Synthesis of 1, 2- and 1, 3-divinylpyrrole

Full text of DOI:10.1021/jo9811322

10022
J . Org. Chem. 1998, 63, 10022-10026
Ch a r t 1
Syn th esis of 1,2- a n d 1,3-Divin ylp yr r ole
Roberta Settambolo,*,† Manuela Mariani,‡ and
Aldo Caiazzo‡
Istituto di Chimica Quantistica ed Energetica Molecolare
del CNR and Dipartimento di Chimica e Chimica
Industriale, via Risorgimento 35, 56126 Pisa, Italy
Sch em e 1
Received J une 12, 1998
Vinylpyrroles having the double bond conjugated to the
heteroaromatic ring represent a very important hetero-
cycles class. They are synthons to indole ring systems
via Diels-Alder reaction with various active dienophiles1
as well as bifunctional monomers for the preparation of
conducting and nonlinear optics materials.2 Despite the
great interest in their use, these compounds have been
until now poorly utilized, both their instability and the
difficulty of preparing 3-substituted derivatives likely
being a consistent limitation.
Z
pared by the procedures depicted in the Schemes 1 and
2. 2a was prepared by direct N-vinylation with acetylene
of the corresponding 3-vinylpyrrole (1a ) (Scheme 1). 1,2-
Divinylpyrrole (6a ) was obtained from 2-formylpyrrole
(3a ) via indirect N-vinylation (N-chloroethylation/dehy-
drochlorination) followed by Wittig methylenation of the
formyl group (Scheme 2). Analogous procedures (Schemes
1-3) allowed the synthesis of the related compounds 2b-
c, 6b,8 and 10.
We first reported3 that 3-vinylpyrroles can be prepared
from pyrrole according to simple general methods and
they can be easily handled at room temperature. Suc-
cessively a similar procedure has been used by Ketcha4
et al., while Wang5 et al. reported the synthesis of some
3-vinylpyrroles substituted on the aromatic ring by the
Stille coupling reaction. Recently we demonstrated that
the three vinylpyrrole isomers as well as the 2- and
3-vinylpyrrole N-tosylated can be submitted to rhodium-
catalyzed hydroformylation conditions without any de-
composition, conveniently giving 2-pyrrolylpropanals.6
Owing to our interest into the hydroformylation of vinyl
heteroaromatic substrates6,7 and on the basis of our
experience in the synthesis of vinylpyrrolyl derivatives,3
it seemed a very attractive challenge to try the prepara-
tion and to test the reactivity of the divinylpyrroles, a
heterocycles class of compounds unknown in the litera-
ture.
Resu lts
Dir ect N-vin yla tion of 3-Alk en ylp yr r oles: P r ep a -
r a tion of th e 1,3-Divin ylp yr r oles 2a -c (Sch em e 1).
(a ) 1,3-Divin ylp yr r ole (2a ). 2a was prepared by treat-
ment of the corresponding 3-vinylpyrrole (1a )3a with
acetylene, in KOH (30%)/DMSO, at 120 °C, according to
the “superbasic” Trofimov’s conditions9b (Scheme 1). The
reaction was conveniently carried out under acetylene
pressure (10 atm) in a stainless autoclave for 2 h. Then
the recovered mixture was added to brine and extracted
with dichloromethane. After evaporation of the solvent,
1,3-divinylpyrrole was obtained as a yellow dense liquid
(55% yield) by distillation at reduced pressure. 2a is
stable enough to be stored at 0 °C for some weeks without
significative decomposition.
(b) 1,3-Divin ylp yr r oles â-Su bstitu ted in th e 3-Vi-
n yl Gr ou p (2b,c). The same procedure (Scheme 1)
afforded also the 1,3-divinypyrrole analogues, namely
3-(1-propenyl)-1-vinylpyrrole (80:20 trans/cis mixture)
(2b) and 3-(2-phenylethenyl)-1-vinylpyrrole (as trans
isomer) (2c), respectively, from the corresponding 3-(1-
propenyl)pyrrole (1b )3a and 3-(2-phenylethenyl)pyrrole
(1c).3a The N-vinylation occurs without variation of the
cis/trans ratio, the products 2b,c showing the same
regioisomeric content observed in the starting N-unsub-
stituted substrates. Isolation of 2b,c was accomplished
by liquid chromatography on a silica gel column, by
We report here that 1,3-divinylpyrrole (2a ) and 1,2-
divinylpyrrole (6a ) (Chart 1) can be conveniently pre-
* To whom correspondence should be addressed. Phone number:
(050) 918227. Fax: (050) 502270. E-mail: roberta@indigo.icqem.pi.cnr.it.
† Istituto di Chimica Quantistica ed Energetica Molecolare del CNR.
‡ Dipartimento di Chimica e Chimica Industriale.
(1) (a) For a review about indole ring synthesis, see: Gribble, G.
W. Contemp. Org. Synth. 1994, 1, 145. (b) J ones, R. A.; Aznar-Saliente,
T.; Sepulveda-Arques, J . J . Chem. Soc., Perkin Trans. 1 1984, 2451.
(c) Ohno, M.; Shimizu, S.; Eguchi, S. Tetrahedron Lett. 1990, 31, 4613.
(d) Keil, J . M.; Kampchen, T.; Seitz, G. Tetrahedron Lett. 1990, 31,
4581. (e) Hodges, L. M.; Moody, M. W.; Harman, W. D. J . Am. Chem.
Soc. 1994, 116, 7931.
(2) (a) Alagona, G.; Ghio, C.; Cavazza, M.; Nucci, L.; Pergola, F.;
Colligiani, A. Synth. Met. 1994, 67, 235. (b) Niziurski-Mann, R. E.;
Cava, M. P. Heterocycles 1992, 34, 2003. (c) Naarmann, H.; Theophilou,
N. In Electroresponsive Molecular and Polymeric Systems; Marcel
Dekker Inc.: New York, 1988; Vol. 1. (d) Bauerle, P. Adv. Mater. 1993,
5, 879.
(3) (a) Settambolo, R.; Lazzaroni, R.; Messeri, T.; Mazzetti, M.;
Salvadori, P. J . Org. Chem. 1993, 58, 7899. (b) Settambolo, R.;
Mazzetti, M.; Pini, D.; Pucci, S.; Lazzaroni, R. Gazz. Chim. Ital. 1994,
124, 173.
(4) Xiao, D.; Ketcha, D. M. J . Heterocycl. Chem. 1995, 32, 499.
(5) Wang, J .; Scott, A. I. Tetrahedron Lett. 1995, 39, 7043.
(6) (a) Settambolo, R.; Caiazzo, A.; Lazzaroni, R. J . Organomet.
Chem. 1996, 506, 337. (b) Settambolo, R.; Caiazzo, A.; Lazzaroni, R.
Synth. Commun. 1997, 27, 4111.
(8) Trofimov, B. A.; Oleinikova, E. B.; Sigalov, M. V.; Skvortsov, Yu.
M.; Mikhaleva, A. I. Zh. Org. Khim. 1980, 16, 410.
(7) (a) Settambolo, R.; Pucci, S.; Bertozzi, S.; Lazzaroni, R. J .
Organomet. Chem. 1995, 489, C50. (b) Caiazzo, A.; Settambolo, R.;
Uccello-Barretta, G.; Lazzaroni, R. J . Organomet. Chem. 1997, 548,
279.
(9) (a) Trofimov, B. A. In The Chemistry of Heterocyclic Compounds;
J ohn Wiley and Sons Inc.: New York, 1992; Vol. 48. (b) Tarasova, O.
A.; Mal’kina, A. G.; Mikhaleva, A. I.; Brandsma, L.; Trofimov, B. A.
Synth. Commun. 1994, 24, 2035.
10.1021/jo9811322 CCC: $15.00 © 1998 American Chemical Society
Published on Web 12/05/1998

Notes
J . Org. Chem., Vol. 63, No. 26, 1998 10023
eluting with a 10:1 hexane/EtOAc mixture and 1:1
benzene/hexane mixture, respectively.
phase-transfer conditions adopted for 3a . The successive
reaction of 4b with DBU in hot DMSO gave 2-acetyl-1-
vinylpyrrole (5b). Whereas in the case of 2-formyl-1-
vinylpyrrole (5a ) a good yield of the isolated pure product
was obtained, the purification of 2-acetyl-1-vinylpyrrole
was more difficult, this compound appearing quite un-
stable during the elution on a silica gel column; never-
thless the saturation of the eluent mixture (5:3 hexane/
EtOAc) with NH3 permitted us to obtain 5b, as a pale
yellow liquid, in 55% yield. The treatment of 5b under
Wittig conditions gave 6b. Then the isolation of 2-(1-
methylethenyl)-1-vinylpyrrole, as a pure colorless liquid,
has been accomplished by distillation at reduced pres-
sure. 6b can be stored at 0 °C without any decomposition
for some weeks.
Interestingly 2c has been also obtained directly from
the corresponding 3-(2-phenylethenyl)-1-tosylpyrrole (1d )
(Scheme 1), precursor of 3-(2-phenylethenyl)pyrrole (1c),3a
by treatment of 1d with acetylene in KOH (30%)/DMSO,
the N-detosylation and the N-vinylation occurring in “one
pot”.
As observed for 1,3-divinylpyrrole, the new compounds
2b,c are stable at low temperatures, although they are
quite unstable at room temperature.
In d ir ect N-Vin yla tion of 2- a n d /or 3-Acylp yr -
r oles: P r ep a r a tion of th e 1,2-Divin ylp yr r oles 6a ,b
(Sch em e 2) a n d of 3-(1-Meth yleth en yl)-1-vin ylp yr -
r ole (10) (Sch em e 3). (a ) 1,2-Divin ylp yr r ole (6a ). 6a
was prepared in two steps by dehydrohalogenation of
1-(2-chloroethyl)-2-formylpyrrole (4a ) to give 2-formyl-
1-vinylpyrrole (5a ) followed by Wittig methylenation of
the formyl group of 5a . The intermediate 4a was ob-
tained, in quantitative yield, by treatment of the com-
mercial pyrrole-2-carboxyaldehyde (3a ) in 1,2-dichloro-
ethane, both as an organic solvent and a reactant, with
50% aqueous NaOH, under catalytic phase-transfer con-
ditions. Unlike that reported in the literature10 for the
preparation of 4a , the use of tetrabutylammonium hy-
drogen sulfate (molar ratio 1:10 with respect to the sub-
strate) resulted to be more convenient than the utilization
of tetrabutylammonium iodide, the isolation of the final
product being easier and the yield being very good (97%).
The dehydrochlorination of 4a to give 5a was ac-
complished by treatment of 4a with DBU in anhydrous
DMSO at 80 °C. Isolation of 5a , as a chemically pure
yellow oil, was accomplished by liquid chromatography
on a silica gel column, by eluting with a 3:1 hexane/
AcOEt mixture (80% yield).11 The Wittig methylenation
of 5a with methyltriphenylphosphonium bromide and
sodium amide in THF (molar ratio substrate/ylide ) 1:2;
reaction time 1 h) provided 1,2-divinylpyrrole, as an oily
residue.12 The isolation of 1,2-divinylpyrrole, as a pure
oil (45% yield), was accomplished by distillation at
reduced pressure.
Unlike that observed for the analogous 1-chloroethyl-
2-formylpyrrole (4a ), the intermediate 4b was not directly
transformed into 2-(1-methylethenyl)-1-vinylpyrrole (6b)
with a ylide excess, the desired product being obtained
in very low amount together with various unidentified
products.13
(c) 3-(1-Meth yleth en yl)-1-vin ylp yr r ole (10). 10 was
prepared from 3-acetylpyrrole (7) via N-chloroethylation
and N-dehydrohalogenation in “one pot” to give 3-acetyl-
1-vinylpyrrole (9) followed by Wittig methylenation of the
carbonyl group of 9 (Scheme 3). 7 was easily obtained
from the corresponding N-tosylated substrate14 by treat-
ment with 5 M aqueous NaOH in dioxane. In a first
attempt to obtain 8, 3-acetylpyrrole was treated with
dichloroethane under the same phase-transfer conditions
adopted for 3: the expected 3-acetyl-1-(2-chloroethyl)-
pyrrole (8) together with the N-dehydrohalogenation
product 3-acetyl-1-vinylpyrrole (9) in a 60:40 mixture was
obtained. To completely convert the substrate 8 into 9 a
longer reaction time was adopted (6 h), but formation of
polymeric material was observed too. Finally 3-acetyl-1-
vinylpyrrole (9) was obtained in “one pot”, in good yield
of isolated pure product (88%), by heating 3-acetylpyrrole
with an excess of NaOH (1:35 substrate/NaOH) and 1,2-
dichloroethane, at reflux. The Wittig methylenation of 9
with methyltriphenylphosphonium bromide and sodium
amide in THF (Scheme 3) provided 3-(1-methylethenyl)-
1-vinylpyrrrole (10) as an oily residue, after distillation
at reduced pressure (45% yield). 10 is characterized by
the same stability shown by the analogous substrates.
It is noteworthy that the same olefin was conveniently
prepared from 4a via N-dehydrohalogenation and meth-
ylenation in “one pot”, under stressed Wittig conditions
(molar ratio substrate/ylide ) 1:3; reaction time 7 h)
(overall yield 45%). 6a is stable enough to be distilled
without significative decomposition and stable for some
weeks at 0 °C.
Discu ssion
The synthetic pathways here depicted use two N-
vinylation methods previously described in the litera-
ture9,10 but employed in this work for the first time in
the synthesis of divinylpyrroles. With respect to the
original version, some modifications and improvements
have been accomplished by us. As far as the direct
N-vinylation is concerned, the reaction was conveniently
carried out in a stainless autoclave under acetylene
pressure instead of in a glass flash at atmospheric
pressure.9b In light of our experience in the high-pressure
(b) 2-(1-Meth yleth en yl)-1-vin ylp yr r ole (6b). The
same reaction sequence adopted for 6a (Scheme 2) also
afforded 2-(1-methylethenyl)-1-vinylpyrrole (6b) via for-
mation of 2-acetyl-1-chloroethylpyrrole (4b). This com-
pound was prepared (93% yield) on refluxing the com-
mercial 2-acetylpyrrole (3b ) under the same catalytic
(10) Gonzalez, C.; Greenhouse, R.; Tallabs, R. Can. J . Chem. 1983,
61, 1697.
(11) The compound 5a is prepared in the literature10 by heating 1-(2-
chloroethyl)-2-formylpyrrole with sodium hydride in mineral oil in dry
acetonitrile at 50 °C, but no isolation conditions are reported. An
analogous attempt to prepare 5a carried out by us did not give the
desired product: indeed, uncharacterized polymeric material was
recovered from the reaction mixture as the main product.
(12) The base used in the ylide formation was crucial in order to
promote the double transformation: an attempt carried out with the
same phosphonium salt and butyllithium base, under analogous
experimental conditions, only favored the methylenation of the formyl
group but not the N-dehydrohalogenation, affording 1-(2-chloroethyl)-
2-vinylpyrrole (40% yield).
(13) It is likely possible that, under stressed Wittig conditions, there
is a competition between the methylenic proton adjacent to the nitrogen
atom and the methylic proton adjacent to the carbonyl group: in fact
a
volatile component (GC-MS control) compatible with a bicyclic
structure, generated from the intramolecular substitution of the
chloride atom by the carbanion deriving from the methyl group, was
detected by GC-MS control.
(14) Kakushima, M.; Hamel, P.; Frenette, R.; Rokach, J . J . Org.
Chem. 1983, 48, 3214.

10024 J . Org. Chem., Vol. 63, No. 26, 1998
Notes
Sch em e 2
Sch em e 4
The synthesis of 9 being easy and convenient, it seemed
interesting to verify if this compound could be used as
an intermediate in the preparation of 1,3-divinylpyrrole.
The key of the synthetic pathway could be the reduction
of the carbonyl group of 9 to hydroxyl group to give 11
and the successive dehydration to obtain a vinyl group
in position 3, according to the reaction sequence success-
fully adopted in the synthesis of 3-alkenylpyrroles from
3-acyl-1-tosylpyrroles.3 Although 3-(1-hydroxyethyl)-1-
vinylpyrrole (11) has been obtained in very good yield
(>90%) by using diisobutylaluminum hydride in THF,
at 0 °C, as a chemoselective reducting system, no attempt
to dehydrate 11 gave the desired product15 (Scheme 4).
Probably the Wittig methylenation of 3-formyl-1-vi-
nylpyrrole could be an alternative synthetic approach to
1,3-divinylpyrrole, but the insertion of a formyl group on
3 annular position is more difficult than the insertion of
an acyl group on the same position;16 hence, this approach
is not convenient.
Sch em e 3
On the basis of that reported for the synthesis of 1,3-
divinylpyrroles, the direct N-vinylation of 2-monovinyls
was, in principle, a possible way to obtain 1,2-divinylpyr-
roles. However 2-alkenylpyrroles are not easily available
and they are generally obtained in low yield,17 because
of their trend to polymerize. It is noteworthy that 2-vinyl-
1-tosylpyrrole has been previously prepared by us in good
yield,6b but it is not deprotected17 under the basic hy-
drolysis conditions successfully adopted for the analogous
3-substituted in the synthesis of 3-alkenylpyrroles: then
the indirect N-vinylation of 2-acylpyrroles followed by
Wittig reaction seems to be the best way to 1,2-divi-
nylpyrroles.
reactions, we think that the use of an autoclave, when
available, ensures high safety and makes easier the
operative conditions. An interesting application of this
procedure resulted the preparation of 3-(2-phenylethe-
nyl)-1-vinylpyrrole from the corresponding N-tosylated
substrate, without preventive N-detosylation. The pres-
ence of an electron-withdrawing group in the 3 annular
position is crucial in order to obtain “one pot” deprotection
and N-vinylation of the substrate; indeed analogous
attempts carried out on 3-vinyl-1-tosylpyrrole and 3-(1-
propenyl)-1-tosylpyrrole have been unsuccessful, leading
mixtures of unreacted substrate, detosylated product, and
3-alkenyl-1-vinylpyrroles in very low amount.
Con clu sion s
The synthetic routes herein depicted represent conve-
nient and simple methods for the preparation of 1,2- and/
or 1,3-divinylpyrroles from commercially available 2-a-
cylpyrroles and easily synthesizable 3-acylpyrroles and
3-vinylpyrroles. The procedures employ inexpensive re-
agents and provide pure products after simple purifica-
tion processes. The newly prepared divinylpyrroles and
the various intermediates are stable enough to be handled
at room temperature and can be prepared in a consistent
scale (hundreds of milligrams). The easy accessibility to
the divinylpyrroles suggests the use of these compounds
as useful intermediates in various research fields. In
particular they could substitute the more investigated
As far as the indirect N-vinylation is concerned, we
showed that this procedure can be conveniently applied
to 2-acylpyrroles as well as 3-acylpyrroles. In particular
in the case of 2-acyl derivatives a convenient N-dehy-
drohalogenation and methylenation in “one pot” under
Wittig conditions was set up in the synthesis of 1,2-
divinylpyrrole (Scheme 2). In addition the original N-
chloroethylation and N-dehydrohalogenation in “one pot”
of 3-acetylpyrrole to give 3-acetyl-1-vinylpyrrole (9) proved
to be a convenient key intermediate in the preparation
of 10. This last synthetic sequence can constitute, in our
opinion, an approach of general utility in the preparation
of 3-vinyliden-1-vinylpyrroles, as an alternative route to
the direct N-vinylation with acetylene of the correspond-
ing 3-vinylidenpyrroles.3b
(15) The treatment of 11 with DMSO at 100 °C, previously used in
the preparation of 3-alkenylpyrroles from the corresponding 3-(2-
hydroxyalkyl)pyrroles,3 gave polymerization products; under this limit
temperature the reaction did not occur. Polymeric material was also
obtained by using methanesulfonyl chloride/triethylamine as dehydrat-
ing system. A final attempt carried out with hot aqueous NaOH and
ethanol gave only traces of the desired product together with unreacted
starting substrate.
(16) Demopoulos, V. J . Org. Prep. Proced. Int. 1986, 18, 278.
(17) Caiazzo, A. Thesis of Laurea, University of Pisa, 1996; p 81.

Notes
J . Org. Chem., Vol. 63, No. 26, 1998 10025
2-formylpyrrole (3a ) (3.0 g, 3.2 × 10-2 mol) and tetrabutylam-
monium hydrogen sulfate (1.1 g, 3.2 × 10-3 mol) in 1,2-
dichloroethane (60 mL). The mixture was then heated to reflux
temperature, with vigorous stirring, for 1 h. The cooled mixture
was diluted with water and extracted with dichloromethane. The
combined organic extracts were washed with water, dried (Na2-
SO4), and evaporated in vacuo to give 4.8 g (3.1 × 10-2 mol, 97%
yield) of 4a as a yellow oil.
2-Acetyl-1-(2-ch lor oeth yl)p yr r ole (4b). This was prepared
by using the same procedure employed for the N-chloroethylation
described above but with 3b (7.0 g, 6.4 × 10-2 mol) and yielded
4b (10.2 g; 5.9 × 10-2 mol, 93% yield) as a colorless semisolid:
1H NMR δ 7.02 (m, 1H), 6.95 (m, 1H), 6.17 (m, 1H), 4.60 (t, 2H),
3.82 (t, 2H), 2.45 (s, 3H); MS m/e 171 (M+, 32), 156 (32), 136
(100), 120 (17.8). Anal. Calcd for C8H10NOCl: C, 55.99; H, 5.87;
N, 8.16. Found: C, 55.88; H, 5.96; N, 8.17.
divinylbenzenes as cross-linking agents in polymerization
processes. On the other hand, analogously to that re-
ported for the simple N-vinylpyrrole,2a they can be
considered polyfunctional precursors to electroconducting
organic polymers, being reactive both at the exocyclic
double bonds and at positions R to the pyrrole ring. In
addition the presence of a C-vinyl group and a N-vinyl
group on the same aromatic ring makes the divinylpyr-
roles interesting substrates in order to study the influ-
ence of the vinyl group nature on typical double bond
reactions. To this regard, the hydroformylation reaction
is now under investigation.
Exp er im en ta l Section
2-Acyl-1-vin ylp yr r oles. Gen er a l P r oced u r e. 2-F or m yl-
1-vin ylp yr r ole (5a ). DBU (3 mL, 2.0 × 10-2 mol) was added to
a stirred solution of 1-(2-chloroethyl)-2-formylpyrrole (4a ) (1.0
g, 6.4 × 10-3 mol) in anhydrous DMSO, heated at 80 °C. After
6 h, the mixture, cooled to room temperature, was diluted with
water and extracted with dichloromethane. The combined
organic layers were treated with water and dried over anhydrous
Na2SO4, and the solvent was evaporated under reduced pressure
to give a residue which was chromatographed on silica gel, by
eluting with 75:25 hexane/EtOAc to afford 5a (0.62 g, 5.12 ×
10-3 mol, 80% yield) as a pale yellow oil: 1H NMR δ 9.60 (s,
1H), 7.94 (dd, 1H, J ) 8.8, 15.8 Hz), 7.38 (m, 1H), 6.98 (m, 1H),
6.33 (m, 1H), 5.24 (dd, 1H, J ) 1.3, 15.8 Hz), 4.89 (dd, 1H, J )
1.3, 8.8 Hz); MS m/e 121 (M+, 100), 106 (40.8), 92 (40), 78 (7),
65 (53). Anal. Calcd for C7H7NO: C, 69.41; H, 5.82; N, 11.56.
Found: C, 69.50; H, 5.85; N, 11.60.
2-Acetyl-1-vin ylp yr r ole (5b). This was prepared by using
the same procedure employed for the N-dehydrohalogenation
described above but with 4b (4.0 g, 2.3 × 10-2 mol) and yielded
5b (1.7 g, 1.26 × 10-2 mol, 55% yield), as a pale yellow oil (SiO2;
5:3 hexane/EtOAc saturated with NH3): 1H NMR δ 7.97 (dd,
1H, J ) 8.8, 15.7 Hz), 7.26 (m, 1H), 7.00 (m, 1H), 6.23 (m, 1H),
5.18 (dd, 1H, J ) 1, 15.7 Hz), 4.85 (d, 1H, J ) 8.8 Hz), 2.44 (s,
3H); MS m/e 135 (M+, 100), 120 (69.3), 107 (14), 92 (84.8), 65
(50). Anal. Calcd for C8H9NO: C, 71.09; H, 6.71; N, 10.36.
Found: C, 71.05; H, 6.66; N, 10.45.
3-Acetyl-1-vin ylp yr r ole (9). To a stirred solution of 3-acetyl-
pyrrole (7) (1.2 g, 1.1 × 10-2 mol) and tetrabutylammonium
hydrogen sulfate (0.37 g, 1.1 × 10-3 mol) in 1,2-dichloroethane
(6 mL), at 0 °C, was added 21 mL of 50% aqueous NaOH. The
resulting mixture was refluxed for 1.5 h, allowed to cool, diluted
with water, and extracted with methylene chloride. The com-
bined organic extracts were washed with water, dried (Na2SO4),
and evaporated in vacuo to give a pale yellow residue which was
chromatographed on silica gel, by eluting with 3:5 hexane/EtOAc
to afford 9 (1.3 g, 9.7 × 10-3 mol, 88% yield) as a colorless oil:
1H NMR δ 7.45 (m, 1H), 6.89 (m, 1H), 6.82 (dd, 1H, J ) 15.7,
8.9 Hz), 6.66 (m, 1H), 5.26 (dd, 1H, J ) 1.66, 15.7 Hz), 4.85 (dd,
1H, J ) 1.66, 8.9 Hz), 2.42 (s, 3H); MS m/e 135 (M+, 43), 120
(100), 92 (37), 65 (26), 39 (11). Anal. Calcd for C8H9NO: C, 71.09;
H, 6.71; N, 10.36. Found: C, 71.05; H, 6.65; N, 10.42.
All reagents were of commercial quality. Schlosser-Schaub
“instant ylide” reagent (methyltriphenylphosphonium bromide
+ sodium amide) was purchased from Fluka. Silica gel (70-
230 mesh) was purchased from Merck. DMSO was refluxed and
then distilled over calcium hydride. THF was refluxed and
distilled over Na/K.
Microanalyses were performed at the Laboratorio di Mi-
croanalisi, Istituto di Chimica Organica, Facolta` di Farmacia,
Universita` di Pisa. 1H NMR spectra (200 MHz) were recorded
in CDCl3.
3-Vinylpyrrole (1a ), 3-(1-propenyl)pyrrole (1b ), 3-(2-phe-
nylethenyl)pyrrole (1c), and 3-(2-phenylethenyl)-1-tosylpyrrole
(1d ) were synthesized as described in the literature.3a
1,3-Divin ylp yr r oles. Gen er a l P r oced u r e. 1,3-Divin ylp yr -
r ole (2a ). A mixture of 3-vinylpyrrole (1a ) (1.5 g, 1.6 × 10-2
mol), KOH (machine-powdered) (1.1 g, 2.9 × 10-2 mol), and
anhydrous DMSO (6 mL) was introduced into a stainless steel
autoclave equipped with a magnetic stirrer. Acetylene was
introduced (10 atm), and the autoclave was then heated to 120
°C for 2 h. After cooling to room temperature, the crude reaction
mixture was treated with brine and extracted thoroughly with
methylene chloride. The organic extracts were dried over
anhydrous Na2SO4 and concentrated to give a yellow oil which
was distilled at reduced pressure to afford 2a (1.05 g, 8.8 × 10-3
mol, 55% yield) as a yellowish oil: bp 65 °C, 2 × 10-3 mbar; 1H
NMR δ 6.88 (m, 1H), 6.81 (m, 1H), 6.74 (dd, 1H, J ) 8.6, 16.0
Hz), 6.57 (dd, 1H, J ) 10.8, 18.0 Hz), 6.38 (m, 1H), 5.44 (dd, 1H,
J ) 1.7, 18.0 Hz), 5.06 (dd, 1H, J ) 2.2, 16.0 Hz), 5.00 (dd, 1H,
J ) 1.7, 10.8 Hz), 4.62 (dd, 1H, J ) 2.2, 8.6 Hz); MS m/e 119
(M+, 75.8), 104 (7.8), 91 (53.0), 65 (58.8), 51 (26.9), 39 (100). Anal.
Calcd for C8H9N: C, 80.63; H, 7.61; N, 11.75. Found: C, 80.55;
H, 7.65; N, 11.82.
3-(1-P r op en yl)-1-vin ylp yr r ole (2b). This was prepared
according to the general procedure except that 1b (1.2 g, 2.1 ×
10-2 mol) was used: yield 1.40 g (1.05 × 10-2 mol, 50% yield) of
2b as a yellow liquid (SiO2; 10:1 hexane/EtOAc); 1H NMR δ
6.90-6.70 (m, 3H), 6.37 (m, 1H, trans isomer), 6.30 (m, 1H, cis
isomer), 6.05 (m, 1H, trans isomer), 5.97 (m, 1H, cis isomer),
5.80 (m, 1H, trans isomer), 5.12 (d, 1H, J ) 16.5 Hz), 4.67 (d,
1H, J ) 10 Hz), 1.97 (d, 3H, cis isomer), 1.92 (d, 3H, trans
isomer); MS m/e 133 (M+, 100), 117 (35.5), 106 (69), 91 (15), 77
(34.5), 65 (19.6), 51 (38). Anal. Calcd for C9H11N: C, 81.16; H,
8.32; N, 10.52. Found: C, 81.10; H, 8.25; N, 10.60.
1,2-Divin ylp yr r oles. Gen er a l P r oced u r e. 1,2-Divin ylp yr -
r ole (6a ). Meth od 1. To a stirred mixture of anhydrous THF
(20 mL) and Schlosser-Schaub reagent (4.0 g, 9.6 × 10-3 mol
of methyltriphenylphosphonium bromide), under a nitrogen
atmosphere, a solution of 2-formyl-1-vinylpyrrole (5a ) (0.580 g,
4.8 × 10-3 mol) in anhydrous THF (12 mL) was added. The
reaction mixture was stirred at room temperature for 1 h and
then treated with a 50% aqueous solution of NaOH and extracted
with ethyl ether. The combined organic extracts were washed
with water, dried (Na2SO4), and evaporated in vacuo to give a
residue which was distilled at reduced pressure to afford 6a
(0.257 g, 2.16 × 10-3 mol, 45% yield) as a yellow oil: bp 30 °C,
3-(2-P h en yleth en yl)-1-vin ylp yr r ole (2c). Meth od 1. This
was prepared according to the general procedure except that 1c
(2.0 g, 1.2 × 10-2 mol) was used: yield 1.17 g (6.0 × 10-3 mol,
50% yield) of 2c as a yellow solid (SiO2; 1:1 hexane/benzene):
1
mp 112-113 °C; H NMR δ 7.54-6.78 (m, 10 H), 6.57 (m, 1H),
5.18 (d, 1H, J ) 15 Hz), 4.72 (d, 1H, J ) 10 Hz); MS m/e 195
(M+, 100), 180 (7), 167 (22.7), 152 (17.2), 141 (18.6), 115 (25.5).
Anal. Calcd for C14H13N: C, 86.12; H, 6.71; N, 7.17. Found: C,
86.08; H, 6.68; N, 7.25.
1
2 × 10-3 mbar; H NMR δ 6.99 (dd, 1H, J ) 8.9, 15.3 Hz), 6.95
Meth od 2. 2c was also prepared by using the same procedure
employed for the N-vinylation described above but with 1d (0.50
g, 3.0 × 10-3 mol): yield 0.234 g (1.2 × 10-3 mol, 40% yield) of
2c.
2-Acyl-1-(2-ch lor oet h yl)p yr r oles. Gen er a l P r oced u r e.
1-(2-Ch lor oeth yl)-2-for m ylpyr r ole (4a). A 50% aqueous NaOH
(30 mL) solution was added, at 0 °C, to a stirred solution of
(m, 1H), 6.62 (dd, 1H, J ) 11.2, 17.4 Hz), 6.37 (m, 1H), 6.20 (m,
1H), 5.50 (dd, 1H, J ) 1.46, 17.4 Hz), 5.15 (dd, 1H, J ) 1.10,
15.3 Hz), 5.13 (dd, 1H, J ) 1.46, 11.2 Hz), 4.76 (d, 1H, J ) 8.9
Hz); MS m/e 119 (M+, 62), 118 (100), 104 (15), 91 (14.3), 65 (11).
Anal. Calcd for C8H9N: C, 80.63; H, 7.61; N, 11.75. Found: C,
80.62; H, 7.55; N, 11.80.

10026 J . Org. Chem., Vol. 63, No. 26, 1998
Notes
Meth od 2. To a stirred mixture of anhydrous THF (40 mL)
and Schlosser-Schaub reagent (10.0 g, 2.4 × 10-2 mol of
methyltriphenylphosphonium bromide), under a nitrogen atmo-
sphere, a solution of 1-(2-chloroethyl)-2-formylpyrrole (4a ) (1.5
g, 9.5 × 10-3 mol) in anhydrous THF (30 mL) was added. The
reaction mixture was stirred at room temperature for 7 h and
then treated with a 50% aqueous solution of sodium hydroxide
and extracted with ethyl ether. The combined organic extracts
were washed with water, dried (Na2SO4), and evaporated in
vacuo to give a residue which was distilled at reduced pressure
to afford 6a (0.512 g, 4.3 × 10-3 mol, 45% yield) as a yellow oil.
2-(1-Meth yleth en yl)-1-vin ylp yr r ole (6b). Using the same
procedure employed for the methylenation described above but
with 5b (0.65 g, 4.8 × 10-3 mol) yielded, after distillation at
reduced pressure, 6b (0.255 g; 1.92 × 10-3 mol, 40% yield) as a
(55), 91(16.5), 77 (11). Anal. Calcd for C9H11N: C, 81.16; H, 8.32;
N, 10.52. Found: C, 81.30; H, 8.35; N, 10.45.
3-(1-Meth yleth en yl)-1-vin ylp yr r ole (10). Using the same
procedure employed for the methylenation described above but
with 3-acetyl-1-vinylpyrrole (9) (1.0 g, 7.4 × 10-3 mol) yielded,
after distillation at reduced pressure, 10 (0.443 g; 3.3 × 10-3
mol, 45%yield) as a colorless oil: bp 40 °C, P ) 2 × 10-3 mbar;
1H NMR δ 6.89 (m, 1H), 6.82 (m, 1H), 6.76 (dd, 1H, J ) 8.65,
15.50 Hz), 6.40 (m, 1H), 5.21 (m, 1H), 5.07 (dd, 1H, J ) 1.46,
15.50 Hz), 4.82 (m, 1H), 4.62 (dd, 1H, J ) 1.46, 8.70 Hz), 2.02
(m, 3H); m/z 133 (M+, 100), 118 (68), 106 (9.5), 93 (33), 77 (14),
65 (27), 51 (25), 39 (42). Anal. Calcd for C9H11N: C, 81.16; H,
8.32; N, 10.52. Found: C, 81.17; H, 8.32; N, 10.60.
Ack n ow led gm en t. We are grateful to Professor
Raffaello Lazzaroni for helpful discussions during the
course of this work.
1
colorless liquid: bp 40 °C, P ) 1 × 10-3 mbar; H NMR δ 7.05
(dd, 1H, J ) 8.8, 15.7 Hz), 6.98 (m, 1H), 6.21-6.16 (m, 2H), 5.18
(m, 1H), 5.14 (dd, 1H, J ) 1.3, 15.7 Hz), 4.91 (m, 1H), 4.71 (d,
1H, J ) 8.8 Hz), 2.08 (m, 3H); m/z 133 (M+, 98), 118 (100), 104
J O9811322