Synthesis and characterization of alkyl and aryl-(4-methyl-6-nitro- quinolin-2-yl)amines: X-ray structures of ethyl and cyclohexyl-(4-methyl-6- nitro-quinolin-2-yl)amine

Article abstract of DOI:10.1081/SCC-200066685

We have synthesized and characterized a series of alkyl and aryl-(4-methyl-6-nitro-quinolin-2-yl)amines through a high-yield, three-step procedure starting from 4-methylquinolin-2-ol. Nitration using concentrated nitric/sulfuric acids, followed by chlorination in phosphorus oxychloride, yielded 2-chloro-4-methyl-6-nitro-quinoline. All of the intermediates and aminated products have been characterized by multinuclear (¹H and ¹³C) NMR spectroscopy, elemental analysis, and, in the case of the two title compounds (ethyl and cyclohexyl-(4-raethyl-6-nitro-quinolin-2-yl) amine), a single crystal X-ray structure was obtained to verify the nature of the new materials. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1081/SCC-200066685

Synthetic Communicationsw, 35: 2067–2077, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200066685
Synthesis and Characterization of Alkyl and
Aryl-(4-methyl-6-nitro-quinolin-2-yl)amines:
X-Ray Structures of Ethyl and Cyclohexyl-
(4-methyl-6-nitro-quinolin-2-yl)amine
Melody R. Heiskell
Louisiana Scholars’ College, Northwestern State University,
Natchitoches, Louisiana, USA
Martin D. Rudd
Department of Chemistry, University of Wisconsin—Fox Valley,
Menasha, Wisconsin, USA
Benjamin B. Penn
Institute for Non Linear Optics, NASA Marshall Space Flight Center,
Huntsville, Alabama, USA
Jason A. Kautz
Department of Chemistry and Biochemistry, Baylor University,
Waco, Texas, USA
Abstract: We have synthesized and characterized a series of alkyl and aryl-(4-methyl-
6-nitro-quinolin-2-yl)amines through a high-yield, three-step procedure starting from
4-methylquinolin-2-ol. Nitration using concentrated nitric/sulfuric acids, followed
by chlorination in phosphorus oxychloride, yielded 2-chloro-4-methyl-6-nitro-
quinoline. All of the intermediates and aminated products have been characterized by
multinuclear (1H and 13C) NMR spectroscopy, elemental analysis, and, in the case of
Received in the USA March 28, 2005
Address correspondence to Martin D. Rudd, Department of Chemistry, University
of Wisconsin—Fox Valley, Menasha, WI 54952, USA. Tel/Fax: 920 832 2694;
E-mail: mrudd@uwc.edu
2067

2068
M. R. Heiskell et al.
the two title compounds (ethyl and cyclohexyl-(4-methyl-6-nitro-quinolin-2-yl)amine),
a single crystal X-ray structure was obtained to verify the nature of the new materials.
Keywords: Quinolinamines, substituted amines, X-ray structure
INTRODUCTION
There has been a burgeoning interest in the chemistry and physics of materials
that possess nonlinear optical (NLO) properties. As part of this extensive
effort, we have prepared a series of novel organic compounds based around
substituted quinolinamines that we believe may possess some of the properties
necessary for further investigation as NLO materials. As such, materials that
possess second-order NLO properties have been of considerable relevance
because they involve possible applications in emerging optical electronic
technologies.[1,2] Organic systems have been particularly attractive for the
investigation of NLO responses because of their electrical nonlinearities. In
addition, it is often found that organic systems possess several advantages
over inorganic systems,[3] including higher optical-damage thresholds,
cheaper and easier synthesis, and flexible molecular design. Typically,
organic molecules containing conjugated p systems with an asymmetrical
charge distribution possess very large second-order NLO properties. Such
examples include azo dyes and Schiff bases.[4] Quaternary ammonium salts
derived from quinolinium iodide were also shown to have a second-order
NLO response in their crystalline form,[5] which results in a blue-shifted
absorption. The quaternary ammonium salt (substituted quinolinium) served
as a strong electron acceptor and, in addition to the nature of the charge-
transfer processes and intermolecular forces, the solid-state packing of the
crystals was a key factor in governing the properties of these materials.
With this in mind, we looked for a synthetic route to prepare some nonionic
substituted quinolines.
RESULTS AND DISCUSSION
We have successfully prepared a series of N-alkyl and N-aryl substituted
quinolinamines derived from readily available starting materials. Our choice of
starting material was 4-methylquinolin-2-ol (1), which we determined could
be readily nitrated using a standard organic-nitration method (concentra-
ted sulfuric/nitric acids) adapted from a previously described literature
method.[6] Yields in this nitration step were considerably reduced if the temp-
erature was allowed to rise above 08C during the course of the addition of the
acid mixture. After pure samples of 4-methyl-6-nitro-quinolin-2-ol (2) were
obtained, they were subsequently chlorinated in the 2-position using phos-
phorus oxychloride, forming 2-chloro-4-methyl-6-nitroquinoline in high

Synthesis of Alkyl and Aryl-(4-methyl-6-nitro-quinolin-2-yl)amines
2069
Figure 1. Synthesis of the substituted quinolines.
yield. Once established, the substitution of this halogen at the electron-
deficient 2-position is relatively facile[7] and can be accomplished by a wide
variety of aryl and alkylamines (4–10). We also found that yields of all the
products were higher if the syntheses were performed under the typically
moisture- and oxygen-free conditions of a Schlenk apparatus. The synthetic
route is shown in Figure 1.
All of the new compounds were characterized by multinuclear NMR
spectroscopy (see Experimental) and elemental analysis to confirm their
molecular formulas. The NMR spectra of 2 and 3 show the expected
patterns of splitting and substitution. Upon formation of the (quinolin-2-yl)
amines, the NMR spectra show characteristic peaks associated with the
alkyl and aryl substituents.
The molecular structures of (5) and (8) are shown in Figures 2 and 3
respectively and a discussion of their structures is detailed in the Experimental
section.
CONCLUSIONS
Using a facile, three-step synthesis, we have been able to prepare a variety of
alkyl and aryl substituted quinolines in high yield. The reactions can be
performed on both micro and macro scales with success. Purification of
these new compounds is reasonably straightforward. We have shown that
compound (3) is reactive to a considerable array of amines and thus is a
useful synthetic intermediate in designing new substituted quinolinamines.

2070
M. R. Heiskell et al.
Figure 2. Molecular structure of (5) showing the atomic numbering.
We are currently undertaking experimental work to recrystallize these
materials in noncentrosymmetric space groups using alternative solvents
and techniques.
EXPERIMENTAL
All reactions were carried out under an atmosphere of dry nitrogen or argon
gas using conventional Schlenk line techniques. All solvents were dried and
Figure 3. Molecular structure of (8) showing the atomic numbering.

Synthesis of Alkyl and Aryl-(4-methyl-6-nitro-quinolin-2-yl)amines
2071
purified according to literature methods prior to use; THF was distilled from
sodium metal under an atmosphere of nitrogen. Phosphorus oxychloride and
the amines were used as supplied (Aldrich). 4-Methyl-quinolin-2-ol was
purchased from Aldrich Chemical Co. and recrystallized from tetrahydrofuran
prior to use. NMR spectra were recorded on a Varian VXR400 at 400 MHz
(1H) and 100 MHz (13C) at Iowa State University and are referenced to
tetramethylsilane at 0 ppm. Elemental analyses were performed by Atlantic
Microlab Inc. (Norcross, GA). Melting points are uncorrected.
Synthesis of 4-methyl-6-Nitro-quinolin-2-ol (2). In a typical synthesis,
4-methyl-quinolin-2-ol (5.0 g, 3.1 mmol) was dissolved, with stirring, into
concentrated sulfuric acid (20mL) for a period of 1 h. A pressure-equalizing
dropping funnel was attached to the three-necked flask equipped with a
thermometer and an inert gas inlet. A mixture of concentrated nitric acid and
sulfuric acid (1:1, total 20mL) was added dropwise to a cooled (258C)
solution of the quinolinol over a period of 2 h. At no point was the temperature
of the solution allowed to rise to 08C. After the addition was complete, the
solution was stirred at 08C for 1 h and then allowed to warm to room temperature.
The solution remained clear and colorless. It was poured into an ice-water bath
(200 g of ice, 100 mL of distilled water), immediately producing a thick white
precipitate, which was filtered off and recrystallized from hot glacial acetic
acid as an off-white microcrystalline powder. Yield: 5.10 g, 90%. Melting
point: 328–3328C (dec.). Analytically pure samples can be obtained by a
further recrystallization from tetrahydrofuran. In our experience, however,
yields are not affected in the subsequent steps by trace amounts of acetic acid.
Elemental analysis: required for C10H8N2O3 C: 58.82%; H: 3.95%; N: 13.72%;
found C: 58.77%; H: 4.01%; N: 13.77%. 1H NMR (d6-DMSO): 2.48 (s, CH3),
6.56 (s, 1H), 7.42 (d, 1H), 8.34 (dd, 1H), 8.50 (s, 1H) (N-H not observed).
Synthesis of 2-chloro-4-methyl-6-nitro-quinoline (3). In a typical synthesis,
(2) (3.0 g, 14.7 mmol) was suspended in dry tetrahydrofuran (30 mL) in a
Schlenk flask attached to a reflux condenser. To this flask was added phos-
phorus oxychloride (2.0 mL, 3 molar excess) and the reaction was refluxed
for 45 min, during which time the solution became clear and colorless.
Upon cooling, long, thin, colorless needle crystals of 2-chloro-4-methyl-6-
nitro-quinoline began to form. The mixture was poured into an ice-water
bath (100 g of ice, 50 mL of water) and the white precipitate was collected
and dried by washing with a little cold tetrahydrofuran. Recrystallization
from hot toluene yielded a crop of colorless needle crystals. Yield: 3.0 g,
90%. Melting point: 208–2128C. Elemental analysis: required for
C10H7ClN2O2 C: 53.95%; H: 3.17%; N: 12.58%; found C: 53.91%;
1
H: 3.11%; N: 12.51%. H NMR (d6-acetone): 2.85 (s, CH3), 2.91 (s, CH3),
7.64 (s, 1H), 8.15 (d, 1H), 8.55 (dd, 1H), 9.02 (d, 1H).
Synthesis of ethyl-(4-methyl-6-nitro-quinolin-2-yl)amine (5). This parti-
cular amine is used as an example, but the method is applicable to all of

2072
M. R. Heiskell et al.
the amines used in this article. Into a 50-mL Schlenk flask was placed (3),
(1.0 g, 45 mmol) and DMSO (10 mL). Ethylamine (1.0 mL, 1.1 molar equiva-
lents) was added via a syringe and the mixture was heated to 808C for 2 h. The
color changed from colorless to yellow-orange during this time. The solution
was poured into an ice-water mix (50 g of ice, 50 mL of water) and filtered
under vacuum. The precipitate was then recrystallized from toluene to give
1.1 g (90%) of bright yellow crystals, which were collected and dried. X-ray
quality crystals were grown by slow diffusion of heptane into a toluene
solution of (5) at –108C. Microanalytical data and NMR spectra for
compounds 4–10 are shown. All the products obtained in this reaction were
yellow to yellow-orange microcrystalline powders that could be recrystallized
from toluene/heptane as described.
Methyl-(4-methyl-6-nitro-quinolin-2-yl)amine (4) (81%) as a yellow micro-
crystalline powder, mp 204–2088C. Elemental analysis: C11H11N3O2% C
(found/theoretical) 60.93/60.82; %H (found/theoretical) 5.16/5.10; dH: 2.64
(s, 3H,); 3.12 (d, 3H, N–CH3); 5.05 (s, br, 1H, N–H), 6.57 (s, 1H),
7.67 (d, 1H), 8.29 (d of d, 1H), 8.69 (d, 1H); dC: 19.0, 28.7, 38.2, 113.4,
120.6–127.5, 141.8, 146.4, 152.4, 159.4.
Ethyl-(4-methyl-6-nitro-quinolin-2-yl)amine (5) (90%) as a yellow-orange
microcrystalline powder, mp 180–1828C. Elemental analysis: C12H13N3O2%
C
(found/theoretical) 62.33/62.23; %H (found/theoretical) 5.63/5.67;
dH:1.30 (t, 3H, CH3–CH2), 2.58 (s, 3H, CH3), 3.56 (d of t, 4H, CH2–CH3);
5.01 (s, br, 1H, N–H), 6.54 (s, 1H), 7.62 (d, 1H), 8.27 (d of d, 1H), 8.66
(d, 1H); dC: 15.1, 19.0, 36.6, 113.3, 121.2–127.4, 141.7, 146.5, 152.5, 158.8.
sButyl-(4-methyl-6-nitro-quinolin-2-yl)amine (6) (77%) as a yellow
powder, mp 162–1648C. Elemental analysis: C14H17N3O2% C (found/
theoretical) 64.51/64.85; %H (found/theoretical) 6.57/6.61; dH: 0.98
(t, 3H, [CH3–CHCH2CH3]), 1.27 (d, 3H, [CH3–CHCH2 CH3]), 1.63
(m, 1H, [CH3–CHCH2 CH3]), 2.62 (s, 3H CH3), 4.11 (s, br, N–H), 6.56
(s, 1H), 7.63 (d, 1H), 8.27 (d of d, 1H), 8.65 (d, 1H); dC: 10.6, 19.0, 19.2,
20.7, 30.1, 31.2, 48.6 (d), 121.1–126.9, 141.9, 146.3, 151.9, 158.2.
iButyl-(4-methyl-6-nitro-quinolin-2-yl)amine (7) (72%) as a yellow-orange
powder, mp 166–1688C. Elemental Analysis: C14H17N3O2% C (found/theor-
etical) 64.98/64.85; %H (found/theoretical) 6.67/6.61; dH: 1.01 (d, 6H,
[(CH3)2CH–CH2)]), 1.93 (m, 1H, [(CH3)2CH–CH2)]), 2.60 (s, 3H, CH3),
3.34 (t, 3H, [(CH3)2CH–CH2]), 5.11 (s, br, N–H), 6.56 (s, 1H), 7.62
(d, 1H), 8.27 (d of d, 1H), 8.67 (d, 1H); dC: 19.0, 20.6, 28.7, 49.4, 113.0,
121.2–127.4, 141.7, 146.6, 152.4, 159.1.
Cyclohexyl-(4-methyl-6-nitro-quinolin-2-yl)amine (8) (78%) as an
orange microcrystalline powder. Elemental analysis: C16H19N3O2% C
(found/theoretical) 67.36/67.35; %H (found/theoretical) 6.81/6.71; dH:

Synthesis of Alkyl and Aryl-(4-methyl-6-nitro-quinolin-2-yl)amines
2073
1.17–2.12 (m, 11H, Cy), 2.57 (s, 3H, CH3), 4.99 (s, br, 1H), 6.53 (s, 1H), 7.59
(d, 1H), 8.25 (d of d, 1H), 8.65 (d, 1H); dC: 19.2, 25.1, 25.9, 33.6, 50.0, 113.3,
121.1, 122,5, 123.6, 127.3, 141.6, 146.4, 152.6, 158.2.
Phenyl-(4-methyl-6-nitro-quinolin-2-yl)amine (9) (80%) as an orange
powder. Elemental analysis: C16H19N3O2% C (found/theoretical) 68.59/
68.81; %H (found/theoretical) 4.70/4.69; dH: 2.64 (s, 3H, CH3), 6.88
(s, 1H), 7.17 (m, 2H), 7.41 (t, 2H), 7.60 (m, 2H), 7.74 (d, 1H), 8.34 (d, 1H),
8.74 (d, 1H); dC: 19.2, 113.5, 121.1, 121.8, 123.4, 123.8, 124.6, 128.2,
129.6, 139.2, 142.7, 147.5, 151.7, 156.8.
Benzyl-(4-methyl-6-nitro-quinolin-2-yl)amine (10) (85%) as an orange
microcrystalline powder. Elemental Analysis: C17H15N3O2% C (found/
theoretical) 69.71/69.61; %H (found/theoretical) 5.21/5.15; dH: 2.17
(s, 3H, CH3), 2.63 (s, 3H, CH3), 4.76 (d, 2H, CH2–Ph), 6.62 (s, 1H), 7.26–
7.48 (m, 5H, Ph), 7.74 (d, 1H), 8.45 (d of d, 1H), 8.71 (d, 1H); dC: 19.2,
42.1, 113.3, 121.3, 121.9, 123.3, 123.9, 124.9, 128.3, 129.9, 140.1, 142.9,
148.2, 152.0, 156.9.
To confirm the structures of these novel compounds, two samples were
chosen for X-ray structural analysis. In the case of the two samples chosen,
X-ray quality crystals were grown by slow diffusion of heptane into a
toluene solution in a freezer. The pertinent structural information for the
compounds is shown in Table 1.
X-Ray Structure Determination of (5)
Experimental details: Diffracted intensities were collected on an Enraf-Nonius
CAD-4 operating in the v-2u scan mode, using graphite-monochromated
MoKa X-radiation. Final unit cell dimensions were determined from the
setting angles of 25 accurately centered reflections. Crystal stability during
the data collection was monitored by measuring the intensities of three
standard reflections every hour. Data were collected at a constant rate,
5.178 min21 in v, with a scan range of 1.15 þ 0.34tanu. The data were
corrected for Lorentz, polarization, and X-ray absorption effects, the latter
by a numerical method based on the measurement of six crystal faces.
The structure was solved by direct methods and successive difference
Fourier syntheses were used to locate all nonhydrogen atoms using SHELXTL
version 5.03.[8] Refinements were made by full-matrix least-squares on all F2
data using SHELXL-97.[9] Anisotropic thermal parameters were included for
all nonhydrogen atoms. All hydrogen atoms except H(1) were included in
calculated positions and allowed to ride on their parent atoms with fixed
isotropic thermal parameters (Uiso ¼ 1.2Uiso of the parent atom or Uiso
¼
1.5Uiso of the parent for Me hydrogens). H(1) was located in difference
Fourier maps and allowed to refine freely with Uiso ¼ 1.2Uiso N(2). Methyl

2074
M. R. Heiskell et al.
Table 1. Crystal-structure data and refinement details for compounds (5) and (8)
Compound
Parameter
5
8
Empirical formula
Formula weight
Crystal color, habit
Crystal size
C12H13N3O2
231.25
C16H19N3O2
285.34
Yellow blocks
0.65 ꢀ 0.55 ꢀ 0.25 mm
Orthorhombic
Pbcm
Yellow plates
0.92 ꢀ 0.44 ꢀ 0.08 mm
Monoclinic
P2(1)/n
Crystal system
Space group
˚
A (A)
8.0685(14)
21.458(5)
6.818(3)
90
6.3495(7)
21.783(4)
11.0252(14)
90
˚
B (A)
˚
C (A)
a
b
g
90
90
99.135(10)
90
3
˚
V (A )
1180.5(6)
4
1505.6(4)
4
0.71073
Z
l
0.71073
900
849
Reflections collected
Independent reflections
Data/parameters
Final R
3261
1964
849/112
0.0521
0.1287
1964/239
0.0514
0.1182
wR2
R indices (all data)
WR2
Largest difference peak
0.0799
0.1480
0.0914
0.1378
0.230/20.144
0.170/20.180
hydrogens were refined as idealized disordered methyl groups, that is, with two
sets of three hydrogens rotated 60 degrees from one another. The N(H)Et side
chain was found to be disordered over a mirror plane; as a result, the occu-
pancies of C11 and C12 were fixed at 50%. Insignificant residual electron
density in the difference Fourier syntheses was found near the carbon atoms
in the N(H)Et side chain. The molecular structure is shown in Figure 2.
X-Ray Structure Determination of (8)
Experimental details: The X-ray data was collected and the structure solved
using the same method described previously, but with the following differ-
ences. Diffracted intensities were collected on an Enraf-Nonius CAD–4
operating in the v-4/3u scan mode. Data were collected at a constant rate,
5.178min21 in v, with a scan range of 1.20 þ 0.34tanu. The data were
corrected for Lorentz, polarization, and X-ray absorption effects, the latter
by a semiempirical method based on azimuthal scans of c-data. The methyl

Synthesis of Alkyl and Aryl-(4-methyl-6-nitro-quinolin-2-yl)amines
2075
Table 2. Potential hydrogen bonds and C–H ꢁ ꢁ ꢁ O interactions
Donor–H ꢁ ꢁ ꢁ Acceptor
D–H
H ꢁ ꢁ ꢁ A
D ꢁ ꢁ ꢁ A
D–H ꢁ ꢁ ꢁ A
Compound 5
N2–H1 ꢁ ꢁ ꢁ O1a
N2–H1 ꢁ ꢁ ꢁ O2a
Compound 8
0.75(5)
0.75(5)
2.52(5)
2.51(5)
3.099(4)
3.254(4)
135(4)
175(5)
N2–H2 ꢁ ꢁ ꢁ O2b
0.86(3)
0.91(3)
2.38(3)
2.43(3)
3.223(3)
3.328(4)
164(3)
169(2)
C3–H3 ꢁ ꢁ ꢁ O1b
Symmetry transformations used to generate equivalent atoms: a1 2 x, y 2 0.5,
b
0.5 2 z; 1.5 þ x, 1.5–y, 0.5 þ z.
(C17) hydrogens were included in calculated positions as ideally disordered
methyl hydrogens, that is, two sets of three hydrogens rotated 60 degrees
from one another with fixed isotropic thermal parameters (Uiso ¼ 1.5Uiso of
the parent). The molecular structure is shown in Figure 3.
Potential hydrogen bonding distances are shown in Table 2. The X-ray
structure of 5 reveals two bifurcated intermolecular N–H ꢁ ꢁ ꢁ O hydrogen
bonding interactions that can be seen in the packing diagram represented in
Figure 4. A facet of this phenomenon is that molecules of 5 are held
together, although somewhat weakly, in infinite two-dimensional ribbons
that run parallel to the crystallographic b axis. Inspection of the crystal
packing of 8 also reveals the presence of an extended two dimensional
structure. The chains in 8 are loosely held in place by the formation of one
N–H ꢁ ꢁ ꢁ O and an additional C–H ꢁ ꢁ ꢁ O intermolecular contact; see Figure 5.
Crystallographic data (excluding structure factors) for the structures in
this article have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication numbers 248571 [ethyl-(4-
methyl-6-nitro-quinolin-2-yl)amine] and 248572 [cyclohexyl-(4-methyl-6-
nitro-quinolin-2-yl)amine]. Copies of the data can be obtained, free of
charge, upon application via http:// www.ccdc.cam.ac.uk/data_request/cif,
by e-mailing data_request@ccdc.cam.ac.uk, or by contacting CCDC 12,
Figure 4. Crystal packing of (5).

2076
M. R. Heiskell et al.
Figure 5. Crystal packing of (8).
Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223 336033. Supplemen-
tary information, including tables of bond lengths, bond angles, atomic
coordinates and the X-ray data have been deposited with the Cambridge
Crystallographic Data Centre.
ACKNOWLEDGMENTS
M. D. R acknowledges support from NASA and the Louisiana Board of
Regents through the LaSpace Program (NASA Grant NGT5-40115 and
BOR Contract NASA/LEQSF 2001-2005-LaSpace). We are grateful to
Scott McKinley (Iowa State University) for assistance in obtaining the
NMR spectra and to Wayne Hyde for his helpful discussions. We thank
Margaret Cochran (Louisiana Scholars’ College) and Austin Temple (NSU)
for their constant support of this undergraduate research through the NASA-
JOVE program and we thank UW—Fox Valley for travel assistance.
REFERENCES
1. (a) Lindsay, G. A.; Singer, K. D. eds. Polymers for Second Order Nonlinear Optics;
ACS Symposium Series 601; American Chemical Society: Washington, DC, 1995;
(b) Marder, S. R.; Sohn, J. E.; Stucky, G. A. eds. Materials for Non-Linear Optics:
Chemical Perspectives; ACS Symposium Series 455, American Chemical Society:
Washington, DC, 1991.
2. (a) Burland, D. A. Optical nonlinearities in chemistry. Chem. Rev. 1994, 94, 1;
(b) Marks, T. J.; Ratner, M. A. Angew. Chem. Int. Ed. Engl. 1995, 34, 155.
3. Whitall, I. R.; McDonaugh, A. M.; Humphrey, M. G.; Samoc, M. Adv. Organomet.
Chem. 1998, 42, 291.

Synthesis of Alkyl and Aryl-(4-methyl-6-nitro-quinolin-2-yl)amines
2077
`
4. Di Bella, S.; Fragala, I.; Ledoux, I.; Diaz-Garcia, M. A.; Marks, T. J. J. Am. Chem.
Soc. 1997, 119, 9950.
5. Zelichenok, A.; Burtman, V.; Zenou, N.; Yitzchaik, S.; Di Bella, S.; Meshulam, G.;
Kotler, Z. J. Phys. Chem. B 1999, 103, 8702.
6. Austin, M. W.; Ridd, J. H. J. Chem. Soc. 1963, 4204.
7. Claret, P. A. Comprehensive Organic Chemistry; Barton, D., Oilis, W. D., Eds.;
Pergamon Press: Oxford, 1979; Vol. 4, Chap.16, p. 155.
8. SHELXTL Version 5.03, Bruker AXS: Madison, WI, 1995.
¨
9. Sheldrick, G. M. University of Gottingen: Germany, 1997.