One pot hydroformylation/intramolecular aldol condensation reactions of 1-allyl-2-carbonylpyrroles: A new entry into hydroindolizines synthesis

Article abstract of DOI:10.1081/SCC-120022467

7-Formyl-5-methyl-5,6-dihydroindolizine and 7-formyl-6-methyl-5,6-dihydroindolizine were obtained via a domino hydroformylation/cyclization/dehydration reactions sequence starting from the corresponding 1-allyl-2-formylpyrroles. An intramolecular aldol condensation between the carbon atom adjacent to the formyl group in the chain of the produced aldehydes and the carbonyl group directly bonded to the pyrrole ring most likely generates the indolizine structure. 7-Formyl-6,8-dimethyl-5,6-dihydroindolizine was similarly synthesized by using 2-acetyl-1-(2-methylprop-2-enyl) pyrrole.

Full text of DOI:10.1081/SCC-120022467

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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 17, pp. 2953–2961, 2003
One Pot Hydroformylation/Intramolecular Aldol
Condensation Reactions of 1-Allyl-2-
carbonylpyrroles: A New Entry into
Hydroindolizines Synthesis
Roberta Settambolo,1 Sandra Miniati,2
and Raffaello Lazzaroni2,
*
1ICCOM-CNR, Pisa, Italy
2Universita di Pisa, Dipartimento di Chimica e Chimica
Industriale, Pisa, Italy
ABSTRACT
7-Formyl-5-methyl-5,6-dihydroindolizine and 7-formyl-6-methyl-
5,6-dihydroindolizine were obtained via a domino hydroformyla-
tion/cyclization/dehydration reactions sequence starting from the
corresponding 1-allyl-2-formylpyrroles. An intramolecular aldol
condensation between the carbon atom adjacent to the formyl
group in the chain of the produced aldehydes and the carbonyl
group directly bonded to the pyrrole ring most likely generates the
*Correspondence: Raffaello Lazzaroni, Universita di Pisa, Dipartimento di
Chimica e Chimica Industriale, Via Risorgimento 35, 56126 Pisa, Italy; E-mail:
lazza@dcci.unipi.it.
2953
DOI: 10.1081/SCC-120022467
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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2954
Settambolo, Miniati, and Lazzaroni
indolizine structure. 7-Formyl-6,8-dimethyl-5,6-dihydroindolizine
was similarly synthesized by using 2-acetyl-1-(2-methylprop-2-enyl)
pyrrole.
Key Words: Hydroformylation; Catalysis; Aldol condensation;
Allylpyrroles; Indolizines.
In the last decade the hydroformylation of olefins has become an
attractive synthetic transformation because it can be integrated in
tandem or domino reactions sequence, thanks to the versatility of the
carbonyl group in the produced aldehydes. Thus, reduction, nucleophilic
addition or aldol condensation can occur with enormous synthetic
implications.[1] During our studies on the rhodium catalyzed hydro-
formylation of simple and alkyl substituted 1-allylpyrroles, we found
that the formed 4-(pyrrol-1-yl)butanals give rice, under oxo conditions,
to 5,6-dihydroindolizines via a tandem intramolecular cyclization/
dehydration sequence[2] (Sch. 1).
The 5,6-dihydroindolizines are almost unknown in literature, the
synthetic examples being very few and of very different type. Cliff et al.
prepared 2-alkyl- or 2-phenyl-substituted 5,6-dihydroindolizines by
treatment of the corresponding fully unsaturated structures with various
metals.[3] 7-Carboxyethyl-5,6-dihydroindolizine has been synthesized
starting from 2-formylpyrrole by using carboethoxycyclopropyltriphenyl-
phosphonium salt as a cycloalkenylation reagent.[4] Katritzky et al.
prepared 2-phenyl-5,6-dihydroindolizine via formation of 2-[(benzotria-
zol-1-yl)methyl]pyrrole as a convenient intermediate.[5] In general hydro-
indolizines at various degree of unsaturation are an interesting and
topical subject occurring in natural products[5,6] and the discovery of
general synthetic strategies to these compounds is an important goal
for the organic chemist. In order to investigate the potentialities of the
hydroformylation based protocol into the synthesis of new 5,6-dihydroin-
dolizines substituted with an electron-withdrawing group on the pyrrole
ring, we prepared the 1-allylpyrroles 1a–c bearing a formyl or acetyl
group on the C2 pyrrole carbon atom. Under oxo conditions the
Scheme 1.

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1-Allyl-2-carbonylpyrroles
2955
Scheme 2. (i) Rh4(CO)12, 100 atm CO:H2 (1:1), 100ꢀC, toluene, 0.5–2 h. (ii) The
same conditions as (i), 70 h under N2 atmosphere, after CO and H2 removal. (iii)
The same conditions as (i), EtONa/EtOH, 5 min, after CO and H2 removal.
compounds 1a generates a mixture of the branched (3a) and the linear
(2a) isomers (Sch. 2-A) while the vinylidenic substrates 1b and 1c exclu-
sively give rise to the pyrrolylbutanals 2b and 2c (Sch. 2-B). All the
formed linear aldehydes 2a–c selectively gave the corresponding 5,6-dihy-
droindolizines 20a–c characterized by the presence of a formyl group on
C7 carbon atom, via a one pot hydroformylation/intramolecular aldol
condensation sequence (Sch. 2).
The 2-substituted 1-allylpyrroles 1a–c were easily prepared from
2-formylpyrrole and 2-acetylpyrrole respectively by treatment with
3-chlorobut-1-ene and 3-chloro-2-methylprop-1-ene respectively under
phase transfer conditions. The hydroformylation of the substrates 1a–c
was carried out in the presence of Rh4(CO)12 as catalyst precursor.[7,8]
After 0.5 h at 100ꢀC, the starting olefin 1a was completely converted
into the isomeric dialdehydes 4-(2-formylpyrrol-1-yl)pentanal (2a) and
2-methyl-3-(2-formylpyrrol-1-yl)butanal (3a) (2a/3a ¼ 68/32; 2a þ 3a ¼
98%) (Sch. 2-A). A very low amount of 5-methyl-7-formyl-5,6-dihydro-
indolizine (20a) (<2%) was also found. For longer reaction times, an
increase of the dihydroindolizine 20a was observed together with the
reduction of the carbonyl group of both branched and linear dialdehydes
3a and 2a to the corresponding hydroxyl groups (GC-MS control).
When, at complete pyrrolylolefin conversion, the CO/H2 gas mixture

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2956
Settambolo, Miniati, and Lazzaroni
was removed and the autoclave was heated at 100ꢀC for additional 70 h,
the dialdehyde 2a disappeared and 20a was formed (Sch. 2-A), the
branched dialdehyde 3a staying unreacted during all reaction time.
Under the same hydroformylation conditions as for 1a, the vinylidenic
olefin 2-formyl-1-(2-methylprop-2-enyl)pyrrole (1b) was selectively
converted into 7-formyl-6-methyl-5,6-dihydroindolizine (20b) (Sch. 2-B)
via formation of the sole aldehyde 3-methyl-4-(2-formylpyrrol-1-yl)buta-
nal (2b). 2-Acetyl-1-(2-methylprop-2-enyl)pyrrole (1c) was submitted to
the same hydroformylation conditions adopted for 2-formylderivatives
1a–b; the aldehyde 3-methyl-4-(2-acetylpyrrol-1-yl)butanal (2c) was
obtained as the exclusive product (Sch. 2-A). This compound does not
cyclize under the above conditions even for long heating time. However
by treating the crude oxo-mixture with EtONa/EtOH for few minutes,
the corresponding 7-formyl-6,8-dimethyl-5,6-dihydroindolizine (20c) was
selectively obtained (Sch. 2-A). Under these last experimental conditions
the dihydroindolizines 20a and 20b were also obtained from 2a and 2b
respectively. The above findings suggest that the indolizine structures
20a–c come from the dialdehydes 2a–c likely via an intramolecular aldol
addition between the carbon adjacent to the formyl group in the chain
and the carbonyl group directly bonded to pyrrole ring. Then a bicyclic
hydroxyaldehyde should form (Sch. 2), which very easily undergoes water
elimination to give a double bond conjugated with both pyrrole and
formyl group. Whereas in the first two cases a rhodium carbonyl species
likely plays an annulation-catalyst role, although at very low rate, in the
last one this species is not sufficiently active to overcome the electron-
donor effect of the methyl group bonded to the carbonyl in position two
of the pyrrole ring. It is to note that, unlike what observed by us for
1-allylpyrroles characterized by an unsubstituted pyrrole ring or an alkyl
substituted one,[2] the annulation of 2a–c on C5 pyrrole carbon atom
does not occur, the above described aldol condensation being the exclu-
sive process. In fact no traces of 3-formyl or 3-acetyl-5,6-dihydroindo-
lizines, isomers of 20a–c, were detected. Because of the presence of an
electron-withdrawing group on the pyrrole C2 carbon atom, the C5
carbon atom is not nucleophilic enough to bear the electrophilic attack
of the carbonyl moiety.
It is to note that under aldol condensation the branched aldehydes 3a
is not stable, giving rise to the corresponding 2-formylpyrrole and the
unsaturated aldehydes 2-methylbut-2-enal respectively via a N-dealkyla-
tion promoted by the basic conditions adopted (Sch. 3).
It is to remark that this process makes the 7-formyl-5-methyl-5,6-
dihydroindolizine isolation via chromatographic elution very easy thanks
to the very different rf of the involved compounds.

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1-Allyl-2-carbonylpyrroles
2957
Scheme 3.
The formyl dihydroindolizines 20a–c are new compounds and were
1
isolated and characterized by H and 13C NMR spectroscopy, GC-MS,
and elemental analysis. They are stable enough to be handled easily at
room temperature without any decomposition and can be stored at 0ꢀC
for long periods. All the newly linear aldehydes obtained also were
isolated and characterized, these diacyl compounds being much more
stable of the analogous ones coming from the previously investigated
hydroformylation of 1-allylpyrroles substituted with electrondonor
groups.[2]
In conclusion the results reported here constitute the first example
of indolizine skeleton building from 1-allyl-2-carbonylpyrroles via a
selective tandem hydroformylation/aldol condensation reactions
sequence. In light of these findings as well as of our previous data on
hydroformylation/cyclodehydration of 1-allylpyrroles,[2] we would like to
stress that the 4-(pyrrol-1-yl)butanals, until now unknown in literature,
are easily available via oxo from easily available 1-allylpyrroles and
constitute versatile and convenient intermediates for indolizine moiety
synthesis (Sch. 4).
EXPERIMENTAL
N-Allylation of 2-carbonylpyrroles. General procedure. Preparation of
2-formyl-1-(2-methylprop-2-enyl)pyrrole (1b). To a stirred mixture of 50%
X=CHO,COCH
1
X=H, CH CH
2
3
3
R1
X
N
N
N
X
R =H, CH
3
O
R
R
R
O
Scheme 4.

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2958
Settambolo, Miniati, and Lazzaroni
aqueous NaOH (20 mL) solution, 2-formylpyrrole (3.0 g, 31.6 mmol)
and tetrabutylammonium hydrogen sulfate (1.2 g, 3.5 mmol) in toluene
(50 mL), was added 3-chloro-2-methylprop-1-ene (3.3 mL, 3.0 g,
32.9 mmol). The mixture was then heated at 70ꢀC, with vigorous stirring,
for 1 h. The cooled mixture was diluted with water and extracted with
ether. The combined organic extracts were washed with water, dried
(Na2SO4), and evaporated in vacuo. The residue was submitted
under distillation at reduced pressure (b.p. 30ꢀC, P ¼ 0.2 mm Hg)
1
giving 4.2 g (28.2 mmol; 85% yield) of 1b as a colorless oil. H NMR
(200 MHz, CDCl3) ꢀ 9.57 (s, 1H), 6.94 (d, J ¼ 3.3 Hz, 2H), 6.26 (t,
J ¼ 3.3 Hz, 1H), 4.90 (s, 2H), 4.84 (s, 1H), 4.49 (s, 1H), 1.75 (s, 3H);
13C NMR (50 MHz, CDCl3) ꢀ 179.5, 142.0, 131.7, 131.4, 124.3, 111.9,
109.7, 53.8, 19.8. MS m/e 149 (Mþ, 55), 132 (100), 120 (43), 94 (62).
Anal. calcd. for C9H11NO: C, 72.48; H, 7.38; N, 9.40. Found: C, 72.39;
H, 7.30; N, 9.45.
2-Formyl-1-(1-methylprop-2-enyl)pyrrole (1a). (75% yield), as a color-
less oil. B.p. 28ꢀC, P ¼ 0.2 mmHg. H NMR (200 MHz, CDCl3) ꢀ 9.53
1
(s, 1H), 7.09 (m, 1H), 6.93 (dd, J ¼ 1.67; 3.99 Hz, 1H), 6.25 (dd, J ¼ 2.67;
3.93 Hz, 1H), 6.10–5.89 (m, 2H), 5.19–5.00 (dd, J ¼ 19.8; 25.7 Hz, 2H),
1.52 (d, J ¼ 6.8 Hz, 3H); 13C NMR (50 MHz, CDCl3)
ꢀ 179.0,
131.7, 138.3, 127.8, 125.0, 115.8, 110.0, 54.0, 20.5. MS m/e 149
(Mþ, 30), 148 (30), 132 (63), 120 (20), 106 (26), 94 (100). Anal. calcd.
for C9H11NO: C, 72.48; H, 7.38; N, 9.40. Found: C, 72.40; H, 7.31;
N, 9.48.
2-Acetyl-1-(2-methylprop-2-enyl)pyrrole (1c). (80% yield), as a yellow
oil (SiO2; hexane/EtOAc ¼ 3:1); 1H NMR (200 MHz, CDCl3) ꢀ 6.97
(dd, J ¼ 1.7; 4.0 Hz, 1H), 6.85 (t, J ¼ 2.1 Hz, 1H), 6.17 (dd, J ¼ 3.8;
4.0 Hz, 1H), 4.90 (s, 2H), 4.79 (m, 1H), 4.37 (m, 1H), 2.45 (s, 3H), 1.72
(s, 3H); 13C NMR (50 MHz, CDCl3) ꢀ 188.0, 142.5, 130.2, 130.1, 119.8,
110.3, 108.0, 54.1, 27.0, 19.8. MS m/e 163 (Mþ, 30), 148 (100), 120 (63),
106 (25), 94 (44), 80 (35). Anal. calcd. for C10H13NO: C, 73.62; H, 7.98;
N, 8.60. Found: C, 73.55; H, 7.92; N, 8.65.
Hydroformylation of 1-allylpyrroles 1a–c. General procedure. (i)
Preparation of 3-methyl-4-(2-formylpyrrol-1-yl)butanal (2b). A solution
of 2-formyl-1-(2-methylprop-2-enyl)pyrrole (1b) (0.50 g, 3.35 mmol) and
Rh4(CO)12 (6.3 mg, substrate/Rh ¼ 100/1) in toluene (6 mL) was intro-
duced by suction into an evacuated 25 mL stainless steel reaction
vessel. Carbon monoxide was introduced, the autoclave was then
rocked, heated to 100ꢀC and hydrogen was rapidly introduced to
100 atm (CO/H2 ¼ 1/1) total pressure. After 2 h at 100ꢀC the conversion
was complete and the CO/H2 gas mixture was removed. From the reac-
tion mixture 3-methyl-4-(2-formylpyrrol-1-yl)butanal (2b) was obtained

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1-Allyl-2-carbonylpyrroles
2959
(0.42 g, 2.35 mmol, 70% yield) as a colorless oil by column chromatogra-
phy (SiO2; hexane/EtOAc ¼ 1:1); 1H NMR (200 MHz, CDCl3) ꢀ 9.65
(t, J ¼ 1.6 Hz, 1H), 9.54 (s, 1H), 6.97–6.91 (m, 2H), 6.25 (m, 1H), 4.25
(d, J ¼ 7.8 Hz, 2H), 2.70–2.15 (m, 3H), 0.97 (d, J ¼ 6.7 Hz, 3H); 13C NMR
(50 MHz, CDCl3) ꢀ 201.1, 179.4, 131.8, 131.6, 125.2, 109.8, 53.9, 47.7,
30.3, 17.9. MS m/e 179 (Mþ, 4), 161 (52), 150 (100), 132 (25), 118 (41),
117 (39), 108 (40), 94 (17), 80 (46). Anal. calcd. for C10H13NO2: C, 67.04;
H, 7.26; N, 7.82. Found: C, 66.95; H, 7.31; N, 7.88.
4-(2-Formylpyrrol-1-yl)pentanal (2a). Isolated as a colorless oil (SiO2;
hexane/EtOAc ¼ 1:1) (60% yield) from 0.5 h time hydroformylation
1
mixture; H NMR (200 MHz, CDCl3) ꢀ 9.65 (t, J ¼ 1.2 Hz, 1H), 9.52
(d, J ¼ 1.1 Hz, 1H), 7.14 (m, 1H), 6.91 (dd, J ¼ 1.7; 4.0 Hz, 1H), 6.29
(dd, J ¼ 2.7; 4.0 Hz, 1H), 5.4 (m, 1H), 2.54–2.27 (m, 2H), 2.12–2.0 (m,
2H), 1.48 (d, J ¼ 6.8 Hz, 3H); 13C NMR (50 MHz, CDCl3) ꢀ 200.7, 179.5,
131.8, 127.0, 125.3, 110.4, 52.1, 40.3, 30.0, 21.5. MS m/e 179 (Mþ, 2), 150
(52), 122 (26), 94 (100). Anal. calcd. for C10H13NO2: C, 67.04; H, 7.26;
N, 7.82. Found: C, 67.10; H, 7.20; N, 7.85.
3-Methyl-4-(2-acetylpyrrol-1-yl)butanal (2c). Isolated as a colorless
oil (SiO2; hexane/EtOAc ¼ 4:1) (75% yield) from 2.0 h time hydroformy-
1
lation mixture; H NMR (200 MHz, CDCl3) ꢀ 9.62 (t, J ¼ 2.0 Hz, 1H),
6.98 (dd, J ¼ 4.1; 1.7 Hz, 1H), 6.83 (t, J ¼ 2.1 Hz, 1H), 6.13 (dd, J ¼ 4.1;
2.5 Hz, 1H), 4.22 (d, J ¼ 7.0 Hz, 2H), 2.58 (m, 1H), 2.43 (s, 3H), 2.50–2.15
(m, 2H), 0.95 (d, J ¼ 6.3 Hz, 3H); 13C NMR (50 MHz, CDCl3) ꢀ 201.8,
188.2, 130.9, 130.2, 121.3, 107.5, 54.8, 47.9, 30.0, 27.1, 17.3. MS m/e 193
(Mþ, 2), 150 (100), 122 (35), 108 (15), 95 (27), 80 (32). Anal. calcd. for
C11H15NO2: C, 68.39; H, 7.77; N, 7.25. Found: C, 68.30; H, 7.71; N, 7.31.
(ii) Preparation of 7-formyl-6-methyl-5,6-dihydroindolizine (20b). After CO
and H2 removal, the crude reaction mixture coming from (i) was heated
at 100ꢀC for additional 70 h: the formation of a single product was
observed. From the reaction mixture 7-formyl-6-methyl-5,6-dihydroindo-
lizine (20b) was obtained as a yellow oil (SiO2; hexane/EtOAc ¼ 1:1)
1
(0.40 g, 75% yield); H NMR (200 MHz, CDCl3) ꢀ 9.47 (s, 1H), 7.15
(s, 1H), 6.82 (s, 1H), 6.51 (m, 1H), 6.27 (dd, J ¼ 2.6, 1.6 Hz, 1H), 3.98
(dd, J ¼ 12.6; 5.0 Hz, 1H), 3.86 (dd, J ¼ 12.6; 1.3 Hz, 1H), 3.20 (m, 1H),
1.05 (d, J ¼ 6.84 Hz, 3H); 13C NMR (50 MHz, CDCl3) ꢀ 190.6, 135.2,
135.1, 127.6, 125.9, 113.3, 110.7, 50.4, 26.5, 17.9. MS m/e 161 (Mþ,
100), 146 (47), 132 (19), 118 (61), 117 (93), 90 (18). Anal. calcd. for
C10H11NO: C, 74.53; H, 6.83; N, 8.70. Found: C, 74.15; H, 6.58; N, 8.80.
7-Formyl-5-methyl-5,6-dihydroindolizine (20a). Prepared as a red
oil according to the general procedure starting from 1a. The product
was eluted with SiO2; hexane/EtOAc ¼ 4:1, (60% yield); 1H NMR
(200 MHz, CDCl3) ꢀ 9.54 (s, 1H), 7.22 (s, 1H), 6.91 (bs, 1H), 6.53

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Settambolo, Miniati, and Lazzaroni
(dd, J ¼ 3.7; 1.3 Hz, 1H), 6.27 (dd, J ¼ 3.7; 2.7 Hz, 1H), 4.18 (m, 1H), 2.86
(dd, J ¼ 16.7; 5.7 Hz, 1H), 2.42 (dd, J ¼ 16.7; 1.2 Hz, 1H), 1.44
(d, J ¼ 6.3 Hz, 3H); 13C NMR (50 MHz, CDCl3) ꢀ 191.2, 135.9, 128.7,
127.9, 123.4, 114.5, 110.8, 45.0, 27.9, 20.0. MS m/e 161 (Mþ, 95),
146 (55), 132 (48), 118 (80), 117 (100), 104 (15), 91 (25). Anal. calcd.
for C10H11NO: C, 74.53; H, 6.83; N, 8.70. Found: C, 74.20; H, 6.69;
N, 8.85.
7-Formyl-6,8-dimethyl-5,6-dihydroindolizine (20c). Prepared as a red
oil according to the general procedure starting from 1c. The product
was eluted with SiO2; hexane/EtOAc ¼ 2:1, (75% yield); 1H NMR
(200 MHz, CDCl3) ꢀ 10.89 (s, 1H), 6.81 (bs, 1H), 6.62 (dd, J ¼ 3.8;
1.3 Hz, 1H), 6.28 (dd, J ¼ 3.8; 2.6 Hz, 1H), 3.93 (dd, J ¼ 12.3; 4.6 Hz,
1H), 3.81 (d, J ¼ 12.3 Hz, 1H), 3.25 (m, 1H), 2.42 (s, 3H), 0.98 (d,
J ¼ 7.0 Hz, 3H); 13C NMR (50 MHz, CDCl3) ꢀ 188.3, 141.6, 130.1,
129.7, 125.7, 111.5, 110.0, 50.2, 29.6, 26.4, 18.0. MS m/e 160 (Mþ ꢁ15,
80), 146 (20), 132 (55), 131 (38), 130 (26), 117 (36). Anal. calcd. for
C11H13NO: C, 75.43; H, 7.43; N, 8.00. Found: C, 75.13; H, 7.20; N, 8.12.
2-Methyl-3-(2-formylpyrrol-1-yl)butanal (3a). Isolated as a colorless
oil (SiO2; hexane/EtOAc ¼ 1:1) from 0.5 h time hydroformylation mix-
ture (the diastereomeric ratio, A/B ¼ 40/60, being in favor of the isomer
with higher retention time). 1H NMR (200 MHz, CDCl3) isomer B ꢀ 9.66
(d, J ¼ 2.2 Hz, 1H), 9.53 (bs, 1H), 7.18–7.10 (m, 1H), 6.98–6.91 (m, 1H),
6.34–6.25 (m, 1H), 5.74 (q, J ¼ 7.0 Hz, 1H), 3.05–2.75 (m, 1H), 1.53 (d,
1
J ¼ 7.0 Hz, 3H), 0.95 (d, J ¼ 7.0 Hz, 3H); H NMR (200 MHz, CDCl3)
isomer A ꢀ 9.61 (d, J ¼ 1.8 Hz, 1H), 9.53 (bs, 1H), 7.18–7.10 (m, 1H),
6.98–6.91 (m, 1H), 6.34–6.25 (m, 1H), 5.57 (q, J ¼ 7.4 Hz, 1H), 3.05–2.75
(m, 1H), 1.47 (d, J ¼ 7.2 Hz, 3H), 1.07 (d, J ¼ 7.1 Hz, 3H); 13C NMR
(50 MHz, CDCl3) isomer A ꢀ 202.0, 179.5, 128.2, 126.1, 110.3, 53.2,
52.5, 16.9, 9.1; 13C NMR (50 MHz, CDCl3) isomer B ꢀ 202.1, 179.6,
128.3, 125.8, 110.4, 52.1, 52.9, 19.0, 10.7. MS m/e 151 (Mþ ꢁ28, 29),
122 (22), 94 (100).
ACKNOWLEDGMENTS
Financial support by MIUR is gratefully acknowledged.
REFERENCES
1. Eilbracht, P.; Barfacker, L.; Buss, C.; Hollmann, C.; Kitsos-
Rzychon, B.E.; Kranemann, C.L.; Rische, T.; Roggenbuck, R.;
Schmidt, A. Chem. Rev. 1999, 99, 3329 and references cited therein.

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1-Allyl-2-carbonylpyrroles
2961
2. (a) Lazzaroni, R.; Settambolo, R.; Caiazzo, A.; Pontorno, L. J.
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Received in the UK November 19, 2002

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