Selective hydroformylation-acetalization of various olefins using simple and efficient Rh-phosphinite complex catalyst

Article abstract of DOI:10.1016/j.tetlet.2013.08.061

A simple and efficient Rh-phosphinite complex catalyst was studied for the selective hydroformylation of various olefins. The influence of various reaction parameters including the effect of temperature, pressure, catalyst loading, time, and solvents was studied. The protocol was also applied for the synthesis of various acetals via tandem hydroformylation-acetalization of olefins in alcohols as solvents. High activity and selectivity for acetal formation was achieved in the absence of co-catalysts with admirable substrate to catalyst mole ratio (TON 2500). The developed protocol works for a wide range of olefins to synthesize corresponding aldehydes and acetals under optimized reaction conditions.

Full text of DOI:10.1016/j.tetlet.2013.08.061

Tetrahedron Letters xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Selective hydroformylation–acetalization of various olefins using
simple and efficient Rh-phosphinite complex catalyst
⇑
Shoeb R. Khan, Bhalchandra M. Bhanage
Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai 400019, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple and efficient Rh-phosphinite complex catalyst was studied for the selective hydroformylation of
various olefins. The influence of various reaction parameters including the effect of temperature, pres-
sure, catalyst loading, time, and solvents was studied. The protocol was also applied for the synthesis
of various acetals via tandem hydroformylation–acetalization of olefins in alcohols as solvents. High
activity and selectivity for acetal formation was achieved in the absence of co-catalysts with admirable
substrate to catalyst mole ratio (TON 2500). The developed protocol works for a wide range of olefins
to synthesize corresponding aldehydes and acetals under optimized reaction conditions.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 29 June 2013
Revised 16 August 2013
Accepted 18 August 2013
Available online xxxx
Keywords:
Hydroformylation
Acetalization
Aldehydes
Acetals
Rh-phosphinite complex
Hydroformylation is one of the well studied homogeneously
catalyzed reaction and also one of the large scale industrial appli-
cations of homogeneous catalysis. The annual production of several
million tons of oxo chemicals attests its importance. The catalytic
hydroformylation is an elegant, clean, and atom-efficient method
to prepare wide range of aldehydes by the reaction of olefins with
syngas.1 In many cases, aldehydes are not the final products and
are further converted into alcohols, esters, amines, acetals, and
many more.2 The tandem reaction is always advantageous over
multistep synthesis since it minimizes the waste, multiple reaction
steps and the number of purification processes which fulfills the
criteria of sustainability and green chemistry. Several transition
metal-based catalysts involving Rh, Pt, Co, and Ru are used for this
reaction. Rhodium complexes of modified phosphorous containing
ligand show high activity and selectivity at mild reaction condi-
tions and hence are generally preferred for hydroformylation
reactions.3
The direct synthesis of acetals from olefins is one of the inter-
esting applications of tandem reaction. Acetal formation under
hydroformylation conditions may be needed either to protect the
sensitive aldehyde group from side reactions or for synthetic pur-
poses.4 Considering the importance of acetals as organic solvents,
additives for fuel and intermediates in the pharmaceutical, per-
fumery, and agricultural industries,5 several methods have been
developed for their synthesis. Fernandez and Castillon reported
the acetalization of olefins using [Rh2(l-OMe)2-(cod)2] with pyrid-
inium p-toluenesulfonate (PPTS) as co-catalyst.6 The acetal forma-
tion under hydroformylation condition can be increased in the
presence of acid catalyst or by acidified resins,7 and special ligands
with rhodium which can provide an acidic pH.8 Besides this, there
are a few reports wherein acetal formation was achieved under
acid-free conditions. El Ali et al. reported acid-free acetalization
of alkenes using RhCl3Á3H2O/P(OPh)3 as an effective catalytic sys-
tem for this transformation.9 Recently, Gusevskaya and co-workers
reported the synthesis of fragrance acetals using Rh/P(O-o-tBuPh)3
catalytic system in the absence of acid co-catalyst.10 In spite of
their potential utility, most of the reported protocols suffer from
one or more drawbacks such as use of acid co-catalysts, harsh reac-
tion conditions, or low substrate to catalyst mole ratio. Literature
reports reveal that the hydroformylation as well as hydroformyla-
tion–acetalization reactions using rhodium metal with phosphite/
phosphinite ligands are more effective than the conventional Rh-
triphenyl phosphine based catalysts.11 Even with high activity,
performance, and stability there are very few reports on Rh-phos-
phite/phosphinite complexes.12 Some of the best results with these
ligands are obtained using the family of calixarenes, which are
known as sophisticated molecular cages and claw-like ligands,13
pyranoside,14 and furanoside15 ligands. However, multistep syn-
thetic procedures and high cost of these ligands limit their indus-
trial applications.
Hence, the development of simple and atom efficient catalytic
system is always a key issue in the case of hydroformylation and
related reactions. In continuation of our interest in the develop-
ment of homogeneous catalytic system,16 we herein report a facile
⇑
Corresponding author. Tel.: +91 22 33612601; fax: +91 22 33611020.
E-mail addresses: bm.bhanage@ictmumbai.edu.in, bm.bhanage@gmail.com
(B.M. Bhanage).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.08.061
Please cite this article in press as: Khan, S. R.; Bhanage, B. M. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.08.061

2
S. R. Khan, B. M. Bhanage / Tetrahedron Letters xxx (2013) xxx–xxx
and highly efficient protocol for hydroformylation reaction and for
one-pot hydroformylation–acetalization process under acid-free
condition using a known Rh-phosphinite complex catalyst.
To optimize the reaction conditions, series of experiments were
performed on the hydroformylation of hexene as a model system
using Rh-phosphinite complex as a catalyst (Scheme 1). The Rh-
phosphinite complex used was synthesized according to the
reported procedure in the literature.18 The influences of various
reaction parameters such as effect of temperature, solvent, catalyst
loading, syngas pressure, and time were studied and the results ob-
tained are summarized in Table 1.
found that increasing the molar ratio from 1000:1 to 2500:1 does
not have a significant impact in the conversion and selectivity of
the desired aldehyde products (Table 1, entries 7, 3, and 8),
whereas, with further increase in the substrate to rhodium mole
ratio up to 3333:1, decreases the conversion of hexene (Table 1, en-
try 9). This decrease in conversion was due to a decrease in the
amount of catalyst from 0.04 mol % (Sub/Rh mole ratio 2500:1)
to 0.03 mol % (Sub/Rh mole ratio 3333:1). The influence of syngas
(CO/H2) pressure on the hydroformylation reaction was then inves-
tigated. It was observed that lowering the syngas pressure from 40
to 30 bar did not have any prominent effect on the reaction out-
come, but with further decrease in pressure to 25 bar decreases
the conversion of the desired product (Table 1, entry 11). We fur-
ther studied the effect of reaction time ranging from 8 to 4 h and
it was found that within a period of 6 h, reaction provided maxi-
mum yield and selectivity for linear aldehyde formation (Table 1,
entries 3, 12, and 13). To check the activity and selectivity of the
developed Rh-phosphinite complex with a ligand-free system,
the reaction of 1-hexene was carried out using [Rh(cod)Cl]2 as a
catalyst and was compared. However, low conversion addresses
the importance of the ligand in hydroformylation reaction (Table 1,
entry 14). Hence, the optimized reaction conditions for the hydro-
formylation of hexene were; hexene (5 mmol), Rh-phosphinite
complex (0.002 mmol), and CO/H2 (30 bar) at a temperature of
60 °C for 6 h in THF (15 mL) as solvent.
Initially, the reaction was studied at different temperatures in
the range of 50–110 °C (Table 1, entries 1–4). A high temperature
significantly promotes the side reaction like hydrogenation with
suppression of
a-formylation and thus provided higher branched
selectivity (Table 1, entry 1).19 It was found that regioselectivity
for linear aldehyde formation increases with a decrease in temper-
ature to 60 °C without affecting the conversion. Further decrease in
the reaction temperature to 50 °C led to the poor conversion of
hexene. Thus, further studies were carried out at 60 °C, which
was found to provide optimum conversion and selectivity toward
desired aldehyde (Table 1, entry 3). It was observed that the nature
of solvent affects the selectivity of the reaction product. The small
amount of substrate isomerization was observed when toluene
was used as a reaction solvent provided moderate conversion
and poor selectivity for linear aldehyde, whereas low conversion
and considerable amount of acetal formation were obtained in
methanol (Table 1, entries 5 and 6). It was observed that tetrahy-
drofuran (THF) provides good yield and selectivity of the desired
product and hence was used for further studies (Table 1, entry
3). Next, we studied the substrate to catalyst molar ratio. It was
With these optimized reaction conditions, the scope of the
developed protocol was extended for the hydroformylation of a
variety of aliphatic, aromatic, and cyclic olefins and the results ob-
tained are summarized in Table 2.20 The model reaction of hexene
provided good conversion and selectivity toward linear aldehyde
(Table 2, entry 1).
Cl
O
Rh
PPh
2
H
O
Rh-Complex
CO/H2
H
O
O
Ph P
2
Rh
Cl
Scheme 1. Hydroformylation of hexene using Rh-phosphinite complex catalyst.
Table 1
Effect of reaction parameters on hydroformylation of hexenea
Entry
Temp (°C)
Solvent
Sub/Rh (mole ratio)
CO/H2 pressure (bar)
Time (h)
Conversionc (%)
Aldehyde (%)
Linear:isoc (%)
Reduction (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14b
110
90
60
50
60
60
60
60
60
60
60
60
60
60
THF
THF
THF
THF
Toluene
MeOH
THF
THF
THF
THF
THF
THF
THF
2000
2000
2000
2000
2000
2000
1000
2500
3333
2500
2500
2500
2500
2500
30
30
30
30
30
30
30
30
30
40
25
30
30
30
8
8
8
8
8
8
8
8
8
8
8
6
4
6
100
100
100
44
94
68
100
100
73
100
88
100
89
34
92
95
99
99
43:57
49:51
71:29
69:31
52:48
67:33
71:29
72:28
69:31
65:35
70:30
72:28
73:27
67:33
8
5
—
1
97
3
13:87d
99
—
—
1
3
4
1
—
1
99
97
96
99
99
99
73
THF
27
a
b
c
Reaction conditions: hexene (5 mmol), Rh-phosphinite complex (as indicated), solvent (15 mL), 600 rpm.
[Rh(cod)Cl]2 used as a catalyst.
Conversion and selectivity (lin/iso) were determined by GC analysis.
Acetal formation.
d
Please cite this article in press as: Khan, S. R.; Bhanage, B. M. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.08.061

S. R. Khan, B. M. Bhanage / Tetrahedron Letters xxx (2013) xxx–xxx
3
Table 2
might be due to an increase in
p
-electron density on the
a
-carbon
Hydroformylation of various olefinsa
of styrene, which favors the attack of electropositive Rh metal, pro-
viding higher selectivity for branched aldehyde.17 The cyclic olefins
are known to react slowly for their hydroformylation, but under
present catalytic conditions cyclic olefins also endow with very
good conversion and selectivity for the formation of cyclopentane-
carbaldehyde and cyclohexanecarbaldehyde (Table 2, entries 10
and 11).
The scope of developed catalytic protocol was further extended
for the hydroformylation–acetalization tandem reaction. This
domino reaction involves the hydroformylation of olefin to an
aldehyde followed by the reaction of resulting aldehyde with alco-
hol to produce hemiacetal which finally reacts with another equiv-
alent of an alcohol to give the acetal (Scheme 2). The acetal
formation generally takes place in acidic condition, because a base
simply deprotonates the –OH group of the hemiacetal. The devel-
oped Rh-phosphinite complex contains RhCl residue which could
derive the acidic condition in the system and hence was not acti-
vated by hydrogen to eliminate the HCl under vacuum before per-
forming the reaction.
Entry Olefins
Conversion Aldehydee Lin:isod Reduction
(%)
100
98
(%)
99
99
(%)
(%)
1
2
72:28
69:31
1
1
3
5
7
3
4
95
96
98
96
73:27
67:33
2
4
5
79
97
99
36:74
12:88
3
6b
100
—
7b
8b
99
99
99
17:83
19:81
—
—
100
In order to get the maximum conversion and selectivity for the
desired acetal, the reaction was optimized with respect to various
parameters and the optimum reaction conditions for the hydrofor-
mylation–acetalization reaction of olefins were; Rh-phosphinite
complex (0.002 mmol), olefins (5 mmol) in alcohol (15 mL), and
30 bar of CO/H2 pressure at 80 °C for 8 h.
These optimized reaction conditions were then applied for the
hydroformylation–acetalization reaction of various olefins with
different alcohols, which provided good to excellent yields of the
corresponding acetals (Table 3, entries 1–9).21 The reaction of hex-
ene in methanol confers very good conversion and selectivity for
acetal formation (Table 3, entry 1).
9b
100
100
97
99
97
98
10:90
—
—
3
Cl
10b,c
11b,c
—
2
a
Reaction conditions: olefin (5 mmol), Rh-phosphinite complex (0.002 mmol),
THF (15 mL), CO/H2 (1:1) 30 bar, temperature (60 °C), time (6 h), 600 rpm.
b
Toluene as solvent.
Reaction time 8 h.
Conversion and selectivity (lin/iso) were determined by GC analysis.
Chemoselectivity for aldehyde product to total reaction product.
c
d
e
The acetalization of hexene was also studied by varying the
type of alcohols. Hexene reacts smoothly with ethanol providing
an excellent yield of corresponding acetal (Table 3, entry 2). Hex-
ene with n-butanol undergoes the acetalization with high conver-
sion (95%) and selectivity (81%) for the formation of the desired
acetal (Table 3, entry 3). It was observed that the regioselectivity
toward the linear acetal formation increases from methanol to n-
butanol at the expense of acetal selectivity. This change in the
selectivity might be due to the increase in steric hindrance from
methanol to n-butanol.11d The scope of developed protocol was
then further investigated for different olefins in methanol to pro-
duce their corresponding acetals (Table 3, entries 4–9). Styrene re-
acts efficiently in the presence of methanol to provide (1,1-
dimethoxypropan-2-yl)benzene as a major product. The presence
of an electron donating or electron withdrawing substituent on
the styrene did not affect the reactivity and offered good conver-
sion and selectivity for acetal formation (Table 3, entries 5–7). Like-
wise hydroformylation, in case of aryl olefins the branched product
was formed predominantly because of the formation of stable ben-
zyl rhodium intermediate. With cyclic olefins (cyclopentene and
cyclohexene here), the reaction was quite slow (Table 3, entries 8
The screened aliphatic olefins such as 1-octene, 1-decene, and
1-dodecene also offered good selectivity for aldehyde formation
with almost 98% conversion (Table 2, entries 2–4). The aromatic
olefin such as styrene reacts efficiently in both THF and toluene
as solvents providing 2-phenylpropanal as a major product. Tolu-
ene was a promising solvent for aromatic olefins since good regi-
oselectivity for branched aldehydes was achieved (Table 2, entry
6). The poor selectivity in THF may be due to the interaction of
the polar solvent with a benzylrhodium intermediate promoting
the linear aldehyde formation. Substituted styrene like 3-methyl-
styrene and p-tert-butylstyrene were found to react efficiently, fur-
nishing good yield and selectivity for the corresponding products
(Table 2, entries 7 and 8). Furthermore, p-chlorostyrene also pro-
vided almost complete conversion and good selectivity for
branched aldehyde formation (Table 2, entry 9).
It was observed that the regioselectivity for branched product
faintly increases with electron-withdrawing substituent on a phe-
nyl ring in the order p-(CH3)3CPh < m-CH3Ph < HPh < p-ClPh. This
OR''
OR'
OH
H
R''OH
R'OH
R
R
OR'
O
R
Rh
OR'
HO
R
OR'
R''O
R
R
H
CO/H2
O
R''OH
R'OH
R
Acetal
Hemiacetal
Aldehyde
Scheme 2. One-pot hydroformylation–acetalization sequence.
Please cite this article in press as: Khan, S. R.; Bhanage, B. M. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.08.061

4
S. R. Khan, B. M. Bhanage / Tetrahedron Letters xxx (2013) xxx–xxx
Table 3
References and notes
Hydroformylation–acetalization of various olefinsa
1. (a) van Leeuwen, P. W. N. M.; Claver, C. Rhodium Catalyzed Hydroformylation;
Entry Olefins
Alcohol Conversionc Acetald Lin:isoc Other
Kluwer Academic: Dordrecht, 2000; (b) Franke, R.; Selent, D.; Borner, A. Chem.
Rev. 2012, 112, 5675–5732.
(%)
(%)
(%)
(%)
2. (a) Weissermel, K.; Arpe, H. J. Industrial Organic Chemistry; VCH: New York,
1993; (b) Roelen, O. Patent 949,548, 1938; Ger. 1938.
1
2
CH3OH
EtOH
n-
100
97
99
98
46:54
55:45
1
2
3. (a) Beller, M.; Cornils, B.; Frohning, C. D.; Kohlpaintner, C. W. J. Mol. Catal. A:
Chem. 1995, 104, 17–85; (b) Ungvary, F. Coord. Chem. Rev. 1997, 167, 233–260.
4. (a) Eilbracht, P.; Barfacker, L.; Buss, C.; Hollmann, C.; Kitsos-Rzychon, B. E.;
Kranemann, C. L.; Rische, T.; Roggenbuck, R.; Schmidt, A. Chem. Rev. 1999, 99,
3329–3365; (b) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes,
P. Chem. Rev. 2000, 100, 2741–2769.
3
95
81
62:38
19
butanol
4
CH3OH
CH3OH
100
99
38:62
1
5. Vieira, C. G.; da Silva, J. G.; Penna, C. A. A.; dos Santos, E. N.; Gusevskaya, E. V.
Appl. Catal. A 2010, 380, 125–132.
5
6
99
98
37:63
2
6. Fernandez, E.; Castillon, S. Tetrahedron Lett. 1994, 35, 2361–2364.
7. (a) Balue, J.; Bayon, J. C. J. Mol. Catal. A 1999, 137, 193–203; (b) Diwakar, M. M.;
Deshpande, R. M.; Chaudhari, R. V. J. Mol. Catal. A 2005, 232, 179–186; (c)
Parrinello, G.; Stille, J. K. J. Am. Chem. Soc. 1987, 109, 7122–7127.
8. Soulantica, K.; Sirol, S.; Koinis, S.; Pneumatikakis, G.; Kalck, P. J. Organomet.
Chem. 1995, 498, 10–13.
9. El Ali, B.; Tijani, J.; Fettouhi, M. J. Mol. Catal. A 2005, 230, 9–16.
10. de Freitas, M. C.; Vieira, C. G.; dos Santos, E. N.; Gusevskaya, E. V. ChemCatChem
2013, 5, 1884–1890.
CH3OH
CH3OH
96
97
99
39:61
36:64
3
1
7
100
Cl
11. (a) van Rooy, A.; Orij, E. N.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.
Organometallics 1995, 14, 34–43; (b) Nozaki, K.; Sakai, N.; Nanno, T.;
Higashijima, T.; Mano, S.; Horiuchi, T.; Takaya, H. J. Am. Chem. Soc. 1997, 119,
4413–4423; (c) Francio, P.; Leitner, W. Chem. Commun. 1999, 1663–1664; (d)
Diebolt, O.; Cruzeuil, C.; Muller, C.; Vogt, D. Adv. Synth. Catal. 2012, 354, 670–
677.
12. (a) Baker, M. J.; Harrison, K. N.; Orpen, A. G.; Pringle, P. G.; Shaw, G. J. Chem. Soc.,
Chem. Commun. 1991, 803–804; (b) Buisman, G. J. H.; Vos, E. J.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M. J. Chem. Soc., Dalton. Trans. 1995, 409–417.
13. Jeunesse, C.; Dieleman, C.; Steyer, S.; Matt, D. J. Chem. Soc. Dalton. Trans. 2001,
881–892.
8b
9b
CH3OH
CH3OH
97
95
98
99
—
—
2
1
a
Reaction conditions: olefin (5 mmol), Rh-phosphinite complex (0.002 mmol),
alcohol (15 mL), CO/H2 (1:1) 30 bar, temperature (80 °C), time (8 h), 600 rpm.
b
Reaction temperature 100 °C.
Conversion and selectivity (lin/iso) were determined by GC analysis.
Chemoselectivity for acetal product to total reaction product.
c
d
14. Rajanbabu, T. V.; Ayer, T. A. Tetrahedron Lett. 1994, 35, 4295–4298.
15. Dieguez, M.; Palmies, O.; Ruiz, A.; Casillion, S.; Claver, C. Chem. Commun. 2000,
1607–1608.
16. (a) Khan, S. R.; Khedkar, M. V.; Qureshi, Z. S.; Bagal, D. B.; Bhanage, B. M. Catal.
Commun. 2011, 15, 141–145; (b) Khan, S. R.; Bhanage, B. M. Appl. Organometal.
Chem. 2013, 27, 313–317.
17. Panda, A. G.; Bhor, M. D.; Ekbote, S. S.; Bhanage, B. M. Catal. Lett. 2009, 131,
649–655.
and 9). However, very good conversion (up to 97%) and remarkable
acetal selectivity were obtained at 100 °C.
In conclusion, the present study reports a simple and efficient
protocol for hydroformylation reactions by using a well-defined
Rh-phosphinite complex as a versatile catalyst. The reaction sys-
tem was optimized with respect to various parameters and applied
for the hydroformylation of a range of substrate furnishing good to
excellent yields of the desired products. Furthermore, the catalytic
system was also useful for the synthesis of various acetals via
hydroformylation–acetalization sequence in alcohol as a solvent.
Different olefins in various alcohols are well tolerated under the
optimized reaction conditions and lead to the highly selective for-
mation of the corresponding acetals in the absence of any acid co-
catalysts. The developed protocol works at milder reaction condi-
tions with the additional advantage of high TON in comparison
with previously reported protocols. Thus, we believe that the pres-
ent catalytic system constitutes a versatile and economically
attractive method for the synthesis of valuable chemicals.
18. Balakrishna, M. S.; Suresh, D.; Kumar, P.; Mague, J. T. J. Organomet. Chem. 2011,
696, 3616–3622.
19. The thermogravimetric analysis (TGA) of the Rh-phosphinite complex was
carried out to provide information on the degradation pattern when
decomposed under nitrogen. The complex was found to be stable up to
220 °C with a weight loss of only 3.55% which might be due to solvent loss.
After that it gradually decomposes with temperature to 64.85% at 350 °C.
Hence, the decomposition temperature of the complex was determined to be
220 °C. A total weight loss was observed at 430 °C. Thus TGA of the Rh-
phosphinite catalyst shows that the catalyst is thermally stable at the reaction
temperature.
20. General procedure for catalytic hydroformylation reaction: in
a typical
experiment, to a high pressure reactor (autoclave) of 100 mL capacity, Rh-
phosphinite complex (0.002 mmol, 2 mg), olefin (5 mmol), and THF (15 mL)
were added. The reactor was then flushed with nitrogen, followed by syngas
(1:1 mixture of CO and H2 gas) at room temperature; next, the reaction was
pressurized to 30 bar syngas and heated to 60 °C at a stirring speed of 600 rpm
for 6 h. After completion of reaction, the reactor was cooled to room
temperature, and the remaining CO/H2 gas was carefully vented, and the
reactor was opened. The reaction mixture was analyzed by gas
chromatography (GC).
Acknowledgments
21. General procedure for catalytic hydroformylation–acetalization reaction: reactions
were performed in high pressure reactor (autoclave) of 100 mL capacity. The
autoclave was charged with olefin (5 mmol), Rh-phosphinite complex
(0.002 mmol, 2 mg), and alcohol (as a solvent and reactant) (15 mL). The
reactor was then flushed with nitrogen, followed by syngas (1:1 mixture of CO
and H2 gas) at room temperature. Subsequently, the autoclave was pressurized
to 30 bar syngas and heated to 80 °C at a stirring speed of 600 rpm for 8 h.
Further procedures were same as discussed earlier. All products obtained are
well known in the literature and were confirmed by GC–MS analysis.
The author (S.R.K.) is greatly thankful to the Council of Scientific
and Industrial Research (CSIR) India for providing senior research
fellowship (SRF).
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.tetlet.2013.08.061.
Please cite this article in press as: Khan, S. R.; Bhanage, B. M. Tetrahedron Lett. (2013), http://dx.doi.org/10.1016/j.tetlet.2013.08.061