Protonation of diarylacetylenes in superacid HSO3F and their oxidation in the HSO3F/PbO2 system: One-pot synthesis of polysubstituted naphthalenes

Article abstract of DOI:10.1002/ejoc.200800548

In the superacid HSO₃F, diarylacetylenes bearing one electron-withdrawing group (NO₂, CN, COMe, CO₂Me) in each arene ring form stable ions, protonated at these groups. Oxidation of such diarylacetylenes in the HSO₃

Full text of DOI:10.1002/ejoc.200800548

FULL PAPER
DOI: 10.1002/ejoc.200800548
Protonation of Diarylacetylenes in Superacid HSO3F and Their Oxidation in
the HSO3F/PbO2 System: One-Pot Synthesis of Polysubstituted Naphthalenes
Aleksander V. Vasilyev,*[a] Andrey O. Shchukin,[a] Stéphane Walspurger,[b] and
Jean Sommer*[b]
Keywords: Alkynes / Protonation / Oxidation / Radical ions / Electrocyclic reactions
In the superacid HSO3F, diarylacetylenes bearing one elec-
tron-withdrawing group (NO2, CN, COMe, CO2Me) in each
arene ring form stable ions, protonated at these groups. Oxi-
dation of such diarylacetylenes in the HSO3F/PbO2 system
at –75 to –50 °C over 2–2.5 h, followed by quenching of the
reaction mixture with hydrochloric (or hydrobromic) acid at
–60 to 25 °C, resulted in the formation of (E,E)-1,4-dichloro
(or dibromo)-1,2,3,4-tetraarylbuta-1,3-dienes. These butadi-
enes spontaneously undergo electrocyclic transformation
into polysubstituted naphthalenes at room temperature.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
stituents in the superacid HSO3F, their one-electron oxi-
dation in the HSO3F/PbO2 system and further electrocyclic
transformations of their oxidation products.
For this study, we synthesised (Experimental Section) a
series of symmetrically substituted compounds, 1a–e, each
bearing two electron-withdrawing groups (COMe, CN,
NO2, CO2Me), polymethyl-substituted dinitro diarylacetyl-
enes 1f–h, compound 1i, with two dimethylamino groups in
both para positions in its aromatic rings, and the nonsym-
metrical diarylacetylene 1j (Figure 1).
Introduction
Oxidation of alkynes is widely used in organic synthe-
sis.[1,2] One-electron oxidation of acetylene compounds with
intermediate formation of acetylene cation radicals affords
various valuable multifunctional compounds in one-pot re-
actions.[3–7]
One of the most efficient oxidants for the generation of
organic cation radicals is lead dioxide (PbO2) in acidic me-
dia.[8] The CF3CO2H/CH2Cl2/PbO2 system has been suc-
cessfully utilised for the preparative oxidation of different
acetylene derivatives.[4–6] The main limitation of this oxidat-
ive system is the impossibility of achieving cation radical
formation of deactivated diarylacetylenes bearing strongly
electron-withdrawing substituents (NO2, CN, COMe,
CO2Me, etc.), due to their high oxidative potentials.[4] The
use of stronger acid, in the form of neat hydrogen fluoride,
results in the production of cation radicals of such deacti-
vated diarylacetylenes, which in the HF/PbO2 system leads
to the formation of 1,4-difluoro-1,2,3,4-tetraarylbuta-1,3-
dienes.[7] In our recent preliminary communication we dem-
onstrated in principle the use of superacid HSO3F along
with PbO2 for the one-electron oxidation of 1,2-bis(4-ace-
tylphenyl)acetylene.[9]
Figure 1. Diarylacetylenes used in this study.
In this report we present data on the protonation of di-
Because of the tremendous protonation capability of su-
arylacetylenes bearing strongly electron-withdrawing sub- peracidic media,[10] triple bonds of rather basic acetylenes
may undergo protonation with the formation of extremely
reactive vinyl cations, which are further transformed into
secondary products.[11–16] Thus, before starting the oxi-
dation of diarylacetylenes in the HSO3F/PbO2 system one
has to be sure that diarylacetylenes are stable in HSO3F
and that no electrophilic reactions – such as vinyl sulfonate
formation,[11,12,15c,15d] dimerisation[11,13,16] or other trans-
formations[14,15a,b,16] – will take place.
[a] Department of Organic Chemistry, Saint-Petersburg State For-
est Technical Academy,
Institutsky per. 5, Saint-Petersburg, 194021, Russia
Fax: +07-812-550-08-15
E-mail: aleksvasil@mail.ru
[b] Laboratoire de Physico-Chimie des Hydrocarbures, Associé au
CNRS, Institut de Chimie, Université L. Pasteur,
67000 Strasbourg, France
E-mail: sommer@chimie.u-strasbg.fr
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One-Pot Synthesis of Polysubstituted Naphthalenes from Diarylacetylenes
The proton and carbon spectra clearly demonstrate the
Results and Discussion
exclusive formation of the protonated forms 2a–h and 2j.
No specific signals of products of acetylene transformations
in HSO3F, such as vinyl protons[11,14,15c,15d] or vinyl cationic
carbons,[14] could be observed. Diarylacetylenes 1a–h and
1j do not undergo protonation at the triple bond in HSO3F
at –80 °C. Compounds 1a and 1e, with acetyl and meth-
oxycarbonyl groups, form doubly protonated structures 2a
NMR spectra of compounds 1a–h and 1j dissolved in
neat HSO3F at –80 or 0 °C show the formation of stable
ions 2a–h and 2j, fully protonated (or specifically solvated)
at their electron-withdrawing groups (Scheme 1). Chemical
shifts for the 1H NMR spectra of ions 2a–h and 2j in
HSO3F at –80 and at 0 °C are given in Table 1. 13C NMR
spectra of ions 2a–c, 2e and 2f (HSO3F, –80 and 0 °C), to-
gether with those of their corresponding neutral precursors
1a–c, 1e and 1f (CDCl3, 25 °C), are presented in Table 2.
1
and 2e, respectively. Their H NMR spectra in HSO3F at
–80 °C contain the corresponding signals of protons at-
tached to oxygen atoms at δ = 13.29 ppm for ion 2a and at
δ = 12.72 ppm for ion 2e (Table 1). Other acceptors – the
nitro groups in compounds 1c, 1d and 1f–h and the cyano
groups in compound 1b do not give rise to any definite
signals for bonded protons due to fast proton exchange in
HSO3F (compare with our previous NMR observations[15]).
Hexa- and octamethyl-substituted substrates 1g and 1h give
stable ions 2g and 2h in HSO3F at –80 °C, but at higher
temperatures protonation of the acetylene triple bonds oc-
curs and secondary reactions take place at 0 °C. The same
behaviour is observed for compounds 1b, 1d and 1j
(Table 1).
For 13C NMR spectra it is worth mentioning the down-
field shifts of the acetylene carbon signals due to the pro-
tonation of electron-withdrawing substituents in the aro-
matic rings. The difference in the chemical shifts of, for in-
stance, the acetylene carbon atoms in neutral precursor 1f
and its protonated form 2f reaches values of up to ∆δ = ca.
9 ppm in HSO3F at 0 °C (cf. the signals in Table 2).
Upon dissolution of the bis-dimethylamino-substituted
diarylacetylene 1i in HSO3F at –80 °C, the formation of the
diprotonated form of vinyl fluorosulfonate 3 was detectable
Scheme 1. Protonation of diarylacetylenes bearing electron-wih-
drawing substituents in the superacid HSO3F.
Table 1. 1H NMR spectra of ions 2a–h and 2j in HSO3F at –80
and 0 °C.
T
Chemical shifts δ [ppm]
1
by H NMR (Scheme 2). The proton spectrum of species 3
[°C]
(spin–spin interaction constants J)
H arom.
contains a broad singlet at δ = 7.44 ppm, corresponding to
the overlapped signals of the vinyl proton and two protons
of the protonated dimethylamino groups (Experimental
Section). Vinyl fluorosulfonate 3 is formed by addition of
HSO3F to the acetylene bond of the N,N-diprotonated
form of initial 1i. The addition occurs despite the electron-
withdrawing character of the dimethylammonium groups
NMe2H+, which just slightly deactivate the triple bond
towards the protonation. In a preparative-scale experiment
in HSO3F (Experimental Section) diarylacetylene 1i gives
ketone 4 as the product of hydrolysis of vinyl fluorosulfo-
nate 3 (Scheme 2).
X, Y[a]
2a
–80
8.01 (s, 4 H), 8.56 (s, 4 H)
3.34 (s, 6 H, 2ϫMe),
13.39 (s, 2 H, 2ϫC=OH+)
3.89 (s, 6 H, 2ϫMe)
0
8.03 (d, J = 7.5 Hz, 4 H),
8.59 (d, J = 7.5 Hz, 4 H)
8.00 (d, J = 5.7 Hz, 4 H),
8.27 (d, J = 5.7 Hz, 4 H)
8.09 (s, 4 H), 8.69 (s, 4 H)
8.06 (d, J = 8.6 Hz, 4 H),
8.64 (d, J = 8.6 Hz, 4 H)
8.05–8.61 (m, 8 H)
2b[b] –80
–
–
2c
–80
0
–
–
2d[b] –80
2e
–80
7.95 (s, 4 H), 8.23 (s, 4 H)
4.64 (s, 6 H, 2ϫMeO),
12.72 (s, 2 H, 2ϫC=OH+)
After studying the stability of diarylacetylenes in HSO3F
we carried out preparative oxidation of diarylacetylenes 1a–
d in the HSO3F/PbO2 system (Scheme 3).
0
–80
0
7.96 (d, J = 8.3 Hz, 4 H),
8.25 (d, J = 8.3 Hz, 4 H)
7.99 (s, 2 H), 8.88 (s, 2 H)
4.69 (s, 6 H, 2ϫMeO)
2f
2.75 (s, 6 H, 2ϫMe),
2.77 (s, 6 H, 2ϫMe)
2.76 (s, 6 H, 2ϫMe),
2.81 (s, 6 H, 2ϫMe)
2.81 (s, 12 H, 4ϫMe),
3.04 (s, 6 H, 2ϫMe)
2.26 (s, 12 H, 4ϫMe)
3.05 (s, 3 H, MeO),
NMR spectra show the complete protonation of the elec-
tron-withdrawing substituents in ions 2a–d in HSO3F
(Scheme 1), but nonprotonated compounds 1a–d in equilib-
rium may undergo one-electron oxidation by PbO2 in
HSO3F,[17] as shown in Scheme 3. Oxidations of diaryl-
acetylenes 1a–d were carried out for 2–2.5 h at –75 or
–50 °C in the HSO3F/PbO2 system. Quenching of the su-
peracidic reaction mixtures with frozen concentrated hydro-
chloric acid at –60 °C then resulted in the formation of
(E,E)-1,4-dichloro-1,2,3,4-tetraarylbuta-1,3-dienes 5a–d.
7.97 (s, 2 H), 8.83 (s, 2 H)
7.62 (s, 2 H)
2g[b] –80
2h[b] –80
–
2j[b]
–80
7.71 (s, 1 H),
8.14 (d, J = 8.7 Hz, 2 H),
8.33 (s, 1 H),
6.58 (s, 2 H, OCH2O)
8.83 (d, J = 8.7 Hz, 2 H)
[a] Substituents X and Y are shown in Scheme 1. [b] Unstable at
0 °C.
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A. V. Vasilyev, A. O. Shchukin, S. Walspurger, J. Sommer
Table 2. 13C NMR spectra of compounds 1a–c, 1e and 1f and their protonated forms 2a–c, 2e and 2f.
FULL PAPER
Solvent T [°C]
Chemical shifts δ, ppm (spin–spin interaction constants J, Hz)
Csp[a]
Aromatic C atoms[b]
R, X, Y[c]
C-1
C-2 and C-6
131.8
C-3 and C-5
128.3
C-4
1a CDCl3
2a HSO3F
25[d]
91.6
127.4
136.6
197.2 (2ϫC=O) 26.6
(2ϫMe)
–80
97.4 (s)
138.0 (s)
134.1 (d, J =
167.7 Hz)
138.2 (d, J = 166.5
Hz), 132.9 (d, J =
169.3 Hz)[e]
129.3 (s)
219.0 (s, 2ϫC=OH+),
25.4 (q, J = 131.6 Hz,
2ϫMe)
0
98.2 (t,
J = 4.6 Hz)
139.0 (t,
J = 8.4 Hz)
134.5 (dd, J =
170.1, 5.6 Hz)
135.9 (br. d, J =
164.1 Hz)
129.8 (t,
J = 7.6 Hz)
219.3 (q, J = 3.2 Hz,
2ϫC=OH+), 25.40
(q, J = 132.0 Hz, 2ϫMe)
118.0 (2ϫCN)
107.4 (2ϫCNH+)
–
1b CDCl3
25[d]
91.3
94.4
92.0
93.4 (s)
126.6
133.6
128.8
138.3 (s)
132.0
136.5
132.6
138.3 (d, J =
170.5 Hz)
135.5
131.9
133.8
123.8
128.6 (d, J =
174.1 Hz)
128.3
112.2
100.8
147.6
142.5 (t,
J = 7.4 Hz)
143.7
2b HSO3F –80[d]
1c CDCl3
2c HSO3F
25[d]
–80
–
0[d]
99.4
91.3
138.0
127.3
–
1e CDCl3
2e HSO3F
25[d]
131.6
129.6
129.9
166.4 (2ϫC=O)
52.3 (2ϫMeO)
–80
94.2 (s)
94.9
134.0 (s)
135.0
131.9 (d, J =
166.1 Hz)
132.2
133.7 (d, J =
169.7 Hz)
134.0
121.6 (s)
121.8
181.5 (s, 2ϫC=OH+), 63.0
(q, J = 154.1 Hz, 2ϫMeO)
182.0 (2ϫC=OH+),
63.4 (2ϫMe)
0[d]
1f
2f
CDCl3
HSO3F
25[d]
–80
93.8
102.3 (s)
127.6
139.2 (s)
139.2 and 136.0
143.8 (s) and 138.9
(d, J = 170.1 Hz)
125.62 and 131.1
130.4 (d, J = 171.3
Hz) and 140.3 (s)
148.3
144.2 (s)
20.3 (2ϫMe), 20.0 (2ϫMe)
19.6 (q, J = 126.8 Hz,
2ϫMe), 22.3
(q, J = 22.32 Hz, 2ϫMe)
19.8 (q, J = 133.6 Hz,
2Me), 22.3 (q, J =
133.2 Hz, 2ϫMe)
0
102.8 (d,
J = 4.0 Hz)
139.5 (m,
J = 4.8 Hz)
144.0 (m, J = 5.2 Hz) 130.7 (dm, J =
144.2 (m,
J = 6.8 Hz)
and 139.3
166.5, 4.8 Hz) and
(dm, J = 169.3,
4.4 Hz)
141.4 (t, J = 4.8 Hz)
[a] Acetylene carbon atoms. [b] Aromatic atom C-1 is the ipso-carbon to the acetylene triple bond, other atoms C-2 to C-6 are counted
from C-1. [c] Substituents R, X and Y are shown in Schemes 1 and 2. [d] Spectrum with 13C–1H decoupling. [e] Two nonequivalent signals
due to the protonation of carbonyl group and restricted rotation around bond C-4–C(OH+)Me (see the same phenomenon in our previous
works[15a,15b]).
Scheme 3. Oxidation of diarylacetylenes 1a–d in the HSO3F/PbO2
system (quenching with HCl) to afford butadienes 5a–d and further
transformations of the latter into naphthalenes 6a–c.
Scheme 2. Formation of vinyl fluorosulfonate 3 and ketone 4 from
diarylacetylene 1i.
ture of compound 6a was determined by X-ray diffraction
1
analysis.[9] Periodic monitoring of the H NMR spectra of
After storage in air at room temperature, crystalline bu- compounds 5a–c showed their complete conversion into
tadienes 5a–c became amorphous substances and were naphthalenes 6a–c at room temperature in 30–60 d (Experi-
slowly transformed into secondary products. After mental Section).
recrystallisation (Experimental Section) these products were
The most plausible mechanism for explaining the forma-
found to be substituted naphthalenes 6a–c. The exact struc- tion of compounds 5 and 6 is outlined in Scheme 4. One-
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Eur. J. Org. Chem. 2008, 4632–4639

One-Pot Synthesis of Polysubstituted Naphthalenes from Diarylacetylenes
Scheme 4. Mechanism of the formation of butadienes 5a–d and naphthalenes 6a–c.
electron oxidation of substrates 1 into cation radicals A may ily undergo electrocyclic ring-opening into butadienes 5 in
lead to cyclobutadiene dications B,[18] which can be formed the reaction quenching temperature range between –60 and
in two ways: one possible pathway is a cation radical dimer- 25 °C.[21] On the other hand, the possibility that the inter-
isation (path a) and another is a dimerisation reaction be- mediacy of dication C could also lead to the same products
tween species A and initial 1 followed by one-electron oxi- by the same solvolysis process cannot be excluded.
dation (path b).[19]
Knowing the exact structure of naphthalenes 6,[9] it is
Alternative formation of butadiene dications C seems to possible to speculate about the electrocyclic transformations
be unfavourable, especially in the presence of electron-with- of nonisolable cyclobutenes 7 into naphthalenes 6 and to
drawing groups,[15] as the vinyl cation formation would determine the definite stereochemical configurations of
most probably suffer from a high energetic barrier.[11,13,14] compounds 7, 5 and 8 (Scheme 4) on the basis of symmetry
However, our experimental results do not allow us to disre- rules.[22]
gard this reaction pathway entirely.
For the final formation of naphthalenes 6, cyclobutadi-
Previously, stable aromatic dications B were obtained enes 7 should possess a trans arrangement of substituents
from dibromo-substituted cyclobutenes in superacids at low in the cyclobutene ring. Under thermal conditions the ring-
temperature and characterised by NMR spectroscopic opening of trans-cyclobutadienes 5 is a four-electron con-
methods.[20] In our low-temperature 1H NMR spectroscopic rotatory process,[22] leading to (E,E)-butadienes 5. Only bu-
study we tried to generate and directly to observe the for- tadiene structure 5 with the E,E configuration[23] has a suit-
mation of dications B from the PbO2 oxidation of com- able conformation for further six-electron disrotatory ring
pounds 1a and 1c dissolved in HSO3F at –80 or –50 °C in closure into compounds 8. In this electrocyclic reaction the
NMR tubes. However, the spectra revealed the formation arene Ca=Cb bond of compounds 5 is one of the double
of complex mixtures. While these samples were stored in bonds of a triene system involved in cyclisation.[24] It is true
NMR tubes at –50 °C for 10 d, regular spectral checking that pericyclic reactions generally occur at higher tempera-
1
did not show any changes in their H NMR spectra. After tures, but with these compounds, never studied before, the
10 d storage, the quenching of these special samples with strongly electron-withdrawing groups may facilitate the re-
HCl (–60 °C) in the same way as for the preparative reac- action.
tions (vide supra) led to butadienes 5a and 5c. The complex
At the final step of this transformation a favourable trans
character of the 1H NMR spectra of the oxidation mixtures elimination of an HCl molecule from derivatives 8 occurs,
is strong evidence for the formation of several intermediate leading to naphthalenes 6. The driving force of this reaction
species. On one hand, it could be that dication B exists in is the aromatisation into the naphthalene system.
equilibrium with the corresponding fluorosulfonates before
The alternative formation of cyclobutenes 7 with cis con-
solvolysis by HCl to give dichlorocyclobutenes 7, which eas- figuration of substituents must be excluded because in this
Eur. J. Org. Chem. 2008, 4632–4639
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A. V. Vasilyev, A. O. Shchukin, S. Walspurger, J. Sommer
FULL PAPER
case the conrotatory cyclobutene ring-opening should give
isomeric (E,Z)-butadienes 5,[25] which would exhibit four
1
nonequivalent arene rings in their H and 13C NMR spec-
tra. In contrast, the NMR spectra of compounds 5a–d
clearly show only two pairs of nonequivalent arene rings
(Experimental Section), corresponding to (E,E)- or (Z,Z)-
butadienes 5. The (Z,Z) isomers of 5, however, do not have
any suitable conformation for further thermal electrocyclic
transformation into compounds 8.
It is worth noting the influence of electron-withdrawing
substituents R in the aromatic rings of butadienes 5a–c
(Scheme 3) on their ring-closure into compounds 8a–c and
further conversion into naphthalenes 6a–c. The stronger the
acceptor R, the more easily the cyclisation proceeds. Thus,
oxidation of acetyl- and cyano-substituted diarylacetylenes
1a and 1b gives only butadienes 5a and 5b (Scheme 3),
which are transformed into naphthalenes 6a and 6b in ap-
proximately 60 d at room temperature. In contrast, the oxi-
dation of compound 1c, with more strongly accepting nitro
groups,[26] leads to butadiene 5c in admixture with com-
pound 6c, which is already formed under the thermal condi-
tions of reaction mixture quenching (–60 to 25 °C). The
complete conversion of butadiene 5c into naphthalene 6c is
achieved in less time (around 30 d) at room temperature
(see Experimental Section).
Butadiene 5d, containing 3-nitrophenyl rings (moderate
acceptor[26]), is rather stable. Storage of this compound at
room temperature over four months (≈120 d) has not shown
any significant transformation into naphthalene 6.
We have also carried out the oxidation of substrate 1c in
the HSO3F/PbO2 system with concentrated hydrobromic
acid as a quenching medium. This led to a mixture of di-
bromo-substituted butadiene 9 together with naphthalene
10 as the major compound, confirming that dibromide 9
was easily transformed into the corresponding naphthalene
by electrocyclisation (Scheme 5).
Scheme 6. Formation and characterisation of cation radical A1.
Conclusions
In superacid HSO3F at –80 or 0 °C, diarylacetylenes
bearing two powerful electron-withdrawing substituents
(NO2, CN, COMe, CO2Me) in their aromatic rings form
stable ions, which are protosolvated at these electron-with-
drawing groups. Such deactivated diarylacetylenes do not
undergo any protonation at their acetylene carbon atoms,
and no electrophilic reactions occur at the acetylene triple
bonds in HSO3F.
One-electron oxidation of the diarylacetylenes in the
HSO3F/PbO2 system at –75 to –50 °C in 2–2.5 h with subse-
quent quenching of the reaction mixtures with concentrated
hydrochloric (or hydrobromic) acid results in the formation
of (E,E)-1,4-dichloro-(or dibromo)-1,2,3,4-tetraarylbuta-
1,3-dienes. These butadienes are spontaneously electrocycl-
ically transformed into substituted naphthalenes[28] at room
temperature.
This work and previous studies have shown the efficiency
of cation radical transformations of acetylene compounds
in new carbon–carbon bond-forming reactions.[3–7] In these
processes the diarylacetylenes can be considered suitable
precursors for the synthesis of conjugated butadienes,[7,9]
which can be further used for the preparation of polymers,
in Diels–Alder chemistry and in other electrocyclic trans-
formations.
Experimental Section
General: 1H and 13C NMR spectra of compounds were recorded
with a Bruker AM 500 spectrometer at 500 and 125 MHz, respec-
tively. The residual proton solvent peak CDCl3 (δ = 7.26 ppm) for
1H NMR spectra and the signal of CDCl3 (δ = 77.0 ppm) for 13C
NMR spectra were used as references. 1H and 13C NMR experi-
ments in superacid HSO3F were performed on a Bruker AC 400
spectrometer at 400 and 100 MHz, respectively. NMR spectra in
HSO3F were referenced to the signal of CH2Cl2 added as internal
Scheme 5. Oxidation of diarylacetylene 1c in the HSO3F/PbO2 sys-
tem (quenching with HBr) to afford butadiene 9 and naphthalene
10.
Intermediate formation of diarylacetylene cation radicals
A in the HSO3F/PbO2 system (Scheme 4) was verified by
low-temperature ESR through the generation of cation rad-
ical A1 from compound 1j (Scheme 6). The ESR spectrum
of cation radical A1 is a triplet with hyperfine splitting con-
stant aH = 19 G caused by spin interaction of an unpaired
electron with two protons of the OCH2O group.[27]
1
standard: δ = 5.32 ppm for H NMR spectra, and δ = 53.84 ppm
for 13C NMR spectra. Low-resolution mass spectra (electron im-
pact, ionisation energy 70 eV) were obtained with a MKh-1321 ma-
chine. ESR spectra in the HSO3F/PbO2 system were recorded at
190 K (–83 °C) with a Bruker ESR spectrometer. The preparative
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One-Pot Synthesis of Polysubstituted Naphthalenes from Diarylacetylenes
reactions were monitored by thin-layer chromatography carried out
on silica gel plates (Silufol UV-254) with use of UV light for detec-
tion. Column chromatographic separations were performed on sil-
ica gel Chemapol 40/100 (0.04–0.10 mm) with elution with hexane/
chloroform mixtures. Diarylacetylenes 1a–j were prepared by our
reported procedures.[4a,4b] Synthesis and characteristics of com-
pounds 1a and 1b[4b] and 1c–f, 1h and 1i[4a] were published pre-
viously.
ene 1a (178 mg, 0.68 mmol) with PbO2 (162 mg, 0.68 mmol) in
HSO3F (4 mL) at –50 °C in 2.5 h. Yield 202 mg (96%). Character-
istics were published previously.[9]
(E,E)-1,4-Dichloro-1,2,3,4-tetrakis(4-cyanophenyl)buta-1,3-diene
(5b): This compound was obtained by the oxidation of diarylacetyl-
ene 1b (129 mg, 0.57 mmol) with PbO2 (135 mg, 0.57 mmol) in
HSO3F (4 mL) at –50 °C in 2.5 h. Yield 126 mg (84%). M.p. 178–
181 °C (decomp.). 1H NMR (500 MHz, CDCl3, 25 °C): δ = 7.20
(d, J = 8.1 Hz, 4 H, Ar), 7.48 (d, J = 8.1 Hz, 4 H, Ar), 7.50 (d, J
= 8.0 Hz, 4 H, Ar), 7.54 (d, J = 8.0 Hz, 4 H, Ar) ppm. 13C NMR
(125 MHz, CDCl3, 25 °C): δ = 112.4, 113.0, 117.7, 117.9, 128.8,
130.3, 132.0, 132.1, 135.7, 137.6, 142.2, 142.3 ppm. MS: m/z (%) =
530 [M + 4]+, 528 [M + 2]+, 526 (37) [M]+, 491 (100), 455 (68), 353
(29), 228 (17), 130 (9), 102 (15). C32H16Cl2N4 (527.40): calcd. C
72.87, H 3.06, N 10.62; found C 72.95, H 2.98, N 10.70.
1,2-Bis(2,4,6-trimethyl-3-nitrophenyl)acetylene (1g): This com-
pound was obtained from (2,4,6-trimethyl-3-nitrophenyl)acetylene
and 1-iodo-2,4,6-trimethyl-3-nitrobenzene by the reported pro-
cedure.[4a,4b] Yield 20%. M.p. 210–213 °C. 1H NMR (500 MHz,
CDCl3, 25 °C): δ = 2.29 (s, 6 H, 2ϫMe), 2.46 (s, 6 H, 2ϫMe),
2.51 (s, 6 H, 2ϫMe), 7.04 (s, 2 H, Ar) ppm. MS: m/z = 352 [M]+.
C20H20N2O4 (352.14): calcd. C 68.17, H 5.72, N 7.95; found C
68.10, H 5.80, N 8.02.
(E,E)-1,4-Dichloro-1,2,3,4-tetrakis(4-nitrophenyl)buta-1,3-diene
(5c): This compound was obtained by the oxidation of diarylacetyl-
ene 1c (200 mg, 0.75 mmol) with PbO2 (180 mg, 0.75 mmol) in
HSO3F (5 mL) at –50 °C in 2 h. Yield 143 mg (63%). M.p. 257–
260 °C (decomp.). 1H NMR (500 MHz, CDCl3, 25 °C): δ = 7.30
(d, J = 8.9 Hz, 4 H, Ar), 7.64 (d, J = 8.8 Hz, 4 H, Ar), 8.07 (d, J
= 8.9 Hz, 4 H, Ar), 8.15 (d, J = 8.8 Hz, 4 H, Ar) ppm. MS: m/z
(%) = 610 [M + 4]+, 608 [M + 2]+, 606 (28) [M]+, 571 (57), 525
(100), 358 (39). C28H16Cl2N4O8 (607.35): calcd. C 55.37, H 2.66,
N 9.22; found C 55.43, H 2.70, N 9.25.
1-(2-Acetyl-4,5-methylenedioxyphenyl)-2-(4-nitrophenyl)acetylene
(1j): This compound was obtained from (4-nitrophenyl)acetylene
and 1-acethyl-1-iodo-4,5-methylenedioxybenzene by the reported
procedure.[4a,4b] Yield 17%. M.p. 179–181 °C. 1H NMR (500 MHz,
CDCl3, 25 °C): δ = 2.71 (s, 3 H, Me), 6.08 (s, 2 H, OCH2O), 6.18
(s, 1 H, Ar), 7.30 (s, 1 H, Ar), 7.66 (d, J = 8.9 Hz, 2 H, Ar), 8.22
(d, J = 8.9 Hz, 2 H, Ar) ppm. MS: m/z = 309 [M]+. C17H11NO5
(309.27): calcd. C 66.02, H 3.58, N 4.53; found C 65.98, H 3.63, N
4.58.
(E,E)-1,4-Dichloro-1,2,3,4-tetrakis(3-nitrophenyl)buta-1,3-diene
(5d): This compound was obtained by the oxidation of diarylacetyl-
ene 1d (200 mg, 0.75 mmol) with PbO2 (180 mg, 0.75 mmol) in
HSO3F (5 mL) at –75 °C in 2 h. Yield 152 mg (67%). M.p. 292–
Experiments in Superacid HSO3F: Generation and identification of
ions 2a–h, 2j (Tables 1 and 2) and 3 by NMR in HSO3F at –80 and
1
0 °C were carried out by our reported method.[15] Ion 3: H NMR
(400 MHz, HSO3F, –80 °C): δ = 3.33 (s, 6 H, 2ϫMe), 3.38 (s, 6 H,
2ϫMe), 7.44 (s, 3 H, =CH, 2ϫNH+), 7.60 (d, J = 5.4 Hz, 4 H,
Ar), 7.72 (d, J = 5.4 Hz, 4 H, Ar) ppm.
1
294 °C. H NMR (500 MHz, CDCl3, 25 °C): δ = 7.63–7.68 (m, 4
H, Ar), 7.89–7.91 (m, 4 H, Ar), 8.06–8.18 (m, 6 H, Ar), 8.37 (t, J
= 2.0 Hz, 2 H, Ar) ppm. MS: m/z (%) = 610 [M + 4]+, 608 [M +
2]+, 606 (100) [M]+, 571 (74), 525 (69), 429 (20), 350 (34), 337 (26),
169 (29), 150 (30). C28H16Cl2N4O8 (607.35): calcd. C 55.37, H 2.66,
N 9.22; found C 55.35, H 2.70, N 9.23.
1,2-Bis(4-dimethylaminophenyl)ethanone (4): This compound was
obtained by the following procedure. Diarylacetylene 1i (200 mg)
was dissolved in HSO3F (3 mL) at –75 °C (dry ice/acetone bath).
After stirring at this temperature for 1 h, the reaction mixture was
quenched with an ice/water mixture (≈150 mL) and neutralised
with solid NaHCO3. The aqueous phase was extracted with diethyl
ether (3ϫ50 mL), and the organic layer was washed with saturated
NaHCO3 and water and then dried with Na2SO4. After solvent
evaporation under reduced pressure, the residue was purified by
column chromatography. Product 4 was isolated in 45 % yield
Conversion of Butadienes 5a–c into Naphthalenes 6a–c: Compounds
5a–c underwent spontaneous transformation into naphthalenes 6a–
c on keeping in the air at room temperature over ca. 1–2 months
(30–60 d). Compounds 6a–c were purified by recrystallisation.
6-Acetyl-2,3,4-tris(4-acetylphenyl)-1-chloronaphthalene (6a): This
compound was obtained from butadiene 5a (100 mg) in 60 d. Yield
30 mg (32%). Characteristics and X-ray analysis data were pub-
lished previously.[9]
1
(90 mg). M.p. 200–202 °C. H NMR (500 MHz, CDCl3, 25 °C): δ
= 2.86 (s, 6 H, 2ϫMe), 3.03 (s, 6 H, 2ϫMe), 4.02 (s, 2 H, CH2),
6.66 (d, J = 8.5 Hz, 2 H, Ar), 6.70 (d, J = 8.8 Hz, 2 H, Ar), 7.11
(d, J = 8.5 Hz, 2 H, Ar), 7.90 (d, J = 8.8 Hz, 2 H, Ar) ppm. MS:
m/z (%) = 282 (23) [M]+, 148 (100), 134 (45), 118 (12). C18H22N2O
(282.38): calcd. C 76.56, H 7.85, N 9.92; found C 76.59, H 7.90, N
10.01.
1-Chloro-6-cyano-2,3,4-tris(4-cyanophenyl)naphthalene (6b): This
compound was obtained from butadiene 5b (100 mg) in 60 d. Yield
49 mg (53%). Recrystallised from ethanol. M.p. 230–233 °C (de-
comp.). 1H NMR (500 MHz, CDCl3, 25 °C): δ = 6.86 (d, J =
8.2 Hz, 2 H, Ar), 7.19 (d, J = 8.3 Hz, 2 H, Ar), 7.21 (d, J = 8.6 Hz,
2 H, Ar), 7.27 (d, J = 8.6 Hz, 2 H, Ar), 7.55 (d, J = 8.2 Hz, 2 H,
Ar), 7.62 (d, J = 8.3 Hz, 2 H, Ar), 7.82 (d, J = 1.5 Hz, 1 H, Ar),
7.87 (dd, J = 8.8, 1.5 Hz, 1 H, Ar), 8.61 (d, J = 8.8 Hz, 1 H,
Ar) ppm. MS: m/z (%) = 492 [M + 2]+, 490 (100) [M]+, 455 (26).
C32H15ClN4 (490.94): calcd. C 78.29, H 3.08, N 11.41; found C
78.30, H 3.05, N 11.39.
General Procedure for Oxidation of Diarylacetylenes 1a–d in the
HSO3F/PbO2 System: Diarylacetylenes 1a–d (0.75 mmol) were dis-
solved in HSO3F (5 mL) at –75 °C (dry ice/acetone bath), and
PbO2 (0.75 mmol) was then added with vigorous magnetic stirring.
After stirring at –75 or –50 °C for 2–2.5 h (see below conditions
for synthesis of individual compounds), the reaction mixture was
quenched with frozen concentrated hydrochloric acid (≈50 mL) at
–60 °C. The mixture was diluted with water, and warmed up to
room temperature. Solid residue was filtered off, washed with water,
and dried in air. Finally, reaction products 5a–d were purified by
column chromatography.
1-Chloro-6-nitro-2,3,4-tris(4-nitrophenyl)naphthalene (6c): This
compound was obtained from butadiene 5c (100 mg) in 30 d. Yield
51 mg (45%). Recrystallised from acetone. M.p. Ͼ330 °C. 1H NMR
(500 MHz, CDCl3, 25 °C): δ = 7.44 (d, J = 8.6 Hz, 2 H, Ar), 7.61
(d, J = 8.5 Hz, 2 H, Ar), 7.67 (d, J = 8.4 Hz, 2 H, Ar), 7.88 (d, J
(E,E)-1,2,3,4-Tetrakis(4-acetylphenyl)-1,4-dichlorobuta-1,3-diene = 8.4 Hz, 2 H, Ar), 8.17 (d, J = 8.5 Hz, 2 H, Ar), 8.23 (d, J =
(5a): This compound was obtained by the oxidation of diarylacetyl- 8.6 Hz, 2 H, Ar), 8.42 (d, J = 2.2 Hz, 1 H, Ar), 8.56 (dd, J = 9.3,
Eur. J. Org. Chem. 2008, 4632–4639
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4637

A. V. Vasilyev, A. O. Shchukin, S. Walspurger, J. Sommer
FULL PAPER
[8]
[9]
A. P. Rudenko, Russ. J. Org. Chem. 1994, 30, 1946–1980.
A. O. Shchukin, A. V. Vasilyev, G. K. Fukin, Russ. J. Org.
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G. A. Olah, G. K. S. Prakash, J. Sommer, Superacids, Wiley,
New York. 1985.
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Buck, J. W. d. Haan, Recueil Trav. Chim. 1972, 91, 164–170; c)
A. E. v. d. Hout-Lodder, H. M. Buck, J. W. d. Haan, L. J. M.
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4937–4939; b) H.-U. Siehl, F.-P. Kaufman, K. Hori, J. Am.
Chem. Soc. 1992, 114, 9343–9349.
a) A. V. Vasilyev, S. Walspurger, M. Haouas, J. Sommer, P. Pale,
A. P. Rudenko, Org. Biomol. Chem. 2004, 2, 3483–3489; b)
A. V. Vasilyev, S. Walspurger, P. Pale, J. Sommer, M. Haouas,
A. P. Rudenko, Russ. J. Org. Chem. 2004, 40, 1769–1778; c) S.
Walspurger, A. V. Vasilyev, J. Sommer, P. Pale, P. Yu. Savechen-
kov, A. P. Rudenko, Russ. J. Org. Chem. 2005, 41, 1485–1492;
d) A. V. Vasilyev, S. Walspurger, S. Chassaing, P. Pale, J. Som-
mer, Eur. J. Org. Chem. 2007, 5740–5748.
a) P. Yu. Savechenkov, A. P. Rudenko, A. V. Vasilyev, G. K. Fu-
kin, Russ. J. Org. Chem. 2005, 41, 1316–1328; b) S. A. Aristov,
A. V. Vasilyev, G. K. Fukin, A. P. Rudenko, Russ. J. Org. Chem.
2007, 43, 691–705.
A. P. Rudenko, F. Pragst, Russ. J. Org. Chem. 1998, 34, 1589–
1626.
For the formation of cyclobutadiene cation radicals from al-
kynes, see: a) J. L. Courtneidge, A. G. Davis, J. Lusztyk, J.
Chem. Soc., Chem. Commun. 1983, 893–894; b) Q. B. Broxter-
man, H. Hogeveen, R. F. Kingma, Tetrahedron Lett. 1984, 25,
2043–2046.
2.2 Hz, 1 H, Ar), 8.78 (d, J = 9.3 Hz, 1 H, Ar) ppm. MS: m/z (%)
= 572 [M + 2]+, 570 (100) [M]+, 540 (20), 350 (24), 337 (20), 174
(18). C28H15ClN4O8 (570.89): calcd. C 58.91, H 2.65, N 9.81; found
C 58.94, H 2.65, N 9.80.
[10]
[11]
[12]
Oxidation of Diarylacetylene 1c in the HSO3F/PbO2 System with
Subsequent Reaction Quenching with Hydrobromic Acid: Diaryl-
acetylene 1c (200 mg, 0.75 mmol) was dissolved in HSO3F (5 mL)
at –50 °C (dry ice/acetone bath), and PbO2 (180 mg, 0.75 mmol)
was then added with vigorous magnetic stirring. After stirring at
this temperature during 2 h, the reaction mixture was quenched
with cooled concentrated hydrobromic acid (≈50 mL) at –60 °C.
The mixture was diluted with water, and allowed to warm to room
temperature. The solid residue was filtered off, washed with water,
and dried in air. Column chromatography separation of products
9 and 10 failed. Spectral characteristics of the individual com-
pounds 9 and 10 were obtained from the spectra of the mixture.
[13]
[14]
[15]
(E,E)-1,4-Dibromo-1,2,3,4-tetrakis(4-nitrophenyl)buta-1,3-diene (9):
1
Yield 50 mg (19%). H NMR (500 MHz, CDCl3, 25 °C): δ = 7.33
(d, J = 9.0 Hz, 4 H, Ar), 7.61 (d, J = 9.0 Hz, 4 H, Ar), 8.07 (d, J
= 9.0 Hz, 4 H, Ar), 8.11 (d, J = 9.0 Hz, 4 H, Ar) ppm. MS: m/z =
698 [M + 4]+, 696 [M + 2]+, 694 [M]+.
1-Bromo-6-nitro-2,3,4-tris(4-nitrophenyl)naphthalene (10): Yield
1
90 mg (39%). H NMR (500 MHz, CDCl3, 25 °C): δ = 7.29 (d, J
[16]
= 8.0 Hz, 2 H, Ar), 7.31 (d, J = 9.0 Hz, 2 H, Ar), 7.52 (d, J =
9.0 Hz, 2 H, Ar), 7.97 (d, J = 8.0 Hz, 2 H, Ar), 8.20 (d, J = 9.0 Hz,
2 H, Ar), 8.21 (d, J = 1.5 Hz, 1 H, Ar), 8.22 (d, J = 9.0 Hz, 2 H,
Ar), 8.27 (dd, J = 9.0, 1.5 Hz, 1 H, Ar), 8.78 (d, J = 9.0 Hz, 1 H,
Ar) ppm. MS: m/z = 616 [M + 2]+, 614 (100) [M]+.
[17]
[18]
Acknowledgments
[19]
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A.V.V and A.O.S. thank the Government of the City of Saint-Pe-
tersburg for financial support of this work. S.W. and J.S. thank the
Locker Hydrocarbon Research Institute, U.S.C., Los Angeles, for
continuous support.
[1] A. H. Haines, Methods for the Oxidation of Organic Com-
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[2] K. Yoshida, Electrooxidation in Organic Chemistry: The Role
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[5] Oxidation of acetylene ketones: a) A. V. Vasilyev, A. P. Rud-
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b) A. V. Vasilyev, A. P. Rudenko, S. A. Aristov, G. K. Fukin,
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mensky, P. Yu. Savechenkov, A. P. Rudenko, Russ. J. Org.
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[20]
[21]
[9]
See our preliminary communication for detailed analysis of
13C NMR spectra to verify the final isolation of butadienes 5
rather than cyclobutenes 7.
[22]
[23]
[24]
R. B. Woodward, R. Hoffman, The Conservation of Orbital
Symmetry, VCH, Weinheim, 1970.
Compare with X-ray analysis of (E,E)-1,2,3,4-tetraaryl-1,4-di-
fluorobutadiene-1,3 structures from ref.[7]
For other examples of such thermal electrocyclic reactions, see:
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[25]
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4638
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 4632–4639

One-Pot Synthesis of Polysubstituted Naphthalenes from Diarylacetylenes
[26] For the estimation of electron-withdrawing group power by
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Commun. 1966, 31, 65–89.
[28]
Review on the synthesis of substituted naphthalenes: C. B.
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[27] ESR spectra of other acetylenes: a) C. N. R. Rao, M. C. R. Sy-
mons, J. Chem. Soc. Perkin Trans. 2 1985, 991–1000; b) J. L.
Courtneidge, A. G. Davis, Acc. Chem. Res. 1987, 20, 90–97; c)
refs.[5b,5c]
Received: June 5, 2008
Published Online: August 15, 2008
Eur. J. Org. Chem. 2008, 4632–4639
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4639