Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultrasound irradiation

Article abstract of DOI:10.1016/j.ultsonch.2012.10.018

The solvent-free indium-promoted reaction of alkanoyl chlorides with sterically and electronically diverse arylstannanes is a simple and direct method for the regioselective synthesis of primary, secondary and tertiary alkyl aryl ketones in good to excellent isolated yields (42-84%) under mild and neutral conditions. The protocol is also adequate for the synthesis of aryl vinyl ketones. Reaction times are drastically reduced (from 3-32 h to 10-70 min) under ultrasonic irradiation. Evidences for the involvement of a homolytic aromatic ipso-substitution mechanism, in which indium metal acts as radical initiator, are presented. It is possible the transference of two aryl groups from tin, thus improving effective mass yield, working with diarylstannanes as starting substrates.

Full text of DOI:10.1016/j.ultsonch.2012.10.018

Ultrasonics Sonochemistry xxx (2012) xxx–xxx
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Indium-mediated regioselective synthesis of ketones from arylstannanes
under solvent-free ultrasound irradiation
,1
⇑
⇑
Marcos J. Lo Fiego, Mercedes A. Badajoz, Claudia Domini, Alicia B. Chopa , María T. Lockhart
Instituto de Química del Sur (CONICET-UNS), Departamento de Química, Universidad Nacional del Sur, Avenida Alem 1253, Bahía Blanca B8000CPB, Argentina
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2012
Received in revised form 26 October 2012
Accepted 31 October 2012
Available online xxxx
The solvent-free indium-promoted reaction of alkanoyl chlorides with sterically and electronically
diverse arylstannanes is a simple and direct method for the regioselective synthesis of primary, second-
ary and tertiary alkyl aryl ketones in good to excellent isolated yields (42–84%) under mild and neutral
conditions. The protocol is also adequate for the synthesis of aryl vinyl ketones. Reaction times are dras-
tically reduced (from 3–32 h to 10–70 min) under ultrasonic irradiation. Evidences for the involvement of
a homolytic aromatic ipso-substitution mechanism, in which indium metal acts as radical initiator, are
presented. It is possible the transference of two aryl groups from tin, thus improving effective mass yield,
working with diarylstannanes as starting substrates.
Keywords:
Ultrasound
Solvent-free
Aromatic ketones
Arylstannanes
Indium
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
(o-dichlorobenzene, 180 °C) for the selective synthesis of tertiary
alkyl aryl ketones in good to high yields, without the generation
Ketones are vital building blocks in organic synthesis as well as
an important functionality found in several natural products and
pharmaceutical compounds. The Friedel–Crafts (F–C) acylation of
aromatic compounds is the most common route for the synthesis
of aromatic ketones [1]. Nevertheless, intrinsic limitations of F–C
reactions are the substituent-directing effects, the reactivity sub-
strate requirements and the fact that recovery and recycling of
the catalyst is seldom possible after aqueous work-up and a large
amount of toxic waste is generated. On the other hand, Pd-
catalyzed cross-coupling reactions of acyl halides with organome-
tallic reagents provide a direct procedure for the synthesis of
isomeric ketones [2]; a drawback is that Pd-catalysts are expensive
and that it is usually necessary to find the appropriate catalytic
protocol for each pair of reactants. We have been involved in the
synthesis of arylstannanes as well as in their application as inter-
mediates in organic synthesis [3]; recently, based on the excep-
tional leaving group ability of the trialkylstannyl group in
electrophilic aromatic substitutions we have developed new
straightforward procedures for the regiospecific [4] mono-, bi-
and triaroylation of aromatic rings by the reaction of mono-,
bi- and tristannylarenes with different aroyl chlorides [5].
Moreover, we have proposed an efficient catalyst-free route
of alkylbenzenes as by-products, by the reaction of arylstannanes
with tertiary aliphatic acyl chlorides [6]. Unfortunately, under a
similar protocol acyl chlorides bearing
a-hydrogens lead only to
protodestannylated products due to the presence of HCl generated
under the reaction conditions, probably, by a b-elimination of the
alkanoyl chloride [6]. In recent years, the development of
indium-mediated synthetic methods has grown up in the literature
due to the special properties of indium metal [7]. Thus, it is unaf-
fected by air, moisture or oxygen at ambient temperature and,
most importantly, the element itself is without any apparent tox-
icity. In this respect, we have established that indium metal is a
promoter of the solvent-free reaction of aroyl chlorides with arylst-
annanes applied to the synthesis of hindered benzophenones [5c].
Based on this experience we considered interesting to explore the
application of a similar protocol for the synthesis of alkyl aryl ke-
tones, specially taking into account the above mentioned limita-
tion found in our catalyst-free route [6].
In the last decades, ultrasound irradiation has emerged as an
eco-environmental technology in green chemistry [8]. It has been
increasingly used as an alternative energy source to promote sev-
eral organic transformations in higher yields, shorter reaction
times and milder conditions, being considered a clean and useful
protocol compared with traditional methods [9]. A literature sur-
vey demonstrates that many synthetic protocols using metals or
organometallic reagents could be promoted by ultrasonic irradia-
tion [10]. Thus, it has beneficial effects on indium-mediated reac-
tions [10,11], and the existence of SET pathways may be
⇑
Corresponding authors. Tel.: +54 291 4595101/3537; fax: +54 291 4595187
(M.T. Lockhart).
E-mail address: lockhart@criba.edu.ar (M.T. Lockhart).
Member of CIC.
1
1350-4177/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2012.10.018
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018

2
M.J. Lo Fiego et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
probable in these type of reactions [7]. Additionally, many solvent-
free protocols can be conducted smoothly by sonication [12].
On the base of these antecedents we considered really interest-
ing to study the effect produced by ultrasonic irradiation on our
protocol.
Thus, we report herein the synthetic potential of the ultrasound
irradiated, solvent-free, indium-promoted reaction of acid chlo-
rides with arylstannanes; we have checked the reusability of the
indium metal and a special work-up was carried out to recover
the organotin by-products. The study resulted in an attractive pro-
cess for the synthesis of alkyl aryl ketones under mild and neutral
conditions.
It should be mentioned that each reaction was, in principle, per-
formed at the lowest temperature which allowed keeping the stir-
ring of the reaction mixture during reaction time. Nevertheless, it
is important to note that an increase in reaction temperature
causes a sharp reduction of reaction times (entries 3 vs. 4; 8 vs. 9).
We carried out control experiments which showed that no reac-
tion occurred in the absence of indium, indicating that the metal
acts as a promoter of these reactions. On the other hand, the addi-
tion of galvinoxyl radical (0.5 equiv) to a couple of reactions pro-
duced a marked retardation effect and they did not proceed
efficiently comparing with blank ones. Based on these results, we
believe that these reactions proceed initially through a single-elec-
tron transfer (SET) from indium to the acyl chloride with genera-
tion of an acyl radical,3 which reacts with the arylstannane
through a homolytic ipso aromatic substitution affording the ketone.
The selective ipso-substitution is a consequence of the enhanced
hyperconjugation of the unpaired electron with the b-carbon-tin
bond (b-effect) [14]. The tin radical should be rapidly lost and reacts
with the alkanoyl chloride, regenerating the acyl radical (Scheme 1).
It should be mentioned that the reaction also takes place using sub-
stoichiometric amounts (0.2 equiv) of In(0) although the yield de-
crease from 84% to 71% (entries 9 and 10).
2. Results and discussion
We started our study by synthesizing a series of sterically and
electronically diverse arylstannanes (1a–h) which were then sub-
jected to the reaction with different acid chlorides (2a–g) under
the conditions we have previously established, that is, solvent-free,
in the presence of indium powder [5c].
An analysis of the results summarized in Table 1 shows that
electronic effects have a notable influence in the reaction; thus,
arylstannanes bearing electron-releasing groups gave the corre-
sponding ketones even at room temperature meanwhile the pres-
ence of electron-withdrawing groups made it necessary to work at
higher temperatures (for example, compare entry 2 with 3 and 4).
Moreover, the reaction of 2a with 1h, bearing a p-cyano substitu-
ent, was negative even after 72 h at 80 °C and the starting substrate
was almost recovered (entry 7). On the other hand, the substitution
pattern of the aromatic ring did not greatly affect the reaction and
ortho-, para- and meta-substitution were well tolerated. In general,
the reactions gave, as a single product, the corresponding ketones
resulting from the strict ipso-substitution of the stannyl group,
allowing the synthesis of ketones with high specificity. Thus, even
the more sterically hindered 2,6-dimethylphenylstannane (1g) was
also successfully ipso-acyldestannylated giving the corresponding
ketones 3ga, 3gb, 3gf and 3gg in good isolated yields (47–75%).
It should be mentioned that in experiments 6, 14 and 22 traces
of an isomeric ketone were detected (GC), generated by direct acyl-
ation of the aromatic ring followed by protodestannylation. On the
other hand, the negative reaction between 1g and 2c is probably
due to steric effects (entry 19). Unfortunately, it was not possible
to overcome the strong para-directing effect of the OMe group pro-
ducing, whatever the acyl chloride employed, high amounts of the
ketone generated by direct acylation of the ring (entries 1 and 18),
being these results consistent with those obtained previously in
the aroylation of arylstannanes [5c].
A global evaluation of the results indicates that the method can
be used to produce ketones either from primary, secondary or ter-
tiary alkanoyl chlorides.2 By the way, due to its low boiling point,
the reactions with acetyl chloride must be carried out in solution
being benzotrifluoride chosen as solvent in view of its properties
(entry 23) [13]. Furthermore, experiment 22 shows that by using
cinnamoyl chloride (2g) afforded the desired ketone although in
moderate yield (47%). On the other hand, electron withdrawing
groups on the acyl chloride moiety showed a negative effect. Thus,
while the reaction of pivaloyl chloride (2d) with 1b produced the de-
sired ketone in 55% yield (22 h, 60 °C), under analogous conditions
the reaction of the similar acyl chloride 2e with 1b was negative
and the starting substrate was almost recovered after 24 h of reac-
tion (entries 20 and 21).
Next, since sonication is able to affect heterogeneous systems
which include radical mechanisms [9], we studied the effect pro-
duced by ultrasonic irradiation over these reactions.
The optimal conditions for carrying out the irradiated reactions
were found by the reaction of tributylstannyl-3-chlorobenzene (1f)
and butanoyl chloride (2a) in the presence of indium (Table 2). The
model reaction was carried out using an ultrasonic probe (from
Cole-Parmer ultrasonic homogenizer-4710 of 20 kHz and 375 W)
equipped with a 10 mm diameter titanium horn. Experiments
were conducted in closed glass reactors along with the horn im-
mersed in a bath. The first experiments were performed in a
water/detergent bath [15] (60 °C initial temperature) working at
70% and 90% of output power and in a pulsed mode with different
duty cycles (70% or 80%). The results indicated that the reaction
proceeded similarly under the diverse conditions employed so, in
the following, 70% of power out and 70% duty cycles were used.
Moreover, as cavitation is dependent on temperature [16], one
experiment was performed at 100 °C (initial temperature, oil
bath); under these conditions product 3fa was obtained in a simi-
lar yield but in really shorter reaction time (3 min). Probably, the
increase in the reaction rate at 100 °C is due to the decrease of
the reaction mixture viscosity (solvent-free) which improves the
molecular diffusion [12a]. These results enable us to affirm that
in comparison with the conventional method (Table 1, entry 5)
the major advantage of ultrasound application is the significant de-
crease in the reaction time (from 5 h at 80 °C under classical con-
ditions to 10 min at 60 °C or 3 min at 100 °C, under irradiation).
The optimized conditions were applied to a representative
series of reactions, shown in Table 3, in order to compare with
those reactions carried out by the conventional method (Table 1).
It should be mentioned that the reactions were performed at the
lowest temperature which kept a homogeneous mixture of sub-
strate and reactant.
The results obtained show that, in all cases, sonication dramat-
ically reduced the reaction times without significantly affecting the
yields. Once more, ultrasound enhanced the rate of a reaction and,
consequently, reduced energy consumption. Comparing experi-
ments 4 and 5, the reaction took place even using sub-stoichiome-
tric amounts of indium but giving lower yields of ketone (62% vs.
47%). On the other hand, experiments 7 and 9 show that it was pos-
sible to performed reactions, in a reasonable reaction time, without
2
It was found that 2.0 equiv. of tertiary acyl chloride is required in order to shorten
3
reaction times.
Indium metal is capable of promoting SET processes. See Ref. [7].
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018

M.J. Lo Fiego et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
3
Table 1
Indium-mediated reactions of arylstannanes with acid chlorides.
In(0)
ArSnR3
R'COCl
ArCOR'
+
temp, time
neat
1
2
3
Entrya
1
1
Ar
2
R’
Temp. (°C)
Time (h)
3
ArCOR0
Yield (%)b
Tracesc
1a
3-MeOC6H4
2a
Pr
r.t.
r.t.
r.t.
6
3aa
O
O
2
3
1b
1e
3-MeC6H4
3-FC6H4
2a
2a
Pr
Pr
6
3ba
3ea
49
5d
O
24
O
F
4
5
1e
1f
3-FC6H4
3-ClC6H4
2a
2a
Pr
Pr
80
80
5
5
3ea
3fa
55
49
O
Cl
6
7
1g
1h
2,6-Me2C6H3
4-CNC6H4
2a
2a
Pr
Pr
80
80
6
3ga
3ha
72e
0f
O
72
O
NC
8
1b
3-MeC6H4
2b
ACH(Ph)CH2CH3
r.t.
100
3bb
64
O
9
1b
1b
1c
3-MeC6H4
3-MeC6H4
4-MeC6H4
2b
2b
2b
ACH(Ph)CH2CH3
ACH(Ph)CH2CH3
ACH(Ph)CH2CH3
80
80
80
6
6
3
3bb
3bb
3cb
84
71
76
10g
11
O
O
12
13
14
15
1d
1e
1g
1b
2-MeC6H4
3-FC6H4
2b
2b
2b
2c
ACH(Ph)CH2CH3
ACH(Ph)CH2CH3
ACH(Ph)CH2CH3
1-Ad
80
80
r.t.
80
3
7
3db
3eb
3gb
3bc
65
61
O
F
2,6-Me2C6H3
3-MeC6H4
32
25
75e
42d
O
O
16h
17h
1b
1d
3-MeC6H4
2-MeC6H4
2c
2c
1-Ad
1-Ad
80
80
5
14
3bc
3dc
69
51
O
O
18h
19h
20h
21h
1a
1g
1b
1b
3-MeOC6H4
2,6-Me2C6H3
3-MeC6H4
2c
2c
2d
2e
1-Ad
60
80
60
60
10
24
22
24
3ac
3gc
3bd
3be
0c
O
O
1-Ad
Tracesf
55
t-Bu
O
O
3-MeC6H4
AC(CH2Cl)2CH3
0f
Cl
Cl
(continued on next page)
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018

4
M.J. Lo Fiego et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
Table 1 (continued)
Entrya
22
1
Ar
2
R’
Temp. (°C)
Time (h)
3
3
ArCOR0
Yield (%)b
47e
1g
2,6-Me2C6H3
2g
ACH@CHPh
60
3gg
O
23i
1g
2,6-Me2C6H3
2f
ACH3
r.t.
8
3gf
57
O
a
b
c
d
e
f
All reactions were conducted in solventless conditions using 1.0 equiv of 1, 1.2 equiv of 2 and 1.0 equiv of indium metal, unless otherwise stated.
Isolated yields from 1.0 mmol scale experiment (column chromatography).
High yield of para-isomer (GC).
Together with starting substrate (GC).
Together with traces of isomer.
Starting substrate was almost recovered.
In presence of 0.2 equiv of In(0).
g
h
i
2.0 equiv of 2 were used.
In solution of CF3C6H5 (1.0 M in 1).
R'COCl
In(0)
Table 3
Indium-mediated reactions of arylstannanes with acid chlorides under ultrasonic
irradiation.
SnR3
R3SnCl
InCl
In(0)
R'CO
ArSnR3
R'COCl
ArCOR'
+
neat
1
2
3
)
)
)
)
R'COCl
R3Sn
COR'
Entrya
1
2
Temp.b (°C)
Time (min)
3
Yieldc (%)
R3Sn
1
2
3
4
1b
1e
1b
1e
1e
1b
1b
1b
1b
2a
2a
2b
2b
2b
2c
2c
2d
2d
60
60
80
80
80
80
80
80
80
10
10
30
45
45
20
53
40
70
3ba
3ea
3bb
3eb
3eb
3bc
3bc
3bd
3bd
47
55
79
62
47
70
70
55
52
COR'
5d
6e
7
8e
9
Scheme 1. Proposed mechanistic pathways for the indium-mediated homolytic
aromatic ipso-substitution of aryltins.
a
All reactions were conducted in solventless conditions using 1.0 equiv of 1,
1.2 equiv of 2 and 1.0 equiv of indium metal, unless otherwise stated.
b
Water/detergent bath (60 °C); oil bath (80 °C).
Isolated yields.
In(0) (0.2 equiv).
2 (2.0 equiv).
c
d
e
Table 2
Optimizing conditions for ultrasound.
SnBu3
O
O
Cl
In(0)
neat
+
Cl
existence of a chemical ultrasound enhancement [9a,b]. The in-
tense local temperature and high pressure produced during cavita-
tion promoted the cleavage of the carbon-halogen bond of the acid
chloride (sonolysis) generating an acyl radical and initiating the
radical process to give the corresponding ketone, although in lower
yields compared with the indium-catalyzed reaction. Ultrasound
exerts a dual effect on the indium-assisted reaction (heteroge-
neous system); on the one hand, it favors the radical reaction
and, on the other hand, it enhances the activity of the metal. In this
way, cavitation generates microinjects of liquid which bombard
the solid surface, removing contaminating coatings. It is known
that clean metal surfaces favor the single-electron transfer (SET)
from metals (indium) to an organic compound (the acyl chloride)
increasing the reaction rate [9a,c].
A drawback of the synthetic protocol is the generation of an
equimolecular amount of triorganotin chlorides. Because of the
environmental problems caused by the well-known toxicity of tri-
organotin residues, we considered really important to trap them
and applied a special work up in order to recover the trialkyltin
chlorides produced (see Section 3). With the main goal of decreas-
ing the level of pollution we also considered interesting to study
the possibility of transferring more than one aryl group attached
Cl
)
)
)
)
3fa
2a
1f
Entry Power (%) Duty cycles (%) Temp.a (°C) Time (min) Yieldb (%)
1
2
3
4
70
90
90
70
70
70
80
70
60
60
60
10
10
10
3
53
49
52
54
100
a
Water/detergent bath (60 °C); oil bath (100 °C).
Isolated yields.
b
using an excess of tertiary alkanoyl chlorides (compare with en-
tries 6 and 8), thus improving the traditional method (minimiza-
tion of the reagents correspondingly minimized waste).
In order to evaluate the role of ultrasound in the reaction sys-
tem we repeated experiments 6 and 7 (Table 3) but in the absence
of indium, that is, under homogeneous conditions. After the same
reaction times (20 min and 53 min, respectively) the correspond-
ing ketones were obtained (23% and 36%, respectively) together
with starting substrate. The presence of ketone supports the
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018

M.J. Lo Fiego et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
5
Table 4
use of no solvent; (iii) readily available, non-toxic and reusable metal
catalyst; (iv) accessible substrates and reactants; (v) improved effec-
tive mass yield [17]; (vi) specificity of the reaction; and (vii) simplic-
ity in the isolation of the products. These characteristics make this
procedure very attractive.
Indium-mediated reactions of diarylstannanes with acid chlorides under ultrasonic
irradiation.
In(0)
Ar2SnR2
R'COCl
ArCOR'
+
neat
2
3
)
)
)
)
Entrya
Ar
2
Temp.b (°C)
Time (min)
3
Yieldc (%)
3. Experimental
1
2
3
4
5
6
3-MeC6H4
3-MeC6H4
3-MeC6H4
3-ClC6H4
3-FC6H4
2a
2b
2c
2a
2a
2b
60
80
80
60
60
80
6
15
25
6
6
10
3ba
3bb
3bc
3fa
3ea
3eb
36
61
60
33
41
42
3.1. General methods
All reactions were carried out under a dry nitrogen atmosphere.
Acid chlorides were commercially available and fractionally dis-
tilled under nitrogen before use. Aryltributylstannanes 1a–f were
prepared by transmetallation of the appropriate Grignard reagents
with tributyltin chloride in anhydrous THF. Aryltrimethylstann-
anes 1g and 1h were obtained by photostimulated reaction with
Me3SnNa in liquid ammonia, according to the literature proce-
dures; the former from the corresponding commercial aryl chloride
[18] and the latter from the synthesized (4-cyanophenyl) trimethy-
lammonium methylsulfate [3b]. Reactions were monitored by
thin-layer chromatography carried out on silica gel plates (60F-
254) and visualized under UV light or using 5% phosphomolybdic
acid in ethanol. Column chromatography was performed over silica
gel 60 (70–230 mesh) doped with 10% of potassium fluoride [5a].
The NMR spectra were recorded on a 300 MHz spectrometer
(300.1 MHz for 1H, 75.5 MHz for 13C). Chemical shifts (d) are re-
ported in ppm downfield from tetramethylsilane, with residual
non deuterated solvent resonance as internal reference (CDCl3: d
7.27 for 1H and d 77.0 for 13C) and coupling constants (J) are in
Hz. Identity and purity of the products (crude or purified) were
established using a GC/MS instrument (HP5-MS capillary column,
3-FC6H4
a
All reactions were conducted in solventless conditions using 1.0 equiv of Ar2-
SnR2, 2.0 equiv of 2 and 1.0 equiv of indium metal.
b
Water/detergent bath (60 °C); oil bath (80 °C).
Isolated yields referred to stoichiometric equation.
c
to the metal. For this purpose, we applied the ultrasound protocol
to the reaction of acyl chloride 2b with tributylphenylstannane,
dibutyldiphenylstannane, butyltriphenylstannane and tetraphe-
nylstannane, as model systems. The results are summarized in
Eq. (1) and the yields are referred to the stoichiometric equation.
O
4-n
O
Cl
Ph
Ph4-nSnBun
Cl4-nSnBun
+
Ph
))
)
In(0), 80°C, )
Ph
n
3
2
1
0
ð1Þ
50 min
30 min
15 min
7 min
84 %
52 %
25 %
5 %
30 m ꢀ 0.25 mm ꢀ 0.25
lm) equipped with 5972 mass selective
detector operating at 70 eV (EI). Program: 50 °C for 2 min with in-
crease 10 °C/min to 280 °C. For gas–liquid chromatography (GC) an
instrument equipped with a flame-ionization detector and a HP5
The results obtained showed that while diphenylstannane is a suit-
able substrate giving the ketone in an acceptable yield (52%), tri-
and tetraphenylstannanes afforded only 25% and 5% of ketone,
respectively, together with large amounts of protodestannylation
product.
Next, we synthesized a series of diarylstannanes in order to
study their reactivity towards different alkanoyl chlorides (Table
4).
capillary column (30 m ꢀ 0.25 mm ꢀ 0.25
lm) was used. External
sonication was carried out using an ultrasonic probe (from Cole-
Parmer 4710 series ultrasonic homogenizer of 20 kHz and
375 W) equipped with a 10 mm diameter titanium horn, which
was immersed either in a water–detergent [15] or in an oil bath.
The physical and spectroscopic characteristics of compounds
3bc, 3dc and 3bd have been reported upon in a previous paper
[5a].
It can be seen that, in general, diarylstannanes are appropriate
substrates as the corresponding ketones are obtained in acceptable
yields implying the use of sub-stoichiometric amounts of organotin
compounds. In addition, from a sustainable point of view, the
byproduct to be separated is Bu2SnCl2 which is less toxic than Bu3-
SnCl and easily converted into insoluble (Bu2SnO)n (see Section 3).
Moreover, it is important to mention that indium metal is stable
under both reaction conditions employed and we were able to re-
cover (ca. 90%)4 and reuse it without significant changes in the yield
of the following reactions. This is really significant taking into ac-
count that indium has been defined as a rare metal and that, due
to the many uses of indium in technology, there has been an increas-
ing demand and, consequently, significantly increased costs.In con-
clusion, the method provides a facile and specific access to a wide
range of alkyl aryl ketones via arylstannanes. These partners are
attractive due to their availability, air- and moisture-stability, and
their compatibility with a variety of functional groups. Moreover,
the transfer of two aryl groups from tin reduced the amount of
non-benign organotin subproducts. The difficulties connected with
organotin removal were largely solved in the workup and, in addi-
tion, these by-products were recovered and not rejected.The striking
advantages of the method are (i) energy saving by sonication; (ii) the
Under silent conditions, indium-mediated reactions were car-
ried out following the experimental procedure described in our lat-
est work [5c].
3.2. Representative procedure for ultrasound assisted indium-
mediated reactions. Synthesis of 1-(3-chlorophenyl)butanone (3fa;
Table 2, entry 1) [19]
In a flame dried Schlenk tube (fitted with a Teflon plug valve)
1.2 mmol (0.127 g) of butanoyl chloride (2a) was added to a stirred
mixture of 1.0 mmol (0.402 g) of tributyl(3-chlorophenyl)stannane
(1f) and indium powder (0.148 g, 1.0 mmol) under a nitrogen gas
stream. After purging the system with nitrogen by means of three
pump-fill cycles, the tube was capped and immersed in a water–
detergent bath at 60 °C. The ultrasonic titanium horn was placed
into the bath to a distance of 10 mm to the wall and 5 mm from
the bottom of the Schlenk tube and ultrasound was applied in a
pulsed mode (duty cycle = 70%; output power = 70%) for 10 min.
After addition of 10% (m/v) solution of NaOH (2 mL) and 10 lL of
tetradecane (internal standard), the mixture was stirred at room
temperature for 15 min and then diluted with DCM (5 mL). Once
the stirring was stopped for about 5 min, the supernatant liquid
4
Purity and identity proof of indium metal were obtained by differential scanning
calorimetric (DSC) analysis.
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018

6
M.J. Lo Fiego et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
mixture was decanted into a separatory funnel. The silvery-white
solid, settled at the bottom of the Schlenk tube, was washed with
acetone (2 ꢀ 5 mL), deionized water (2 ꢀ 5 mL), and then vac-
uum-dried at room temperature. As indicated by DSC analysis,
the dried sample (0.133 g) meant a 90% recovered yield of pure in-
dium. On the other hand, the organic phase was successively
washed with water and brine, dried over Na2SO4, filtered, analyzed
by GC, and then concentrated in vacuo. Purification by column
chromatography on silica gel (60 Å, 70–230 mesh) doped with
10% of KF (hexanes/DCM 8:2) gave 0.096 g (53%) of 3fa as a color-
3.2.5. 2-Phenyl-1-(4-methylphenyl)butanone (3cb; Table 1, Entry 11)
[21]
Colorless oil. m
max/cmꢁ1 1692 (CO). 1H NMR (300 MHz, CDCl3) d
(ppm) 7.80 (d, J = 8.2 Hz, 2H), 7.22–7.14 (m, 4H), 7.10–7.06 (m, 3H),
4.33 (t, J = 7.2 Hz, 1H), 2.22 (s, 3H), 2.11 (m, 1H enantiotropic), 1.76
(m, 1H enantiotropic), 0.80 (t, J = 7.4 Hz, 3H); 13C NMR (75.5 MHz,
CDCl3) d (ppm) 199.6 (CO), 143.4 (C), 139.9 (C), 134.6 (C), 129.1
(CH), 128.7 (CH), 128.2 (CH), 126.8 (CH), 55.3 (CH), 27.1 (CH2),
21.4 (CH3), 12.3 (CH3); MS m/z (% rel. intensity, ion) 238 (2, M+Å),
119 [100, (MePhCO+)], 91 [51, (PhCHþ2 Þ].
less oil. m
max/cmꢁ1 1692 (CO). 1H NMR (300 MHz, CDCl3) d (ppm)
7.92 (m, 1H), 7.82 (m, 1H), 7.52 (ddd, J = 1.0 Hz, J = 1.9 Hz,
J = 7.9 Hz, 1H), 7.39 (t, J = 7.8 Hz, 1H), 2.92 (t, J = 7.2 Hz, 2H),
1.77 (m, 2H), 1.00 (t, J = 7.4 Hz, 3H); 13C NMR (75.5 MHz, CDCl3)
d (ppm) 198.9 (CO), 138.7 (C), 134.9 (C), 132.7 (CH), 129.9 (CH),
128.2 (CH), 126.1 (CH), 40.6 (CH2), 17.6 (CH2), 13.8 (CH3); MS m/
z (% rel. intensity, ion) 182 (5, M+Å), 139 [100, (M+ÅAPrÅ)], 111 [56,
(ClPh+)]. (3fa is also found in Table 1, entry 5 and in Table 4, entry
4).
3.2.6. 2-Phenyl-1-(2-methylphenyl)butanone (3db; Table 1, entry 12)
Colorless oil. m
max/cmꢁ1 1693 (CO). 1H NMR (300 MHz, CDCl3) d
(ppm) 7.74 (m, 1H), 7.50–7.36 (m, 8H), 4.50 (t, J = 7.3 Hz, 1H), 2.54
(s, 3H), 2.46 (m, 1H enantiotropic), 2.07 (m, 1H enantiotropic), 1.16
(t, J = 7.4 Hz, 3H); 13C NMR (75.5 MHz, CDCl3) d (ppm) 204.4 (CO),
139.2 (C), 138.9 (C), 137.7 (C), 131.5 (CH), 130.6 (CH), 128.6 (CH),
128.4 (CH), 127.7 (CH), 126.9 (CH), 125.3 (CH), 58.8 (CH), 26.5
(CH2), 20.5 (CH3), 12.3 (CH3); MS m/z (% rel. intensity, ion) 238
(1, M+Å), 119 [100, (MePhCO+)], 91 [59, (PhCHþ2 Þ]. Anal. Calcd. for
C17H18O: C 85.67, H 7.61. Found: C 85.90, H 7.63.
3.2.1. 1-(3-Methylphenyl)butanone (3ba; Table 1, entry 2; Table 3,
entry 1 and Table 4, entry 1) [20]
Yellow oil. m
max/cmꢁ1 1690 (CO). 1H NMR (300 MHz, CDCl3) d
3.2.7. 2-Phenyl-1-(3-fluorophenyl)butanone (3eb; Table 1 entry 13;
Table 3, entry 4 and Table 4, entry 6)
(ppm) 7.79–7.74 (m, 2H), 7.38–7.30 (m, 2H), 2.94 (t, J = 7.3 Hz,
2H), 2.42 (s, 3H), 1.78 (m, 2H), 1.02 (t, J = 7.4 Hz, 3H); 13C NMR
(75.5 MHz, CDCl3) d (ppm) 200.6 (CO), 138.3 (C), 137.2 (C), 133.5
(CH), 128.5 (CH), 128.4 (CH), 125.3 (CH), 40.6 (CH2), 21.3 (CH3),
17.8 (CH2), 13.9 (CH3). MS m/z (% rel. intensity, ion) 162 (18,
M+Å), 147 [3, (M+ÅAMeÅ)], 134 [5, (M+ÅACH2CH2)], 119 [100,
(M+ÅAPrÅ)].
White solid, m.p. 55 °C.
(300 MHz, CDCl3) (ppm) 7.64 (d, J = 7.6 Hz, 1H), 7.54 (d,
m
max/cmꢁ1 1689 (CO). 1H NMR
d
J = 9.5 Hz, 1H), 7.30–7.06 (m, 7H), 4.29 (t, J = 7.2 Hz, 1H), 2.12 (m,
1H enantiotropic), 1.78 (m, 1H enantiotropic), 0.83 (t, J = 7.3 Hz,
3H); 13C NMR (75.5 MHz, CDCl3) d (ppm) 198.8 (d, J = 1.9 Hz, CO),
162.8 (d, J = 248 Hz, C), 139.3 (C), 139.2 (CH), 130.1 (d, J = 7.5 Hz,
CH), 128.9 (CH), 128.2 (CH), 127.1 (CH), 124.3 (d, J = 2.7 Hz, CH),
2
119.7 (d, J = 21.7 Hz, CH), 115.4 (d, JCF = 22 Hz, CH); 115,4 (d,
3.2.2. 1-(3-Fluorophenyl)butanone (3ea; Table 1, entry 4; Table 3,
entry 2 and Table 4, entry 5)
2JCF = 22 Hz, CH); 55,8 (CH2); 27,0 (CH2); 12,2 (CH3). MS m/z (%
rel. intensity, ion) 242 (9, M+Å), 183 [5, (M+ÅAEtCOÅ)], 123 [100,
(FPhCO+)], 91 [92, ðPhCH2þÞ]. Anal. Calcd. for C16H15FO: C 79.32,
H 6.24. Found: C 79.10, H 6.21.
Yellow oil. m
max/cmꢁ1 1692 (CO). 1H NMR (300 MHz, CDCl3) d
(ppm) 7.74 (d, J = 7.7 Hz, 1H), 7.64 (m, 1H), 7.45 (m, 1H), 7.23
(m, 1H), 2.93 (t, J = 7.3 Hz, 2H), 1.78 (m, 2H), 1.01 (t, J = 7.4 Hz,
4
3H). 13C NMR (75.5 MHz, CDCl3) d (ppm) 197.6 (d, JCF = 1.5 Hz,
3.2.8. 2-Phenyl-1-(2,6-dimethylphenyl)butanone (3gb; Table 1, entry
14)
1
3
CO), 163.1 (d, JCF = 247 Hz, C), 139.0 (C), 130.2 (d, JCF = 7.7 Hz,
4
2
CH), 123.7 (d, JCF = 3.0 Hz, CH), 119.8 (d, JCF = 22 Hz, CH), 114.7
Colorless oil. m
max/cmꢁ1 1690 (CO) 1H NMR (300 MHz, CDCl3) d
2
(d, JCF = 22 Hz, CH), 40.6 (CH2), 17.6 (CH2), 13.8 (CH3); MS m/z (%
(ppm) 7.26–7.19 (m, 3H), 7.16 (m, 2H), 7.09 (m, 1H), 7.53 (d,
J = 7.5 Hz, 2H), 3.91 (dd, J = 5.5 Hz, J = 9.5 Hz, 1H), 2.32–2.04 (m,
2H), 1.93 (s, 6H), 0.89 (t, J = 7.4 Hz, 3H); 13C NMR (75.5 MHz, CDCl3)
d (ppm) 209.1 (CO), 141.8 (C), 136.9 (C), 133.4 (C), 129.2 (CH),
128.5 (CH), 128.5 (CH), 127.7 (CH), 127.3 (CH), 62.1 (CH), 24.3
(CH2), 19.2 (CH3), 11.9 (CH3); MS m/z (% rel. intensity, ion) 133
rel. intensity, ion) 166 (12, M+Å), 138 [11, (M+ÅACH2CH2)], 123
[100, (M+ÅAPrÅ)]. Anal. Calcd. for C10H11FO: C 72.27, H 6.67. Found:
C 71.99, H 6.79.
3.2.3. 1-(2,6-Dimethylphenyl)butanone (3ga; Table 1, Entry 6)
Yellow oil. m
max/cmꢁ1 1693 (CO). 1H NMR (300 MHz, CDCl3) 7.04
[100, ðMe2PhCOþÞ], 105 [33, Me2PhþÞ], 91 [20, ðPhCHþÞ]. Anal.
2
(t, 1H, J = 7.6), 6.9 (d, 2H, J = 7.6 Hz), 2.59 (t, 2H, J = 7.3 Hz), 2.13 (s,
6H), 1.66 (m, 2H), 0.92 (t, J = 7.4 Hz, 3H); 13C NMR (77.0 MHz,
CDCl3) 210.3 (CO), 142.5 (C), 132.3 (C), 128.3 (CH), 127.6 (CH),
46.5 (CH2), 19.0 (CH3), 16.7 (CH2), 13.7 (CH3); MS m/z (% rel. inten-
sity, ion) 176 (4, M+Å), 133 [100, (M+ÅAPrÅ)], 105 [39, (Me2PhþÞ].
Anal. Calcd. for C12H16O: C 81.77, H 9.15. Found: C 81.95, H 9.13.
Calcd. for C16H20O: C 85.67, H 7.99. Found: C 85.82, H 7.96.
3.2.9. 1-(2,6-Dimethylphenyl)ethanone (3gf; Table 1, entry 23) [22]
Yellow oil. m
max/cmꢁ1 1690 (CO). 1H NMR (300 MHz, CDCl3) d
(ppm) 7.15 (t, J = 7.1 Hz, 1H), 7.02 (d, J = 7.1 Hz, 2H), 2.48 (s, 3H),
2.26 (s, 6H); 13C NMR (75.5 MHz, CDCl3) d (ppm) 208.0 (CO),
142.6 (C), 132.2 (C), 138.5 (CH), 127.8 (CH), 32.0 (CH3), 19.1
(CH3); MS m/z (% rel. intensity, ion) 148 (21, M+Å), 133 [100, (M+Å-
AMeÅ)], 91 [8, (MePh+)], 77 [41, (Ph+)].
3.2.4. 2-Phenyl-1-(3-methylphenyl)butanone (3bb; Table 1, entry 9
and Table 3, entry 3)
White solid; m.p. 70–71 °C.
m
max/cmꢁ1 1690 (CO). 1H NMR
(300 MHz, CDCl3) d (ppm) 7.77–7.74 (m, 2H), 7.31–7.20 (m, 6H),
7.17 (m, 1H), 4.44 (t, J = 7.2 Hz, 1H), 2.33 (s, 3H), 2.21 (m, 1H enan-
tiotropic), 1.85 (m, 1H enantiotropic), 0.90 (t, J = 7.3 Hz, 3H); 13C
NMR (75.5 MHz, CDCl3) d (ppm) 200.3 (CO), 139.7 (C), 138.2 (C),
137.2 (C), 133.5 (CH), 129.1 (CH), 128.7 (CH), 128.3 (CH), 128.2
(CH), 126.8 (CH), 125.8 (CH), 55.4 (CH), 27.1 (CH2), 21.3 (CH3),
12.2 (CH3); MS m/z (% rel. intensity, ion) 238 (1, M+Å), 119 [100,
(MePhCO+)], 91 [58, (PhCH2+)]. Anal. Calcd. for C17H18O: C 85.67,
H 7.61. Found: C 85.38, H 7.58.
3.2.10. (E)-1-(2,6-Dimethylphenyl)-3-phenyl-2-propenone (3gg; Table
1, Entry 22)
Yellow oil.
m
max/cmꢁ1 1680 (CO) and 1602 (C = C). 1H NMR
(300 MHz, CDCl3) d (ppm) 7.40 (dd, J = 3.0 Hz, J = 6.6, 2H), 7.29–
7.27 (m, 3H), 7.11 (dd, J = 8.0 Hz, J = 16 Hz, 2H), 6.97 (d,
J = 7.6 Hz, 2H), 6.85 (d, J = 16 Hz, 1H), 2.14 (s, 6H); 13C NMR
(75.5 MHz, CDCl3) d (ppm) 200.9 (CO), 146.8(CH), 146.6 (C),
139.9 (C), 134.4 (C), 134.0 (CH), 130.8 (CH), 128.9 (CH), 128.4
(CH), 127.8 (CH), 127.3 (CH), 19.4 (CH3); MS m/z (% rel. intensity,
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018

M.J. Lo Fiego et al. / Ultrasonics Sonochemistry xxx (2012) xxx–xxx
7
ion) 236 (25, M+Å), 221 [9, (M+ÅAMeÅ)], 159 [10, (M+ÅAPhÅ)], 145
(100, C10H9O+) 133 [20, (Me2PhCO+)], 103 [45, (PhCHCH+)]. Anal.
Calcd. for C17H16O: C 86.40, H 6.82. Found: C 86.71, H 6.80.
organic reactions, Synthesis (2007) 1739–1764;
(d) J.S. Yadav, A. Antony, J. George, B.V. Reddy, Recent developments in indium
metal and its salts in organic synthesis, Eur. J. Org. Chem. (2010) 591–605.
[8] (a) T.J. Mason, P. Cintas, in: J. Clark, D. Macquarrie (Eds.), Handbook of Green
Chemistry and Technology, Blackwell Science, Oxford, 2002;
(b) T.J. Mason, Sonochemistry and the environment – Providing a ‘‘green’’ link
between chemistry, physics and engineering, Ultrason. Sonochem. 14 (2007)
476–483.
3.3. Recovering method for organotin chlorides
[9] (a) For reviews see: G. Cravotto, P. Cintas, Power ultrasound in organic
synthesis: moving cavitational chemistry from academia to innovative and
large-scale applications, Chem. Soc. Rev. 35 (2006) 180–196;
(b) R. Cella, H.A. Stefani, Ultrasound in heterocycles chemistry, Tetrahedron 65
(2009) 2619–2641;
The recovery of trialkyltin chlorides was carried out using the
methods resumed in our previous work [5c].
3.3.1. Dibutyltin dichloride
(c) K.S. Suslick, Comprehensive Coordination Chemistry 2, Elsevier Science,
NY, 2003 (Chapter 1.41, 731–739; Papers);
(d) A. Dandia, D.S. Bhati, A.K. Jain, G.N. Sharma, Ultrasound promoted clay
catalyzed efficient and one pot synthesis of substituted oxindoles, Ultrason.
Sonochem. 18 (2011) 1143–1147;
After workup of the reactions carried out with diaryldibutylst-
annanes, the resulting cloudy organic phases (ꢂ5 mL for 1.0 mmol
scale) were centrifuged. The amorphous off-white sediments of
(Bu2SnO)n were washed twice by centrifugation with DCM and re-
served for its further conversion in Bu2SnCl2 [23].
(e) E. Ruiz, H. Rodríguez, J. Coro, E. Salfrán, M. Suárez, R. Martínez-Alvarez, N.
Martín, Ultrasound-assisted one-pot, four component synthesis of 4-aryl 3,4-
dihydropyridone derivatives, Ultrason. Sonochem. 18 (2011) 32–36.
[10] P. Cintas, G. Palmisano, G. Cravotto, Power ultrasound in metal-assisted
synthesis: from classical Barbier-like reactions to click chemistry, Ultrason.
Sonochem. 18 (2011) 836–841.
[11] P.H. Lee, K. Bang, K. Lee, S.-Y. Sung, S. Chang, Ultrasound promoted synthesis of
b-hydroxyesters by reformatsky reaction using indium metal, Synth. Commun.
31 (2001) 3781–3789.
[12] (a) M. Chtourou, R. Abdelhédi, M. Hédi Frikha, M. Trabelsi, Solvent free
synthesis of 1,3-diaryl-2-propenones catalyzed by commercial acid-clays
under ultrasound irradiation, Ultrason. Sonochem. 17 (2010) 246–249;
(b) I. Mohammadpoor-Baltork, M. Moghadam, S. Tangestaninejad, V.
Mirkhani, Z. Eskandari, Ultrasound promoted selective synthesis of 2-aryl-
5,6-dihydro-4H-1,3-oxazines catalyzed by K-10 and KSF montmorillonite
clays: a practical procedure under mild and solvent-free conditions, Ultrason.
Sonochem. 17 (2010) 857–862;
(c) Z. Fu, H. Shao, An efficient synthesis of 3-substituted indole derivates
under ultrasound irradiation, Ultrason. Sonochem. 18 (2011) 520–526.
[13] A. Ogawa, D.P. Curran, Benzotrifluoride: a useful alternative solvent for organic
reactions currently conducted in dichloromethane and related solvents, J. Org.
Chem. 62 (1997) 450–451.
Acknowledgments
This work was partially supported by CONICET, CIC, ANPCYT
and the Universidad Nacional del Sur, Bahía Blanca, Argentina.
CONICET is thanked for a research fellowship to MJL F.
References
[1] (a) M.B. Smith, J. March, March’s Advanced Organic Chemistry, 6th. ed., John
Wiley, New York, 2007;
(b) R.C. Larock, Comprehensive Organic Transformations, Wiley, VCH; New
York, 1999.
[2] For a review of acylation of organometallic reagents with acid chlorides K.
Dieter, Reaction of acyl chlorides with organometallic reagents: a banquet
table of metals for ketone synthesis, Tetrahedron 55 (1999) 4177–4236.
[3] (a) Synthesis: A.B. Chopa, M.T. Lockhart, G.F. Silbestri, Two step synthesis of
arylstannanes from phenols, Organometallics 19 (2000) 2249–2251;
(b) A.B. Chopa, M.T. Lockhart, G.F. Silbestri, Synthesis of arylstannanes from
arylamines, Organometallics 20 (2001) 3358–3360;
[14] A.G. Davies, Metals as surrogates for hydrogen in organic chemistry: anything
hydrogen can do, a metal can do better, J. Chem. Soc., Perkin Trans. 1 (2000)
1997–2010.
[15] (a) We added detergent to water (2.0% v/v) in order to facilitate ultrasound
propagation. See: T.J. Mason, Sonochemistry, Oxford University Press, New
York, 1999;
(c) A.B. Chopa, M.T. Lockhart, V.B. Dorn, Phenols as starting materials for the
synthesis of arylstannanes via SRN1, Organometallics 21 (2002) 1425–1429;
(d) A.B. Chopa, M.T. Lockhart, G.F. Silbestri, Synthesis of bis(trimethylstannyl)
aryl compounds via SRN1 with intermediacy of monosubstitution products,
Organometallics 21 (2002) 5874–5878;
(e) G.F. Silbestri, M.J. Lo Fiego, M.T. Lockhart, A.B. Chopa, Selective synthesis of
mono- and distannylpyridines from chloropyridinols via an SRN1 mechanism,
J. Organomet. Chem. 695 (2010) 2578–2585;
(b) C.C. Nascentes, M. Korn, C.S. Sousa, M.A.Z. Arruda, Use of Ultrasonic Baths
for Analytical Applications: A New Approach for Optimization Conditions, J.
Braz. Chem. Soc. 12 (2001) 57–63.
[16] J.C. de Souza-Barboza, C.P. Btrier, J-L. Luche, Ultrasound in organic synthesis.
13. Some fundamental aspects of the sonochemical Barbier reaction, J. Org.
Chem. 53 (1988) 1212–1218.
[17] T. Hudlicky, D.A. Frey, L. Koroniak, C.D. Claeboe, L.E. Brammer, Towards a
‘‘reagent-free’’ synthesis, Green Chem. 1 (1999) 57–59.
[18] C.C. Yammal, J.C. Podestá, R.A. Rossi, Reactions of Triorganostannyl Ions with
Haloarenes in Liquid Ammonia. Competition between Halogen-Metal
Exchange and Electron-Transfer Reactions, J. Org. Chem. 571 (992) 5720–5725.
[19] F.I. Carroll, B.E. Blough, P. Abraham, A.C. Mills, J.A. Holleman, S.A.
Wolckenhauer, A.M. Decker, A. Landavazo, K.T. McElroy, H.A. Navarro, M.B.
Gatch, M.J. Forster, Synthetic and biological evaluation of bupropion analogues
as potential pharmacotherapies for cocaine addiction, J. Med. Chem. 52 (2009)
6768–6781.
[20] P.J. Wagner, M.J. Thomas, E. Harris, Effects of methyl substitution on the
photoreactivity of phenyl ketones. The applicability to Hammett sigma values
in correlations of excitation energies, J. Am. Chem. Soc. 98 (1976) 7675–7679.
[21] T.P. Smyth, B.W. Corby, Toward a clean alternative to Friedel–Crafts acylation:
(f) . Applications:A.B. Chopa, G.F. Silbestri, M.T. Lockhart, Strategies for the
synthesis of bi- and triarylic materials starting from commercially available
phenols, J. Organomet. Chem. 690 (2005) 3865–3877.
[4] A. Davies, Organotin Chemistry, VCH Verlagsgesellschaft, Weiheim, Germany,
1997.
[5] (a) G.F. Silbestri, R. Bogel Masson, M.T. Lockhart, A.B. Chopa, A catalyst-free
synthesis of asymmetric diaryl ketones from aryltins, J. Organomet. Chem. 691
(2006) 1520–1524;
(b) M.J. Lo Fiego, M.A. Badajoz, G.F. Silbestri, M.T. Lockhart, A.B. Chopa,
Efficient catalyst-free bi- and triaroylation of aromatic rings in a single step, J.
Org. Chem. 73 (2008) 9184–9187;
(c) M.J. Lo Fiego, G.F. Silbestri, A.B. Chopa, M.T. Lockhart, Selective synthetic
routes to sterically hindered unsymmetrical diaryl ketones via arylstannanes, J.
Org. Chem. 76 (2011) 1707–1714.
[6] M.J. Lo Fiego, M.T. Lockhart, A.B. Chopa, Catalyst-free alkanoylation of aromatic
rings via arylstannanes. Scope and limitations, J. Organomet. Chem. 694 (2009)
3674–3678.
[7] (a) B.C. Ranu, Indium metal and its halides in organic synthesis, Eur. J. Org.
Chem. (2000) 2347–2356;
in
situ
formation,
observation,
and
reaction
of
an
acyl
bis(trifluoroacetyl)phosphate and related structures, J. Org. Chem. 63 (1998)
8946–8951.
[22] R.C. Fuson, H.O. House, Diacetylation of m-xylene, J. Org. Chem. 18 (1953)
(b) V. Nair, S. Ros, C.N. Jayan, B.S. Pillia, Indium- and gallium-mediated
carbon–carbon bond-forming reactions in organic synthesis, Tetrahedron 60
(2004) 1959–1982;
496–500.
[23] R.K. Ingham, S.D. Rosenberg, H. Gilman, Organotin compounds, Chem. Rev. 60
(1960) 459–539.
(c) J. Augé, N. Lubin-Germain, J. Uziel, Recent advances in indium-promoted
Please cite this article in press as: M.J. Lo Fiego et al., Indium-mediated regioselective synthesis of ketones from arylstannanes under solvent-free ultra-
sound irradiation, Ultrason. Sonochem. (2012), http://dx.doi.org/10.1016/j.ultsonch.2012.10.018