Easy entry to donor/acceptor butadiene dyes through a MW-assisted InCl3-catalyzed coupling of propargylic alcohols with indan-1,3-dione in water

Article abstract of DOI:10.1016/j.catcom.2014.07.028

In this contribution, the high-yield preparation and optical properties of some donor-acceptor butadiene dyes, generated by coupling of different 1,1-diaryl-2-propyn-1-ols with indan-1,3-dione, are presented. The reactions, which involve the initial Meyer

Full text of DOI:10.1016/j.catcom.2014.07.028

Catalysis Communications 63 (2015) 10–14
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Catalysis Communications
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Short communication
Easy entry to donor/acceptor butadiene dyes through a MW-assisted
InCl3-catalyzed coupling of propargylic alcohols with indan-1,3-dione
in water
a,
Javier Francos a, Javier Borge b, Josefina Díez a, Sergio E. García-Garrido a, , Victorio Cadierno
⁎
⁎
a
Laboratorio de Compuestos Organometálicos y Catálisis (Unidad Asociada al CSIC), Centro de Innovación en Química Avanzada (ORFEO-CINQA),
Departamento de Química Orgánica e Inorgánica, IUQOEM, Facultad de Química, Universidad de Oviedo, Julián Clavería 8, E-33006 Oviedo, Spain
b
Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, Julián Clavería 8, E-33006 Oviedo, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 May 2014
Received in revised form 14 July 2014
Accepted 16 July 2014
Available online 25 July 2014
In this contribution, the high-yield preparation and optical properties of some donor-acceptor butadiene dyes,
generated by coupling of different 1,1-diaryl-2-propyn-1-ols with indan-1,3-dione, are presented. The reactions,
which involve the initial Meyer–Schuster rearrangement of the aromatic alkynols and subsequent condensation
of the resulting enals with the β-dicarbonyl compound, proceeded cleanly in water, under MW irradiation, in the
presence of catalytic amounts of the inexpensive Lewis acid InCl3. A single-crystal X-ray diffraction study of one of
these dyes is also included.
Keywords:
© 2014 Elsevier B.V. All rights reserved.
Homogeneous catalysis
Aqueous catalysis
Indium trichloride
Meyer–Schuster rearrangement
C–C couplings
Butadiene dyes
1. Introduction
synthetically valuable and versatile α,β-unsaturated carbonyl com-
pounds (enals and enones) [13,14].
During the last decades much attention has been paid to the devel-
opment of synthetic organic chemistry in water, because water is
cheaper, safer and environmentally benign compared with traditional
organic solvents [1–3]. The use of microwave irradiation (MW) as a
heating source has also become very popular since MW techniques en-
able high-speed syntheses at lower energetic costs [4–7]. In the search
for synergistic effects and more sustainable synthetic protocols, the
combined use of water and MW irradiation has also been considered,
and a number of stoichiometric and catalytic transformations have
been successfully developed in the most recent years under these ex-
perimental conditions [8–11]. In this context, we have described an ef-
ficient and general MW-assisted protocol for the Meyer–Schuster
rearrangement of propargylic alcohols in water using inexpensive
InCl3 as catalyst (Scheme 1) [12]. It should be recalled that the Meyer–
Schuster reaction represents one of the most straightforward and
atom-economical routes presently available for the preparation of
Based on this aqueous MW-assisted reaction, we report herein the
high yield preparation of a family of push–pull 1,1-diaryl-butadiene-
4,4-diones 4 through the coupling of indan-1,3-dione 1 with different
1,1-diaryl-2-propyn-1-ols 2 (Scheme 2). The process involves the
Knoevenagel condensation of the in situ formed enals 3, resulting from
the Meyer–Schuster rearrangement of the 1,1-diaryl-2-propyn-1-ols,
with the β-dicarbonyl compound. We should note that related tandem
isomerization/condensation processes of propargylic alcohols with
enolizable ketones have been previously described by us and others
using ruthenium catalysts [15–17] and Brønsted acids [18] as promoters
in organic media, but are unprecedented in water.
Polyenic push–pull compounds containing the indanedione frag-
ment as the acceptor group (Fig. 1) have attracted considerable in-
terest since they exhibit relevant optical and electronic properties,
founding applications for example as second-order nonlinear optical
chromophores [19–21]. These species are typically synthesized by
Knoevenagel condensation of indan-1,3-dione 1 with the corre-
sponding aldehyde. The method presented herein opens an alterna-
tive synthetic path starting from propargylic alcohols, via in situ
generation of the aldehyde partner, and also represents a new exam-
ple of an efficient and synthetically useful indium-catalyzed organic
reaction in aqueous media [22,23].
⁎
Corresponding authors. Tel.: +34 985103463, +34 985103453; fax: +34 985103446.
E-mail addresses: garciagsergio@uniovi.es (S.E. García-Garrido), vcm@uniovi.es
(V. Cadierno).
http://dx.doi.org/10.1016/j.catcom.2014.07.028
1566-7367/© 2014 Elsevier B.V. All rights reserved.

J. Francos et al. / Catalysis Communications 63 (2015) 10–14
11
Scheme 1. MW-assisted InCl3-catalyzed Meyer–Schuster rearrangement of propargylic al-
cohols in water.
Fig. 1. General structure of indanedione-based push–pull polyenes.
2. Experimental
3. Results and discussion
2.1. Materials and methods
Following the optimal experimental conditions previously found to
promote the catalytic Meyer–Schuster rearrangement of 1,1-diphenyl-
2-propyn-1-ol 2a into 3,3-diphenylpropenal 3a by indium trichloride,
i.e. employing 1 mol% of InCl3, 1 M solution of 2a in water and MW
heating at 160 °C (300 W) [12], we studied the reaction in the presence
of 1 equivalent of indan-1,3-dione 1. To our delight, clean formation of
the butadienic derivative 2-(3,3-diphenylallylidene)-indan-1,3-dione
4a was observed after 30 min of irradiation, with no side products
being observed in the reaction crude by GC (only traces of the reactants
and the intermediate enal 3a were detected) [30]. Solvent removal and
chromatographic work-up on silica gel provided analytically pure 4a in
88% yield (entry 1 in Table 1). Remarkably, neither an inert atmosphere
nor an organic co-solvent was required. In an independent experiment,
we confirmed that treatment of isolated 3,3-diphenylpropenal 3a with
indan-1,3-dione 1 under identical reaction conditions proceeds cleanly
to generate the butadiene derivative 4a in 85% after 20 min, thus
confirming the proposed Meyer–Schuster/Knoevenagel sequence.
We must note that the condensation between 3a and 1 also takes
place in the absence of InCl3, however a longer irradiation period (2 h)
was in this case needed to generate 4a in high yield (84%). On the
other hand, no reaction occurred when an aqueous mixture of 1,1-
diphenyl-2-propyn-1-ol 2a and indan-1,3-dione 1 was irradiated in
the absence of InCl3. This fact is in complete accord with our previous
observations that showed the need of a Lewis acid to promote the
Meyer–Schuster rearrangement of 2a into 3a. Also of note is the fact
that the use of organic solvents (such as toluene, 1,4-dioxane or DMF)
instead of water led, under identical experimental conditions, to 4a in
very low yields (b30% by CG after 30 min of irradiation).
All reagents were obtained from commercial suppliers and used
without further purification with the exception of propargylic alcohols
2b [24], 2c [25], 2d [26], 2e [27], 2f [27] and 2g [28], which were
prepared by following the methods reported in the literature. Flash
chromatography was performed using Merck silica gel 60 (230–
400 mesh). UV–Vis spectra were linearly recorded in wavelength on a
Perkin-Elmer Lambda 20 spectrometer at 20 °C using a matched pair
of quartz cells 1 cm in path length. Since the individual absorption
bands in the spectra were overlapped, accurate λmax values were deter-
mined by decomposition of the spectra in the sum of Gaussian func-
tions, after applying a smoothing spline algorithm to the observed
data followed by a derivative spectroscopy numerical method (only
the negative peaks of the second derivatives of the smoothed spectra
were used for the estimation of the position of the bands) [29]. All math-
ematical analyses were performed with MATLAB R2012b.
2.2. General procedure for the catalytic synthesis of the
indane-1,3-dione-based dyes
A pressure-resistant septum-sealed glass microwave reactor vial
was charged with indan-1,3-dione 1 (0.146 g, 1 mmol), the correspond-
ing propargylic alcohol (2a–g; 1 mmol), InCl3 (2.2 mg, 0.01 mmol), a
magnetic stirring bar and water (1 mL). The vial was then placed inside
the cavity of a CEM Discover® S-Class microwave synthesizer and
power was held at 300 W until the desired temperature was reached
(160 °C). Microwave power was automatically regulated for the re-
mainder of the experiment to maintain the temperature (monitored
by a built-in infrared sensor). The internal pressure during the reaction
ranged between 15 and 90 psi. After completion of the reaction (see
Table 1), the vial was cooled to room temperature, the reaction mixture
transferred to a flask, the solvent evaporated under vacuum, and the
crude residue purified by flash chromatography over silica gel using
EtOAc/hexane (1:10) as eluent. Characterization data for compounds
4a–g have been included as Supplementary Information in Appendix A.
As shown in Table 1, other 1,1-diaryl substituted propargylic alco-
hols 2b–g also reacted with indan-1,3-dione 1, in water and in the pres-
ence of InCl3 (1 mol%), to afford the corresponding conjugated 2-(3,3-
diarylallylidene)-indan-1,3-diones 4b–g in good to excellent yields
(85–95%) after 20–180 min of MW irradiation (see entries 2–7) [31].
A significant influence of the electronic properties of the aryl rings on
the reaction rates was observed. Thus, alkynols with electron-
withdrawing groups showed a lower reactivity (entries 2–3) in compar-
ison with the unsubstituted one (entry 1) and those containing
Scheme 2. MW-assisted InCl3-catalyzed synthesis of butadienes 4 in water.

12
J. Francos et al. / Catalysis Communications 63 (2015) 10–14
Table 1
Synthesis of 2-(3,3-diarylallylidene)-indan-1,3-dione dyes 4a–g by MW-assisted coupling of propargylic alcohols 2a–g with indan-1,3-dione 1 in water.
Entry
1
Alkynol 2a–g
Product 4a–g
Time (min)
30
Yield (%)a
88
2
3
4
5
6
180
180
30
86
90
85
95
90
20
20
7
20
92
Reactions were performed under air atmosphere in a CEM Discover® S-Class microwave synthesizer at 160 °C, through moderation of the initial microwave power (300 W), starting from
1 mmol of the corresponding propargylic alcohol 2a–g (1 M in water), 1 mmol of indan-1,3-dione 1, and 0.01 mmol of InCl3.
a
Isolated yield after chromatographic work-up.
electron-donating functionalities (entries 5–6). As inferred by monitor-
ing the catalytic reactions by GC, the rate limiting step of this tandem
process is in all cases the Knoevenagel condensation between the inter-
mediate enal R1R2C = CHCHO 3a–g and indan-1,3-dione 1, which is ob-
viously favored with electron-rich substrates.
The butadienic compounds 4a–g were characterized by elemental
analyses, mass spectrometry, and IR and NMR (1H, 13C{1H} and 19F
{1H}) spectroscopy, all data being fully consistent with the structural
proposal. In addition, the molecular structure of 4e was determined by
X-ray diffraction analysis, for which good quality crystals could be ob-
tained by slow diffusion of n-hexane into a saturated solution of the
compound in ethyl acetate. An ORTEP-type drawing of the molecule,
along with selected bonding parameters, is shown in Fig. 2. In the struc-
ture it is seen that the indanedione moiety, the butadiene chain and one
of the phenyl groups are largely coplanar, with the second phenyl group
being perpendicularly twisted out of this plane (dihedral angle C(11)–
C(12)–C(13)–C(14) of 67.39(16)°). As expected, the butadiene moiety
reflects some π-electron delocalization, as indicated by the slightly lon-
ger C(9)–C(10) (1.356(2) Å) and C(11)–C(12) (1.363(2) Å), and shorter
C(10)–C(11) (1.424(2) Å), lengths in comparison to those typically
found for Csp2–Csp2 double and single bonds (1.32 and 1.44 Å, respec-
tively) [32].
The optical properties of compounds 4a–g were investigated by
means of UV–Vis spectroscopy in dichloromethane solution. The spectra
showed intense absorption bands in the visible region, with maxima in
the range of 405–565 nm (see Fig. 3 and Table 2). As can be seen in Fig. 3,
the presence of the strong electron-donor dimethylamino substituents
in 4f resulted in a significant bathochromic shift of the absorption
band, indicating a high degree of electronic conjugation for this
compound.
The solvatochromic behavior of these dyes was also briefly evaluat-
ed using 4f, absorbing at the longest wavelength, as model. The UV–Vis

J. Francos et al. / Catalysis Communications 63 (2015) 10–14
13
Table 2
Absorption properties of dyes 4a–g in dichloromethane solution.a
Compound
λ
max (nm)
ε (M−1·cm−1
)
4a
4b
4c
4d
4e
4f
405
405
404
421
453
565
416
35,440
38,230
26,250
34,750
37,184
32,801
18,100
4g
a
Spectra recorded using 6 × 10−5 M solutions.
Table 3
λ
max values of dye 4f in various solvents together with the π azo values of solvents.a
⁎
⁎
Solvent
λ
max (nm)
π
azo
n-Hexane
530
549
558
558
560
564
571
571
575
575
578
578
586
586
587
590
591
592
595
−0.09
0.16
0.37
0.34
0.38
0.40
0.61
0.53
0.63
0.58
0.62
0.62
0.80
0.86
0.82
0.86
0.91
0.89
1.00
Diethyl ether
Ethyl acetate
1,4-Dioxane
Toluene
Benzene
2-Butanone
Acetone
Acetonitrile
Chlorobenzene
Chloroform
Dichloromethane
Pirydine
N,N-dimethylformamide
Benzonitrile
Ethanol
Fig. 2. ORTEP-type view of the structure of compound 4e showing the crystallographic la-
beling scheme. Thermal ellipsoids are drawn at the 30% probability level. Selected bond dis-
tances (Å) and angles (°): C(7)–O(1) = 1.218(2); C(7)–C(9) = 1.480(2); C(8)–O(2) =
1.218(2); C(8)–C(9) = 1.483(2); C(9)–C(10) = 1.356(2); C(10)–C(11) = 1.424(2);
C(11)–C(12) = 1.363(2); C(12)–C(13) = 1.496(2); C(12)–C(20) = 1.471(2); C(7)–
C(9)–C(8) = 107.6(1); C(7)–C(9)–C(10) = 129.5(1); C(8)–C(9)–C(10) = 122.8(1);
C(9)–C(7)–O(1) = 128.0(1); C(9)–C(8)–O(2) = 126.9(1); C(9)–C(10)–C(11)
=
127.0(1); C(10)–C(11)–C(12) = 123.8(1); C(11)–C(12)–C(13) = 120.4(1); C(11)–
C(12)–C(20) = 122.7(1); C(13)–C(12)–C(20) = 117.0(1).
spectra of this compound recorded in different organic solvents showed
a significant bathochromic shift of the absorption maximum with in-
creasing the solvent polarity, i.e. Δλmax = 65 nm on going from n-
hexane to dimethyl sulfoxide (see Table 3). In addition, a good linear
Nitrobenzene
Methanol
Dimethyl sulfoxide
⁎
correlation (r = 0.9926) was observed with the π azo scale [33], one
a
Spectra recorded using 6 × 10−5 M solutions. π azo values taken from reference [33].
⁎
of the most popular empirical scales used for the quantification of sol-
vent polarity (see Fig. 4) [34,35]. This fact clearly indicates the great po-
tential of this type of indan-1,3-dione-based butadiene dyes as new
solvatochromic polarity probes.
Finally, we would like to stress that the present C–C coupling process
is also operative with secondary propargylic alcohols, as exemplified by
the high yield preparation of the known compound 5 [19] starting from
indan-1,3-dione and 1-phenyl-2-propyn-1-ol (2h) (Scheme 3). In com-
plete accord with our previous results in the InCl3-catalyzed Meyer–
Schuster rearrangement of secondary propargylic alcohols [12], only
the E-isomer of compound 5 was formed (3JHH = 15.8 Hz).
allowed us to generate the butadiene derivative 7 [18] in 87% isolated
yield (Scheme 3). All these facts confirm the great potential of this aque-
ous transformation for the construction of keto-functionalized butadi-
ene frameworks.
4. Conclusions
In summary, a new and efficient protocol for the preparation of
indanedione-based butadiene derivatives has been developed employing
inexpensive InCl3 as catalyst, environmentally friendly water as solvent
and microwave irradiation as the heating source. The classical prepara-
tion of this type of compounds involves the Knoevenagel condensation
of indan-1,3-dione with aldehydes, but here we have shown that
propargylic alcohols instead of aldehydes can be alternatively employed
as the starting materials due to the ability of InCl3 to promote the
Meyer–Schuster reaction. Further studies directed to the application of
this new C–C coupling process to the preparation of other butadienic
Also of note is that other 1,3-dicarbonyl compounds, such as 2,4-
pentanedione (6), can be employed. Thus, the reaction of 6 with 1,1-
diphenyl-2-propyn-1-ol (2a), under identical experimental conditions,
⁎
⁎
Fig. 3. UV–Vis spectra of compounds 4a–g in CH2Cl2.
Fig. 4. λmax vs π azo values for dye 4f (fitting results: λmax = 538.10 + 59.35π azo).

14
J. Francos et al. / Catalysis Communications 63 (2015) 10–14
Scheme 3. MW-assisted InCl3-catalyzed synthesis of the 1,3-butadiene compounds 5 and 7 in water.
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Acknowledgments
The financial support from the Spanish MINECO (Project CTQ2010-
14796/BQU) is acknowledged.
Appendix A. Supplementary data
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4a–g, 5 and 7. Supplementary data to this article can be found online at
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