Acid-catalyzed domino reactions of tetraarylbut-2-yne-1,4-diols. Synthesis of conjugated indenes and inden-2-ones

Article abstract of DOI:10.1021/jo500907z

The reaction of tetraarylbut-2-yne-1,4-diols with electron-rich aromatic compounds at room temperature, under p-TsOH catalysis, affords substituted polycyclic aromatic indene derivatives through a domino reaction involving the formation of a cationic allenylium intermediate. This species can undergo a series of competitive intramolecular cascade reactions, leading to a conjugated inden-2-one. This simple method allows the efficient synthesis of substituted indenes and inden-2-ones, in two steps, from aromatic ketones.

Full text of DOI:10.1021/jo500907z

Article
pubs.acs.org/joc
Acid-Catalyzed Domino Reactions of Tetraarylbut-2-yne-1,4-diols.
Synthesis of Conjugated Indenes and Inden-2-ones
Ceu M. Sousa,† Jerome Berthet,‡ Stephanie Delbaere,‡ and Paulo J. Coelho*,†
́
†
́
Centro de Quımica-Vila Real, Universidade de Tras
́
-os-Montes e Alto Douro, 5000-801 Vila Real, Portugal
‡Faculte
France
́
des Sciences Pharmaceutiques et Biologiques, Universite Lille Nord de France, UDSL, CNRS UMR 8516, F-59006 Lille,
́
S
* Supporting Information
ABSTRACT: The reaction of tetraarylbut-2-yne-1,4-diols
with electron-rich aromatic compounds at room temperature,
under p-TsOH catalysis, affords substituted polycyclic
aromatic indene derivatives through a domino reaction
involving the formation of a cationic allenylium intermediate.
This species can undergo a series of competitive intra-
molecular cascade reactions, leading to a conjugated inden-2-one. This simple method allows the efficient synthesis of substituted
indenes and inden-2-ones, in two steps, from aromatic ketones.
Scheme 1. Acid-Catalyzed One-Pot Synthesis of Furans from
Trisubstituted But-2-yne-1,4-diols
INTRODUCTION
■
Domino reactions are a powerful tool for the elegant
construction of complex molecules from simple substrates
with high atom economy. In this type of reaction, multiple C−
C or C−X bonds are formed within the same reaction vessel,
often involving different reactive processes, leading to the
efficient synthesis of intricate molecules. Propargylic alcohols
are versatile molecules that have been used with success in the
domino synthesis of several cyclic compounds, including
furans,1 pyrroles,1,2 tetrahydroquinolines,3 oxazoles,4 indenes,5
pyrimidines,6 and naphthopyrans.7
The reaction of diarylpropynols with naphthols, in acid
medium, produces an ether intermediate which, through a
series of consecutive intramolecular reactions (Claisen
rearrangement, enolization, 1,5-hydrogen shift, and electro-
cyclization) leads to the in situ formation of naphthopyrans and
the loss of one molecule of water.8 These molecules exhibit
important photochromic properties at room temperature and
have been applied with great commercial success to the
production of ophthalmic photochromic lenses.9,10
Curiously, the chemistry of the parent but-2-yne-1,4-diols has
been much less explored, even though they show high reactivity
in acidic medium and can be easily prepared from ketones.11,12
Some but-2-yne-1,4-diols have been successfully converted to
substituted furans13 via a one-pot cascade reaction, involving
the intramolecular electrophilic cyclization of the allenylium
intermediate (Scheme 1), while 4-aminobut-2-yn-1-ols were
efficiently transformed into dihydropyrroles, in high yields, by
treatment with iodine at room temperature.14 We have found
that tetraarylbut-2-yne-1,4-diols can be easily transformed into
indenes and inden-2-ones via a series of acid-catalyzed domino
reactions.
RESULTS AND DISCUSSION
■
Recently, we have shown that the acid-catalyzed reaction of
tetraaryl-but-2-yne-1,4-diols with 2-naphthol, at room tempera-
ture, leads to the in situ formation of photochromic 1-
vinylidenenaphtho[1,2-b]furans through a four-step domino
reaction involving ether formation, Claisen rearrangement,
enolization, and dehydration (Scheme 2).15 Surprisingly, the
substitution of 2-naphthol by the isomeric 1-naphthol, under
the same reaction conditions, leads to a completely different set
of cationic domino reactions which end in the formation of a
conjugated indene.
1,1,4,4-Tetraarylbut-2-yne-1,4-diols 1 and 2 were easily
prepared, in good yields (56−81%), by the reaction of lithium
acetylide with an excess of benzophenones at room tempera-
ture (Scheme 3). The addition of a catalytic amount of p-TsOH
to a solution of diol 1 (Ar = Ph) and 1-naphthol, in CHCl3 at
room temperature, leads to the rapid formation of an orange
solution, from which the yellow dye 3 was easily isolated in
Received: April 24, 2014
© XXXX American Chemical Society
A
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centered at 372 nm (ε = 1.1 × 104 L mol−1 cm−1), with a
significant absorption above 400 nm; therefore, dilute solutions
of 3 exhibit an intense yellow coloration.
Scheme 2. Acid-Catalyzed One-Pot Synthesis of 1-
Vinylidenenaphthofurans from Tetraarylbut-2-yne-1,4-diols
The structure of the polycyclic aromatic compound 3 was
unambiguously established using 2D NMR experiments. In
1
particular, H−1H scalar correlations among H3′a (6.54 ppm),
H4′a (6.94 ppm), H5′a (7.21 ppm), and H6′a (7.39 ppm) were
observed, which suggested the formation of an extra ring that
gives rise to these four nonequivalent aromatic protons.
Furthermore, a 2D HMBC experiment showed several
1H−13C long-range couplings that evidenced the five
quaternary carbons of the indene part (Figure 1): correlations
among the protons H6′a and H6a (both at 7.15 ppm) and
carbon C10 (144.1 ppm); correlation between the proton H3
(6.88 ppm) and the carbon C9 (137.3 ppm); correlations
among the protons H6′a and H4′a and the carbon C2′a (137.6
ppm); correlations among the protons H3′a and H5′a and the
carbon C1′a (143.0 ppm); correlation between the proton H3′a
and the carbon C11 (139.0 ppm). Moreover, the scalar
correlation between proton H3 and carbon C9 proves the
naphthol group addition, resulting in bond formation between
carbons C4 and C9. The phenolic OH signal was not observed
Scheme 3. Synthesis of 1,1,4,4-Tetraarylbut-2-yne-1,4-diols 1
(Ar = Ph) and 2 (Ar = p-MeOPh)
1
in CDCl3, probably due to a fast exchange, but the H NMR
good yield after recrystallization (Scheme 4). This compound
spectrum recorded in DMSO showed its signal at 9.36 ppm.
The formation of dye 3 can be explained by a series of
cascade reactions involving the elimination of two molecules of
water, the generation of allenic intermediates, and two aromatic
Friedel−Crafts type reactions (Scheme 5). The resonance-
stabilized allenylium carbocation A is initially formed by
dehydration of diol 1 and then attacked by 1-naphthol at one of
the triple-bond carbons, which has some electrophilic character,
leading to the formation of the allenic intermediate B. Then,
under the present acidic conditions, this species loses a second
molecule of water to afford the species C, which performs an
intramolecular Nazarov electrocyclization16,17 with formation of
the five-membered ring D, which then provides the highly
conjugated 1H-indene 3.18−20
displays a strong and broad band in the UV−vis spectrum,
a
Scheme 4. Synthesis of 1H-Indene Dye 3
a
1
Red arrows are related to long-range H−13C scalar couplings.
1
Figure 1. H−13C NMR HMBC of 3 in CDCl3.
B
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Scheme 5. Proposed Mechanism for the Formation of 1H-
Indene Dye 3 from Tetraphenylbut-2-yne-1,4-diol 1 and 1-
Naphthol
Table 1. Reactions of Tetraarylbut-2-yne-1,4-diol 2 with
Different Aromatic Compounds
product (yield, %)
starting aromatic compd
1-naphthol
phenol
4a (56)
4b (23)
4c (20)
5 (17)
5 (20)
5 (15)
1-methoxynaphthalene
anisole
signal at 203 ppm in the 13C NMR spectrum, and exhibits an
unexpected singlet in the 1H NMR spectrum at 4.52 ppm. The
3-diphenylmethylene-1H-inden-2(3H)-one structure of this dye
was unambiguously established using 2D NMR experiments:
1H−1H scalar couplings were measured in 2D-COSY experi-
4
ments from the doublet signal of H3′a (6.29 ppm, J = 2.5 Hz)
up to H6′a (7.09 ppm) through H5′a (6.78 ppm). Dipolar
contacts were evidenced among the singlet signal (H10) at 4.51
ppm and the aromatic protons H6′a and H2a/6a at 7.09 ppm.
1H−13C long-range scalar correlations were measured between
H10 (4.51 ppm) and the carbonyl function C9 at 203 ppm.
Finally, the benzhydrylidene part of the compound was
highlighted by two 1H−13C long-range correlations among
the protons H2′/6′ (7.17 ppm) and H2″/6″ (7.28 ppm) and the
carbon C12 at 151.5 ppm.
The inden-2-one dye 5 is probably formed by a competitive
reaction in which the reactive allenylium carbocation, formed
after dehydration of diol 2, performs a set of intramolecular
cascade reactions instead of being attacked by the aromatic
compound present in the solution. In fact, treatment of diol 2
with p-TsOH for 24 h, at room temperature, affords directly the
inden-2-one 5 (30%; Scheme 7); however, the diol 1, with four
phenyl groups, did not react under these conditions or under
reflux, probably due to the lower reactivity of the unsubstituted
phenyl rings.
Under the same conditions the reaction of diol 2, bearing
four p-methoxy substituents, with 1-naphthol gave the
corresponding 1H-indene dye 4a. However, the reaction of 2
with phenol and 1-methoxynaphthalene, at room temperature,
gave a mixture of two distinct dyes which were isolated by
chromatography: the expected 1H-indenes 4b,c and the second
yellow dye 5. With anisole, only the dye 5 was formed and
isolated in a rather low yield (15%) (Scheme 6 and Table 1).
The steric constraints of 1H-indenes 4a−c dictate that the
phenol, naphthol, or 1-methoxynaphthalene rings cannot be
coplanar with the rest of the molecule and therefore they all
exhibit similar λmax values (389−396 nm). This evidence is
confirmed by the fact that the λmax values of phenolic dyes 4a,b
do not change upon addition of base (NBu4OH). Similar 1-
diarylmethylene-indenes have been prepared by palladium-
catalyzed arylation of butadiynes21 and acetylenes,22 by acid-
catalyzed intramolecular rearrangement of dimethylenecyclo-
propanes,23 or by palladium-catalyzed intramolecular cycliza-
tion of 2-alkenylphenylacetylenes24 and 1,2-dialkynylben-
zenes.25 However, all of these methods involve not easily
accessible starting materials. These polycyclic compounds, also
called benzofulvenes, are important precursors in polymer
synthesis.26−30
Scheme 7. Synthesis of Inden-2-one 5 by Acid-Catalyzed
Intramolecular Cyclization of Diol 2
The spectroscopic data of compound 5 pointed to a structure
quite different from that of indenes 4a−c. This dye shows an
absorption band in the IR spectrum at 1715 cm−1 associated
with a CO bond, which was confirmed by the presence of a
We propose that, after acid-catalyzed dehydration of diol 2,
the carbocation A undergoes a rearrangement leading to the
isomeric vinylic carbocation D, which then performs an
Scheme 6. Synthesis of Dyes 4a−c and 5 from Tetraarylbut-2-yne-1,4-diol 2
C
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with AcOEt (3 × 40 mL). The organic phase was dried (Na2SO4) and
the solvent slowly removed under reduced pressure. During the
solvent evaporation, the ketone, a white solid, was removed by
fractionation precipitation. The remaining oil was purified by
chromatography (petroleum ether/ethyl acetate), affording the diols
as white solids.
1,1,4,4-Tetraphenylbut-2-yne-1,4-diol (1). Yield: 3.80 g, 81%. Mp:
201.4−203.0 °C. 1H NMR (400 MHz, CDCl3): δ 7.59 (d, J = 7.9 Hz,
8H), 7.39−7.23 (m, 12H), 2.86 (s, 2H, OH). EI-MS (TOF): m/z (%)
372 (32), 371 (11), 370 (14), 356 (28), 344 (22), 267 (22), 265 (27),
252 (11), 208 (10), 207 (14), 182 (64), 181 (10), 179 (13), 178 (17),
165 (19), 05 (100), 77 (50). HRMS: calcd for C28H20O (M − H2O)
372.1514, found 372.1503.
intramolecular electrophilic substitution to give the enol E.
Finally, this compound, under the present acidic conditions,
isomerizes to the inden-2-one 5 (Scheme 8).16,17
Scheme 8. Proposed Mechanism for the Formation of Inden-
2-one 5 from But-2-yne-1,4-diol 2
1,1,4,4-Tetrakis(4-methoxyphenyl)but-2-yne-1,4-diol (2). Yield:
1
1.42 g, 56%. Mp: 136.5−138.0 °C. H NMR (400 MHz,CDCl3): δ
7.48 (d, J = 8.7 Hz, 8H), 6.83 (d, J = 8.7 Hz, 8H), 3.77 (s, 12H,
OCH3), 2.80 (s, 2H, OH). EI-MS (TOF): m/z (%) 492 (11), 490
(10), 476 (23), 464 (14), 243 (10), 242 (81), 211 (33), 135 (100),
107 (15), 92 (19), 77 (19). HRMS: calcd for C32H28O5 (M − H2O)
492.1937, found 492.1936.
Synthesis of 4-(3-Phenyl-1-(diphenylmethylene)-1H-inden-
2-yl)naphthalen-1-ol (3). A solution of 1-naphthol (250 mg; 1.73
mmol), diol 1 (1.1 equiv), and p-toluenesulfonic acid hydrate
(catalytic) in CHCl3 (15 mL) was stirred at room temperature for 2
h. Water (40 mL) was added to the deep orange solution, the organic
layer was separated, and the aqueous phase was extracted with ethyl
acetate (2 × 25 mL). The organic extracts were dried with anhydrous
Na2SO4, and the solvent was removed under reduced pressure, leaving
an orange oil which was crystallized from CH2Cl2 and petroleum ether
to afford indene 3 (583 mg; 67%) as a yellow solid. UV−vis: λmax 372
nm (CHCl3, ε = 1.1 × 104). Mp: 241.2−242.0 °C. IR (KBr, cm−1):
3438, 3059, 2359, 2337, 1630, 1587, 1436, 1336, 1272, 1218, 1179,
1043, 750, 700. 1H NMR (300 MHz, CDCl3): δ 6.26 (broad, H3′/4′/5′),
6.38 (d, J = 7.6 Hz, H2), 6.54 (d, J = 7.8 Hz, H3′a), 6.66 (broad, H2′/6′),
6.84 (d, J= 7.6 Hz, H3), 6.94 (t, J = 7.4 Hz, H4′a), 7.15 (broad, H2a‑6a),
7.20 (t, J = 7.2 Hz, H5′a), 7.31 (m, H6/7), 7.39 (d, J = 7.2 Hz, H6′a),
7.45 (m, H6″), 7.57 (m, H2″), 7.84 (d, J = 8.4 Hz, H5), 7.87 (d, J = 8.3
Hz, H8). 13C NMR (75 MHz, CDCl3): δ 107.9, 119.8, 121.0, 123.7,
123.8, 124.3, 125.0, 125.5, 125.8, 126.3, 126.6, 126.9, 127.7, 127.8,
128.4, 128.8, 129.2, 129.5, 130.1, 130.6, 134.0, 135.2, 137.3, 137.5,
139.0, 140.6, 143.0, 143.4, 144.0, 149.9. EI-MS (TOF): m/z (%) 498
(100), 422 (22), 421 (97), 420 (27), 344(8), 315 (5). HRMS: calcd
for C38H26O 498.1984, found 498.1983.
Synthesis of Indene Dyes 4a−c and Inden-2-one 5. A solution
of the aromatic compound (0.35 mmol), diol 2 (1.1 equiv; 195 mg;
0.38 mmol) and p-toluenesulfonic acid hydrate (catalytic) in CHCl3
(15 mL) was stirred at room temperature for 2 h. After water addition
(30 mL) the organic phase was separated and the aqueous phase was
extracted with diethyl ether (2 × 25 mL). The combined organic
extracts were dried (Na2SO4), and the solvent was removed under
reduced pressure. The residue was purified by crystallization (CH2Cl2/
petroleum ether) (compound 4a) or column chromatography (0−25%
EtOAc/petroleum ether) (compounds 4b,c, 5) to afford one or two
dyes.
While inden-1-ones are common compounds, 3-methylide-
neinden-2-ones are quite rare. A similar unsubstituted orange
inden-2-one was previously prepared in two steps by
Co2(CO)8-catalyzed deoxygenation of diphenylketene under a
high pressure of CO at 120 °C for 40 h, followed by basic
hydrolysis.31 This compound exists preferentially in the ketonic
form rather than in the enolic form (E in Scheme 8), and
therefore it may be converted into substituted indenes by
nucleophilic addition/elimination reactions.
CONCLUSION
■
In conclusion, under catalytic acidic conditions, tetraarylbut-2-
yne-1,4-diols easily lose one water molecule, giving cationic
allenylium intermediates that can react with electron-rich
aromatic compounds to afford, through a domino reaction,
substituted polycyclic aromatic indene derivatives. The
allenylium intermediate derived from tetrakis(p-methoxy-
phenyl)but-2-yne-1,4-diol is very reactive and can perform a
competitive intramolecular cascade reaction leading to an
unusually colored inden-2-one. All of these complex trans-
formations occur in a one-pot reaction at room temperature
and constitute a simple synthesis of unusual polycyclic indenes
and inden-2-ones.
With 1-naphthol as the starting material, the red dye 4a (120 mg;
56% yield) was obtained.
EXPERIMENTAL SECTION
All reactions were monitored by thin-layer chromatography on
aluminum plates coated with silica gel 60 (0.25 mm). NMR spectra
were recorded at 298 K using 300, 400, or 500 MHz spectrometers.
■
4-(1-(Bis(4-methoxyphenyl)methylene)-6-methoxy-3-(4-methox-
yphenyl)-1H-inden-2-yl)naphthalen-1-ol (4a). UV−vis: λmax = 395
nm (CHCl3, ε = 1.3 × 104). Mp: 127.5−129.8 °C. IR (KBr, cm−1):
3438, 2930, 2359, 1601, 1501, 1465, 1251, 1172, 1029, 836. 1H NMR
(500 MHz, T = 353 K, DMSO-d6): δ 3.51 (s, OCH3), 3.51 (s, OCH3),
3.67 (s, OCH3), 3.85 (s, OCH3), 5.98 (broad, H3′/5′), 6.10 (d, J = 2.2
Hz, H3′a), 6.40 (broad, H2′/6′), 6.47 (d, J = 7.8 Hz, H2), 6.72 (d, J = 8.5
Hz, H3a/5a), 6.74 (dd, J = 1.8 Hz and J = 8.3 Hz, H5′a), 6.84 (d, J = 7.7
Hz, H3), 7.05 (d, J = 8.6 Hz, H2a/6a), 7.00−7.15 (broad, H3″/5″/6″), 7.12
(d, J = 8.4 Hz, H6′a), 7.22 (t, J = 7.9 Hz, H7), 7.26 (t, J = 7.3 Hz, H6),
7.40 (broad, H2″), 7.66 (d, J = 8.3 Hz, H5), 7.86 (d, J = 8.2 Hz, H8),
9.37 (broad, OH). 13C NMR (75 MHz, T = 353 K, DMSO-d6): δ
55.41, 55.44, 55.47, 55.9, 107.9, 110.4, 112.0, 112.6, 113.9, 114.5,
114.8, 120.0, 122.0, 123.9, 124.5, 125.7, 125.9, 126.0, 127.9, 128.5,
1
The new compounds were determined to be >95% pure by H NMR
spectroscopy. IR spectra were obtained using KBr pellets. Wave-
numbers (λmax) are reported in cm−1. UV−vis spectra were recorded in
CHCl3. Melting points were determined in open capillary tubes and
are uncorrected.
Synthesis of Diols 1 and 2. A suspension of lithium acetylide−
ethylenediamine complex (90%, 2.475 g, 26.9 mmol) and 1.5 equiv of
benzophenone or 4,4′-dimethoxybenzophenone in dry THF (50 mL)
was stirred at room temperature for 3 days. The mixture was then
filtered and the solvent evaporated under reduced pressure. The
residue was diluted with water (75 mL) and this solution extracted
D
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130.36, 130.45, 131.9, 132.5, 133.8, 135.6, 135.8, 136.1, 137.9, 139.5,
141.9, 149.1, 152.1, 157.6, 158.4, 158.8, 160.3. EI-MS (TOF): m/z
(%) 618 (100), 511 (11), 367 (13), 339 (7). HRMS: calcd for
C42H34O5 618.2406, found 618.2411.
With phenol as the starting material, two dyes were isolated: the
yellow-orange solid 5 (17%, less polar) and the red solid 4b (23%,
more polar).
ASSOCIATED CONTENT
* Supporting Information
One- and two-dimensional NMR spectra of all new
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail for P.J.C.: pcoelho@utad.pt.
Notes
4-(1-(Bis(4-methoxyphenyl)methylene)-6-methoxy-3-(4-meth-
oxyphenyl)-1H-inden-2-yl)phenol (4b). UV−vis: λmax 389 nm
(CHCl3, ε = 1.7 × 104). Mp: 202.2−204.9 °C. IR (KBr, cm−1):
■
1
3457, 3952, 2833, 1601, 1501, 1465, 1279, 1243, 1172, 1029, 836. H
NMR (300 MHz, DMSO-d6): δ 3.45 (s, OCH3), 3.61 (s, OCH3), 3.74
(s, OCH3), 3.85 (s, OCH3), 5.88 (d, J = 1.8 Hz, H3′a), 6.20 (d, J = 8.5
Hz, H2), 6.43 (d, J = 9 Hz, H3′), 6.54d, J = 8.5 Hz, H3), 6.67 (dd, J =
1.8 Hz and J = 8.2 Hz, H5′a), 6.72 (d, J = 8.8 Hz, H2′), 6.85 (d, J = 8.8
Hz, H3a), 7.02 (d, H6′a), 7.05 (d, J = 8.3 Hz, H2a), 7.08 (d, J = 8.5 Hz,
H3″), 7.25 (d, J =8.3 Hz, H2″), 8.94 (s, OH). 13C NMR (75 MHz,
DMSO-d6): δ 55.1, 55.4, 55.5, 55.8, 109.9, 111.8, 112.9, 113.9, 114.3,
114.7, 119.8, 127.4, 127.8, 131.1,132.0, 132.5, 133.7, 133.9, 135.9,
136.2, 136.7, 136.9, 139.5, 140.8, 148.8, 155.1, 157.6, 158.4, 159.4,
160.4. EI-MS (TOF): m/z (%) 568 (100), 553 (14), 460 (3), 417 (3),
284 (3). HRMS: calcd for C38H32O5 568.2250, found 568.2256.
With 1-methoxynaphthalene as the starting material, two dyes were
isolated: the orange solid 4c (20%) and the yellow-orange solid 5
(20%).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We acknowledge the FCT (Portugal’s Foundation for Science
and Technology) and FEDER (program COMPETE) for
■
́
financial support to the research units Centro de Quımica-Vila
Real. The 300 and 500 MHz NMR facilities were funded by the
Reg
Jeunesse de l′Education Nationale et de la Recherche
(MJENR), and the Fonds Europeens de Developpement
́ ̀
ion Nord-Pas de Calais (France), the Ministere de la
́
́
Reg
́
ional (FEDER).
REFERENCES
■
1-(1-(Bis(4-methoxyphenyl)methylene)-6-methoxy-3-(4-meth-
oxyphenyl)-1H-inden-2-yl)-4-methoxynaphthalene (4c). UV−vis:
λmax 396 nm (CHCl3, ε = 1.5 × 104). Mp: 239.7−241.8 °C. IR
(KBr, cm−1): 3438, 3002, 2959, 2930, 2830, 2366, 1601, 1501, 1458,
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1251, 1172, 1086, 1029, 822, 767. H NMR (300 MHz, CDCl3): δ
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3.53 (s, OCH3), 3.56 (s, OCH3), 3.72 (s, OCH3), 3.88 (s, 2 × OCH3),
5.76 (broad, H3′/5′), 6.11 (broad, H2′/6′), 6.31 (d, J = 2.1 Hz, H3′a),
6.42 (d, J = 7.9 Hz, H2), 6.69 (d, J = 8.8 Hz, H3a/5a), 6.76 (dd, J = 2.3
Hz and J = 8.3 Hz, H5′a), 6.89 (d, J = 7.9 Hz, H3), 6.96 (m, H3″/5″),
7.11 (d, H6′a), 7.11 (d, J = 8.6 Hz, H2a/6a), 7.15 (dd, 2.5 Hz and J = 8.7
Hz, H6″), 7.29 (m, H6/7), 7.51 (dd, J 2 Hz and J = 8.2 Hz, H2″), 7.81
(m, H5), 7.96 (m, H8). 13C NMR (75 MHz, CDCl3): δ 54.98, 55.02,
55.18, 55.34, 55.41, 103.6, 109.6, 111.2, 112.4, 113.2, 113.8, 114.2,
120.1, 121.3, 124.3, 125.2, 125.6, 126.2, 126.2, 127.9, 128.2, 129.8,
130.4, 132.0, 132.7, 133.5, 133.8, 135.8, 136.3, 138.1, 138.4, 139.5,
148.9, 154.0, 157.7, 158.2, 158.6, 160.1. EI-MS (TOF): m/z (%) 632
(100), 311 (7), 255 (6), 243 (8) 237 (16), 236 (27), 152 (5). HRMS:
calcd for C43H36O5 632.2563, found 632.2562.
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Starting from anisole only the yellow/orange solid 5 was isolated.
3-(Bis(4-methoxyphenyl)methylene)-5-methoxy-1-(4-methoxy-
phenyl)-1H-inden-2(3H)-one (5). UV−vis: λmax 394 nm (CHCl3, ε =
1.2 × 104). Mp: 90.7−92.7 °C. IR (KBr, cm−1): 3438, 2952, 2830,
1715, 1601, 1572, 1501, 1479, 1295, 1251, 1172, 1029, 829. 1H NMR
(300 MHz, CDCl3): δ 3.51 (s, OCH3), 3.80 (s, OCH3), 3.81 (s,
OCH3), 3.88 (s, OCH3), 4.52 (s, H10), 6.29 (d, J = 2.7 Hz, H3′a), 6.78
(dd, J = 2.5 Hz and J = 8.2 Hz, H5′a), 6.81 (d, J = 8.9 Hz, H3′/5′), 6.86
(d, J = 8.7 Hz, H3a/5a), 6.97 (d, J = 8.9 Hz, H3″/5″), 7.09 (d, J = 8.5 Hz,
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H
2″/6″). 13C NMR (75 MHz, CDCl3): δ 55.9, 55.22, 55.28, 55.4, 56.8,
107.5, 112.8, 114.0, 114.1, 115.7, 126.6, 129.5, 129.9, 131.7, 131.9,
132.4, 133.0, 133.6, 133.9, 142.4, 151.6, 158.4, 158.7, 160.5, 160.7,
203.0. EI-MS (TOF): m/z (%) 492 (100), 464 (34), 449 (22), 434
(10), 433 (27), 357 (26), 341 (11), 254 (15), 239 (13), 226 (35), 211
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(catalytic). The mixture was stirred at room temperature for 1 day.
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The aqueous phase was extracted with CHCl3 (3 × 25 mL), and the
organic phases were dried with Na2SO4 and concentrated under
reduced pressure. The residue was purified by crystallization (CH2Cl2/
petroleum ether) to give 5 as yellow-orange crystals (29 mg; 30%).
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E
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