Hydration of aromatic terminal alkynes catalyzed by iron(III) sulfate hydrate under chlorine-free conditions

Article abstract of DOI:10.1016/j.tetlet.2014.01.083

The hydration of aromatic terminal alkynes performed in acetic acid in the presence of catalytic hydrate iron^III sulfate, Fe₂(SO ₄)₃·nH₂O (4-9 mol %), yields the derived aryl methyl ketones with good to excellent yields. Under comparable conditions (18 mol %, 95 C, 24 h), bifunctional substrates were transformed into the monoacetyl or the diacetyl derivatives, depending on the structure of the aromatic diyne. The reaction is compatible with aryl substituents of different nature and ring positions, including hydroxyl, carbonyl groups, and cumulated hydrocarbons. The soft character of the non nucleophilic sulfate anion allows for activation of the triple bond toward carbonoxygen bond formation in the Br?nsted acidic medium. The proposed protocol is based on readily available and non toxic materials, in the absence of chlorine atoms in either the solvent or the metal catalyst.

Full text of DOI:10.1016/j.tetlet.2014.01.083

Tetrahedron Letters 55 (2014) 1608–1612
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Hydration of aromatic terminal alkynes catalyzed by iron(III) sulfate
hydrate under chlorine-free conditions
⇑
Mauro Bassetti , Samuele Ciceri, Federico Lancia, Chiara Pasquini
Istituto di Metodologie Chimiche del CNR, Sezione Meccanismi di Reazione, and Dipartimento di Chimica, Università degli Studi di Roma ‘La Sapienza’, P.le A. Moro 5, 00185 Roma, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The hydration of aromatic terminal alkynes performed in acetic acid in the presence of catalytic hydrate
ironIII sulfate, Fe2(SO4)3ꢀnH2O (4–9 mol %), yields the derived aryl methyl ketones with good to excellent
yields. Under comparable conditions (18 mol %, 95 °C, 24 h), bifunctional substrates were transformed
into the monoacetyl or the diacetyl derivatives, depending on the structure of the aromatic diyne. The
reaction is compatible with aryl substituents of different nature and ring positions, including hydroxyl,
carbonyl groups, and cumulated hydrocarbons. The soft character of the non nucleophilic sulfate anion
allows for activation of the triple bond toward carbonAoxygen bond formation in the Brønsted acidic
medium. The proposed protocol is based on readily available and non toxic materials, in the absence
of chlorine atoms in either the solvent or the metal catalyst.
Received 10 October 2013
Revised 14 January 2014
Accepted 21 January 2014
Available online 27 January 2014
Keywords:
Alkynes
Hydration
Iron sulfate hydrate
Methyl ketones
Iron catalysis
Ó 2014 Elsevier Ltd. All rights reserved.
The addition of water to the triple bond allows for the transfor-
mation of alkynes into carbonyl derivatives. The process requires
the use of an electrophilic catalyst for the activation of the unsat-
urated moiety toward the Markovnikov addition of oxygen nucle-
ophiles with formation of a C–O bond.1 Historically, mercuric ions
in dilute acidic conditions were the promoters of choice for the
synthesis of ketones from terminal and internal alkynes. Due to
heavy environmental concerns, other catalysts, among which com-
plexes of copper, silver, ruthenium, osmium, rhodium, palladium,
platinum, and more recently gold, have been proposed as valid
alternatives to toxic mercuric ion salts.2 The transformation can
also proceed in the presence of aqueous strong inorganic or organic
acids without a metal catalyst,1,2 in which cases achieving mild
reaction conditions remains a desirable goal.3 The metal catalyzed
processes are often accelerated by protonic acids.
anhydrous FeCl3 and H2O in dichloromethane,5 Darcel and cowork-
ers showed that catalytic FeCl3 in 1,2-dichloroethane (DCE) can be
used efficiently for the transformation of terminal alkynes into the
corresponding methyl ketones,6 thus paving the way for the devel-
opment of iron catalysts in this transformation. Recently, by com-
bining FeCl3 (10–20 mol %) with AgNTf2 (30–60%) in dioxane, and
generation in situ of catalytically active ironIII triflimide, Fe(NTf2)3,
high regioselectivity was achieved in the water addition to both
terminal and internal alkynes.7 Whereas ironIII salts are in general
more active than ironII species, FeCl2ꢀ4H2O in the presence of
methansulfonic acid showed high reaction efficiency for the hydra-
tion of various alkynes in DCE.8
In this work, we have explored the reactivity of iron salts in ace-
tic acid, a medium which provides a Brønsted acidic source other
than being environmentally more benign than halogenated sol-
vents.9 The use of acetic acid is common in the catalytic hydration
of alkynes promoted by mercury1,10 and other catalytic systems,1,11
including a silver-catalyzed (AgBF4) procedure recently reported.12
In addition, phenylacetylene was transformed into acetophenone
in high yield by reaction with stoichiometric amounts of both FeCl3
and acetic acid.13 Starting from preliminary experiments based on
FeCl3, we wish to report that commercial ironIII sulfate is an effi-
cient promoter of the hydration reaction, thus providing a simple
procedure based on chlorine-free and readily available sources.
The catalytic activity of FeCl3 (10 mol %) was tested using
phenylacetylene (1) as the model substrate. At room temperature,
H2O
cat
O
R
R
In the search of increasingly sustainable and more affordable
methodologies, iron salts have recently emerged as appropriate
catalysts for the alkyne hydration process, while iron catalysis in
general is witnessing a sort of renaissance in synthetic organic
chemistry.4 After the discovery that phenylacetylene was
converted into acetophenone in the presence of stoichiometric
formation of
a-chlorostyrene as major product (2) and acetophe-
⇑
Corresponding author. Tel.: +39 06 4991 3769; fax: +39 06 4991 3629.
E-mail address: mauro.bassetti@uniroma1.it (M. Bassetti).
none (3) was observed under either nitrogen or oxygen
http://dx.doi.org/10.1016/j.tetlet.2014.01.083
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

M. Bassetti et al. / Tetrahedron Letters 55 (2014) 1608–1612
1609
Table 1
Cl
O
FeCl3 (10%)
AcOH
Hydration of phenylacetylene catalyzed by iron salts in acetic acida
+
Me
Ph
Ph
Ph
1
2
3
Iron salt
O
Me
AcOH
95 °C, 24 h
Ph
Ph
Scheme 1. Conversion of phenylacetylene in neat AcOH.
1
3
Entry
Salt (mol %)
Atmos
1b (%)
3b (2)c (%)
atmospheres, in the absence of added water (Scheme 1). The con-
version proceeded slowly and no further changes occurred after
6 days, when the reaction mixture was composed of 1, 2, and 3
in relative GC percentages 53:32:10. An atmosphere of air or the
addition of water inhibited the process.14 When the reaction was
performed at 105 °C for 48 h, the values changed into 22:29:48
(1:2:3), indicating higher conversion and preferred transformation
into acetophenone upon raising the temperature (Scheme 1).
The hydrochloration reaction constituted therefore a major
drawback for the use of FeCl3 in acetic acid. This competitive
process yielding 2 is well documented in the addition of water to
alkynes using stoichiometric or catalytic FeCl3,5,6 whereas halovi-
nyl derivatives were synthesized upon reaction of alkynes with
ironIII halides in the presence of stoichiometric amounts of carbox-
ylic acids.13
In spite of this chemoselectivity limitation, these experiments
indicated that the iron-catalyzed hydration of phenylacetylene is
feasable in AcOH, whereas other protic solvents which were
screened in previous works proved to be unsuitable.5,6,7a Therefore,
we investigated the activities of other iron salts in oxidation states
II and III and different ligand environments, the changes in the nat-
ure of the counteranions being specifically intended to suppress
the competitive hydrochloration process. For direct comparison,
the conversions were determined by GC after 24 h at 95 °C and
the results are shown in Table 1. Traces or low yields of the ketone
3 were observed in the presence of ironII salts (Table 1, entries
1–3), ferrous chloride being appreciably less active than FeCl3
(Table 1, entries 1 and 5), while the catalytic activity varied largely
within the series of ferric ions. Those complexes with bidentate
oxygen donor ligands acetylacetonate (acac) or acetate were inac-
tive (Table 1, entries 6 and 7), whereas the perchlorate or the ni-
trate salts induced extensive transformation of the alkyne,
although with poor or no conversion into the desired ketone or
other identifiable products (Table 1, entries 8 and 9). Remarkably,
phenylacetylene was hydrated to acetophenone in the presence of
ironIII sulfate hydrate, Fe2(SO4)3ꢀnH2O (I), with conversions larger
than 80% and catalyst loadings as low as 4 mol % (8 mol % in iron).
This iron salt exhibited similar activities under air or nitrogen, and
in the presence of added water (Table 1, entries 10–12). Essentially
full conversion is achieved using 8 mol % of I. The reactions pro-
moted by Fe2(SO4)3ꢀnH2O proceeded in a milky gray heterogeneous
mixture, with a progressive color change from neutral to orange.
The use of methanol instead of acetic acid gave no evidence of
the formation of acetophenone, as well as changing iron sulfate
with iron phosphate (entry 14).
1
2
3
4
5
6
7
8
FeCl2ꢀ4H2O (10)
FeS (10)
Air
Air
Air
N2
Air
N2
Air
Air
Air
N2
Air
Air
Air
Air
48
23
72
40
32
100
100
—
25
5
4
7
<1
100
25 (11)
1
3
30 (29)
34 (32)
—
FeSO4ꢀ7H2O (10)
FeCl3 (10)
FeCl3 (10)
Fe(acac)3 (10)
IronIII acetated (5)
Fe(ClO4)3ꢀ9H2O (10)
Fe(NO3)3ꢀ9H2O (10)
Fe2(SO4)3ꢀnH2O (4)
Fe2(SO4)3ꢀnH2O (4)
Fe2(SO4)3ꢀnH2O (4)
Fe2(SO4)3ꢀnH2O (8)
FePO4 (10)
—
10e
e
9
—
10
11
12f
13
14
84
85
90
99
—
a
Reaction conditions:
(4-10 mol %).
GC yield ( 1%), determined by response factor vs 1,2-diphenylethane as internal
standard.
1 (300 lL, 2.73 mmol), AcOH (10 mL), iron salt
b
c
d
e
f
Relative GC area %.
[Fe3O(OAc)3(H2O)3]OAc.
With formation of unidentified species.
In the presence of H2O (0.50 mL, 28 mmol).
Table 2
Hydration of arylalkynes catalyzed by ironIII sulfate hydrate (8 mol %) in acetic acida
R
Fe2(SO4)3 nH2O
R
O
AcOH, 95 °C
4
5
Entry
R Group
Time (h)
Ketone
Yieldb (%)
1
2
3
4
4
5
6c
4-NMe2
4-OMe
2-OMe
3,4,5-(OMe)3
4-CH@CH2
4-Br
6
7
7
24
24
50
168
5a
5b
5c
5d
5e
5f
81
76
76
75
54
70
28
4-CF3
5g
a
Reaction conditions: alkyne: 1-2 mmol (0.3–0.4 M in acetic acid), I (8 mol %), in
air.
Isolated yields, after column chromatography.
The reaction was performed at 120 °C.
b
c
with increasing electron-withdrawing character of the substituent,
p-bromophenylacetylene (4f) requiring 50 h of reaction at 95 °C,
and p-trifluoromethylphenylacetylene (4g, rp ꢁ CF3 = 0.53) seven
days at 120 °C for a poor conversion into methyl ketone 5g. Along
this trend, p-nitrophenylacetylene (rp ꢁ NO2 = 0.81) gave no evi-
dence of transformations when kept for several days at 120 °C.
The steric hindrance provided by adjacent phenyl rings in
cumulated hydrocarbons did not hinder significantly the reactivity
of the triple bond (Table 3). Only a modest reduction of yield
was found in the transformation of the most congested 1-
ethynylanthracene.
The scope of the reaction was investigated for substrates featur-
ing hydroxyl functional groups, which may be sensitive to the ace-
tic acid solvent and also hinder, as Lewis bases, the catalytic
activity of the ironIII center.6 The reaction of the aliphatic alcohol
12 is outlined in Scheme 2.
The activity of the catalytic system based on Fe2(SO4)3ꢀnH2O in
AcOH was then investigated for different arylacetylenes. The
substrates, conditions, products, and reaction yields are shown in
Tables 2–4. The reaction time and yields depended largely on the
nature of the aryl substituent. High conversions into ketone were
observed with electron rich alkynes, such as those featuring dimeth-
ylamino or methoxy groups (Table 2, entries 1–4). In the case of 4-
Me2NAC6H4AC„CH (4a), when kept in acetic acid for 24 h at 95 °C,
the formation of the hydration product was observed even in the ab-
sence of the iron salt (5a, 57% isolated yield). These transformations
can be regarded as a valid alternative to catalysis by gold complexes,
as in the case of (NHC)AuBr3 (10 mol %, NHC = N,N0-bis(2,6-diisopro-
pylphenyl)imidazol-2-ylidene) used in MeOH at reflux.15
The triple bond was hydrated with conversion comparable to
that of the electron rich aromatic alkynes (overall 76% isolated
yields of 13 and 14), while the OH function was abundantly
acetylated, as indicated by the signals of compound 13 at d 2.52
(COMe) and 2.04 (OCOMe) ppm in the 1H NMR spectrum, and
4-Ethynylstyrene (4e) reacted regio-selectively at the triple
bond affording 4-vinylacetophenone (5e). The reactivity decreased

1610
M. Bassetti et al. / Tetrahedron Letters 55 (2014) 1608–1612
Table 3
the substrate initial concentration from 0.3 to 2.0 M, the alkyne
was consumed in 24 h at the same temperature and the yield of
the ketone was raised to 57%.
Hydration of terminal alkynes catalyzed by ironIII sulfate hydrate in acetic acida
Entry
1
Alkyne
Ketone
Yieldb (%)
The scope of the reaction of terminal aromatic alkynes was
studied for bifunctional substrates. 1,4-Diethynlylbenzene (20)
was allowed to react in the presence of Fe2(SO4)3ꢀnH2O
(18 mol %) and afforded 1-(4-ethynylphenyl)ethanone (21) as the
monohydrated product in 67% isolated yield (Table 4, entry 1). It
is worth mentioning that the more active catalytic system based
on indiumIII trifluoromethanesulfonate and tosyl acid gave a mix-
ture of products including 21 (29%) and 1,4-diacetylbenzene
(46%).18 When the reaction was performed on 1,3-diethynlylben-
zene (22) under the same conditions used for diyne 20 (24 h,
95 °C), both triple bonds were hydrated to a good extent to afford
the diacetyl derivative 24 along with a separable amount of the
monoacetylated product 23. Along the same lines, the diethynyl
compounds 25 and 27, featuring lipophilic alkyl chains, were trans-
formed in excellent yields into the corresponding diacetyl deriva-
tives 2619 and 28,20 respectively (Table 4, entries 3 and 4). While
1,4-diacetylbenzene did not form from 20 due to the electronwith-
drawing effect of the generated acetyl group of 21 in para position,
the triple bonds at the 1,3 sites of the same ring, at the 1,4 posi-
tions of an electron rich dioctyloxybenzene moiety (25), or at the
distant 2,7 positions in a fluorene skeleton (27) were both reactive.
These reactions indicate the compatibility of the catalytic system
with the carbonyl group.
O
61
6
7
O
2
3
75
54
8
9
O
11
10
a
Reaction conditions: Fe2(SO4)3ꢀnH2O (8 mol %), 95 °C, 24 h.
b
Isolated yields, after column chromatography.
Table 4
Hydration of diethynyl substratesa
Entry
Diyne
Ketone (yield %)b
O
(67)
1
20
21
O
O
O
+
2
22
23 (15)
Regarding the striking effect of the counteranions of the ironIII
salts shown in Table 1, it is worth recalling that some of the most
active mercury-based catalytic systems are those which involved
the addition or generation in situ of sulfate salts.2 This is the case
of the Hg2+/H2SO4 catalysts,10a,21 of the sulfonated polystyrene
resins,11a,22 or of mercuryII sulfate in sulfuric acid used in the
industrial synthesis of acetaldeyde.23 The switch of the ironIII
counteranion from chloride to sulfate in the Brønsted acidic
medium has provided a selective catalytic system for the hydration
of terminal aromatic alkynes. This stems from the consequent
elimination of the competitive hydrochloration process and from
the presence of a soft low-coordinating anion in place of the hard
chloride ligand. Non-nucleophilic sulfate anions can favor access
of the alkyne to the metal center but also modulate the hard-soft
character of the ironIII cation. In fact, proper interaction of the soft
24
(44)
OC8H17
OC8H17
O
3c
(70)
O
C8H17
O
O
C8H17O
25
26
O
4d
(89)
28
27
a
b
c
Reaction conditions: Fe2(SO4)3ꢀnH2O (I, 18 mol %), 95 °C, 24 h.
Isolated yields, after column chromatography.
Compound 25 (300 mg, 0.78 mmol), I (79 mg), AcOH (2.6 mL).
Compound 27 (160 mg, 0.37 mmol), I (37 mg), AcOH (1.2 mL).
d
the corresponding ones at d 196.8 and 171.0 in the 13C NMR spec-
trum.16 By contrast, ethynyl phenol 15 was hydrated essentially to
the corresponding ketone 16 and only to a minor extent to the bis-
acetylated product 17 (Scheme 3).
In the case of the propargylic alcohol 1-octyn-3-ol (18) treated
under similar conditions (0.3 M, I 8 mol %, 95 °C, 24 h), the hydro-
xyl function was chemioselectively acetylated to afford compound
19, CH3(CH2)4C(OCOMe)C„CH, isolated in 53% yield, with no evi-
dence of hydration of the triple bond. The use of ironIII sulfate hy-
drate as catalyst for acetylation reactions has been previously
documented.17
p-nucleophilic triple bond with the iron center, with activation to-
ward oxygenAcarbon bond formation, requires a relatively soft Le-
wis acidity of the metal which is favored by soft anions. A detailed
description of the effect of low-coordinating ligands on the Lewis-
acid character of the ironIII center in the alkyne hydration process,
and the possible role of Lewis/Brønsted co-catalysis, can be found
in the article by Leyva-Pérez, Corma, and co-workers regarding
the catalytic system based on Fe(NTf2)3 in 1,4-doxane.7a Accord-
ingly, an additional effect of Fe2(SO4)3ꢀnH2O can be that of a Lewis
acid enhancing the acidity of the proton donor species in the reac-
tion mixture, upon formation of hydrato or acetato complexes.
Since coordinated water molecules in I (n ffi 9) and moisture in
the medium can affect both the Lewis acid strength of the iron cen-
ter, we wished to compare the efficiency of the reaction under
standard conditions (hydrated salt I, glacial AcOH from the bottle,
and air atmosphere) with one performed with attempted exclusion
The catalytic system proved to be of lower efficiency for alkyl
alkynes, requiring the use of more forcing conditions: 1-octyne
was converted into 2-octanone in 18% yield (GC) after 5 days at
120 °C, with 10% load of the iron catalyst. However, by increasing
O
(OCH2CH2)3OCOMe
Fe2(SO4)3 nH2O
8 mol%
13 48%
+
O
Fe2(SO4)3 nH2O
O
8 mol%
O
+
(OCH2CH2)3OH
AcOH, 95 °C
20 h
O
O
HO
16 71%
(OCH2CH2)3OH
14 28%
HO
AcOH, 24 h
95 °C
12
15
17 6%
Scheme 2. Reaction of 2-{2-[2-(4-ethynylphenoxy) ethoxy]ethoxy}-ethanol (12,
Scheme 3. Reaction of 3-hydroxyphenylacetylene (15, 0.5 M) in the presence of
0.4 M) in the presence of ironIII sulfate hydrate in acetic acid.
ironIII sulfate hydrate in acetic acid.

M. Bassetti et al. / Tetrahedron Letters 55 (2014) 1608–1612
1611
of water. To this aim, a sample of the sulfate iron salt was kept at
120 °C under vacuum for 24 h, which changed the original whitish
gray crystals into a pale yellow powder (II),24 the resulting 19%
mass reduction corresponding to an approximate loss of six water
molecules from the pristine Fe2(SO4)3ꢀnH2O. The reaction profiles
for the hydration promoted by either salt I in air or by salt II under
argon are shown in Figure 1. In the latter case, phenylacetylene
was converted into the acetyl product by less than 50% after
24 h, thus indicating a marked lower activity of the ‘dried’ salt II.
By contrast, the addition of extra water to the medium did not
cause the expected full conversion of 1 into acetophenone (Table 1,
entry 12). It is evident that coordinated water molecules influence
the activity of the catalytic system, either by changing the Lewis
acidity of the ironIII center, by assisting formation of intermediates
as non-innocent ligands, or acting as attacking species to the acti-
vated triple bond. The key step, oxygenAcarbon bond formation,
may proceed by attack of H2O, as most common in metal catalyzed
hydration processes,1,2,5–8 and/or of AcOH. In fact, it is established
that hydration reactions can proceed in organic acidic media in the
absence of extra water, in which cases acetic acid under Lewis acid
activation10b,c,25 or formic acid alone26 react with the triple bond
by addition and subsequent transformation of the resulting enol
esters into the carbonyl products. Essentially, the organic acids
act as formal water donors. The fact that yields near 80% cannot
be achieved by exclusive direct addition of water to the triple bond
using loadings of I of 4 mol % (almost 0.3 equiv H2O; Table 1, en-
tries 10, 11 and Fig. 1) supports the concurrence of an acid addi-
tion-vinyl ester hydrolysis sequence in the catalytic system
formed by Fe2(SO4)3ꢀnH2O in acetic acid.
alkynes, as for p-Br-phenylacetylene which was converted into 5f
(Table 2, entry 5) with 80% yield after 40 h at 80 °C in dioxane,
although substrates with strongly electron-withdrawing groups
were not tested. Remarkably, the system showed high efficiency
and regioselectivity in the reaction of internal alkynes, either aro-
matic or aliphatic. FeCl2ꢀ4H2O catalyzes the hydration of various
terminal arylalkynes, of aliphatic alkynes, of internal alkynes, and
of propargylic alcohols under mild conditions (1–19 h, 60 °C), but
still relies on the use of a halogenated solvent (DCE) and stoichiom-
etric methansulfonic acid as a strong proton donor.8
The scope of this iron-based catalytic system for the hydration
of internal alkynes is currently under investigation and will be re-
ported in due course.
Acknowledgments
Financial support from MIUR, PRIN project no. 2010JMAZML–
MultiNanoIta, is gratefully acknowledged.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2014.
01.083.
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14. Moisture or aqueous homogeneous conditions can suppress the Lewis acidic
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anhydrous FeCl3 than of the metal hydrated species.5,6
3,0
mmol
2,5
2,0
1,5
1,0
0,5
0,0
15. De Frémont, P.; Singh, R.; Stevens, E. D.; Petersen, J. L.; Nolan, S. P.
Organometallics 2007, 26, 1376–1385.
16. 4-{2-[2-(2-Acetoxyethoxy)-ethoxy]-ethoxy}acetophenone (13). 1H NMR:
d = 7.91 (d, 2H, J = 8.9 Hz), 6.93 (d, 2H, J = 9.0 Hz), 4.22 (m, 4H), 3.86 (m, 2H),
3.70 (m, 6H), 2.53 (s, 3H), 2.05 (s, 3H) ppm. 13C NMR: d = 196.8, 171.0, 162.6,
130.5, 130.3, 114.1, 70.7, 70.5, 69.5, 69.1, 67.5, 63.4, 26.6, 20.9 ppm. GC–MS (m/
z, M+ = 310.1): 310 (19%), 162 (25%), 147 (15%), 121 (20%), 87 (100%), 43 (65%).
FT-IR (neat, KBr): 3073, 2880, 1738, 1679, 1600, 1575, 1510, 1454, 1421, 1360,
1306, 1256, 1174, 1130, 1056, 958, 838, 594.
0
1
2
3
4
5
6
7
8
23,5 23,6 23,7 23,8 23,9 24 24,1 24,2
time (h)
Figure 1. Conversion of phenylacetylene (2.73 mmol, Ç) into acetophenone (ꢂ),
under the following conditions: (i) iron sulfate hydrate I (60 mg, 3.9 mol %), AcOH
(9.1 mL), air (solid trace); or (ii) iron sulfate hydrate II (46 mg, 0.11 mmol,
3.7 mol %), AcOH (9.1 mL)/Ac2O (20
evaluated in the presence of 1,2-diphenylethane as internal standard.
lL), argon (dashed trace). Conversions were
17. Shi, L.; Zhang, G.; Pan, F. Tetrahedron 2008, 64, 2572–2575.
18. Gao, Q.; Li, S.; Pan, Y.; Xu, Y.; Wang, H. Tetrahedron 2013, 69, 3375–3781.

1612
M. Bassetti et al. / Tetrahedron Letters 55 (2014) 1608–1612
19. The diketone 15 is a coupling partner with dihalides in a palladium-catalyzed
condensation polymerization to form polyketones Wang, D.; Wei, P.; Wu, Z.
Macromolecules 2000, 33, 6896–6898.
144.6, 136.2, 127.99, 127.95, 127.91, 124.05, 123.98, 123.91, 120.5, 55.33,
44.16, 34.76, 33.70, 33.68, 28.03, 28.01, 27.04, 27.02, 26.81, 22.62, 13.88, 10.09,
10.07. FT-IR (neat on KBr): 2958, 2926, 2857, 1683, 1606, 1578, 1460, 1433,
1357, 1246, 956, 822, 755, 701, 592. Anal. Calcd for C35H50O2: C, 83.61; H,
10.02. Found: C, 84.34; H, 10.76.
20. 9,9-Bis(20-ethylhexyl)-2,7-diacetylfluorene (28). Fe2(SO4)3ꢀnH2O (I, 37 mg,
0.068 mmol), glacial acetic acid (1.2 mL), and 2,7-diethynyl-9,9-(di-20-
ethylhexyl)-fluorene (27, 0.160 g, 0.37 mmol) were introduced into a 25 mL
Schlenk tube equipped with a magnetic bar and air condenser. The tube was
immersed into an oil bath (95 °C) and the heterogeneous reaction mixture,
slowly changing color from light yellow to bright orange, was kept under
stirring for 24 h, when the TLC analysis showed consumption of the diyne. The
mixture was poured into water/chloroform, extracted with chloroform, and the
combined organic extracts washed with aqueous sodium bicarbonate (Â2) and
then water. After the addition of anhydrous sodium sulfate and filtration, the
solvent was removed under vacuum and the crude oil purified by column
chromatography over silica, using hexane/chloroform (8:2 to 1:1) as eluent.
Removal of solvent under vacuum afforded 0.155 g of 28 (0.33 mmol, yield
88%). 1H NMR (300 MHz, CDCl3): d = 8.07–7.85 (m, 4H), 7.85 and 7.82 (2 s, 2H),
2.673, 2.670, 2.667 (6H), 2.08 (d, J = 6 Hz, 4H), 0.9–0.6 (m, 22H), 0.52–0.36 (m,
8H). 13C NMR (75 MHz): d = 197.82, 197.74, 197.66, 152.05, 152.02, 151.98,
21. (a) Kutscheroff, M. Chem. Ber. 1884, 17, 13–29; (b) Stacy, G. W.; Mikulec, R. A. In
Org. Synth. Coll.; Rabjohn, N., Ed.; John Wiley & Sons: New York, 1963; Vol. 4, pp
13–15.
22. Olah, G. A.; Meidar, D. Synthesis 1978, 671–672.
23. Ponomarev, D. A.; Shevchenko, S. M. J. Chem. Ed. 2007, 84, 1725–1726. In the
acetylene hydration process, ironIII sulfate was used as an additive for the
reoxidation of metallic mercury to Hg2+
.
24. The thermogravimetric analysis of II under nitrogen exhibited a 13% weight
loss in the range 100–285 °C (see the Supplementary data), suggesting an
approximate molecular formula Fe2(SO4)ꢀ3H2O.
25. Fahey, R. C.; Lee, D.-J. J. Am. Chem. Soc. 1968, 90, 2124–2131.
26. (a) Menashe, N.; Reshef, D.; Shvo, Y. J. Org. Chem. 1991, 56, 2912–2914; (b)
Menashe, N.; Shvo, Y. J. Org. Chem. 1993, 58, 7434–7439.