Heterocyclic derivatives of fullerene C60. 1. Synthesis of new fulleropyrazolines by the 1,3-dipolar cycloaddition of nitrile imines

Article abstract of DOI:10.1023/B:COHC.0000027890.05668.07

New stable [6,6]-closed cycloadducts, fulleropyrazolines containing aryl, hetaryl, trifluoromethyl, and other substituents in the five-membered ring, have been obtained by the 1,3-dipolar cycloaddition of nitrile imines to C ₆₀. Two methods of generating nitrile imines in situ have been used, the dehydrohalogenation of the corresponding hydrazonoyl halides by the action of triethylamine and the thermal decomposition of 2,5-diaryltetrazoles.

Full text of DOI:10.1023/B:COHC.0000027890.05668.07

Chemistry of Heterocyclic Compounds, Vol. 40, No. 2, 2004
HETEROCYCLIC DERIVATIVES
OF FULLERENE C60. 1. SYNTHESIS OF
NEW FULLEROPYRAZOLINES BY THE
1,3-DIPOLAR CYCLOADDITION OF NITRILE IMINES
M. V. Reinov, M. A. Yurovskaya, D. V. Davydov, and A. V. Streletskii
New stable [6,6]-closed cycloadducts, fulleropyrazolines containing aryl, hetaryl, trifluoromethyl, and
other substituents in the five-membered ring, have been obtained by the 1,3-dipolar cycloaddition of
nitrile imines to C60. Two methods of generating nitrile imines in situ have been used, the dehydro-
halogenation of the corresponding hydrazonoyl halides by the action of triethylamine and the thermal
decomposition of 2,5-diaryltetrazoles.
Keywords: hydrazonoyl halides, 2,5-diaryltetrazoles, [6,6]-closed cycloadducts, nitrile imines, fullerene
C60, fulleropyrazolines, 1,3-dipolar cycloaddition.
1,3-Dipolar cycloaddition of nitrile imines to C60 is the standard method for annelating the pyrazoline
ring to the fullerene sphere (see review [1] and cited literature). Further development of investigations in this
direction may be connected primarily with the synthesis of new representatives of this class of compounds or
secondly with the application of new methods of generating nitrile imines. Both aspects have been studied in the
present work.
The known method of generating nitrile imines in situ (route A), the dehydrohalogenation of substituted
hydrazonoyl halides by the action of triethylamine, has made possible a significant expansion of the variety of
1,3-disubstituted fulleropyrazolines.
The cycloadducts 5a-i synthesized contain aryl and trifluoromethyl substituents in the five-membered
heterocyclic fragment.
The starting materials for generating nitrile imines 4a-c in situ, the hydrazonoyl chlorides 3a-c, were
obtained by the action of PCl5 [2] on the hydrazides of the appropriate acids 1a-c. The preparation of nitrile
imine precursors 4d-i by this method was unsuccessful. Good results were obtained on generating nitrile imines,
not from the corresponding hydrazonoyl chlorides but from the bromides 3d-i, which, in turn, were synthesized
by the bromination of hydrazones 2d-i by the action of NBS [3]. An interesting fact may be noted that on
bromination
of
p-ethoxybenzaldehyde
phenylhydrazone
(2e)
under
these
conditions
the
p-bromophenylhydrazonoyl bromide of p-ethoxybenzaldehyde (3f) is formed in parallel. This was indicated by
the isolation of cycloadduct 5f together with fulleropyrazoline 5e from the reaction mixture obtained on
interacting the unexpected bromination product, fullerene, and triethylamine.
__________________________________________________________________________________________
Moscow M. V. Lomonosov State University, Moscow 119234, Russia; e-mail:
yumar@org.chem.msu.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 223-228,
February, 2004. Original article submitted November 1, 2003.
188
0009-3122/04/4002-0188©2004 Plenum Publishing Corporation

R1
N
R2
Et3N
O
C
PCl5
R1
R1
N
H
NHNHR2
NNHR2
route A
X
1a–c
NBS
3a–c,
X=Cl
3d–i, X=Br
CH
R2
2d–i
N
N
R1
R2
R1
N
C60
N
_
+
PhBr, 120 oC,
2 x
4a–i
5a–m
PhBr, 155 oC, 3 x
N
N
N
R2
R1
route B
N
R2
N
N
_
PhBr, 155 oC
+
R1
4j–m
6j–m
1–4 a R1= p-O2NC6H4, R2= Ph; b R1=Ph, R2= p-O2NC6H4; c R1= Ph, R2=2,4-Cl2C6H3;
d R1= R2= p-O2NC6H4; e R1= p-EtOC6H4, R2=Ph; f R1= p-EtOC6H4, R2= p-BrC6H4;
g R1= CF3, R2= Ph; h R1= CF3, R2= p-MeC6H4; i R1= CF3, R2= о-MeOC6H4;
3–5 j R1= 2-thienyl, R2= p-MeC6H4; k R1= R2=Ph; l R1= 4-Py, R2= Ph;
m R1= Ph, R2= р-МеOC6H4
All the hydrazonoyl halides 3a-i synthesized were used for generating in situ the corresponding nitrile
imines 4a-i by the action of triethylamine directly in the reaction mixture already containing C60. Reaction was
carried out in bromobenzene. The cycloaddition of nitrile imines 4a-i leads smoothly to the formation of stable
[6,6]-closed monofulleropyrazolines 5a-i. Literature data indicate that mainly monoadducts are formed as a
result of cycloaddition of nitrile imines [3]. However, there is a reference [4] that on interacting
1,3-diphenylnitrile imine with C60 under similar conditions the monoadduct is not formed but the main
compound isolated is the bisadduct. In our case the addition of practically all the nitrile imines 4a-i leads to the
formation of monoadducts as the chief product, when using nitrile imine 4h the bisadduct was recorded as a side
product (according to data of MALDI mass spectrometry).
In addition to the described standard method we used for the first time a procedure (route B),
preparatively simple, for generating nitrile imines by the thermal decomposition of 2,5-diaryltetrazoles.
Cycloadducts 5j-m, containing aryl and hetaryl substituents such as thienyl and pyridyl in the pyrazoline
fragment, were synthesized by this method. The availability of 2,5-diaryltetrazoles of various structure generates
a greater possibility for functionalization of the fullerene spheroid than route A, which is limited by the
availability of the appropriate hydrazonoyl halides.
5-(2-Thienyl)-2-p-tolyltetrazole (6j) was obtained by the known procedure of [5]. For the synthesis of
the remaining diaryltetrazoles 6k-m we developed a new original procedure. Several methods of obtaining
2,5-diaryltetrazoles are known. It is possible to synthesize them by regioselective arylation of 5-aryltetrazoles
under the action of diaryliodonium salts in the presence of palladium and copper catalysts in DMF [6], or on
189

oxidation of stannylated 5-aryltetrazoles with Cu(II) acetate in the presence of Ar2I+X- in CH2Cl2 [7]. Our
method comprises the regioselective arylation of 5-aryltetrazoles by various diaryliodonium salts in water using
metallic copper catalyst.
Ar1
H
N
N
_
Cu, KOH
N
N
1
N
N
+
Ar2 I X
+
N
H2O, 100 oC
N
Ar2
Ar2
Ar1 = Ph, p-MeO-С6Н4; Ar2 = Ph, 4-Py
The simplicity of carrying out the experiment (reaction in water), the ease of isolating the desired
compounds, and the fairly high yields (60-85%), depending on the structure of the iodonium salt, serve as an
irrefutable advantage of the proposed method of synthesis of diaryltetrazoles 6.
Thermal decomposition of tetrazoles 6 at a temperature of the order of 150°C in bromobenzene solution
in the presence of fullerene-60 leads to the intermediate formation in situ of the corresponding nitrile imines
4j-m and their subsequent cycloaddition. Bromobenzene is the optimum solvent for carrying out the reaction.
The reaction also proceeds in chlorobenzene and toluene but the yields of the cycloadducts were far less.
Assignment of the synthesized fulleropyrazolines 5a-m to the [6,6]-closed isomers was made on the
basis of 13C NMR data. Analysis of all the obtained adducts was unsuccessful, because of the difficulties linked
with the long time for accumulation of 13C NMR spectral signals due to the low solubility of adducts. Two
signals were present in the spectra of adducts 5b and 5h in the 75-110 ppm region which correspond to the C(3)
and C(4) nuclei of the pyrazoline ring. When forming [5,6]-open fulleroid structures the signals of the C(3) and
C(4) atomic nuclei will not be present in the aliphatic portion of the spectrum. The 1H NMR spectral data indicate
the presence in adducts 5a-m of an annelated five-membered heterocyclic fragment. The main characteristics are
the signals in the 7.6-8.3 region assigned to the ortho protons of the N-aryl substituent, and in the 8.1-8.4 ppm
region assigned to the ortho protons of the C-aryl substituent. Such a large displacement towards low field
compared with the initial hydrazonoyl halides is caused by intramolecular charge-transfer between the fullerene
fragment and the aryl substituents of the fulleropyrazoline ring [3,8]. The MALDI spectra confirm that
monocycloaddition proceeds under the indicated conditions.
EXPERIMENTAL
1
13
13
The H and C NMR spectra were recorded on a Varian XL 400 instrument (1H at 400 and C at 100
MHz), internal standard was TMS. The NMR spectra of the fullerene adducts 5 were obtained for solutions in
CS2–acetone-d6, 5:1. Mass spectral analysis by the MALDI method was carried out on a Vision 2000 instrument
with a N2 laser, the wavelength of the radiation of which was 336 nm, and a time of flight mass analyzer. As
matrices we successfully used orthorhombic sulfur, [3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]-
malononitrile (DCTB), and 9-nitroanthracene. Both negative and positive ions were recorded. Each mass
spectrum was obtained by summing the signals of 20 to 50 laser impulses. The order of preparing samples of
substances for analysis was as follows: several drops (less than 1 µl) of a saturated toluene solution of the matrix
were applied to a metallic target with the aid of a fine capillary to form, after evaporation of the solvent, a thin
film. A fraction of the substance being analyzed, obtained by TLC, was also dissolved in toluene, after which the
surface of the matrix film was moistened with several drops of this solution with the aid of a fine capillary. The
best conditions for analysis were achieved on using this procedure with a matrix of sulfur or DCTB when
recording negative ions. In the mass range of the substance being analyzed the molecular radical-anion [M]-· had
the greatest intensity, while the intensity of the C60-· fragment ion was low.
190

A check on the progress of reactions and the purity of the compounds obtained was effected by TLC on
Silufol UV 254 plates. Separation and purification of substances were carried out on columns of silica gel
L 40/100, eluting with hexane–benzene, 3:1.
Hydrazides 1a-c and hydrazonoyl halides 2a-c were synthesized by the procedure of [2].
Phenylhydrazonoyl Chloride of p-Nitrobenzaldehyde (3a). Yield 55%; mp 184-188°C. H NMR
1
spectrum (CDCl3), δ, ppm: 7.10 (1H, t, 4-H); 7.35 (2H, m, 3-, 5-H); 7.48 (2H, d, 2-, 6-H); 8.23 (2H, d, 2'-, 6'-H);
8.40 (2H, d, 3'-, 5'-H); 10.56 (1H, s, NH). Found, %: C 56.76; H 3.66; N 15.61. C13H10ClN3O2. Calculated, %:
C 56.64; H 3.66; N 15.24.
p-Nitrophenylhydrazonoyl Chloride of Benzaldehyde (3b). Yield 70%; mp 190-195°C. Found, %:
C 56.70; H 3.64; N 15.35. C13H10ClN3O2. Calculated, %: C 56.64; H 3.66; N 15.24.
2,4-Dichlorophenylhydrazonoyl Chloride of Benzaldehyde (3c). Yield 47%; mp 90°C. IR spectrum
1
o
(nujol), ν, cm-1: 1600 (C=N), 3330 (NH). H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.16 (1H, dd, J = 8.8,
mJ = 2.3, 5-H); 7.26 (1H, d, mJ = 2.3, 3-H); 7.35 (3H, m, 3'-, 4'-, 5'-H); 7.45 (1H, d, °J = 8.8, 6-H); 7.86 (2H, m,
2'-, 6'-H); 8.63 (1H, s, NH).
Phenylhydrazone of p-Ethoxybenzaldehyde (2d). p-Ethoxybenzaldehyde (1.39 g, 9.3 mmol) was
added to a solution of phenylhydrazine (1 g, 9.3 mmol) in methanol (10 ml) and the mixture was heated until the
beginning of solid precipitation, after which the reaction mixture was cooled. The solid was filtered off and used
directly in the next stage.
p-Nitrophenylhydrazone of p-Nitrobenzaldehyde (2e). A solution of p-nitrobenzaldehyde (0.99 g,
6.5 mmol) was added with stirring to a hot solution of p-nitrophenylhydrazine (1 g, 6.5 mmol) in methanol
(20 ml). The mixture was heated for several minutes and cooled. The precipitated solid was filtered off.
Phenylhydrazone of Trifluoroacetaldehyde (2g), p-Tolylhydrazone of Trifluoroacetaldehyde (2h),
and o-Methoxyphenylhydrazone of Trifluoroacetaldehyde (2i). CF3CH(OH)2 (15 mmol), obtained by the
procedure of [9], was added to a solution of freshly distilled arylhydrazine (10 mmol) in methanol (10 ml), and
the mixture was stirred at ~20°C for 1 h in an inert atmosphere. After the end of the reaction the methanol was
distilled off at ~20°C, benzene (20 ml) was added to the reaction mixture, and the solution dried over sodium
sulfate. A large portion of the benzene was distilled off at ~20°C, hexane (10 ml) was added, and the mixture
cooled. The resulting crystals were filtered off, and used in the next stage without further purification.
Hydrazonoyl Halides (3d-i). N-Bromosuccinimide (NBS) (36 mg, 0.2 mmol) was added to a solution of
hydrazone 2 (0.21 mmol) in bromobenzene (10 ml), and the mixture was stirred for 20 min. The synthesis of
compounds 3e and 3f was carried out at 0°C, of compound 3d at 70-80°C, and of the remaining hydrazonoyl
halides at room temperature. The precipitated succimide was filtered off and the solution obtained was used in
the next stage.
5-(2-Thienyl)-2-(p-tolyl)tetrazole (6j) was obtained by the procedure of [5].
Diaryltetrazoles (6k-m) (General Method). Potassium hydroxide (1 mmol) was added as aliquots of a
titrated aqueous solution with stirring to 5-aryltetrazole (1 mmol) in water (10 ml), then diaryliodonium salt
(1.5 mmol) and freshly activated metallic copper (1.5 mmol) were added after homogenization of the solution.
The reaction mixture was boiled for 16 h in a stream of argon. After the end of the reaction the solution was
extracted three times with chloroform. The extract was dried over Na2SO4 and passed through a layer of Al2O3
(separation from the initial 5-aryltetrazole and salts). The solution obtained was evaporated, and the residue
crystallized from CCl4 or CHCl3.
2,5-Diphenyltetrazole (6k). Yield 60%; mp 100°C. UV spectrum (EtOH), λmax (log ε): 272 nm (4.24).
Mass spectrum, m/z (I, %): 223 (2) [M+H]+·, 222 (<1) [M]+·, 194 (40) [M-N2]+·, 103 (10) [M-N2-C6H5N]+·, 91
1
(100) M-N2-C7H5N]+·. H NMR spectrum (acetone-d6), δ, ppm: 7.54-7.62 (4H, m, m-HPh); 7.67-7.71 (2H, m,
p-HPh); 8.20-8.24 (4H, m, o-HPh).
2-(p-Methoxyphenyl)-5-phenyltetrazole (6l). Yield 85%; mp 101-102°C. UV spectrum (EtOH),
λ
max (log ε): 300 nm (4.10). Mass spectrum, m/z (I, %): 253 (3) M+H]+·, 252 (<1) [M]+·, 224 (20) [M-N2]+·, 121
191

1
(100) [M-N2-C6H5N]+·, 106 (25) [M-N2-C6H5N-CH3]+·, 103 (10) [M-N2-C7H7NO]+·. H NMR spectrum
l
l
(acetone-d6), δ, ppm: 2.88 (3H, s, CH3O); 7.45 (2H, d, 2-, 6-HAr ); 7.55-8.10 (5H, m, Ph); 8.20 (2H, d, 3-, 5-HAr ).
2-Phenyl-5-(4-pyridyl)tetrazole (6m). Yield 72%; mp 146°C. UV spectrum (EtOH), λmax (log ε):
270 nm (4.41). Mass spectrum, m/z (I, %): 224 (1) [M+H]+·, 223 (<1) [M]+·, 195 (20) [M-N2]+·, 104 (5)
1
[M-N2-C6H5N]+·, 91 (100) [M-N2-C6H4N2]+·, 64 (40) [M-N2-C6H4N2-HCN]+·. H NMR spectrum (DMSO-d6),
δ, ppm: 7.30-7.90 (5H, m, Ph); 7.60 (2H, d, 4-Py); 8.10 (2H, d, 4-Py).
Fulleropyrazolines (5a-i) (General Method). A solution of hydrazonoyl halide 3 (0.21 mmol) in
bromobenzene (10 ml) was added with stirring during 1.5 h to a solution of fullerene C60 (50 mg, 0.07 mmol)
and triethylamine (50 µl) in bromobenzene (20 ml) at 120-130°C. The mixture was stirred at this temperature for
a further 2 h, the solvent was distilled off, and the residue treated with methanol. The resulting solid was filtered
off, and washed several times with methanol. The adduct was isolated from the mixture obtained by column
chromatography. Eluents were benzene–hexane, 1:1 (for adducts 5a-c), benzene–hexane, 1:3 (for compounds
5d-f), and benzene–hexane 1:10 (for adducts 5g-i).
Fulleropyrazolines (5j-m) (General Method). A solution of fullerene C60 (50 mg, 0.07 mmol) and
tetrazole 6 (0.2 mmol) in bromobenzene was boiled for 3 h. The mixture was then treated analogously to the
previous procedure. Eluents were benzene–hexane, 1:3 (for adducts 5j,k,m), and benzene–ethyl acetate, 10:1
(for 5l).
1
3-(p-Nitrophenyl)-1-phenylpyrazolo[4',5':1,2]fullerene[60] (5a). H NMR spectrum, δ, ppm (J, Hz):
7.47 (3H, m, 3-, 4-, 5-HPh); 7.93 (2H, d, 2-, 6-HPh); 8.30 (2H, d, J = 9.1, 2-, 6-Hp-NO C H ); 8.60 (2H, d, J = 9.1, 3-,
2
6 4
5-Hp-NO C H ). MALDI mass spectrum: [M]-· 959.7.
2
6 4
1
1-(p-Nitrophenyl)-3-phenylpyrazolo[4',5':1,2]fullerene[60] (5b). H NMR spectrum, δ, ppm: 7.54
(3H, m, 3-, 4-, 5-HPh); 8.25 (6H, m, 2-, 3-, 5-, 6-Hp-NO C H ; 2-, 6-HPh). C NMR spectrum, δ, ppm: 75 (Csp3);
13
2
6 4
106 (Csp3); 129, 135, 138.5, 139, 140, 141, 145.5, 146.5, 149, 151.4, 152, 152.5, 152.6, 153, 153.8, 154, 154.5,
155, 155.2, 155.5, 155.7, 156, 156.8, 157.3, 159, (Csp2). MALDI mass spectrum: [M]-· 960.
1
1-(2,4-Dichlorophenyl)-3-phenylpyrazolo[4',5':1,2]fullerene[60] (5c). H NMR spectrum, δ, ppm
(J, Hz): 7.42 (1H, dd, oJ = 8.47, mJ = 2.36, 5-H); 7.47 (3H, 3-, 4-, 5-HPh); 7.60 (1H, d, mJ = 2.36, 3-HC H Cl ); 7.88
6
3
2
(1H, d, oJ = 8.47, 6-HC H Cl ); 8.23 (2H, d, 2-, 6-HPh). MALDI mass spectrum: [M]-· 983.7.
6
3
2
1
1-(p-Nitrophenyl)-3-(p-nitrophenyl)pyrazolo[4',5':1,2]fullerene[60] (5d). H NMR spectrum, δ, ppm
(J, Hz): 8.31 (2H, d, J = 6.8, 2-, 6-Hp-NO C H ); 8.33 (2H, d, J = 6.8, 3-, 5-Hp-NO C H ); 8.39 (2H, d, J = 9, 2'-,
2
6
4
2 6 4
6'-Hp-NO C H ); 8.62 (2H, d, J = 9, 3'-, 5'-Hp-NO C H ).
2
6
4
2 6 4
3-(p-Ethoxyphenyl)-1-phenylpyrazolo[4',5':1,2]fullerene[60] (5e). 1H NMR spectrum, δ, ppm (J, Hz):
1.46 (3H, t, J = 6.9, CH2CH3); 4.10 (2H, q, J = 6.9, CH2CH3); 6.95 (2H, d, J = 8.6, 3-, 5-Hp-EtOC H ); 7.17, (1H, t,
6
4
4-HPh); 7.40 (2H, t, 3-, 5-HPh); 7.88 (2H, d, 2-, 6-HPh); 8.14 (2H, d, J = 8.6, 2-, 6-Hp-EtOC H ). MALDI mass
6
4
spectrum: [M]-· 958.2.
1-(p-Bromophenyl)-3-(p-ethoxyphenyl)pyrazolo[4',5':1,2]fullerene[60] (5f). 1H NMR spectrum,
δ, ppm (J, Hz): 1.46 (3H, t, J = 6.9, CH2CH3); 4.10 (2H, q, J = 6.9, CH2CH3); 6.96 (2H, d, J = 8.9, 3-,
5-Hp-EtOC H ); 7.52 (2H, d, J = 9, 3-, 5-HPh); 7.84 (2H, d, J = 9, 2-, 6-HPh); 8.14 (2H, d, J = 8.9, 2-, 6-Hp-EtOC H ).
6
4
6 4
MALDI mass spectrum: [M]-· 1038.
1
1-Phenyl-3-trifluoromethylpyrazolo[4',5':1,2]fullerene[60] (5g). H NMR spectrum, δ, ppm: 7.29
(1H, m, 4-HPh); 7.38 (2H, m, 3-, 5-HPh); 7.56 (1H, d, 2-, 6-HPh). MALDI mass spectrum: [M]-· 907.
1-(p-Tolyl)-3-trifluoromethylpyrazolo[4',5':1,2]fullerene[60] (5h). 1H NMR spectrum, δ, ppm (J, Hz):
2.41 (3H, s, CH3); 7.26 (2H, d, J = 8.6, 3-, 5-Hp-CH C H ); 7.69 (2H, d, J = 8.6, 2-, 6-Hp-CH C H ). 13C NMR
3
6
4
3 6 4
spectrum, δ, ppm: 31.7 (CH3); 83.8 (Csp3); 96.3 (Csp3); 129.5 (CF3); group of signals 135-161 (Carom and Cful);
179 (C=N). MALDI mass spectrum: [M]-· 920.7.
1
1-(o-Methoxyphenyl)-3-trifluoromethylpyrazolo[4',5']fullerene[60] (5i). H NMR spectrum, δ, ppm:
3.90 (3H, s, CH3O); 7.06 (2H, m, 3-, 5-Ho-CH OC H ); 7.41 (1H, m, 4-Ho-CH OC H ); 7.65 (1H, m, 6-Ho-CH OC H ).
3
6
4
3
6
4
3
6 4
MALDI mass spectrum: [M-H]-· 935.
192

1
3-(2-Thienyl)-1-p-tolyl)pyrazolo[4',5':1,2]fullerene[60] (5j). H NMR spectrum, δ, ppm (J, Hz): 7.10
(1H, m, 4-HThienyl); 7.22 (2H, d, J = 8, 3-, 5-HPh); 7.48 (1H, d, 3-HThienyl); 7.72 (2H, d, J = 8, 2-, 6-HPh); 7.91 (1H,
d, 5-HThienyl). MALDI mass spectrum: [M]-· 935.
1
1,3-Diphenylpyrazolo[4',5':1,2]fullerene[60] (5k). H NMR spectrum, δ, ppm: 7.43 (6H, m, 3-, 4-,
5-HPh; 3'-, 4'-, 5'-HPh); 7.89 (2H, d, 2-, 6-HPh); 8.23 (2H, d, 2', 6'-HPh). MALDI mass spectrum: [M]-· 915.
1-Phenyl-3-(4-pyridyl)pyrazolo[4',5':1,2]fullerene[60] (5l). MALDI mass spectrum: [M]-· 916.
1
1-(p-Methoxyphenyl)-3-phenylpyrazolo[4',5':1,2]fullerene[60] (5m). H NMR spectrum, δ, ppm
(J, Hz): 3.81 (3H, s, CH3O); 6.94 (2H, d, J = 9.5, 3-, 5-Hp-CH OC H ); 7.45 (3H, m, 3-, 4-, 5-HPh); 7.73 (2H, d,
3
6 4
J = 9.5, 2-, 6-Hp-CH OC H ); 8.23 (2H, d, 2-, 6-HPh). MALDI mass spectrum: [M-H]-· 944.3.
3
6 4
The authors are grateful to O. V. Boltalina for helpful comments. A. V. Streletskii is grateful to the
Volkswagen Fund (Project No. I-77/855) and the RFFI fund (Project No. 03-03-32855) for material support.
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