Chemistry of 1,3-diarylpropynones in superacids

Article abstract of DOI:10.1039/b412323a

In superacids with H₀ = -14 to -20, it has been found that 1,3-diarylpropynones ArC≡CCOAr′ are either protonated on oxygen of carbonyl groups with the formation of stable ions ArC≡CC(O ⁺H)Ar′ or undergo further transformations when t

Full text of DOI:10.1039/b412323a

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A R T I C L E
Chemistry of 1,3-diarylpropynones in superacids
A. V. Vasilyev,a S. Walspurger,b M. Haouas,b J. Sommer,*b P. Pale*c and A. P. Rudenkoa
a Saint-Petersburg Forest Technical Academy, Institutsky per.5, Saint-Petersburg, 194021,
Russia; Fax: 7 8125500815; Tel: 7 8125500698. E-mail: aleksvasil@hotmail.com
b Laboratoire de physico-chimie des hydrocarbures, associe´ au CNRS, Institut Le Bel,
Universite´ L. Pasteur, 67000, Strasbourg, France; Fax: 33 390241487; Tel: 33 390241486.
E-mail: sommer@chimie.u-strasbg.fr
c Laboratoire de synthe`se et re´activite´ organique, associe´ au CNRS, Institut Le Bel,
Universite´ L. Pasteur, 67000, Strasbourg, France; Fax: 33 390241517.
E-mail: ppale@chimie.u-strasbg.fr
Received 11th August 2004, Accepted 27th September 2004
First published as an Advance Article on the web 2nd November 2004
In superacids with H0 = −14 to −20, it has been found that 1,3-diarylpropynones ArC≡CCOArꢀ are either
protonated on oxygen of carbonyl groups with the formation of stable ions ArC≡CC(O+H)Arꢀ or undergo further
transformations when the highly conjugated system is electron-rich enough. In the latter case, 3-arylindenones are
produced very rapidly and with high efficiency (up to 95% yield in less than 30 min). The influence of the substituents
Ar, Arꢀ and of the reaction conditions on the behavior of 1,3-diarylpropynones and on the intramolecular cyclisation
have been studied. From the collected data, a mechanism has been proposed involving vinyl cations
ArC+=CHCOArꢀ and/or dications ArC+=CHC(O+H)Arꢀ.
Introduction
Activation of organic compounds in superacids1 such as HSO3F
or CF3SO3H has been widely used in order to generate and
investigate various carbocations,2,3 cation-radicals,4 and other
long-lived charged intermediates. Indeed, solvation in weakly
nucleophilic superacids leads to the stabilization of highly
Scheme 1
electron-deficient species (electrophiles or superelectrophiles)5
which can be then studied. Despite a large number of studies in
this field,6 there are only few data available on the behaviour of
acetylenic derivatives in superacids. In original studies, Stang
and Summerville7 and Olah and Spear8 have observed the
addition of CF3SO3H (triflic acid) and HSO3F to alkynes leading
to the formation of vinyl triflates and vinyl fluorosulfonates.
Transformation of some substituted acetylenes into cyclobutenyl
cations with their subsequent oligomerization in HSO3F was
also monitored by NMR spectroscopy.8,9 Although not directly
observed, vinyl cations induced by the protonation of the
triple bond were postulated as highly reactive intermediates. In
fact, arylvinyl cations were observed as kinetically independent
Results and discussion
(a) 1,3-Diarylpropynones: behavior in superacids
When dissolved in fluorosulfonic or triflic acid, 1,3-
diarylpropynones 1a–m exhibit dramatic modifications of their
NMR spectra. Formation of O-protonated ions 2a–m from
the acetylenic ketones 1a–m in HSO3F is evidenced by these
1
modifications (Scheme 2). H NMR spectra of these ions in
HSO3F at −80 ◦C are reported in Table 1, while 13C NMR
spectra of ions 2a, g, i, j and m (HSO3F, −80 ◦C and 0 ◦C)
and their neutral precursors are collected in Table 2 (13C–1H
decoupled spectra). Exact assignments of signals in 13C NMR
spectra have been made on the basis of multiplet analysis of
13C–1H coupled NMR spectra. Two-dimensional heteronuclear
correlations HSQC, HMQC and HMBC 17 also confirmed these
assignments.
1
species and characterized by H and 13C NMR methods in the
system HSO3F–SbF5 at −120 ◦C for the first time in 1992 by
Siehl and coworkers.10 Recently, Muller et al. have reported
a fully characterized vinyl cation, stable at room temperature
due to hyperconjugation with silicon atoms.11 Nevertheless,
the analysis of available literature reveals that the chem-
istry of acetylene compounds in superacids still remains little
understood.
In HSO3F at −80 ◦C, 1H NMR spectra of protonated forms
2a–m clearly showed a new narrow singlet signal around 12–
13.5 ppm corresponding to the proton bonded to carbonyl
group. Integration of spectral signals confirmed that alkynones
1a–m do exist in HSO3F in completely O-protonated forms (Ta-
ble 1). At 0 ◦C, the signal of this proton was not observed due to
a fast exchange with the acidic medium. In HSO3F, diynediones
1l,m were present as dications 2l,m after protonation of the two
carbonyl groups (Scheme 2 and Table 1).
Under these conditions, no proton which could have been
bonded to the electron-withdrawing groups R (NO2, CN,
COMe, CO2Me) present in the ions 2d–k could be detected.
These results are in agreement with the fact that nitro and cyano
groups are specifically solvated in HSO3F4 and that complete
protonation is only observed in systems with higher acidity
such as HSO3F–SbF5.2 Although this can not be detected by
This report is a contribution from our research on 1,3-
disubstituted propynones.12 These compounds have been found
to dimerize by oxidation with PbO2 in acidic media via
cation-radical intermediates leading to interesting polycar-
bonyl synthons.13 Here we wish to report their behaviour in
neat superacid (HSO3F) by studying the protonation of 1,3-
1
diarylpropynones by H and 13C NMR spectroscopy as well
as their transformation into indenones in various superacidic
media (HSO3F and CF3SO3H). This reaction appears to be a
new and efficient way to synthesize indenones.14 The indenone
15
pattern can be found in some natural products as euplectine
and in synthetic biologically active molecules such as C-nor-D-
homosteroids (Scheme 1).16
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 4 8 3 – 3 4 8 9
3 4 8 3
©

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Scheme 2 Protonated 1,3-diarylpropynones. 1a–m, 2a–i, 3a–i, 4a–i, 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), 2,4,5-Me3-3-NO2 (h), 2,3,5,6-Me4-4-NO2 (i), 4-COMe (j), 4-CO2Me (k), 4-PhCOC≡C (l), 2,3,5,6-Me4-4-PhCOC≡C (m); 2j–m, 3j–m, 4j–m, R =
4-COH+Me (j), 4-CO2H+Me (k), 4-PhCOH+C≡C (l), 2,3,5,6-Me4-4-PhCOH+C≡C (m).
Table 1 NMR spectra of the protonated forms (2a-m) in HSO3F at −80◦, d/ppm (J/Hz)
Assignment of signals
+
=
No. of ion
C
OH
H arom.
R
2a
2b
2c
12.75 s (1H)
12.30 s (1H)
12.07 s (1H)
7.58 s (2H), 7.78 s (3H), 7.98 s (2H), 8.16 s (1H), 8.51 s (2H)
7.44 s (2H), 7.77 s (1H), 7.80 s (1H), 7.92 s (2H), 8.28 s (1H)
7.00 s (2H), 7.79 s (2H), 8.13s (1H), 8.35 s (1H), 8.45 s (1H); 8.50 s (1H), 8.53s (1H)
—
2.47 s (3H Me)
2.28 s (3H, Me)
2.62 s (6H, 2Me)
—
2d
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)
2e
2f
13.24 s (1H)
13.26 s (1H)
7.89 s (1H), 7.96 s (1H), 8.35 s (3H), 8.65 s (3H), 8.84 s (1H)
—
—
7.89 t (1H, J 6.5 Hz), 7.95 t (1H, J 6.5 Hz), 8.34 d (2H, J 6.2 Hz), 8.35 t (1H, J 6.5 Hz),
8.41 d (2H, J 6.2 Hz), 8.69 d (1H, J 6.5 Hz), 8.84 d (1H, J 6.5 Hz)
7.67 d (1H, J 8.7 Hz), 7.64 t (1H, J 7.0 Hz), 7.81 t (1H, J 7.0 Hz), 8.19 t (1H, J 7.0 Hz),
8.53 d (1H, J 7.0 Hz), 8.56 d (1H, J 8.7 Hz), 8.68 d (1H, J 7.0 Hz), 9.17 s (1H)
7.54 s (1H), 7.87 s (1H), 7.93 s (1H), 8.28 s (1H), 8.67 s (2H)
2g
2h
2i
12.87 (1H)
12.86 s (1H)
13.36 s (1H)
4.43 s (3H, Me )
2.61s (3H, Me),
2.85s (6H, 2Me)
2,26 s (6H, 2Me),
2.74 s (6H, 2Me)
3.51 s (3H, Me)
4.73 s (3H, Me)
—
7.83 s (1H), 7.90 s (1H), 8.23 s (1H), 8.63 s (1H), 8.67 s (1H)
2j
13.50 s (1H)
13.19 s (1H)
13.47 (2H)
7.90 s (1H), 7.96 s (1H), 8.37 s (3H), 8.72 s (3H), 8.87 s (1H)
7.88 s (1H), 7.94 s (1H), 8.35 s (3H), 8.39 s (2H), 8.68 s (1H), 8.83 s (1H)
7.90 s (4H), 8.33 s (6H), 8.69 s (2H), 8.85 s (2H)
2k
2la
2ma
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 Diprotonated structure
1H NMR, the acetyl group of the cation 2j was also protonated
according to the 13C NMR spectrum. The carbonyl carbon of
this group indeed appeared at d 222.8 ppm (Table 2), that is
25.8 ppm higher than in the starting propynone 1j and well in
the range known (210–223 ppm) for protonated carbonyl groups
of substituted acetophenones in HSO3F and HSO3F–SbF5.18 In
a similar way, protonation of the ester group in ion 2k was
observed only via 13C NMR.
(Scheme 2) was shifted downfield (about Dd 23–32 ppm) in
comparison with the signal of this atom in the neutral molecules
(Table 2). This shift underlined the contribution of the resonance
structures of type 4 (Scheme 2).
Significant shifts of the signals of the atoms C2ꢀ , C3ꢀ and C4ꢀ
between neutral ketones and their protonated forms also showed
a substantial participation of the phenyl ring connected to the
carbonyl group in the distribution of the positive charge (3a–m
in Scheme 2). Thus, in HSO3F, the signal of atom C4ꢀ in the
ions 2a, g, i, j, and m underwent a downfield shift (about Dd
11–14 ppm) compared to the signal in theꢀ neutral molecule. At
−80 ◦C, the two non-equivalent atoms C2 showed shifts about
Dd 2.5–4 ppm and Dd 10–13 ppm higher than the signal C2’ in
neutral 1,3-diarylpropynone (Table 2).
1
Because of the relatively high viscosity of HSO3F, the H
NMR signals of aromatic protons of ions 2a–m were observed
at −80 ◦C as broadened singlets with unresolved fine structure
in most cases (Table 1). However, at 0 ◦C, the NMR spectra
displayed well resolved multiplets typical for aromatic systems.
The NMR signals of the aromatic part reveal interesting
features concerning the delocalization of positive charge in
some of these ions. Due to the partial p-bond character of
the carbonyl carbon–phenyl ring bond, the rotation around
this bond is generally slow on the NMR time scale leading to
non-equivalence on the o,oꢀ-carbons or protons of the phenyl
ring. Such temperature dependant phenomenon is well known
for aromatic carbonyl compounds and strongly promoted by
protonation of the carbonyl oxygen.19
(b) 1,3-Diarylpropynones: stability and reactivity in HSO3F
The stability of 1,3-diarylpropynones depends on the nature of
the substituents borne by the aryl group linked to the acetylenic
end of the ynone system.
Compounds with groups R = hydrogen 1a or electron with-
drawing groups 1g–m existed as stable protonated ions in HSO3F
2a–m. On the contrary, derivatives with R = methoxy group in
the para position quickly underwent secondary transformations
Comparison between 13C NMR spectra of the initial 1,3-
diarylpropynones (CDCl3, 25 ◦C) and their protonated forms
(HSO3F, −80 ◦C and 0 ◦C) in Table 2 showed that the positive
charge of the protonated carbonyl group of ynone ions 2a, g,
i, j, and m was delocalized both on the phenyl ring adjacent to
carbonyl substituent and on the arylacetylene part of molecule.
Indeed, the signal of the b-acetylenic carbon of the ynone system
◦
even at −80 C. Derivatives with R = alkyl groups 1b, c were
stable at −80 ◦C, but showed similar transformations at 0 ◦C.
The presence of electron-donating groups in the arylalkynyl
part of 1,3-diarylpropynones, specially at the para position, does
increase the electron density on the ynone system, mainly on
3 4 8 4
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 4 8 3 – 3 4 8 9

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the acetylenic bond. Such higher electron density would favour
further reactions. This effect is clearly reflected in the calculated
HOMO energies of selected 1,3-diarylpropynones 1a, b, n, and
e. Compared to the parent propynone 1a, the para methyl- and
methoxy-substituted 1b and 1n exhibit higher HOMO levels
(−9.405 and −9.192 eV respectively vs. −9.636 eV). Such higher
reactivity and electron density at the triple bond could even lead
to further protonation in superacids. Dicationic intermediates
have been recently suggested by Klumpp et al.20 and Olah
et al.21 as a part of their work in superelectrophilic activation of
phenylpropynoic acid.
If so, one could expect the formation of a vinyl cation either
from the propynone 1 or from the protonated form 2 (Scheme 3,
route a or b). Since one conformation of this cation would
ideally place the carbocationic center close to the acylaryl group,
one would expect a facile ring closure via a Friedel–Crafts type
reaction. An indenone would thus be formed.
Calculations (MOPAC PM3) indicated an overall thermody-
namically favourable process (Fig. 1). However, dicationic inter-
mediates (B in Fig. 1 and Scheme 3) proved to be highly energetic
species. Calculations also showed that the O-protonated forms
of 1,3-diarylpropynones 2 are only slightly more stable that the
corresponding C-protonated form (A in Fig. 1 and Scheme 3).
It is therefore not possible to omit a pathway through such
intermediates (Scheme 3, route b), since both forms could be in
equilibrium.
Fig. 1 Calculation of the energy of some compounds and proposed
intermediates.
(c) Synthesis of indenones from 1,3 diarylpropynones.
In order to identify such transformations and characterize
the corresponding products, preparative reactions starting with
various 1,3-diarylpropynones were performed in superacids.
Attempts to characterize products of reaction obtained in the
presence of HSO3F failed. Indeed, in most cases complex
mixtures of products were obtained probably due to the sul-
fonation of the arene parts of the products. Thus investigations
were performed in triflic acid which is 10 times weaker than
fluorosulfonic acid but which is known to avoid sulfonation
or oxidation as side reactions. Under these conditions, it was
found that 1,3-diarylpropynones 1a, b, n–q indeed gave 3-
arylindenones 5a, b, n–q as major products (Scheme 4 and
Table 3).
As underlined above, the nature of the substituents car-
ried by the aryl groups of 1,3-diarylpropynones play also a
critical role on the formation of 3-arylindenones. Methoxy-
substituted derivatives 1n–p were easily transformed into the
compounds 5n–p under the action of CF3SO3H or HSO3F at
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 4 8 3 – 3 4 8 9
3 4 8 5

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Scheme 3 Proposed mechanism for formation of 3-arylindenones.
group (Scheme 3). This electophilic species can not be the O-
protonated ynone 2, usually stable (see section (b) above, Tables 1
and 2, and entries 1, 3, 10 in Table 3) and without any reactive
conformation. It could be the C-protonated form A (Scheme 3)
due to its proper geometry in one of its conformations and
its probable equilibrium with the O-protonated form 2 (see
calculations above). However, such species could not be detected
by NMR. The fact that stronger acids promote the cyclization
of stable O-protonated propynones (Table 3, entries 2, 4,
11) suggests a further protonation of the O-protonated form.
Such species would be a highly reactive O,C-diprotonated
propynone (B in Scheme 3). Although it was also not possible
to directly observe it by spectroscopy, the intermediacy of such
superelectrophilic species B can thus not be excluded.
Scheme 4 Synthesis of 3-arylindenones. 1, R1 = MeO, R2 = H (n),
3-MeO (o), 3,4-Me2 (p), R1 = H, R2 = 3-MeO (q); 5, R1 = H, R2 = H
(a), R1 = Me, R2 = H (b), R1 = MeO, R2 = H (n), 6-MeO (o), 5,6-Me2
(p), R1 = H, R2 = 6-MeO (q).
low temperatures (Table 3, entries 6–9). However, in the presence
of less activating substituents 1a, b, q transformation into
the corresponding indenones occurred only when acidity was
significantly enhanced by addition of a strong Lewis acid. For
example, 17 mol% of SbF5 in CF3SO3H (H0 ∼ −19)1 promoted
the cyclization of 1a, b, q while in CF3SO3H (H0 = −14.1)
these propynones remained unchanged as O-protonated species
(Table 3, entries 2, 4, 11 vs. 1, 3, 10). Analogously, the propynone
1b gave the indenone 5b in the system HF–SbF5 (2 mol% SbF5)
(H0 ∼ −20)1 (Table 3, entry 5). This difference in reactivity is
clearly related to the electron density of the propynone system.
In order to investigate the regioselectivity of indenone for-
mation, compounds 1o, q with an unsymmetrical arrangement
of methoxy substituent R2 were synthesized. In triflic acid
these compounds gave only one regioisomer 5o, q formed after
a cyclization occurring in para-position to the MeO-group
(Scheme 4). In a similar way, only one isomeric indenone 5p
was formed from the propynone 1p.
Both pathways would lead to protonated indenones D, slightly
more stable than the O- or C-protonated propynones 2 or
A (Fig. 1), which upon work-up and isolation produce 3-
arylindenones 5.
Conclusion
1,3-diarylpropynones, unsubstituted or with electron withdraw-
ing substituents exist as stable O-protonated ions in superacidic
1
medium which have been characterised by H and 13C NMR
at −80 ◦C and 0 ◦C. Enhancement of the basicity of the
propynone system by introduction of alkyl or methoxy groups
leads to intramolecular cyclization leading to 3-arylindenones.
An increase of the acidity of the medium gives the same results,
leading to a variety of 3-arylindenones in excellent yields (up to
95%). This new method offers a very efficient route (reaction time
15–30 min) to 3-arylindenones. Supported by some calculations
and NMR studies, a mechanism have been proposed for this
new reaction.
These results showed that in acids strong enough the b-
acetylenic carbon (Scheme 2) becomes electrophilic enough to
promote a Friedel–Crafts type reaction with the facing aromatic
Table 3 Conditions of preparative synthesis of the 3-arylindenones (5a, b, n–q) from 1,3-diarylpropynones (1a, b, n–q) in various acidic systems
Reaction conditions
No. of compounds
Initial/mmol
Superacidic system
Time/min
T/◦C
Reaction product (yield (%))
1
2
3
4
5
6
7
8
9
1a
1a
1b
1b
1b
1n
1o
1p
1p
1q
1q
0.5
0.5
0.5
0.5
1.0
0.4
0.4
0.4
1.0
0.5
0.5
CF3SO3H, 30 eq.
CF3SO3H/SbF5 (17 mol%), 20 eq.
CF3SO3H, 30 eq.
CF3SO3H/SbF5 (17 mol%), 20 eq.
HF/SbF5 (2 mol%), 250 eq.
CF3SO3H, 20 eq.
CF3SO3H, 20 eq.
CF3SO3H, 20 eq.
HSO3F, 90 eq.
CF3SO3H, 20 eq.
30
30
30
30
30
15
15
15
120
30
30
25
25
25
25
0
−30
−30
−30
−75
25
5a (0)a
5a (43)
5b (0)a
5b (75)
5b (60)
5n (54)
5o (95)
5p (95)
5p (71)
5q (0)a
5q (61)
10
11
CF3SO3H/SbF5, (17 mol%), 20 eq.
25
a No reaction occurred, starting material completely recovered.
3 4 8 6
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 4 8 3 – 3 4 8 9

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231 M+. Anal. calcd for C16H9NO: C, 83.10; H, 3.92; N, 6.06.
Experimental
Found: C, 82.98; H, 4.00; N, 6.01.
General
3-(4-Methoxy-3-n◦itrophenyl)-1-phenylprop-3-yn-1-one 1g. Yield
57%. Mp 138–141 C. 1H NMR (500 MHz, (CD3)2CO): d 4.09
(s, 3H), 7.51 (d, J = 8.9 Hz, 1H), 7.60 (t, J = 7.5 Hz, 2H), 7.73
(t, J = 7.5 Hz, 1H), 8.05 (dd, J = 8.9, 2.0 Hz, 1H), 8.25 (d, J =
7.5 Hz, 2H), 8.28 (d, J = 2.0 Hz, 1H). 13C NMR (125 MHz,
CDCl3): d 56.87, 87.33, 90.01, 112.31, 114.00, 128.73, 129.53,
130.27, 134.38, 136.55, 138.72, 139.53, 154.53, 177.53. IR : m
(cm−1) 1630 (C=O), 2195 (C=C). MS : m/z = 281 M+. Anal.
calcd for C16H11NO4: C, 68.33; H, 3.94; N, 4.98. Found: C,
68.19; H, 4.08; N, 5.12.
1H and 13C NMR spectra of compounds 1a–q and 5a, b, n–q
were recorded on spectrometer Bruker AVANCE 300 (working
frequencies 300 and 75 MHz respectively) or on spectrometer
Bruker AM-500 (working frequencies 500 and 125 MHz respec-
tively). The residual proton-solvent peaks: CDCl3 (d 7.25 ppm)
and (CD3)2CO (d 2.05 ppm) for 1H spectra, CDCl3 (d 77.0 ppm)
for 13C NMR spectra were used as internal references. Spectral
measurements in HSO3F at −80 ◦C and 0 ◦C, and in CF3SO3H
400 (frequencies 400 for 1H and 100 MHz for 13C NMR spectra).
Spectra in the superacids were referenced to the signal of CH2Cl2
added as internal standard (d 5.32 ppm for 1H and d 53.84 ppm
for 13C NMR spectra). Mass spectra (electron impact, ionisation
energy 70 eV) were measured on instrument TSQ 700 Finnigan
MAT or on machine MKh-1321. IR spectra of solutions of the
compounds in CHCl3 were registered on instrument Specord
75IR.
◦
at −30 C were performed on spectrometer Brucker AVANCE
3-(2,4,5-Trimethyl-5-nitrophenyl)-1-phenylprop-3-yn-1-one 1h.
◦
1
Yield 24%. Mp 137–139 C. H NMR (500 MHz, CDCl3): d
2.30 (s, 3H), 2.50 (s, 3H), 2.56 (s, 3H), 7.06 (s, 1H), 7.51 (t, J =
7.6 Hz, 2H), 7.63 (t, J = 7.6 Hz, 1H), 8.18 (d, J = 7.6 Hz, 2H).
13C NMR (125 MHz, CDCl3): d 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. IR : m (cm−1) 1645 (C=O), 2200 (C=C).
MS : m/z = 293 M+. Anal. calcd for C18H15NO3: C, 73.71; H,
5.15; N, 4.78. Found: C, 73.85; H, 5.11; N, 4.82.
Purity of the starting and obtained compounds was controlled
by TLC on the plates Silufol UV-254. Preparative separation and
purification of reaction productss were carried out by column
chromatography on silica-gel Merck 60, eluted gradient with
mixtures of ether-hexanes. Yields of products were determined
after chromatography.
3-(2,3,5,6-Tetramethyl-4-nitrophenyl)-1-phenylprop-3-yn-1-one
1i. Yield 40%. Mp 159–160 ◦C. 1H NMR (500 MHz, CDCl3):
d 2.16 (s, 6H), 2.54 (s, 6H), 7.52 (t, J = 7.5 Hz, 2H), 7.64 (t, J =
7.5 Hz, 1H), 8.20 (d, J = 7.5 Hz, 2H). 13C NMR (125 MHz,
CDCl3): d 14.51, 18.52, 89.69, 95.52, 122.31, 124.85, 128.74,
129.50, 134.24, 136.87, 140.03, 153.69, 177.67. IR : m (cm−1)
1625 (C=O), 2195 (C=C). MS : m/z = 307 M+. Anal. calcd
for C19H17NO3: C, 74.25; H, 5.58; N, 4.56. Found: C, 74.27; H,
5.58; N, 4.60.
Synthesis of 1,3-diarylpropynones
Initial 1,3-diarylpropynones 1a–q were synthesized according to
the method12 previously developed by ourselves by reaction of
terminal arylacetylenes with aroyl chlorides in the presence of
palladium catalysts.
3-(4-Acetyl◦phenyl)-1-phenylprop-3-yn-1-one 1j. Yield 46%.
1
Mp 115–117 C. H NMR (500 MHz, CDCl3): d 2.61 (s, 3H),
1,3-Diphenylpropynone 1a. mp 46–48 ◦C previously ob-
7.51 (t, J = 7.3 Hz, 2H), 7.63 (t, J = 7.3 Hz, 1H), 7.74 (d, J =
8.3 Hz, 2H), 7.98 (d, J = 8.3 Hz, 2H), 8.19 (d, J = 7.3 Hz, 2H). 13C
NMR (125 MHz, CDCl3): d 26.69, 88.72, 91.12, 124.68, 128.37,
128.71, 129.60, 133.06, 134.40, 136.60, 138.08, 177.67, 197.01.
IR : m (cm−1) 1630 (C=O), 1685 ((CH3)C=O), 2200 (C=C). MS
: m/z = 248 M+. Anal. calcd for C17H12O2: C, 82.24; H, 4.87.
Found: C, 82.19; H, 4.86.
tained by ourselves.12
3-(4-Me◦thylphenyl)-1-phenylprop-3-yn-1-one 1b. Yield 66%.
Mp 57–59 C, lit. 58.5–59 ◦C.22 1H NMR (500 MHz, (CD3)2CO):
d 2.41 (s, 3H), 7.34 (d, J = 8.0 Hz, 2H), 7.61 (t, J = 7.5 Hz, 2H),
7.68 (d, J = 8.0 Hz, 2H), 7.72 (t, J = 7.5 Hz, 1H), 8.23 (d, J=
7.5 Hz, 2H). 13C NMR (125 MHz, CDCl3): d 21.75, 86.81, 93.84,
116.96, 128.60, 129.50, 129.53, 133.12, 134.02, 136.96, 141.58,
178.00. IR : m (cm−1) 1630, 1635 (C=O), 2195 (C=C).
3-(2,4,6-Trimethylphenyl)-1-phenylprop-3-yn-1-one 1c. Yield
72%. Mp 71–73 ◦C, lit. 72 ◦C.23 1H NMR (500 MHz, (CD3)2CO):
d 2.31 (s, 3H), 2.52 (s, 6H), 7.02 (s, 2H), 7.59–7.73 (m, 3H), 8.23-
8.25 (m, 2H). IR : m (cm−1) 1620 (C=O), 2190 (C=C).
3-(3-Nitrophenyl)-1-phenyl◦prop-3-yn-1-one 1d. Yield 73%.
Mp 149–151 ◦C, lit. 151-152 C.23 1H NMR (500 MHz, CDCl3):
d 7.53 (t, J = 7.5 Hz, 2H), 7.61-7.67 (m, 2H), 7.97 (d, J =
7.5 Hz, 1H), 8.19 (d, J = 7.5 Hz, 2H), 8.31 (d, J= 8.2 Hz,
1H), 8.49 (s, 1H). 13C NMR (125 MHz, CDCl3): d 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. IR : m (cm−1) 1640 (C=O), 2205 (C=C).
3-(4-Nitrophenyl)-1-phenyl◦prop-3-yn-1-one 1e. Yield 69%.
Mp 146–148 ◦C, lit. 148-149 C.24 1H NMR (500 MHz, CDCl3):
d 7.54 (t, J = 7.4 Hz, 2H), 7.66 (t, J = 7.4 Hz, 1H), 7.83 (d, J =
8.8 Hz, 2H), 8.19 (d, J = 7.4 Hz, 2H), 8.28 (d, J= 8.8 Hz, 2H).
13C NMR (125 MHz, CDCl3): d 89.13, 89.82, 123.78, 126.74,
128.78, 129.58, 133.61, 134.60, 136.38, 148.51, 177.29.
3-(4-Methoxycarbonylphenyl)-1-phenylprop-3-yn-1-one 1.k Yield
◦
1
60%. Mp 98–100 C. H NMR (500 MHz, CDCl3): d 3.92 (s,
3H), 7.51 (t, J = 7.5 Hz, 2H), 7.63 (t, J = 7.5 Hz, 1H), 7.72 (d,
J = 8.2 Hz, 2H), 8.06 (d, J = 8.2 Hz, 2H), 8.19 (d, J = 7.5 Hz,
2H). 13C NMR (125 MHz, CDCl3): d 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. IR : m (cm−1) 1640 (C=O), 1725 ((CH3O)C=O), 2210
(C=C). MS : m/z 264 M+. Anal. calcd for C17H12O3: C, 77.26;
H, 4.58. Found: C, 77.40; H, 4.32.
1,4-Bis(phenylcarbonylethynyl)benzene 1l. Yield 52%. Mp
2
◦
183-185 ◦C, lit. 183–184 C. H NMR (500 MHz, CDCl3):
1
7.51 (t, J = 6.2 Hz, 4H), 7.63 (t, J = 6.2 Hz, 2H), 7.70 (s, 4H),
8.20 (d, J= 6.2 Hz, 4H). 13C NMR (125 MHz, CDCl3): d 88.91,
91.18, 122.37, 128.74, 129.60, 133.05, 134.41, 136.61, 177.62.
IR : m (cm−1) 1620 (C=O), 2200 (C=C).
2,3,5,6-Tetramethyl-1,4-Bis(phenylcarbonylethynyl)benzene
1m. Yield 41%. Mp 222–225 ◦C. 1H NMR (500 MHz, CDCl3):
d 2.54 (s, 12H), 7.25 (t, J = 7.5 Hz, 4H), 7.64 (t, J = 7.5 Hz,
2H), 8.22 (d, J = 7.5 Hz, 4H). 13C NMR (125 MHz, CDCl3):
d 18.58, 91.23, 96.03, 122.74, 128.70, 129.53, 134.12, 137.03,
138.07, 177.84. IR : m (cm−1) 1620 (C=O), 2190 (C=C). MS :
m/z = 390 M+. Anal. calcd for C28H22O2: C, 86.13; H, 5.68.
Found: C, 85.97; H, 5.64.
3-(4-Cyanophenyl)-1-phenylprop-3-yn-1-one 1f. Yield 51%.
◦
1
Mp 151–152 C. H NMR (500 MHz, CDCl3): d 7.51 (t, J =
7.8 Hz, 2H), 7.65 (t, J = 7.8 Hz, 1H), 7.70 (d, J = 8.3 Hz,
2H), 7.75 (d, J = 8.3 Hz, 2H), 8.18 (d, J = 7.8 Hz, 2H). 13C
NMR (125 MHz, CDCl3): d 89.33, 89.56, 113.99, 117.78, 124.87,
128.73, 129.55, 132.24, 133.20, 134.52, 136.40, 177.33. IR : m
(cm−1) 1640 (C=O), 2210 (C=C), 2230 (C=N). MS : m/z =
3-(4-Methoxyphenyl)-1-phenylprop-3-yn-1-one 1.n Yield 53%.
◦
Mp 79–81 ◦C, lit. 81 C.25 1H NMR (300 MHz, (CD3)2CO):
d 3.89 (s, 3H), 7.07 (d, J = 8.7 Hz, 2H), 7.60 (t, J = 7.4 Hz,
2H), 7.71 (t, J = 7.4 Hz, 1H), 7.75 (d, J = 8.7 Hz, 2H), 8.24
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 4 8 3 – 3 4 8 9
3 4 8 7

View Online
(d, J = 7.4 Hz, 2H). 13C NMR (75 MHz, CDCl3): d 55.42, 86.89,
94.36, 111.82, 114.44, 128.57, 129.45, 133.91, 135.14, 137.03,
161.75, 178.00.
CDCl3): d 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. MS : m/z
(Irel,%)=220 (100) M+, 116 (40). Anal. calcd for C16H12O: C,
87.25; H, 5.49. Found: C, 86.51; H, 5.83.
1-(3-Methoxyphenyl)-3-(4-methoxyphenyl)prop-3-yn-1-one 1o.
◦
1
3-(4-Methoxyphenyl)indenone 5n. Yield 54%. Red oil. 1H
NMR (300 MHz, CDCl3): d 3.88 (s, 3H), 5.95 (s, 1H), 7.02
(d, J = 8.7 Hz, 2H), 7.27-7.51 (m, 4H), 7.65 (d, J = 8.7 Hz, 2H).
13C NMR (75 MHz, CDCl3): d 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. MS : m/z (Irel,%) = 236 (100) M+, 206 (17).
Yield 55%. Mp 106–108 C. H NMR (300 MHz, CDCl3): d
3.85 (s, 3H), 3.88 (s, 3H), 6.92 (d, J = 8.8 Hz, 2H), 7.16 (dd, J =
8.1, 1.9 Hz, 1H), 7.41 (t, J = 8.1 Hz, 1H), 7.62 (d, J = 8.8 Hz,
2H), 7.69 (t, J = 1.9 Hz, 1H), 7.83 (dt, J = 8.1, 1.9 Hz, 1H). 13
C
NMR (75 MHz, CDCl3): d 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. MS : m/z (Irel,%) =266 (100) M+, 159 (42), 135
(29). Anal. calcd for C17H14O3: C, 76.68; H, 5.30. Found: C,
76.22; H, 5.27.
6-Methoxy-3-(4-methoxyphenyl)indenone 5o. Yield 95%.
Red-orange crystals, mp 155–157 ◦C. 1H NMR (300 MHz,
CDCl3): d 3.82 (s, 3H), 3.86 (s, 3H), 5.84 (s, 1H), 6.77 (dd, J =
8.1, 2.5 Hz, 1H), 6.98 (d, J = 8.9 Hz, 2H), 7.08 (d, J = 2.5 Hz,
1H), 7.26 (d, J = 8.1 Hz, 1H), 7.62 (d, J = 8.9 Hz, 2H). 13C
NMR (75 MHz, CDCl3): d 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. MS : m/z (Irel,%) = 266 (100) M+, 159 (72),
135 (59). Anal. calcd for C17H14O3: C, 76.68; H, 5.30. Found: C,
76.76; H, 5.27.
3-(4-Methoxyphenyl)-1-(3, 4-dimethylphenyl)prop-3-yn-1-one
1p. Yield 65%. Mp 103–104.5 ◦C. 1H NMR (300 MHz,
CDCl3): d 2.33 (s, 6H), 3.84 (s, 3H), 6.92 (d, J = 8.8 Hz, 2H),
7.25 (d, J = 8.3 Hz, 1H), 7.62 (d, J = 8.8 Hz, 2H), 7.94-7.97
(m, 2H). 13C NMR (75 MHz, CDCl3): d 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. MS : m/z (Irel,%)=264
(100) M+, 236 (35), 221 (22), 159 (14). Anal. calcd for C18H16O2:
C, 81.79; H, 6.10. Found: C, 81.77; H, 6.05.
3-(4-Methoxyphenyl)-5,6-dimethylindenone 5p. Yield 95%.
◦
1
Yellow-orange crystals, mp 155–157 C. H NMR (300 MHz,
CDCl3): d 2.26 (s, 3H), 2.28 (s, 3H), 3.87 (s, 3H), 5.85 (s, 1H),
7.01 (d, J = 8.6 Hz, 2H), 7.13 (s, 1H), 7.27 (s, 1H), 7.63 (d, J =
8.6 Hz, 2H). 13C NMR (75 MHz, CDCl3): d 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. MS : m/z (Irel,%) = 264
(100) M+, 249 (25), 118 (8). Anal. calcd for C18H16O2: C, 81.79;
H, 6.10. Found: C, 81.60; H, 6.16.
1-(3-Methoxyphenyl)-3-phenylprop-3-yn-1-one1.q Yield 72%.
Mp 50–52 ◦C. 1H NMR (300 MHz, CDCl3): d 3.88 (s, 3H), 7.17
(dd, J = 8.2, 1.9 Hz, 1H), 7.38–7.51 (m, 4H), 7.66–7.69 (m, 3H),
7.83–7.87 (m, 1H). 13C NMR (75 MHz, CDCl3): d 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. MS: m/z (Irel,%)=236 (100) M+,
129 (78). Anal. calcd for C16H12O2: C, 81.34; H, 5.12. Found: C,
81.32; H, 5.07.
6-Methoxy-3-phenylindenone 5q. Yield 61%. Red crystals,
◦
1
NMR studies of 1,3-diarylpropynones
mp 84–86 C. H NMR (300 MHz, CDCl3): d 3.84 (s, 3H),
5.91 (s, 1H), 6.79 (dd, J = 8.1, 2.5 Hz, 1H), 7.12 (d, J = 2.5 Hz,
1H), 7.25 (d, J = 8.1 Hz, 1H), 7.48–7.50 (m, 3H), 7.64–7.67
(m, 2H). 13C NMR (75 MHz, CDCl3): d 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. MS : m/z (Irel,%)=236 (100) M+, 135
(26), 129 (83), 105 (12). Anal. calcd for C16H12O2: C, 81.34; H,
5.12. Found: C, 80.92; H, 5.01.
General technique for generation of the ions 2-m in HSO3F or
CF3SO3H.
5-30 mg of substrate 1-m were added to 0.8–1 ml of HSO3F
(mp −89◦) frozen in an NMR tube at ∼−110 ◦C (ethanol-liquid
nitrogen). The temperature was raised up to −78 ◦C and a teflon
capillary with internal diameter 1 mm was entered to the bottom
of the NMR tube, passing through it a weak flow of argon
during 5–15 min in order to obtain a homogeneous solution of
ions (1i–m). The capillary was removed and internal standard
Acknowledgements
1
CH2Cl2 was added. H and 13C NMR spectra of the ions 2–m
AV thanks the NATO for a postdoctoral fellowship. SW thanks
Loker Hydrocarbon Institute, USC, Los Angeles for financial
support. PP and JS thank the CNRS for financial support. The
authors would like to thank Dr R. Graff and J.-D. Sauer for
fruitful discussions about NMR experiments.
were recorded at −80 ◦C and 0 ◦C (Tables 1, 2).
Synthesis of indenones
General procedure for the cyclisation of 1,3-diarylpropynones
1a, b, n–q into 3-arylindenones 5a, b, n–q in superacids.
Substrate 1a, b, n–q (0.4–1.0 mmol) was added to superacidic
system (HSO3F, CF3SO3H or CF3SO3H-SbF5) with vigorous
magnetic stirring at the temperature shown in Table 3. At
this temperature the reaction mixture was stirred for 15 to
120 min (Table 3). Then the reaction mixture was slowly added
dropwise to vigorously stirring ice–water mixture (∼30 ml).
Products 5a, b, n–q were isolated ether after extraction with
CH2Cl2 and subsequent washing of the CH2Cl2 solution with
H2O, aqueous KHCO3, H2O, drying over Na2SO4, and finally
flash-chromatography on silica gel or after filtration of the
solids formed after water quenching and recrystallization from
MeOH–CH2Cl2. Yields of compounds 5a, b, n–q are given in
Table 3.
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3-Phenylindenone 5a. Yield 43%. Red-orange oil, lit. oil.26
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O r g . B i o m o l . C h e m . , 2 0 0 4 , 2 , 3 4 8 3 – 3 4 8 9
3 4 8 9