Protonation and cyclization of 1,3-diarylpropynones in superacids

Article abstract of DOI:10.1007/s11178-005-0097-y

1,3-Diarylpropynones ArC≡CCOAr′ in superacids with H ₀ ranging from -20 to - 14 undergo protonation at the carbonyl oxygen atoms to give stable ArC≡CC(O⁺H)Ar′ ions or at the acetylenic C² atom with formation of reactive Ar

Full text of DOI:10.1007/s11178-005-0097-y

Russian Journal of Organic Chemistry, Vol. 40, No. 12, 2004, pp. 1769–1778. Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 12, 2004,
pp. 1819–1828.
Original Russian Text Copyright © 2004 by Vasil’ev, Walspurger, Pale, Sommer, Haouas, Rudenko.
Protonation and Cyclization of 1,3-Diarylpropynones
in Superacids
A. V. Vasil’ev1, S. Walspurger2, P. Pale2, J. Sommer2, M. Haouas2, and A. P. Rudenko1
1 St. Petersburg State Academy of Forestry Engineering, Institutskii per. 5, St. Petersburg, 194021 Russia
e-mail: aleksvasil@hotmail.com
2 Universite L. Pasteur, rue B. Pascal 4, Strasbourg, 67000 France
Received May 14, 2004
Abstract—1,3-Diarylpropynones ArC≡CCOAr' in superacids with H0 ranging from –20 to –14 undergo
protonation at the carbonyl oxygen atoms to give stable ArC≡CC(O+H)Ar' ions or at the acetylenic C2 atom
with formation of reactive ArC+=CHCOAr' species. The effects of the Ar and Ar' substituents and reaction
conditions on the intramolecular cyclization of ArC+=CHCOAr' to 3-arylinden-1-ones are discussed.
Superacids [1] are widely used as reaction medium
for generation and study of various carbocations [2, 3],
radical cations [4], and other long-lived charged inter-
mediates [1]. Despite numerous publications on this
topic [5], information on the behavior of acetylene
derivatives in superacids is scanty. Stang [6] and Olah
[7] showed that trifluoromethanesulfonic acid and
fluorosulfonic acid add to alkynes with formation of
the corresponding vinyl trifluoromethanesulfonates
and fluorosulfonates. According to the NMR data,
some substituted acetylenes in HSO3F undergo trans-
formation into cyclobutenyl cations with subsequent
oligomerization of the latter [7, 8]. These reactions
were postulated to involve generation of reactive
vinyl-like cations via protonation of carbon atom at
the triple bond. In 1992, Siehl et al. [9] were the first
to detect arylvinyl cations as kinetically independent
species in the system HSO3F–SbF5 and characterize
–80 and 0°C) and their neutral precursors. The signals
in the C NMR spectra were unambiguously assigned
13
on the basis of the proton-coupled spectra and using
HSQC, HMQC, and HMBC two-dimensional hetero-
nuclear correlation techniques [10]. The spectral data
given in Table 2 were obtained from the proton-
decoupled spectra.
The 1H NMR spectra of protonated species IIa–IIm
in HSO3F at –80°C displayed a sharp singlet in the
region δ 12–13.5 ppm, which corresponds to proton
attached to the carbonyl oxygen atom. According to
the signal intensities, alkynones Ia–Im in HSO3F are
protonated completely (Table 1). At 0°C, the above
signal disappears due to fast exchange with the acidic
medium. Diynediones Il and Im in HSO3F undergo
protonation at both carbonyl groups to give the cor-
responding dications IIl and IIm (Scheme 1, Table 1).
1
In the H NMR spectra of compounds Ia–Im in
1
them by H and 13C NMR spectra. Analysis of the
HSO3F we observed no signals assignable to protons
attached to electron-acceptor groups R (NO2, CN,
COMe, CO2Me). The NO2 and CN groups in organic
compounds are solvated by HSO3F [4], and their
protonation occurs in systems with higher acidity, e.g.,
in HSO3F–SbF5 [2, vol. 4, p. 1773]. As follows from
available experimental data shows that the chemistry
of acetylenic compounds in superacids still remains an
unexplored area of organic chemistry.
The goal of the present work was to examine
protonation of 1,3-diarylpropynones in superacids by
1H and 13C NMR spectroscopy, as well as to isolate and
identify products of their transformations. Scheme 1
illustrates the formation of O-protonated species IIa–
IIm from acetylenic ketones Ia–Im in HSO3F. The
1H NMR spectra of IIa–IIm in HSO3F at –80°C are
given in Table 1, and Table 2 contains the 13C NMR
spectra of cations IIa, IIg, IIi, IIj, and IIm (HSO3F,
13
the C NMR spectrum of cation IIj, the acetyl group
therein is protonated. The chemical shift of the carbon-
yl carbon atom in the acetyl group is δC 222.79 ppm
at –80°C (Table 2), i.e., it falls into the δC range 210–
223 ppm typical of protonated substituted aceto-
phenones in HSO3F and HSO3F–SbF5 [11]. The same
applies to the substituent R = CO2Me in IIk. The
1070-4280/04/4012-1769 © 2004 MAIK “Nauka/Interperiodica”

VASIL’EV et al.
1770
Scheme 1.
3
5
2
O
OH
α
C
β
C
1
4
HSO3F
C
C
C
C
1'
2'
R
R
6
3'
4'
Ia–Im
IIa–IIm
OH
OH
C
C
C
C
C
C
R
R
IIIa–IIIm
IVa–IVm
Ia–Im, IIa–IIi, IIIa–IIIi, IVa–IVi, R = H (a), 4-Me (b), 2,4,6-Me3 (c), 3-NO2 (d), 4-NO2 (e), 4-CN (f), 4-MeO-3-NO2 (g), 2,4,6-
Me3-3-NO-2 (h), 2,3,5,6-Me4-4-NO2 (i), 4-COMe (j), 4-CO2Me (k), 4-PhCOC2 (l), 2,3,5,6-Me4-4-PhCOC2 (m); IIj–IIm, IIIj–IIIm,
IVj–IVm, R = 4-C(OH+)Me (j), 4-C(O)(OH+)Me (k), 4-PhC(OH+)C≡C (l), 2,3,5,6-Me4-4-PhC(OH+)C≡C (m).
observed well resolved multiplets typical of aromatic
systems.
different behaviors of the groups R in HSO3F (NO2
and CN in IId–IIi and COMe and CO2Me in IIj and
IIk) are reflected in Scheme 1.
Insofar as fluorosulfonic acid at –80°C is fairly
viscous, signals from aromatic protons in the 1H NMR
spectra of ions IIa–IIm appear mostly as broadened
singlets without fine structure (Table 1). At 0°C, we
The results of our NMR studies allowed us to draw
some conclusions concerning the structure and positive
1
charge delocalization in the examined species. The H
NMR spectra of IIa–IIm, recorded at –80°C, indicated
that the ortho- (2'-H) and meta-protons (3'-H) in the
Table 1. 1H NMR spectra of protonated species IIa–IIm in HSO3F at –80°C
Chemical shifts δ, ppm (J, Hz)
Ion no.
C=OH+
Harom
R
–
12.75 s (1H) 7.58 s (2H), 7.78 s (3H), 7.98 s (2H), 8.16 s (1H), 8.51 s (2H)
12.30 s (1H) 7.44 s (2H), 7.77 s (1H), 7.80 s (1H), 7.92 s (2H), 8.28 s (1H)
IIa
IIb
IIc
2.47 s (3H, Me)
12.07 s (1H) 7.00 s (2H), 7.79 s (2H), 8.13 s (1H), 8.35 s (1H), 8.45 s (1H), 2.28 s (3H, Me), 2.62 s (6H, 2Me)
8.50 s (1H), 8.53 s (1H)
13.15 s (1H) 7.89 s (1H), 7.97 s (1H), 8.07 s (1H), 8.34 s (1H), 8.58 s (1H),
8.69 s (1H), 8.82 s (1H), 8.88 s (1H), 9.13 s (1H)
–
IId
13.24 s (1H) 7.89 s (1H), 7.96 s (1H), 8.35 s (3H), 8.65 s (3H), 8.84 s (1H)
–
–
IIe
IIf
13.26 s (1H) 7.89 t (1H, J = 6.5), 7.95 t (1H, J = 6.5), 8.34 d (2H, J = 6.2),
8.35 t (1H, J = 6.5), 8.41 d (2H, J = 6.2), 8.69 d (1H, J = 6.5),
8.84 d (1H, J = 6.5)
12.87 s (1H) 7.67 d (1H, J = 8.7), 7.64 t (1H, J = 7.0), 7.81 t (1H, J = 7.0), 4.43 s (3H, MeO)
8.19 t (1H, J = 7.0), 8.53 d (1H, J = 7.0), 8.56 d (1H, J = 8.7),
8.68 d (1H, J = 7.0), 9.17 s (1H)
IIg
12.86 s (1H) 7.54 s (1H), 7.87 s (1H), 7.93 s (1H), 8.28 s (1H), 8.67 s (2H)
13.36 s (1H) 7.83 s (1H), 7.90 s (1H), 8.23 s (1H), 8.63 s (1H), 8.67 s (1H)
13.50 s (1H) 7.90 s (1H), 7.96 s (1H), 8.37 s (3H), 8.72 s (3H), 8.87 s (1H)
2.61 s (3H, Me), 2.85 s (6H, 2Me)
IIh
IIi
2,26 s (6H, 2Me), 2.74 s (6H, 2Me)
3.51 s (3H, Me)
IIj
IIk
13.19 s (1H) 7.88 s (1H), 7.94 s (1H), 8.35 s (3H), 8.39 s (2H), 8.68 s (1H), 4.73 s (3H, Me)
8.83 s (1H)
IIla
13.47 s (2H) 7.90 s (4H), 8.33 s (6H), 8.69 s (2H), 8.85 s (2H)
IIma 12.84 s (2H) 7.87 s (2H), 7.92 s (2H), 8.28 s (2H), 8.67 s (2H), 8.71 s (2H)
–
2.77 s (12H, 4Me)
a
Dication.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

PROTONATION AND CYCLIZATION OF 1,3-DIARYLPROPYNONES
1771
Table 2. 13C NMR spectra of 1,3-diarylpropynones Ia, Ig, Ii, Ij, and Im (CDCl3, 25°C) and their protonated forms IIa, IIg,
IIi, IIj, and IIm in HSO3F
Chemical shifts δC, ppma
Comp.
no.
Tempera-
ture, °C
Solvent
C=Ob Cα
Cβ
C1'
C2' c
C3'
C4'
C1 C2, C6 C3, C5 C4
R
–
CDCl3
HSO3F
25
177.92 86.87 093.03 136.89 ~129.52 128.57 134.04 120.11 133.00 128.64 130.73
Ia
–80– 181.87 87.93 116.45 129.68 ~132.18, 131.08 145.07 129.90 137.1 130.21 137.85
~139.84
–
IIa
00
25
183.18 88.59 117.06 130.74 ~136.5 131.47 145.34 131.16 137.38 130.54 138.12
–
CDCl3
HSO3F
177.53 87.32 090.01 136.55 ~129.53 128.73 134.38 112.31 130.27, 139.53, 154.53 56.87
138.72 114.00
Ig
–800 183.38 86.73 119.56 130.19 ~133.16, 131.45 146.84 112.48 138.31, 131.57, 165.16 61.12
~141.44 151.18 118.28
IIg
00
183.82 86.67 122.14 130.70 ~136.0 131.72 146.68 111.53 137.56, 134.37, 164.14 60.20
146.68 118.05
CDCl3
HSO3F
25
177.67 89.69 095.52 136.87 ~129.50 128.74 134.24 122.31 140.03 124.85 153.69 14.51, 18.52
Ii
–800 183.08 93.96 120.79 130.58 ~132.83, 131.32 145.58 123.15 146.22 127.33 154.92 14.14, 18.76
~140.04
IIi
00
25
183.99 94.68 121.43 131.21 ~137.0 131.84 146.41 124.81 146.53 127.99 156.02 14.24, 18.93
CDCl3
HSO3F
177.67 88.72 091.12 136.60 ~129.60 128.71 134.40 124.68 133.06 128.37 138.08 197.0 (C=O),
26.69 (CH3)
Ij
–800 184.35 87.71 118.11 130.16 ~133.71, 131.66 147.81 130.30
~142.30
136.60d
133.06 222.79
(C=OH+),
26.39 (CH3)
IIj
00
185.06 88.22 118.54 130.81 ~136.0 132.14 148.49 130.92 136.63 135.37 133.49 232.36
(C=OH+),
26.47 (CH3)
CDCl3
HSO3F
25
177.84 91.23 096.03 137.03 ~129.53 128.70 134.12 122.74 138.07
–
–
–
–
18.58
18.75
Im
–800 183.13 95.18 123.59 130.66 ~133.12, 131.49 146.13 124.50 143.78
~140.42
IIm
00
183.90 95.64 124.56 131.33 ~136.0 131.86 146.51 125.01 143.96
–
–
18.71
a
For atom numbering, see Scheme 1.
C=OH+ in HSO3F.
b
c
d
Two C2' signals were observed in HSO3F at –80°C (for details, see text).
Merged signals..
Nonequivalence of the C2' nuclei in IIIa–IIIm was
also revealed by 13C NMR spectroscopy. The spectra
of IIa, IIg, IIi, IIj, and IIm at –80°C contained
two different signals from the ortho-carbon atoms, at
δ 132–134 and 140–142 ppm. At 0°C, one broadened
signal at δ 136–137 ppm was observed (Table 2).
An analogous pattern was observed previously for
acetophenone derivatives in superacids [11].
phenyl ring neighboring to the carbonyl group are
nonequivalent. For example, in the spectrum of IIf
we observed two triplets at δ 7.89 and 7.95 ppm,
belonging to the meta-protons (3'-H), and two doublets
at δ 8.69 and 8.84 ppm, which correspond to the
ortho-protons (2'-H) (Table 1). These data suggest that
O-protonated species are contributed by structures
IIIa–IIIm where rotation about the C1'–C(O) bond is
restricted at –80°C. No difference in the chemical
shifts of the meta- and ortho-protons was found at 0°C:
the spectrum contained a doublet at δ 8.74 ppm (2'-H)
and a triplet at δ 7.91 ppm (3'-H). Analogous patterns
were typical of the other cations.
13
Comparison of the C NMR parameters (Table 2)
of the initial ketones (CDCl3, 25°C) and their pro-
tonated forms (HSO3F, –80 and 0°C) shows that both
the phenyl ring conjugated with the carbonyl group
and the arylacetylene moiety participate in delocaliza-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

VASIL’EV et al.
1772
Scheme 2.
O
1
2
3
8
7
(1) H+
O
6
(2) H2O
R
C
C
C
9
R'
4
5
R
R'
Ia, Ib, In–Iq
Va, Vb, Vn–Vq
I, R = MeO, R' = H (n), 3-MeO (o), 3,4-Me2 (p); R = H, R' = 3-MeO (q); V, R = H, R' = H (a); R = Me, R' = H (b); R = MeO,
R' = H (n), 6-MeO (o), 5,6-Me2 (p); R = H, R' = 6-MeO (q).
tion of the positive charge on the carbonyl oxygen
atom in IIa, IIg, IIi, IIj, and IIm. The signal of the Cβ
atom (Scheme 1) in the protonated species is located
~23–32 ppm downfield relative to the corresponding
signal in the spectra of the neutral precursors. This
suggests that resonance structures like IVa–IVm
(Scheme 1) also contribute to delocalization of the
positive charge.
run nos. 6–9), whereas analogous transformations of
ketones Ia, Ib, Iq occurred only in CF3SO3H–SbF5,
17 mol %; H0 ≈ –19) [1] (cf. run nos. 1 and 2, 3 and 4,
and 10 and 11). Likewise, indenone Vb was formed
from compound Ib in HF–SbF5 (2 mol %, H0 ≈ –20)
[1] (run no. 5).
Compounds Io and Iq having a methoxy group in
the meta position (R' = 3-MeO) gave rise to only one
regioisomer Vo and Vq, respectively; this means that
the cyclization involves the para-position with respect
to the methoxy group (Scheme 2). One isomer Vp was
also obtained from ketone Ip.
Considerable differences in the chemical shifts of
C2', C3', and C4' between neutral ketones I and the cor-
responding protonated species indicate a considerable
contribution of the phenyl ring conjugated with the
carbonyl group to delocalization of the positive charge
(structures IIIa–IIIm in Scheme 1). In going from
ketones Ia, Ig, Ii, Ij, and Im to cations IIa, IIg, IIi,
IIj, and IIm (HSO3F), the signal from C4' shifts down-
field by ~11–14 ppm. The chemical shifts of the two
nonequivalent C2' nuclei in the cations (–80°C) are
greater than that of C2' in the intitial ketone by 2.5–4
and 10–13 ppm, respectively (Table 2).
Intramolecular cyclization of 1,3-diarylpropynones
in superacids may be regarded as a new efficient
procedure for the synthesis of 3-arylindenones (reac-
tion time 15–30 min; yield up to 95%; Table 3). Other
methods of synthesis of indenone derivatives from
acetylenic compounds are based on coupling reactions
which require expensive metal-complex catalysts [12]
or on reactions of alkynes with aroyl chlorides in the
presence of AlCl3 [13].
Ketones I in which the substituent R is a hydrogen
atom (Ia), alkyl group (Ib, Ic), or electron-acceptor
group (Id–Im) exist in HSO3F as stable O-protonated
species IIa–IIm, while methoxy derivatives (R =
p-MeO) are rapidly converted into secondary ionic
products even at –80°C. Substrates containing a para-
methoxy group undergo protonation at the acetylenic
Cα atom to give reactive vinyl cations which cannot be
detected by NMR spectroscopy.
We also examined by NMR spectroscopy the be-
havior of 3-arylindenones in superacids. According to
the NMR data, both indenone Vp and the correspond-
ing ketone Ip in CF3SO3H at –30°C give rise to the
same species, O,C-diprotonated 3-arylindenone VIp
(Scheme 3). Table 4 contains the spectral parameters of
dications VIp and VIo. The latter was also generated
in situ in CF3SO3H at –30°C in an NMR ampule in two
ways, from diarylpropynone Io or indenone Vo. These
data support the formation of O,C-diprotonated 3-aryl-
In order to elucidate transformation pathways of
1,3-diarylpropynones in superacids, some experiments
were carried out on a preparative scale. We found that
ketones Ia, Ib, and In–Iq are converted into the
corresponding 3-arylinden-1-ones Va, Vb, and Vn–Vq
as a result of intramolecular cyclization (Scheme 2,
Table 3). Methoxy-substituted derivatives In–Ip were
readily transformed into compounds Vn–Vp by the ac-
tion of CF3SO3H (H0 = –14.1 [1]) or HSO3F (Table 3,
1
indenone species. In the H NMR spectra of VIo and
VIp, a singlet was present at δ ~5.0 ppm which
13
belongs to the CH2 protons (Table 4). In the C NMR
spectra, characteristic signals appeared at δ 45–46
(C2H2), 183–186 (C3 cationic center), and 214–217 ppm
(C=OH+) (Table 4). The observed spectral data re-
semble those reported for the corresponding structural
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

PROTONATION AND CYCLIZATION OF 1,3-DIARYLPROPYNONES
1773
Table 3. Conditions of synthesis of 3-arylindenones Va, Vb, and Vn–Vq from 1,3-diarylpropynones Ia, Ib, and In–Iq,
respectively, in different acid systems
Run Comp. Amount
Temperature,
°C
Acid system
CF3SO3H (3 ml)
Time, min.
Product (yield, %)
no.
01
02
03
04
05
06
07
08
09
10
11
no.
Ia
Ia
Ib
Ib
Ib
In
Io
Ip
Ip
Iq
Iq
of I, mmol
0.5
30
30
25
25
Ia (100)
Va (43)
Ib (100)
Vb (75)
Vb (60)
Vn (54)
Vo (95)
Vp (95)
Vp (71)
Iq (100)
Vq (61)
0.5
CF3SO3H (2 ml)–SbF5 (0.98 g, 17 mol %)
CF3SO3H (3 ml)
0.5
30
25
0.5
CF3SO3H (2 ml)–SbF5 (0.98 g, 17 mol %)
HF (5 ml)–SbF5 (1.1 g, 2 mol %)
CF3SO3H (2 ml)
30
25
1.0
30
00
0.4
15
–30–
–30–
–30–
–75–
25
0.4
CF3SO3H (2 ml)
15
0.4
CF3SO3H (2 ml)
15
1.0
HSO3F (5 ml)
1200
30
0.5
CF3SO3H (2 ml)
0.5
CF3SO3H (2 ml)–SbF5 (0.98 g, 17 mol %)
30
25
fragments of O,C-diprotonated 4-phenyl-3-buten-2-one
[14] and diprotonated naphthols [15]. In the H NMR
On the basis of our experimental data on the
protonation of 1,3-diarylpropynones and their trans-
formations in superacids, we propose a mechanism for
intramolecular cyclization of compounds I to 3-aryl-
indenones V (Scheme 4). According to Scheme 4, the
key intermediate is reactive vinyl cation A which can
be formed either (1) by direct protonation of substrate
I (which is present in a small concentration in the
equilibrium mixture with cation II) at the Cα atom or
(2) via slow second protonation of cation II with
simultaneous deprotonation of the carbonyl group.
Intramolecular electrophilic substitution in cation A
gives cation B which is transformed (through a pro-
tonation–deprotonation sequence) into very stable di-
cation VI; deprotonation of VI during treatment of the
1
spectra of VIo and VIp, four aromatic protons, 2'-H,
2''-H, 3'-H, and 3''-H (Scheme 3) give four separate
signals (Table 4), indicating a large contribution of
structures VIIo and VIIp, where rotation about the
C3–C1' bond is restricted and the positive charge is
delocalized over the methoxyphenyl fragment.
It should be noted that mixing of ketones Io and
Ip with trifluoromethanesulfonic acid at –30°C in
an NMR ampule gives rise to intensely colored solu-
tions due to formation of stable dications VIo and VIp.
According to the NMR data, these cations are quan-
titatively formed from compounds Io and Ip within
several minutes.
Scheme 3.
O
MeO
C
C
C
Me
OH
OH
H
H
Me
CF3SO3H
–30°C
H
H
Ip
2'
Me
1'
Me
3'
4'
O
2''
Me
Me
3''
MeO
MeO
VIp
VIIp
Me
Me
MeO
Vp
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

VASIL’EV et al.
Scheme 4.
OH
1774
H+
C
O
O
H
H+
Ar
C
C
C
Ar
C
C
C
Ar
C
C
R'
R'
R'
I
II
III
O
HO
Ar
O
H
O
2H+
–H+
H
H
C
C
H
R
R
H
R
Ar
–2H+
H
Ar
Ar
R'
A
B
VI
V
H+
I
shielded charged Cβ atom. Studies on the formation of
such cations and their transformations in superacids
will open new prospects in the chemistry of alkynes.
reaction mixture leads to indenone V as final product.
Reaction channel (2) is possible only in strongly acidic
media like CF3SO3H–SbF5 and for compounds with
a sufficiently basic Cα atom. The basicity of the latter
strongly depends on mutual arrangement of substit-
uents in the aryl fragment, and it sharply increases in
going to para-methoxy-substituted substrates. Taking
into account the data on electrophilic reactions of
3-arylpropynoic acid esters in HSO3F and intermolec-
ular reactions of vinyl cations ArC+=CHCO2R generat-
ed therefrom [16], it should be assumed that the trans-
formation of acetylenic ketones I into indenones V in
media with moderate acidity (such as CF3SO3H and
HSO3F) follows channel (1).
EXPERIMENTAL
1
The H and 13C NMR spectra were recorded on
Bruker AM-500 (500 and 125.76 MHz, respectively)
and Bruker AVANCE-300 spectrometers (300 and
75 MHz, respectively) from solutions in chloroform-d
and acetone-d6. The proton chemical shifts were
measured relative to the residual solvent signals
[CHCl3, δ 7.25 ppm; (CHD2)2CO, δ 2.05 ppm], and
the 13C chemical shifts were measured relative to the
1
CDCl3 signal (δC 77.0 ppm). The H and 13C NMR
In order to detect by spectral methods exotic vinyl
cations ArC+=CHCOX with an electron-acceptor group
X (X = Ar, Alk, OAlk, CF3) as kinetically independent
species, special studies should be performed in super-
aicds at very low temperature using substrates with
a weakly nucleophilic aromatic ring and spatially
spectra in superacids (HSO3F and CF3SO3H) were
obtained on a Bruker AVANCE-400 spectrometer at
400 and 100 MHz, respectively, using CH2Cl2 as
internal reference (δ 5.32 ppm, δC 53.84 ppm). The
IR spectra of solutions in CHCl3 were recorded on
a Specord 75IR spectrometer. The mass spectra
Table 4. 1H and 13C NMR spectra of O,C-diprotonated 3-arylindenones VIo and VIp in CF3SO3H at –30°C
1H NMR spectrum, δ, ppm
13C NMR spectrum, δC, ppm
Ion no.
4.25 s (3H, OMe), 4.48 s (3H, OMe), 5.07 s (2H, CH2), 45.71 (CH2), 58.65, 60.93, 130.31, 134.07, 136.98,
VIo
7.52 s (1H, Harom), 7.60 s (1H, Harom), 8.10 s (2H, Harom),
142.42, 142.70, 145.48, 148.12, 171.73, 174.20,
183.71(C3), 217.07 (C=OH+)
a
8.47 s (1H, Harom), 8.84 s (1H, Harom), 9.04 s (1H, Harom
)
2.72 s (3H, Me), 2.82 s (3H, Me), 4.56 s (3H, OMe), 5.05 s 21.37, 22.70, 45.01 (CH2), 61.90, 131.62, 132.88,
(2H, CH2), 7.57 s (1H, Harom), 7.64 s (1H, Harom), 8.47 s 135.61, 136.23, 148.67, 145.90, 162.11, 174.22,
VIp
(1H, Harom), 8.51 s (1H, Harom), 8.70 s (1H, Harom), 9.19 s 186.20 (C3), 214.28 (C=OH+)
a
(1H, Harom
)
a
Signal from the acidic proton on the carbonyl oxygen atom is not observed owing to fast exchange with CF3SO3H.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

PROTONATION AND CYCLIZATION OF 1,3-DIARYLPROPYNONES
1775
(70 eV) were run on MKh-1321 and TSQ 700 Finigan
MAT instruments.
3-(4-Cyanophenyl)-1-phenylpropynone (If).
Yield 51%, mp 151–152°C. IR spectrum, ν, cm–1:1640
1
(C=O), 2210 (C≡C), 2230 (C≡N). H NMR spectrum
The purity of the initial compounds and reaction
products was checked by TLC on Silufol UV-254
plates. The reaction mixtures were separated by
column chromatography on Silica gel 60 (40–63 µm,
Merck) using gradient elution with diethyl ether–
hexane mixtures. The yields were determined from the
fractions isolated by column chromatography.
(500 MHz, CDCl3), δ, ppm: 7.51 t (2H, Harom, J =
7.8 Hz), 7.65 t (1H, Harom, J = 7.8 Hz), 7.70 d (2H,
Harom, J 8.3 Hz), 7.75 d (2H, Harom, J = 8.3 Hz), 8.18 d
(2H, Harom, J = 7.8 Hz). 13C NMR spectrum (125 MHz,
CDCl3), δC, ppm: 89.33, 89.56, 113.99, 117.78, 124.87,
128.73, 129.55, 132.24, 133.20, 134.52, 136.40, 177.33.
Mass spectrum: m/z 231 [M]+. Found, %: C 83.10;
H 3.92; N 6.06. C16H9NO. Calculated, %: C 82.98;
H 4.00; N 6.01. M 231.25.
Initial 1,3-diarylpropynones (Ia–Iq) were synthe-
sized by the procedure developed by us previously
[17]; the data for 1,3-diphenylpropynone (Ia) were
reported in [17].
3-(4-Methoxy-3-nitrophenyl)-1-phenylpropyn-
one (Ig). Yield 57%, mp 138–141°C. IR spectrum, ν,
1
cm–1: 1630 (C=O), 2195 (C≡C). H NMR spectrum
3-(4-Methylphenyl)-1-phenylpropynone (Ib).
Yield 66%, mp 57–59°C; published data [18]: mp 58.5–
59°C. IR spectrum, ν, cm–1: 1630, 1635 (C=O), 2195
(500 MHz, acetone-d6), δ, ppm: 4.09 s (3H, MeO),
7.51 d (1H, Harom, J = 8.9 Hz), 7.60 t (2H, Harom, J =
7.5 Hz), 7.73 t (1H, Harom, J = 7.5 Hz), 8.05 d.d (1H,
1
(C≡C). H NMR spectrum (500 MHz, acetone-d6), δ,
ppm: 2.41 s (3H, Me), 7.34 d (2H, Harom, J = 8.0 Hz),
7.61 t (2H, Harom, J = 7.5 Hz), 7.68 (2H, Harom, J =
8.0 Hz), 7.72 t (1H, Harom, J = 7.5 Hz), 8.23 d (2H,
H
arom, J = 8.9, 2.0 Hz), 8.25 d (2H, Harom, J = 7.5 Hz),
8.28 (1H, Harom, J = 2.0 Hz). Mass spectrum: m/z 281
[M]+. Found, %: C 68.33; H 3.94; N 4.98. C16H11NO4.
Calculated, %: C 68.19; H 4.08; N 5.12. M 281.27.
H
arom, J = 7.5 Hz). 13C NMR spectrum (125 MHz,
CDCl3), δC, ppm: 21.75, 86.81, 93.84, 116.96, 128.60,
1-Phenyl-3-(2,4,6-trimethyl-3-nitrophenyl)pro-
129.50, 129.53, 133.12, 134.02, 136.96, 141.58, 178.00.
pynone (Ih). Yield 24%, mp 137–139°C. IR spectrum,
1
ν, cm–1: 1645 (C=O), 2200 (C≡C). H NMR spectrum
1-Phenyl-3-(2,4,6-trimethylphenyl)propynone
(Ic). Yield 72%, mp 71–73°C; published data [19]:
mp 69–70°C. IR spectrum, ν, cm–1: 1620 (C=O), 2190
(500 MHz, CDCl3), δ, ppm: 2.30 s (3H, Me), 2.50 s
(3H, Me), 2.56 s (3H, Me), 7.06 s (1Harom), 7.51 t
(2H, Harom, J = 7.6 Hz), 7.63 t (1H, Harom, J = 7.5 Hz),
8.18 d (2H, Harom, J = 7.5 Hz). 13C NMR spectrum
(125 MHz, CDCl3), δC, ppm: 16.50, 17.67, 21.24,
88.19, 95.49, 119.70, 128.75, 129.46, 130.07, 131.68,
133.55, 134.29, 136.78, 144.44, 150.40, 177.55. Mass
spectrum: m/z 293 [M]+. Found, %: C 73.71; H 5.15;
N 4.78. C18H15NO3. Calculated, %: C 73.85; H 5.11;
N 4.82. M 293.32.
1
(C≡C). H NMR spectrum (500 MHz, acetone-d6),
δ, ppm: 2.31 s (3H, Me), 2.52 s (6H, Me), 7.02 s
(2H, Harom), 7.59–7.73 m (3H, Harom), 8.23–8.25 m
(2H, Harom).
3-(3-Nitrophenyl)-1-phenylpropynone (Id). Yield
73%, mp 149–151°C; published data [20]: mp 151–
152°C. IR spectrum, ν, cm–1: 1640 (C=O), 2205
(C≡C). 1H NMR spectrum (500 MHz, CDCl3), δ, ppm:
7.53 t (2H, Harom, J = 7.5 Hz), 7.61–7.67 m (2H, Harom),
7.97 d (1H, Harom, J = 7.5 Hz), 8.19 d (2H, Harom, J =
7.5 Hz), 8.31 d (1H, Harom, J = 8.2 Hz), 8.49 s (1H,
Harom). 13C NMR spectrum (125 MHz, CDCl3), δC,
ppm: 87.99, 89.01, 122.00, 125.24, 127.58, 128.80,
129.61, 129.92, 134.60, 136.39, 138.42, 148.16, 177.36.
1-Phenyl-3-(2,3,5,6-tetramethyl-4-nitrophenyl)-
propynone (Ii). Yield 40%, mp 159–160°C. IR spec-
1
trum, ν, cm–1: 1625 (C=O), 2195 (C≡C). H NMR
spec-trum (500 MHz, CDCl3), δ, ppm: 2.16 s (6H,
Me), 2.54 s (6H, Me), 7.52 t (2H, Harom, J = 7.5 Hz),
7.64 t (1H, Harom, J = 7.5 Hz), 8.20 d (2H, Harom, J =
7.5 Hz). Mass spectrum: m/z 307 [M]+. Found, %:
C 74.25; H 5.58; N 4.56. C19H17NO3. Calculated, %:
C 74.27; H 5.58; N 4.60. M 307.35.
3-(4-Nitrophenyl)-1-phenylpropynone (Ie). Yield
69%, mp 146–148°C; published data [20]: mp 148–
149°C. 1H NMR spectrum (500 MHz, CDCl3), δ, ppm:
7.54 t (2H, Harom, J = 7.4 Hz), 7.66 t (1H, Harom, J =
7.4 Hz), 7.83 d (2H, Harom, J = 8.8 Hz), 8.19 d (2H,
3-(4-Acetylphenyl)-1-phenylpropynone (Ij). Yield
46%, mp 115–117°C. IR spectrum, ν, cm–1: 1630
1
H
arom, J = 7.4 Hz), 8.28 d (2H, Harom, J = 8.8 Hz).
(C=O), 1685 (CH3C=O), 2200 (C≡C). H NMR spec-
13C NMR spectrum (125 MHz, CDCl3), δC, ppm:
89.13, 89.82, 123.78, 126.74, 128.78, 129.58, 133.61,
134.60, 136.38, 148.51, 177.29.
trum (500 MHz, CDCl3), δ, ppm: 2.61 s (3H, Me), 7.51
t (2H, Harom, J = 7.3 Hz), 7.63 t (1H, Harom, J = 7.3 Hz),
7.74 d (2H, Harom, J = 8.3 Hz), 7.98 d (2H, Harom, J =
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

VASIL’EV et al.
1776
8.3 Hz), 8.19 d (2H, Harom, J = 7.3 Hz). Mass spec-
trum: m/z 248 [M]+. Found, %: C 82.24; H 4.87.
C17H12O2. Calculated, %: C 82.19; H 4.86. M 248.28.
8.1, 1.9 Hz). 13C NMR spectrum (75 MHz, CDCl3), δC,
ppm: 55.44, 55.48, 86.96, 94.21, 111.88, 112.80,
114.44, 120.72, 122.75, 129.58, 135.16, 138.44,
159.78, 161.76, 177.78. Mass spectrum: m/z 266 [M]+.
Found, %: C 76.68; H 5.30. C17H14O3. Calculated, %:
C 76.22; H 5.27. M 266.30.
1-(3,4-Dimethylphenyl)-3-(4-methoxyphenyl)-
propynone (Ip). Yield 65%, mp 103–104.5°C.
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 2.33 s
(6H, Me), 3.84 s (3H, MeO), 6.92 d (2H, Harom, J =
8.8 Hz), 7.25 d (1H, Harom, J = 8.3 Hz), 7.62 d (2H,
Harom, J = 8.8 Hz), 7.94–7.97 m (2H, Harom). 13C NMR
spectrum (75 MHz, CDCl3), δC, ppm: 19.77, 20.18,
55.41, 86.98, 93.60, 112.08, 114.38, 127.53, 129.83,
130.23, 135.03, 135.10, 136.97, 143.77, 161.60, 177.97.
Mass spectrum: m/z 264 [M]+. Found, %: C 81.79;
H 6.10. C18H16O2. Calculated, %: C 81.77; H 6.05.
M 264.32.
3-(4-Methoxycarbonylphenyl)-1-phenylpropyn-
one (Ik). Yield 60%, mp 98–100°C. IR spectrum, ν,
cm–1: 1640 (C=O), 1725 (C=O, ester), 2210 (C≡C).
1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 3.92 s
(3H, Me), 7.51 t (2H, Harom, J = 7.5 Hz), 7.63 t
(1H, Harom, J = 7.5 Hz), 7.72 d (2H, Harom, J = 8.2 Hz),
8.06 d (2H, Harom, J = 8.2 Hz), 8.19 d (2H, Harom
,
J = 7.5 Hz). 13C NMR spectrum (125 MHz, CDCl3),
δC, ppm: 52.43, 88.52, 91.22, 124.57, 128.70, 129.60,
129.69, 131.73, 132.82, 134.36, 136.62, 166.04, 177.67.
Mass spectrum: m/z 264 [M]+. Found, %: C 77.26;
H 4.58. C17H12O3. Calculated, %: C 77.40; H 4.32.
M 264.28.
1,4-Bis(3-phenyl-3-oxo-1-propynyl)benzene (Il).
Yield 52%, mp 183–185°C; published data [20]:
mp 183–184°C. IR spectrum, ν, cm–1: 1620 (C=O),
1-(3-Methoxyphenyl)-3-phenylpropynone (Iq).
1
1
Yield 72%, mp 50–52°C. H NMR spectrum
2200 (C≡C). H NMR spectrum (500 MHz, CDCl3),
(300 MHz, CDCl3), δ, ppm: 3.88 s (3H, MeO), 7.17 d.d
(1H, Harom, J = 8.2, 1.9 Hz), 7.38–7.51 m (4H, Harom),
7.66–7.69 m (3H, Harom), 7.83–7.87 m (1H, Harom).
13C NMR spectrum (75 MHz, CDCl3), δC, ppm: 55.48,
86.98, 92.99, 112.87, 120.10, 120.94, 122.85, 128.71,
129.67, 130.83, 133.08, 138.26, 159.82, 177.74. Mass
spectrum: m/z 236 [M]+. Found, %: C 81.34; H 5.12.
C16H12O2. Calculated, %: C 81.32; H 5.07. M 236.27.
δ, ppm: 7.51 t (4H, Harom, J = 6.2 Hz), 7.63 t (2H,
H
arom, J = 6.2 Hz), 7.70 s (4H, Harom), 8.20 d (4H,
Harom, J = 6.2 Hz). 13C NMR spectrum (125 MHz,
CDCl3), δC, ppm: 88.91, 91.18, 122.37, 128.74, 129.60,
133.05, 134.41, 136.61, 177.62.
2,3,5,6-Tetramethyl-1,4-bis(3-phenyl-3-oxo-1-
propynyl)benzene (Im). Yield 41%, mp 222–225°C.
IR spectrum, ν, cm–1: 1620 (C=O), 2190 (C≡C).
1H NMR spectrum (500 MHz, CDCl3), δ, ppm: 2.54 s
(12H, Me), 7.25 t (4H, Harom, J = 7.5 Hz), 7.64 t (2H,
General procedure for generation of cations
IIa–IIm in HSO3F and cations VIo and VIp in
CF3SO3H. Fluorosulfonic acid (mp –89°C), 0.8–1 ml,
was placed in an NMR ampule and frozen at about
–110°C (ethanol–liquid nitrogen), and 5–30 mg of
1,3-diarylprpynone Ia–Im was added. The mixture
was allowed to warm up to –78°C, a Teflon capillary
(1 mm i.d.) was immersed into the ampule up to its
bottom, and a weak stream of argon was passed
through the capillary over a period of 5–15 min to
obtain a homogeneous solution. The capillary was
withdrawn, and CH2Cl2 was added as internal refer-
H
arom, J = 7.5 Hz), 8.22 d (4H, Harom, J = 7.5 Hz). Mass
spectrum: m/z 390 [M]+. Found, %: C 86.13; H 5.68.
C28H22O2. Calculated, %: C 85.97; H 5.64. M 390.48.
3-(4-Methoxyphenyl)-1-phenylpropynone (In).
Yield 53%, mp 79–81°C; published data [21]:
1
mp 81°C. H NMR spectrum (500 MHz, acetone-d6),
δ, ppm: 3.89 s (3H, MeO), 7.07 d (2H, Harom, J =
8.7 Hz), 7.60 t (2H, Harom, J = 7.4 Hz), 7.71 t (1H,
Harom, J = 7.4 Hz), 7.75 d (2H, Harom, J = 8.7 Hz),
8.24 d (2H, Harom, J = 7.4 Hz). 13C NMR spectrum
(125 Hz, CDCl3), δC, ppm: 55.42, 86.89, 94.36, 111.82,
114.44, 128.57, 129.45, 133.91, 135.14, 137.03,
161.75, 178.00.
1
ence. The H and 13C NMR spectra of ions IIa–IIm
were recorded at –80 and 0°C (Tables 1, 2). Solutions
containing dications VIo and VIp were prepared in
a similar way from ketones Io and Ip or 3-arylin-
denones Vo and Vp by adding 5–30 mg of the sub-
strate to 0.8–1 ml of CF3SO3H (mp –34°C) frozen at
–78°C in an NMR ampule; the mixture was then
1-(3-Methoxyphenyl)-3-(4-methoxyphenyl)pro-
1
pynone (Io). Yield 55%, mp 106–108°C. H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 3.85 s (3H,
MeO), 3.88 s (3H, MeO), 6.92 d (2H, Harom, J =
8.8 Hz), 7.16 d.d (1H, Harom, J = 8.1, 1.9 Hz), 7.41 t
(1H, Harom, J = 8.1 Hz), 7.62 d (2H, Harom, J = 8.8 Hz),
7.69 t (1H, Harom, J = 1.9 Hz), 7.83 d.t (1H, Harom, J =
1
13
homogenized at –30°C. The H and C NMR spectra
of VIo and VIp were recorded at –30°C (Table 4).
General procedure for the transformation of
1,3-diarylpropynones Ia, Ib, and In–Iq into 3-aryl-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

PROTONATION AND CYCLIZATION OF 1,3-DIARYLPROPYNONES
1777
indenones Va, Vb, and Vn–Vq in superacids. Sub-
strate Ia, Ib, or In–Iq, 0.4–1 mmol, was added under
stirring to appropriate superacidic system (HSO3F,
CF3SO3H, CF3SO3H–SbF5, or HF–SbF5) at a tempera-
ture specified in Table 3. The mixture was stirred at
that temperature for 15–120 min (Table 3). When the
reaction was complete, the mixture was slowly poured
under stirring onto 20–50 cm3 of finely crushed ice.
Compound Vn or Vp was filtered off, washed with
water, dried in air, and recrystallized from MeOH–
CH2Cl2. In the syntheses of compounds Va, Vb, Vn,
and Vq, the mixture (after decomposition with ice)
was extracted with methylene chloride (3×50 ml).
The extracts were combined, washed with water (2×
30 ml), a saturated aqueous solution of KHCO3 (2×
30 ml), and water again (2×30 ml), and dried over
Na2SO4. The solvent was removed, and the residue
was subjected to flash column chromatography using
hexane–diethyl ether as eluent. The yields of Va, Vb,
and Vn–Vq are given in Table 3. These products are
sensitive to daylight, temperature, and nucleophilic
reagents; therefore, all operations during their isolation
should be performed avoiding unnecessary heating and
exposure of their solutions to daylight for a long time.
spectrum (300 MHz, CDCl3), δ, ppm: 3.82 s (3H,
MeO), 3.86 s (3H, MeO), 5.84 s (1H, =CH), 6.77 d.d
(1H, Harom, J = 8.1, 2.5 Hz), 6.98 d (2H, Harom, J =
8.9 Hz), 7.08 d (1H, Harom, J = 2.5 Hz), 7.26 d
(1H, Harom, J = 8.1 Hz), 7.62 d (2H, Harom, J = 8.9 Hz).
13C NMR spectrum (75 MHz, CDCl3), δC, ppm: 55.44,
55.73, 110.24, 114.34, 115.32, 120.22, 122.60, 125.74,
129.13, 135.14, 135.53, 161.16, 161.63, 163.32, 196.67.
Mass spectrum, m/z (Irel, %): 266 (100) [M]+, 159 (72),
135 (59). Found, %: C 76.68; H 5.30. C17H14O3. Cal-
culated, %: C 76.76; H 5.27. M 266.30.
5,6-Dimethyl-3-(4-methoxyphenyl)inden-1-one
(Vp). Yellow–orange crystals, mp 135–137°C.
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 2.26 s
(3H, Me), 2.28 s (3H, Me), 3.87 s (3H, MeO), 5.85 s
(1H, =CH), 7.01 d (2H, Harom, J = 8.6 Hz), 7.13 s (1H,
Harom), 7.27 s (1H, Harom), 7.63 d (2H, Harom, J =
8.6 Hz). 13C NMR spectrum (75 MHz, CDCl3), δC,
ppm: 19.77, 20.53, 55.41, 114.31, 121.11, 123.52,
124.26, 125.82, 129.08, 130.84, 137.22, 141.19,
141.82, 161.42, 162.29, 197.47. Mass spectrum, m/z
(Irel, %): 264 (100) [M]+, 249 (25), 118 (8). Found, %:
C 81.79; H 6.10. C18H16O2. Calculated, %: C 81.60;
H 6.16. M 264.32.
3-Phenylinden-1-one (Va). Red–orange oily sub-
6-Methoxy-3-phenylinden-1-one (Vq). Red crys-
tals, mp 84–86°C. H NMR spectrum (300 MHz,
1
stance; published data [22]: orange oily substance
1
[22]). H NMR spectrum (300 MHz, CDCl3), δ, ppm:
CDCl3), δ, ppm: 3.84 s (3H, MeO), 5.91 s (1H, =CH),
5.98 s (1H, =CH), 7.25–7.69 m (9H, Harom) (cf. [22]).
6.79 d.d (1H, Harom, J = 8.1, 2.5 Hz), 7.12 d (1H, Harom
,
3-(4-Methylphenyl)inden-1-one (Vb). Orange
crystals, mp 54–56°C. H NMR spectrum (300 MHz,
J = 2.5 Hz), 7.25 d (1H, Harom, J = 8.1 Hz), 7.48–
7.50 m (3H, Harom), 7.64–7.67 m (2H, Harom). 13C NMR
spectrum (75 MHz, CDCl3), δC, ppm: 55.77, 110.50,
115.57, 121.72, 122.59, 127.37, 128.90, 130.54, 133.29,
134.71, 135.60, 161.25, 163.74, 196.79. Mass spec-
trum, m/z (Irel, %): 236 (100) [M]+, 135 (26), 129 (83),
105 (12). Found, %: C 81.34; H 5.12. C16H12O2. Calcu-
lated, %: C 80.92; H 5.01. M 236.27.
1
CDCl3), δ, ppm: 2.42 s (3H, Me), 5.96 s (1H, =CH),
7.27–7.36 m (5H, Harom), 7.49–7.56 m (3H, Harom).
13C NMR spectrum (75 MHz, CDCl3), δC, ppm: 21.53,
121.63, 122.34, 122.54, 127.40, 129.18, 129.64,
130.22, 132.55, 132.75, 141.01, 143.99, 162.81,
197.09. Mass spectrum, m/z (Irel, %): 220 (100) [M]+,
116 (40). Found, %: C 87.25; H 5.49. C16H12O. Calcu-
lated, %: C 86.51; H 5.83. M 220.27.
REFERENCES
3-(4-Methoxyphenyl)inden-1-one (Vn). Red oily
1
1. Olah, G.A., Prakash, G.K.S., and Sommer, J., Superacids,
substance. H NMR spectrum (300 MHz, CDCl3), δ,
New York: Wiley, 1985.
ppm: 3.88 s (3H, MeO), 5.95 s (1H, =CH), 7.02 d (2H,
2. Olah, G.A. and Schleyer, P.R., Carbonium Ions, New
Harom, J = 8.7 Hz), 7.27–7.51 m (4H, Harom), 7.65 d
York: Wiley, 1968–1976, vols. 1–5.
13
(2H, Harom, J = 8.7 Hz). C NMR spectrum (75 MHz,
3. Koptyug, V.A., Arenonievye iony. Stroenie i reaktsion-
naya sposobnost’ (Arenium Ions. Structure and Reac-
tivity), Novosibirsk: Nauka, 1983.
CDCl3), δC, ppm: 55.55, 114.50, 122.56, 125.61,
127.10, 127.25, 128.32, 129.27, 132.76, 135.26, 144.03,
161.73, 162.58, 197.20. Mass spectrum, m/z (Irel, %):
236 (100) [M]+, 206 (17). Found, %: C 83.44; H 4.52.
C16H12O2. Calculated, %: C 80.92; H 5.01. M 236.27.
4. Rudenko, A.P., Zh. Org. Khim., 1994, vol. 30, p. 1847;
Rudenko, A.P. and Pragst, F., Russ. J. Org. Chem., 1998,
vol. 34, p. 1588.
6-Methoxy-3-(4-methoxyphenyl)inden-1-one
(Vo). Red–orange crystals, mp 155–157°C. H NMR
5. Prakash, G.K.S. and Schleyer, P.R., Stable Carbocation
Chemistry, New York: Wiley, 1997.
1
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 40 No. 12 2004

VASIL’EV et al.
1778
14. Koltunov, K.Yu., Shakirov, M.M., Repinskaya, I.B., and
Koptyug, V.A., Zh. Org. Khim., 1991, vol. 27, p. 2622;
Koltunov, K.Yu. and Repinskaya, I.B., Zh. Org. Khim.,
1994, vol. 30, p. 90.
6. Stang, P.J. and Summerville, R., J. Am. Chem. Soc.,
1969, vol. 91, p. 4600.
7. Olah, G.A. and Spear, R.J., J. Am. Chem. Soc., 1975,
vol. 97, p. 1845.
15. Repinskaya, I.B., Shakirov, M.M., Koltunov, K.Yu., and
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