N-(2-Methylinden-4-yl)pyrrole as a heterocyclic analog of 2-methyl-4-arylindene. Synthesis of [μ-SiMe2(η5-2- Me-4-(2,4-Me2C4H2N)Ind)2]ZrCl 2

Article abstract of DOI:10.1007/s11172-009-0060-0

A unique strategy for the synthesis of 2-methyl-4-arylindenes was tested for 1-(4-indenyl)- pyrrole. The procedure includes the Paal-Knorr synthesis of a nonsymmetric arylhetaryl fragment followed by intramolecular acylation. The zirconium complex of the

Full text of DOI:10.1007/s11172-009-0060-0

Russian Chemical Bulletin, International Edition, Vol. 58, No. 3, pp. 589—593, March, 2009
589
Nꢀ(2ꢀMethylindenꢀ4ꢀyl)pyrrole as a heterocyclic
analog of 2ꢀmethylꢀ4ꢀarylindene.
5
Synthesis of [μꢀSiMe2(η ꢀ2ꢀMeꢀ4ꢀ(2,4ꢀMe2C4H2N)Ind)2]ZrCl2
P. V. Ivchenko, N. B. Ivchenko, and I. E. Nifant´ev
Department of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 939 4523. Eꢀmail: inpv@org.chem.msu.ru
A unique strategy for the synthesis of 2ꢀmethylꢀ4ꢀarylindenes was tested for 1ꢀ(4ꢀindenyl)ꢀ
pyrrole. The procedure includes the Paal—Knorr synthesis of a nonsymmetric arylhetaryl
fragment followed by intramolecular acylation. The zirconium complex of the 2ꢀmethylꢀ
4ꢀarylindenyl type containing the 1ꢀpyrrolyl substituent was synthesized.
Key words: Paal—Knorr pyrrole synthesis, Friedel—Crafts intramolecular reaction,
indanones, 4ꢀarylindenes, ansaꢀzirconocenes.
Zirconocenes 1 represent a structural type of efficient
catalysis for propene polymerization (see Ref. 1). Presꢀ
ently, the synthesis of these compounds has sufficiently
been developed and can be reduced to the preparation of
corresponding substituted indenes 2. 2ꢀMethylꢀ4(7)ꢀ
phenylindene is traditionally considered as a prototypical
molecule. The variation of substituents in the indenyl ring
allows one to efficiently affect the catalytic properties of
zirconocenes and the properties of polymers formed.
Two main synthetic approaches were developed for
compounds of general formula 2. The first approach,
cyclization of substituted arylpropionic acid to 2ꢀmethylꢀ
4ꢀphenylindanone1 (Scheme 1, route А). An alternative
approach is based on the use of 2ꢀbromobenzyl bromide,
includes the Suzuki reaction2 (Scheme 1, route B), and
which provides, in particular, the synthesis of 2ꢀmethylꢀ
7ꢀphenylindene, is based on the substrate containing the
biaryl fragment (2ꢀbromomethylbiphenyl) and yields the
target product through the stages of malonic synthesis and
Scheme 1
i. 1) EtOH, 2) NaOH, EtOH, Δ, 3) Δ; ii. 1) SOCl , CH2Cl , 2) AlCl , CH2Cl ; iii. ArB(OH)2, Pd(0)
2
2
3
2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 575—579, March, 2009.
1066ꢀ5285/09/5803ꢀ0589 © 2009 Springer Science+Business Media, Inc.

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Ivchenko et al.
thus makes it possible to introduce various aryl (including
heteroaromatic) substituents into the indene molecule.
However, these substituents are bound to the indenyl fragꢀ
ment through the carbon atoms.
the corresponding indenylpyrrole via the Paal—Knorr
reaction. The second route, whose success seemed first
improbable because of possible side reactions, included
the preparation of substituted 1ꢀarylpyrrole and the synꢀ
thesis from the latter of the fiveꢀmembered indanone ring
and target indene, and main difficulties were expected
at the stage of indanone synthesis.
For the first route, orthoꢀaminoꢀ, orthoꢀacetylaminoꢀ,
and orthoꢀnitroiodobenzenes were chosen as the starting
compounds. We planned to obtain methacrylic acid
derivatives by the Heck reaction, to synthesize 4ꢀsubstiꢀ
tuted indanone by the reduction of these derivatives
followed by cyclization, and to prepare indenylpyrrole
from 4ꢀsubstituted indanone by the Paal—Knorr reacꢀ
tion. It turned out that the Heck reaction with methꢀ
acrylic acid proceeds smoothly only in the case of
oꢀiodonitrobenzene. However, we failed to reduce the
product to the corresponding (2ꢀaminophenyl)propionic
acid in high yield.
It seemed rather interesting to synthesize ansaꢀzirconoꢀ
cene containing in position 4 or 7 of the indenyl ring the
hetaryl substituent bound to indene through the heteroꢀ
atom of the cycle. Pyrrolꢀ1ꢀyl is the simplest substituent
of this type. Molecule 3, whose αꢀpositions of the pyrrole
ring are occupied by methyl groups, was chosen as
the target compound to prevent possible difficulties at the
stages of synthesis of the bisindenyl bridged compound
and zirconocene including the reaction of substituted
indene with alkyllithium.
For the second route, we chose accessible anthranylate
4 as the starting compound to synthesize functionalized
1ꢀarylpyrrole. 2,5ꢀDimethylpyrrolꢀ1ꢀyl was chosen as
the pyrrole fragment for the reasons presented above.
Compound 5 can easily be obtained by the Paal—Knorr
reaction of acetonylacetone and ester 4. The reduction of
pyrrolyl benzoate 5 yielded alcohol 6, and the transforꢀ
mation of the latter into mesylate 7 and the malonic
synthesis according to a standard procedure gave arylꢀ
propionic acid 8 (Scheme 2).
Acid chloride 8 was thermally unstable, and the
attempts to prepare it in situ by the Fridel—Crafts inꢀ
tramolecular reaction in the presence of AlCl3 were
unsuccessful. An attempt to synthesize target indanone 9
directly from carboxylic acid 8 using the known3 efficient
method, viz., cyclization in an AlCl3—NaCl melt, showed
Results and Discussion
The Paal—Knorr reaction seems to be most attractive
for the creation of a pyrrole system. Its use for the prepaꢀ
ration of 4(7)ꢀarylindene means, in fact, the application
of the new synthetic approach to the biaryl fragment
of the target molecule, namely, the creation of the
heteroaromatic ring from functionalized arene. Two
general routes that could give molecule 3 were designed.
The first approach assumed the synthesis of 2ꢀmethylꢀ
indeneꢀ4(7)ꢀamine followed by its transformation into
Scheme 2

ansaꢀZirconocene
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 3, March, 2009
591
Scheme 3
i. AlCl3/NaCl, 180—200 °C; ii. LiAlH4, Et2O; iii. oꢀTsOH, benzene, Δ; iv. PPA, 80 °C; v. 1) BuLi, toluene/THF, 2) SiMe2Cl2
Scheme 4
that the cyclization was accompanied by the quantitative
migration of one methyl group of the pyrrole ring to form
isomeric indanone 10 in 79% yield (Scheme 3).
2,4ꢀDimethylꢀ1ꢀ(2ꢀmethylꢀ7ꢀindenyl)pyrrole 12 was
obtained from compound 10 by the reduction of the carꢀ
bonyl group followed by the dehydration of intermediate
alcohol 11. The low yield of compound 12 is caused. most
likely by the fact that one of the αꢀpositions of the pyrrole
substituent is free and accessible for the electrophilic
attack. In this case, cationic intermediates formed upon
the protonation of alcohol 11 with subsequent dehydraꢀ
tion can act as electrophiles.
No indanone 10 was found in the reaction mixture for
the cyclization of 8 in polyphosphoric acid (according
to the NMR spectral data). However, the yield of 9 was
2—4% (Scheme 3) and, hence, the further synthesis of
corresponding indenylpyrrole 3 had no sense.
Compound 12 was used as ligand for the synthesis
of ansaꢀzirconocene. Compound 13 was synthesized in
satisfactory yield by the reaction of the lithium derivative
compound 12 with dimethyldichlorosilane in a toluene—
THF mixture according to a known procedure1 (see
Scheme 3).
ansaꢀZirconocene 14 was obtained by the direct reacꢀ
tion of the dilithium derivative of compound 13 with ZrCl4
(15) in methylene chloride in almost quantitative yield as
a mixture of diastereomers (Scheme 4). Recrystallization
from ether gave 23% pure racꢀform.
14, racꢀform
14, mesoꢀform

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Ivchenko et al.
ture to a solution of compound 6 (79.4 g, 0.395 mol) in CH2Cl2
(450 mL), after which methanesulfonyl chloride (33.9 mL,
0.435 mol) was added dropwise with cooling to –78 °С, and the
mixture was stirred for 1 h. Then cooling was removed, and
the reaction mixture was stirred at room temperature for 4 h.
Then 3.5% HCl (100 mL) was added. The aqueous phase was
extracted with CH2Cl2 (2×100 mL), and the joined organic
phases were washed with a solution of Na2CO3, dried over
MgSO4, and concentrated by evaporation to obtain a blue oil,
which further crystallized completely. The yield was 105.2 g
(96%, dark blue crystals, the color is caused by admixtures),
m.p. 118 °С (after recrystallization from benzene). 1H NMR, δ:
1.90 (s, 6 Н, 2 —СН3); 2.80 (s, 3 Н, —OSO2СН3); 4.78 (s, 2 Н,
—СН2—О—); 5.90 (s, 2 Н, H(3), H(4), pyrrolyl); 7.22—7.25
(m, 1 Н); 7.46—7.50 (m, 2 Н); 7.59—7.63 (m, 1 Н). Found (%):
C, 60.27; H, 6.18. C14H17NO3S. Calculated (%): C, 60.19;
H, 6.13.
Thus, a possibility to synthesize 4ꢀhetarylindenyl
zirconium complexes, viz., structural analogs of bisindenyl
complex 1, was demonstrated using indenylpyrrole 12 and
zirconocene 14 as an example. In addition, it was shown
that the presence of the pyrrole fragment unsubstituted in
the αꢀposition in the molecule of an organic ligand does
not principally prevent the synthesis of organoelement
derivatives and metallocenes using standard procedures.
Experimental
All experiments were carried out in inert atmosphere (argon).
Wholeꢀsealed glass systems of the Schlenk type were used for
crystallization of complex 14. Ethyl anthranylate (2ꢀaminoꢀ
benzoate) was prepared according to a known procedure4 in
60% yield. Ethereal solvents and toluene were distilled over
sodium in the presence of benzophenone (dibenzoꢀ18ꢀcrownꢀ6
was added in the case of toluene). Methylene chloride was
purified by distillation with CaH2. 1H and 13C NMR spectra
were recorded on a Varian VXRꢀ400 instrument in CDCl3 at
20 °C. Elemental analyses for hydrogen and carbon were carried
out on a Carlo Erba automated analyzer (model 1106). Samples
for elemental analysis of oily compounds were preheated at
70—80 °С on a vacuum setup to a constant residual pressure
(about 10–2 Torr).
Ethyl 2ꢀ(2,5ꢀdimethylꢀ1Hꢀpyrrolꢀ1ꢀyl)benzoate (5). A mixture
of ester 4 (18.1 g, 110 mmol) and 2,5ꢀhexanedione (20 mL,
165 mmol) in glacial acetic acid (100 mL) was refluxed for 1 h,
cooled, and poured into water with ice (250 mL). After CH2Cl2
(100 mL) was added, the organic phase was separated, and the
aqueous phase was extracted with CH2Cl2 (5×50 mL). Joined
organic phases were washed with a solution of Na2CO3, dried
over MgSO4, and concentrated by evaporation to obtain the
product as a light brown oil in a yield of 26.3 g (98%). 1H NMR,
δ: 1.23 (t, 3 Н, —О—СН2—СН3, J = 7.2 Hz); 1.94 (s, 6 Н,
—СН3); 4.1 (q, 2 Н, —О—СН2—СН3, J = 7.2 Hz); 5.88 (s,
2 Н, H(3), H(4), pyrrolyl); 7.28 (dd, 1 Н, J = 8 Hz, J = 2 Hz);
7.50 (ddd, 1 Н, J = 8 Hz, J = 8 Hz, J = 2 Hz); 7.60 (ddd, 1 Н,
J = 8 Hz, J = 8 Hz, J = 2 Hz); 7.95 (dd, 1 H, J = 8 Hz, J = 2 Hz).
Found (%): C, 73.99; H, 7.11. C15H17NO2. Calculated (%):
C, 74.05; H, 7.04.
3ꢀ[2ꢀ(2,5ꢀDimethylꢀ1Hꢀpyrrolꢀ1ꢀyl)phenyl]ꢀ2ꢀmethylpropionic
acid (8). A solution of diethyl 2ꢀmethylmalonate (6.8 mL,
0.039 mol) in Et2O (20 mL) was added dropwise to a suspension
of NaH (1.45 g of 60% suspension in oil, 36 mmol) in Et2O
(80 mL) under argon with cooling to 0 °С. Cooling was removed,
and the reaction mixture was stirred for 1.5 h. Then a solution of
compound 7 (8.46 g, 0.03 mol) in Et2O (50 mL) was rapidly
added by small portions to the reaction mixture with cooling to
–40 °С. Cooling was removed, and the mixture was refluxed
for 3 h and stirred at room temperature for 16 h. Then 3% HCl
(100 mL) was added to the reaction mixture, the aqueous phase
was extracted with CH2Cl2 (4×50 mL), and the joined organic
phase was washed with a solution of Na2CO3, dried over MgSO4,
and evaporated. The obtained brown oil was dissolved in alcohol
(45 mL), then mixed with an aqueous solution of KOH (12 g of
KOH in 22.5 mL of H2O), and the mixture was refluxed for 4 h.
The reaction mixture was poured into water (100 mL), the
solution formed was extracted with Et2O (3×50 mL), and the
aqueous phase was acidified with HCl to pH ≈ 1 and extracted
with CH2Cl2 (4×80 mL). The joined organic phases were washed
with a solution of Na2CO3, dried over MgSO4, and evaporated
to dryness. The resulting redꢀbrown solid residue was heated in
an oil bath (160 °С) until gas stopped evolving (about 25 min),
and the product was obtained as a viscous brown oil, which
further crystallized, in a yield of 5.46 g (70%). 1H NMR, δ: 1.06
(d, 3 Н, CH2CHCH3 , J = 7.6 Hz); 1.90 (s, 3 Н); 1.94 (s, 3 Н);
2.56 (sext, 1 Н, —СН2СНCH3—, J = 7.6 Hz); 2.75 (dd, 1 Н,
J = 14 Hz, J = 7.6 Hz), 2.32 (dd, 1 Н, J = 14 Hz, J = 7.6 Hz)
{—СН2—СНМе—}; 5.9 (s, 2 Н, H(3), H(4), pyrrolyl);
7.14—7.17 (m, 1 Н); 7.29—7.36 (m, 3 Н). Found (%): C, 74.61;
H, 7.39. C16H19NO2. Calculated (%): C, 74.68; H, 7.44.
4ꢀ(2,5ꢀDimethylꢀ1Hꢀpyrrolꢀ1ꢀyl)ꢀ2ꢀmethylindanꢀ1ꢀone (9).
Compound 8 (2.57 g, 10 mmol) was added with stirring to
polyphosphoric acid (prepared by dissolution of P2O5 (100 g) in
80 mL of H3PO4) and heated to 120 °C. After 1 h at this
temperature the mixture was poured to water with ice (500 mL).
The resulting mixture was extracted with methylene chloride
(4×25 mL), and the joined organic phases were washed with a
solution of Na2CO3 (2×50 mL), dried over MgSO4, and conꢀ
centrated by evaporation. A broad fraction (Rf in an interval of
0.8—0.4) was separated by column chromatography (silica gel,
benzene—ethyl acetate (5 : 1) as eluent). After the solvent was
removed, the weight of the fraction was 0.1 g. The isolated
[2ꢀ(2,5ꢀDimethylꢀ1Hꢀpyrrolꢀ1ꢀyl)phenyl]methanol (6).
A solution of 5 (26.3 g, 0.108 mol) in Et2O (30 mL) was added
dropwise to a suspension of LiAlH4 (4.1 g, 0.108 mol) in Et2O
(120 mL) under argon with cooling to 0 °С. Then cooling was
removed, and the reaction mixture was stirred at room tempeꢀ
rature for 1 h. Then water was added by small portions to the
reaction mixture until the end of gas evolution. The resulting
mixture was washed with Et2O (6×50 mL), and the joined organic
phases were washed with water (2×100 mL), dried over MgSO4,
and evaporated to obtain a dark brown solid residue, which was
recrystallized from boiling hexane. The yield was 18.12 g (83.5%)
1
of 6 as light beige needleꢀlike crystals (m.p. 107 °С). H NMR,
δ: 1.60 (s, 1 Н, —СН2—ОН); 1.90 (s, 6 Н, —СН3); 4.30 (s, 2 Н,
—СН2—ОН); 5.90 (s, 2 Н, H(3), H(4), pyrrolyl); 7.17 (dd, 1 Н,
J = 7.8 Hz, J = 1.9 Hz); 7.37—7.48 (m, 2 Н); 7.59 (dd, 1 Н,
J = 8.1 Hz, J = 1.6 Hz). Found (%): C, 77.60; H, 7.56.
C13H15NO. Calculated (%): C, 77.59; H, 7.51.
2ꢀ(2,5ꢀDimethylꢀ1Hꢀpyrrolꢀ1ꢀyl)benzyl methanesulfonate (7).
Triethylamine (68.4 mL, 0.494 mol) was added at room temperaꢀ
product was compound
9 insignificantly contaminated

ansaꢀZirconocene
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 3, March, 2009
593
with nonidentified impurities. No isomeric indanone 10 was
observed in compound 9. 1H NMR, δ: 1.26 (d, 3 Н, CH2CHCH3,
J = 8.1 Hz); 1.94 (br.s, 6 Н); 2.32—2.38 (m, 1 Н), 2.66—2.75
(m, 1 Н), 2.98—3.05 (m, 1 Н) {—СН2—СНМе—}); 5.93 (s,
2 H, H(4), H(5), pyrrolyl); 7.44—7.52 (m, 2 Н); 7.82 (m, 1 Н).
4ꢀ(2,4ꢀDimethylpyrrolꢀ1ꢀyl)ꢀ2ꢀmethylindanꢀ1ꢀone (10). The
synthesis was carried out according to a known procedure.3
Melted compound 8 (5.46 g, 21 mmol) was rapidly poured into
the melt of a mixture of AlCl3 (38.5 g) and NaCl (7.7 g) at the
temperature about 200 °С, the mixture was stirred for 3—4 min,
and then the melt was poured into 5% hydrochloric acid with ice
(300 mL). The resulting mixture was extracted with methylene
chloride (5×80 mL), and the joined organic phases were washed
with a solution of Na2CO3 (2×100 mL), dried over MgSO4,
and evaporated. Compound 10 (4.0 g (79%) was obtained as a
brownꢀred oil, which further vitrified. 1H NMR, δ: 1.32 (d, 3 Н,
CH2CHCH3, J = 8.2 Hz); 2.06 (s, 3 Н); 2.14 (s, 3 Н); 2.58 (m,
1 Н), 2.74 (m, 1 Н), 3.22 (m, 1 Н) {—СН2—СНМе—}; 5.95;
6.48 (both s, 1 H each, H(3), H(5), pyrrolyl); 7.45—7.48 (m,
2 Н); 7.79 (m, 1 Н). Found (%): C, 80.34; H, 7.21. C16H17NO.
Calculated (%): C, 80.30; H, 7.16.
2,4ꢀDimethylꢀ1ꢀ(2ꢀmethylꢀ7ꢀ1Hꢀindenyl)ꢀ1Hꢀpyrrole (12).
A suspension of compound 10 (4.0 g, 0.034 mol) in ether
(10 mL) was rapidly added to a suspension of LiAlH4 (1.3 g,
0.017 mol) in Et2O (30 mL) under argon with cooling to –78 °С,
after which cooling was removed, the reaction mixture was stirred
for 2 h, and then water was added slowly by small portions until
gas stopped evolving. Then 5% HCl (30 mL) was added to
the resulting mixture, the mixture was extracted with CH2Cl2
(4×40 mL), and the joined organic phases were washed with
water (2×100 mL), dried over MgSO4, and evaporated. Benzene
(25 mL) and paraꢀtoluenesulfonic acid (0.2 g) were added to the
residue, and the resulting mixture was refluxed for about 2 h
monitoring the reaction by TLC. After the end of the reaction,
the mixture was poured into water (70 mL), the aqueous phase
was extracted with methylene chloride (3×40 mL), and the joined
organic phases were washed with water, dried over MgSO4, and
evaporated. The residue was purified by column chromatography
using hexane—methylene chloride (5 : 1) as eluent. Compound
12 (1.51 g, 40%) was obtained as a light yellow oil. 1H NMR, δ:
2.07 (s, 3 Н); 2.13 (s, 3 Н); 2.15 (s, 3 Н); 3.21 (br.s, 2 Н); 5.91;
6.51 (both s, 1 H each, H(3), H(5), pyrrolyl); 6.53 (m, 1 Н,
=СН—); 6.95—6.98 (m, 1 Н); 7.24—7.30 (m, 2 Н). Found (%):
C, 86.14; H, 7.75. C16H17N. Calculated (%): C, 86.06; H, 7.67.
Bis[4ꢀ(2,4ꢀDimethylꢀ1Hꢀpyrrolꢀ1ꢀyl)ꢀ2ꢀmethylꢀ1Hꢀindenꢀ
1ꢀyl]dimethylsilane (13). A solution of butyllithium (1.6 М in
hexane, 21 mL, 0.033 mol) was rapidly poured on cooling
to –40 °C with stirring in a solution of compound 12 (7.45 g,
0.033 mol) in a mixture of toluene (200 mL) and THF (10 mL).
Then cooling was removed, and the resulting mixture was let to
warm up to room temperature with stirring. The reaction mixture
was cooled to –40 °С, SiMe2Cl2 (2.01 mL, 0.017 mol) was
rapidly poured in, cooling was removed, and the mixture was
stirred at 60 °С for 6 h. A formed precipitate of LiCl was filtered
off, the mother liquor was concentrated by evaporation, and
compound 13 (6.24 g, 73%) as a yellow oil was isolated from
the residue by column chromatography (benzene as eluent).
1H NMR, δ: –0.26, –0.25, –0.20 (all s, 6 Н, Si(CH3)2); 2.08
(s, 6 Н); 2.18 (s, 6 Н); 2.20 (s, 6 Н); 3.83; 3.85 (both s, 2 H,
CH—Si); 5.92; 6.48 (both s, 2 H each, H(3), H(5), pyrrolyl);
6.55 (br.s, 2 Н, =СН—); 7.13—7.17 (m, 2 Н); 7.35—7.39 (m,
2 Н); 7.44—7.48 (m, 2 Н). Found (%): C, 81.28; H, 7.66.
C34H38N2Si. Calculated (%): C, 81.22; H, 7.62.
5
[μꢀ1ꢀDimethylsilylenebis(η ꢀ4ꢀ(2,4ꢀdimethylꢀ1Hꢀpyrrolꢀ
1ꢀyl)ꢀ2ꢀmethylindenꢀ1ꢀyl)]dichlorozirconium(IV) (14). A solution
of butyllithium in hexane (1.6 M, 10.32 mL, 16.5 mmol) was
added to a solution of compound 13 (4.15 g, 8.25 mmol) in Et2O
(50 mL) cooled to –40 °C. The resulting suspension was washed
with Et2O (3×30 mL), and the precipitate was dried. Dilithium
derivative 15a was obtained (4.7 g, 86%). A portion of the product
(3.18 g, 4.8 mmol) was suspended in CH2Cl2 (100 mL) cooled to
–60 °C, and ZrCl4 (1.12 g, 4.8 mmol) was added. The reaction
mixture was let to warm up to room temperature and stirred
for 20 min. The solution was separated by decantation and
concentrated by evaporation. A mixture of racꢀ and mesoꢀforms
of 14 (6.12 g) was obtained in a ratio of 1 : 1 in 96% yield. The
pure racꢀform of 14 was isolated as an orange powder in a yield
of 0.73 g (23%) by recrystallization from ether. 1H NMR for
racꢀ14, δ: 1.35 (s, 6 Н, Si(CH3)2); 2.08 (s, 6 Н); 2.12 (s, 6 Н);
2.25 (s, 6 Н); 5.88 (s, 2 Н); 6.73; 6.75 (both s, 2 H each, H(3),
H(5), pyrrolyl); 7.11 (dd, 2 Н, J = 8.2 Hz, J = 7.5 Hz); 7.18 (d,
2 H, J = 7.5 Hz); 7.66 (d, 2 H, J = 8.2 Hz). We failed to isolate
mesoꢀ14 in the pure form, and the spectral data were obtained by
the comparison of the spectrum of a mixture of the forms with
that of the pure racꢀform. 1H NMR for mesoꢀ14, δ: 1.25, 1.48
(both s, 3 H each, Si(CH3)2); 2.02 (s, 6 Н); 2.05 (s, 6 Н); 2.45
(s, 6 Н); 5.86 (s, 2 Н); 6.64; 6.73 (both s, 2 H each, H(3), H(5),
pyrrolyl); 6.80 (t, 2 H, J = 8.3 Hz, J = 7.5 Hz); 6.97 (d, 2 H,
J = 7.5 Hz); 7.68 (d, 2 H, J = 8.3 Hz).
References
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M. Antberg, V. Dolle, E. F. Paulus, Organometallics, 1994,
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Chem., 1979, 44, 3724.
4. Organic Synthesis, Eds W. H. Carothers, L. F. Fieser, R. C.
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Received January 30, 2008;
in revised form June 20, 2008