Unexpected formation of substituted naphthalenes and phenanthrenes in a GaCl3 mediated dimerization-fragmentation reaction of 2-arylcyclopropane-1,1-dicarboxylates

Article abstract of DOI:10.1016/j.mencom.2014.11.011

Dimethyl 2-arylcyclopropane-1,1-dicarboxylates on heating with GaCl₃ undergo dimerization to afford arylnaphthalenes or phenanthrenes. A possible reaction mechanism including elimination of two dimethyl malonate molecules was proposed, dimethyl malonate gallium complex Ga³⁺[H₂C(CO₂Me)₂]₃(GaCl₄^-)₃ was isolated and characterized by X-ray diffraction analysis.

Full text of DOI:10.1016/j.mencom.2014.11.011

Mendeleev
Communications
Mendeleev Commun., 2014, 24, 346–348
Unexpected formation of substituted naphthalenes and
phenanthrenes in a GaCl3 mediated dimerization–fragmentation
reaction of 2-arylcyclopropane-1,1-dicarboxylates
Roman A. Novikov,a Anna V. Tarasova,a Kyrill Yu. Suponitskyb and Yury V. Tomilov*a
a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian
Federation. Fax: +7 499 135 6390; e-mail: tom@ioc.ac.ru
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation
DOI: 10.1016/j.mencom.2014.11.011
Dimethyl 2-arylcyclopropane-1,1-dicarboxylates on heating with GaCl3 undergo dimerization to afford arylnaphthalenes or
phenanthrenes. A possible reaction mechanism including elimination of two dimethyl malonate molecules was proposed, dimethyl
malonate gallium complex Ga3+[H2C(CO2Me)2]3(GaCl4–)3 was isolated and characterized by X-ray diffraction analysis.
Donor–acceptor cyclopropanes (DACs) containing donor and
acceptor substituents in the vicinal position are widely used in
present-day organic synthesis as the sources of 1,3-dipoles which
are generated from them in the presence of Lewis acids.1–5
Recently, it was shown that donor–acceptor cyclopropanes can
undergo dimerization under the action of Lewis acids and organic
catalysts in the absence of unsaturated substrates and other
scavengers of generated 1,3-dipoles, the dimers having various
origin such as arylidene malonates,6 diarylhexenes,6,7 cyclo-
hexanes,7 tetralins,7–9 dihydroanthracenes,7 pentaleno[1,6-a,b]-
indoles,10 polysubstituted cyclopentanes6,8 and 2-oxabicyclo-
[3.3.0]octanes.11 Among the discovered DAC transformations,
attention should be focused on the dimerization of 2-arylcyclo-
propane-1,1-dicarboxylates 1 to polysubstituted cyclopentanes
and/or tetralins under the action of anhydrous GaCl3,8,9,12 the
ratio of the products being dependent only on the reaction tem-
perature and the amount of gallium trichloride used.
We studied the behaviour of phenylcyclopropane dicarboxylate
1a with GaCl3 under conditions different from those used pre-
viously:8,9 the reaction temperature was raised to 80°C and the
amount of GaCl3 was 1–2 equiv. Under these conditions, a new
route of DAC transformation occurred with the unexpected forma-
tion of 2-phenylnaphthalene 2a, whose molecule did not contain
ester groups (Scheme 1, R = H).† Unlike the previously described
products of donor–acceptor cyclopropanes dimerization,6–11 com-
pound 2a is not a true dimer, although it is formed from two
cyclopropane dicarboxylate molecules. In the course of this
CO2Me
CO2Me
GaCl3 (1–2 equiv.)
2
CH2Cl2, 50–80 °C,
0.5–1.5 h, sealed tube
R1
R3
R2
1
R1
R2
R3
R1
CO2Me
R2
R3
+ 2
CO2Me
2
Yield
(%)
DAC R1 R2 R3
Product
1a
1b
1c
1d
1e
H
H
Cl
H
H
H
H
H
Cl
Br
H
Me
H
H
2a
2b
2c
2d
2e
93
80
22
65
67
H
CO2Me
CO2Me
94
1f
2f
CO2Me
CO2Me
†
1H and 13C NMR spectra were recorded on Bruker AMX-III 400 (400.1
and 100.6 MHz, respectively) and BrukerAVANCE II 300 (300 and 75 MHz,
respectively) spectrometers in CDCl3 containing 0.05% TMS as the internal
59
1
standard. Assignments of H and 13C signals were made with the aid of
1D DEPT-135 and 2D COSY, NOESY, HSQC and HMBC spectra.
Compounds 2 (general procedure). Solid GaCl3 (0.45–0.75 mmol,
150 mol%) was added in one portion to a solution of cyclopropane 1
(0.3–0.5 mmol) in 4 ml of dry CH2Cl2 in dry argon atmosphere at room
temperature under vigorous stirring. The mixture was heated to 80°C
under slight pressure in sealed tube and was stirred for 1 h. Then aqueous
5% HCl solution was added at room temperature to reach pH 3, and the
mixture was extracted with CH2Cl2 (3×10 ml). The organic layer was dried
over MgSO4 and the solvent was removed in vacuo. The residue was
purified by column chromatography on silica gel (benzene–EtOAc, 20:1)
to afford pure compounds 2 in yields specified in Scheme 1.
1g
2g
Scheme 1
reaction, two malonic ester molecules are eliminated, and the
formation of 2a formally corresponds to the dimerization of
phenylacetylene, which was not observed earlier. Other Lewis
acids, e.g., EtAlCl2 or scandium and ytterbium triflates, do not
provide compounds like 2a. Thus, the application of anhydrous
GaCl3 is a unique procedure for performing fragmentation
processes under the conditions of DAC dimerization.
2-Phenylnaphthalene 2a: yield 93%, colourless crystals, mp 97–98°C.
NMR spectra correspond to published data.14
© 2014 Mendeleev Communications. All rights reserved.
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Mendeleev Commun., 2014, 24, 346–348
MeO
H
MeO
O
MeO
O
O
GaCl3
O
GaCl3
O
GaCl3
O
CO2Me
CO2Me
~H+
~H+
Ph
GaCl3
Ph
Ph
Ph
OMe
H
OMe
OMe
1a
I
II
III
fixed by NMR
CO2Me
CO2Me
MeO
O
MeO
O
GaCl3
O
GaCl3
O
Ph
HCl
– GaCl3
MeO2C
CO2Me
3a
OMe
OMe
SEAr
~H+
Ph
OMe
Ph
Isolated minor product
MeO
OMe
MeO
GaCl3
O
Ga
O
O
Ga
O
MeO
HCl
OMe
CO2Me
Cl3
Cl3
O
O
– GaCl3
CO2Me
Ga
V
IV
Cl3
Main product
VIII
MeO
O
MeO
O
GaCl3
GaCl3
CO2Me
CO2Me
O
O
HCl
– GaCl3
– H+
OMe
OMe
Ph
Ph
VII
Ph
H
4a
VI
Isolated minor product
H
O
MeO
CO2Me
HCl
GaCl3
O
– H+
– GaCl3
CO2Me
Ph
Main product
Ph
OMe
VIII
2a
Main product
IX
Scheme 2
The conditions found were successfully extended on other
aryl-substituted cyclopropane dicarboxylates 1. In this case,
dimerization–fragmentation reactions effectively occurred with
cyclopropanes containing phenyl, p-tolyl and 1-naphthyl sub-
stituents, whereas cyclopropanes 1c–e with halogen atoms in the
ortho and meta positions of the benzene ring, were found less
reactive. Interestingly, cyclopropanes with halogen atoms in
the para position of the benzene ring did not form similar
products.
7-Methyl-2-(4-methylphenyl)naphthalene 2b: yield 80%, colourless
crystals, mp 134–136°C. 1H NMR, d: 2.41 (s, 3H, C4'Me), 2.52 (s, 3H,
C7Me), 7.24–7.32 (m, 2H, m-H), 7.30 (dd, 1H, C6H, 3J 8.3 Hz, 4J 1.6 Hz),
7.58–7.64 (m, 2H, o-H), 7.64 (br.s, 1H, C8H), 7.66 (dd, 1H, C3H, 3J 8.4 Hz,
The possible mechanism of this process is outlined on
Scheme 2. Under the action of GaCl3, cyclopropane 1 undergoes
ring opening to afford 1,2-dipolar intermediate II after a number
of consecutive reactions.13 This is a key intermediate in the
dimerization of cyclopropanes 1 into tetralins 3.9 However, this
reaction does not reach the formation of tetralins 3 as a result
of an elevated reaction temperature and the use of a larger amount
of GaCl3. Under these conditions dimeric intermediate V
undergoes the elimination of a malonyl fragment induced by the
Ga atom, which possesses considerable Lewis acidity, like an
acid-catalyzed retro-aldol reaction. As a result, intermediate VI
is generated, which is converted into intermediate VII and the
gallium enolate of malonic ester VIII after proton migration.
Similarly to intermediate V, intermediate VII eliminates the
second malonyl fragment and gives a naphthalene fragment as a
result of aromatization.
To rationalize the stepwise mechanism of the elimination
of malonyl fragments from the DAC dimerization products, one
should note that tetralins 3 are formed as minor reaction products;
in the case of cyclopropane 1a, monoelimination product 4a was
isolated in a yield of ~1%.‡ It is likely that the energetically
favourable aromatization of a six-membered ring is the driving
force of the main process observed. However, it requires the
rupture of two C–C bonds, which, in turn, requires the use of
3
3
4J 1.6 Hz), 7.74 (d, 1H, C5H, J 8.3 Hz), 7.84 (d, 1H, C4H, J 8.4 Hz),
7.92 (br.s, 1H, C1H). 13C NMR, d: 21.2 and 21.8 (2Me), 124.8, 124.9,
127.2, 127.5, 128.12 and 128.16 (6CH), 127.3 and 129.6 (o-C, m-C),
130.9, 134.1, 135.9, 137.1, 138.5 and 138.6 (6C). Found (%): C, 92.85;
H, 6.73. Calc. for C18H16 (%): C, 93.06; H, 6.94.
1-Chloro-6-(2-chlorophenyl)naphthalene 2c: yield 22%, colourless
crystals, mp 46–48°C. IR (CHCl3, n/cm–1): 3020, 2975, 2923, 1646, 1520,
1466, 1419. 1H NMR, d: 7.34 (ddd, 1H, C4'H or C5'H, 3J 7.4 and 7.3 Hz,
4J 2.0 Hz), 7.37 (ddd, 1H, C4'H or C5'H, 3J 7.4 and 7.3 Hz, 4J 2.0 Hz), 7.42
(dd, 1H, C3H, 3J 8.3 and 7.4 Hz), 7.44 (dd, 1H, C3'H or C6'H, 3J 7.3 Hz,
3
4J 2.0 Hz), 7.52 (dd, 1H, C3'H or C6'H, J 7.3 Hz, 4J 2.0 Hz), 7.60 (dd,
1H, C2H, 3J 7.4 Hz, 4J 1.1 Hz), 7.71 (dd, 1H, C7H, 3J 8.7 Hz, 4J 1.7 Hz),
7.81 (br.d, 1H, C4H, 3J 8.3 Hz), 7.91 (d, 1H, C5H, 4J 1.7 Hz), 8.33 (br.d,
3
1H, C8H, J 8.7 Hz). 13C NMR, d: 124.3 (C8), 126.3 (C3), 126.6 (C2),
127.1 and 129.1 (C4' and C5'), 127.5 (C4), 128.8 (C5), 129.0 (C7), 130.2
and 131.7 (C3' and C6'), 130.3 (C8a), 132.0 (C2'), 132.1 (C1), 134.5 (C4a),
138.1 (C6), 140.2 (C1'). MS, m/z (%): 272 (96) [M]+ for 35Cl, 232 (18),
202 (65), 149 (39), 100 (36), 83 (30), 59 (43), 57 (88), 43 (100). Found
(%): C, 70.87; H, 3.80. Calc. for C16H10Cl2 (%): C, 70.35; H, 3.69.
2-(1-Naphthyl)phenanthrene 2f: yield 94%, thick colourless oil. NMR
spectra correspond to published data.15
3-(2-Naphthyl)phenanthrene 2g: yield 59%, colourless crystals, mp 122–
123°C. NMR spectra correspond to published data.16
For characteristics of compounds 2d,e, see Online Supplementary
Materials.
– 347 –

Mendeleev Commun., 2014, 24, 346–348
severe reaction conditions. It is obvious that the elimination
Cl(10)
of the second malonyl fragment proceeds much more rapidly
than that of the first one because aromatization occurs at this
step, as observed experimentally; that is, the reaction does almost
not stop with the formation of monoelimination products 4. Note
that dimeric tetralins 3 do not give even the traces of compounds
2 on the interaction with GaCl3 under the conditions of fragmenta-
tion. This is likely due to the fact that a complex with GaCl3 (like
compound V) should be formed for the elimination of a malonyl
fragment; however, it was found previously13 that substituted
malonates do not produce stable complexes on the interaction
with GaCl3. This complex can be formed only indirectly through
the dimerization of complex II and its fragmentation described
above. In all cases, the above transformations occur with very
high regioselectivity. Thus, cyclopropanes 1d,e,g, which can react
at both ortho positions of the aromatic ring, form only one regio-
isomer. However, the mechanism of this electrophilic substitution
remains unclear.
Cl(5)
Cl(8)
Ga(3)
Ga(4)
Cl(9)
Cl(11)
Cl(7)
Cl(12)
C(15)
C(13)
O(7)
C(7)
C(9)
O(5)
Cl(6)
O(12)
C(12)
C(11)
O(11)
O(10)
O(8)
C(10)
C(6)
C(8)
O(6)
Ga(1)
O(9)
O(2)
C(3)
O(1)
C(1)
C(14)
C(5)
C(4)
C(2)
O(3)
O(4)
Cl(4)
Ga(2)
Cl(3)
Cl(1)
Cl(2)
Note that Ga enolate VIII converted into new complex 5,
whose structure was determined by X-ray diffraction analysis
(Figure 1), in a matter of several days. This complex includes
three fragments of malonic ester and four gallium atoms, three
of which exist in the form of the GaCl4– anions.§
Thus, we found a new uncommon reaction of 2-arylcyclo-
propane-1,1-dicarboxylates with anhydrous GaCl3 on heating
resulting in the regiospecific formation of substituted naphthalenes
and phenanthrenes in good yields. In this case, the dimeric inter-
mediate formed from two DAC molecules undergoes fragmenta-
tion with the elimination of two malonyl fragments as dimethyl
malonate.
Figure 1 X-ray structure of a molecule of 5 in the representation of atoms
as thermal ellipsoids (p = 50%).
This work was supported by the Russian Science Foundation
(grant no. 14-13-01054).
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.mencom.2014.11.011.
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§
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Received: 16th June 2014; Com. 14/4395
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