,
1291, 1343, 1403, 1427, 1498 s, 1530 w, 1553 w,
1710, 2119 (C C), 2830 w, 2913, 2947 sh, 3292 s
( C H). Mass spectrum, m/z (Irel, %): 143 M+ (100),
142 (100), 141 (25), 118 (20), 115 (44), 104 (56),
89 (10), 78 (13), 77 (28), 63 (5), 58 (6), 51 (39), 50
(11), 43 (27), 39 (25), 28 (6).
Pyrroles II IV were separated using a PAKhV-07
preparative chromatograph equipped with a thermal
conductivity detector; 5-m 10-mm column packed
with 5% of XE-60 on Chromaton N-AW-HMDS;
carrier gas helium; oven temperature 150 C; injector
I were similar to those reported in [1]. IR spectrum,
, cm : 604, 654, 728 s, 825 w, 935, 973, 1015 w,
1
1058, 1070, 1090 s, 1281 s, 1314, 1341, 1399, 1431,
1497 s, 1532 sh, 1559, 1688 w, 1733 w, 2126 w
(C C), 2786 w, 2916, 3102, 3125, 3296 s ( C H),
3409. Mass spectrum, m/z (Irel, %): 105 M+ (96), 104
(100), 79 (39), 78 (65), 77 (54), 67 (15), 52 (47), 51
(52), 50 (17), 39 (69), 38 (27), 32 (51), 28 (81).
Distillation of the still residue gave 5 g of a frac-
tion with bp 40 80 C (0.8 mm), which contained
pyrroles II IV. They were separated by preparative
gas liquid chromatography.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 7 2002

EFFICIENT SYNTHESIS OF 1-(2-PROPYNYL)PYRROLE
1075
and detector temperature 200 C. The NMR spectra
were obtained on a Bruker DPX-400 instrument at
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1
400.13 MHz for H and 100.69 MHz for 13C; CDCl3
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The IR spectra were recorded on a Bruker IFS-25
spectrometer from samples prepared as thin films.
The mass spectra (electron impact, 60 eV) were run
on an LKB-2091 GC MS system (38-m SE-54 capil-
lary column, injector temperature 250 C, oven tem-
perature programming from 70 to 200 C at a rate of
10 deg/min, ion source temperature 240 C).
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