Iodine-catalyzed tandem synthesis of terminal acetals and glycol mono esters from olefins

Article abstract of DOI:10.1039/c3cc38085h

A new metal-free protocol is described for the synthesis of terminal acetals by tandem oxidative rearrangement of olefins using oxone as an oxidant in the presence of iodine. Moreover, a one-pot procedure for the preparation of glycol mono esters from olefins is also presented for the first time using the same reagent system. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3cc38085h

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Iodine-catalyzed tandem synthesis of terminal acetals and glycol
mono esters from olefins
Macharla Arun Kumar, Peraka Swamy, Mameda Naresh, Marri Mahender Reddy, Chozhiyath
Nappunni Rohitha, Sripadi Prabhakar, Akella Venkata Subrahmanya Sarma, Joseph Richard
Prem Kumar and Nama Narender*
A novel metal-free protocol for the synthesis of terminal acetals and glycol mono esters from
olefins using oxone as an oxidant in presence of iodine is reported.
Oxone
O
R
(0.75 equiv)
O
I2
(5 mol%)
R
HO
OH
Oxone
O
R
OH
(1.5 equiv)
R = Aryl / Alkyl
O

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Iodine-catalyzed tandem synthesis of terminal acetals and glycol mono
esters from olefins
Macharla Arun Kumar,a Peraka Swamy,a Mameda Naresh,a Marri Mahender Reddy,a Chozhiyath
Nappunni Rohitha,a Sripadi Prabhakar,b Akella Venkata Subrahmanya Sarma,c Joseph Richard Prem
Kumard and Nama Narender*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X
DOI: 10.1039/b000000x
(2KHSO5ꢁKHSO4ꢁK2SO4) in the oxidation reactions is becoming
popular due to its high stability, simple manipulation, nonꢀtoxic
50 nature and is relatively inexpensive. Moreover, the byproducts
associated with oxone are generally recognized as safe.13
A new metal-free protocol is described for the synthesis of
terminal acetals by tandem oxidative rearrangement of
10 olefins using oxone as an oxidant in presence of iodine.
Moreover, one-pot procedure for the preparation of glycol
mono esters from olefins is also presented first time using the
same reagent system.
O
Oxone
(0.75 equiv)
R
I2
O
(5 mol%)
R
Oxone
O
HO
OH
R
OH
Protection of carbonyl function as acetol is known to be the
15 widely used synthetic route for the manipulation of various
multifunctional organic molecules.1 Acetals can also be used for
CꢀC bond formations,2 synthesis of ethers,3 esters,4 and
cyclization of diynes.5 Additionally acetals have enormous
industrial importance due to their potential utility as flavoring
20 agent in distilled beverages, diesel additives and plastic
materials.6 Classical methods for the synthesis of acetals involve
the treatment of aldehydes or ketones with an alcohol by either
protic or Lewis acid catalyst.1 Unfortunately, these procedures
have some disadvantages such as use of corrosive and costly
25 reagents or additives, halogenated solvents, large waste and high
catalyst loading. The palldium(II)ꢀcatalyzed oxidation (wacker
process) of terminal olefins in water furnish the methyl ketones7
and a similar reaction in alcohol gives their corresponding
internal acetals8 and these reactions have been widely studied.
30 Acetalization at the terminal carbon atom of a cheaper terminal
olefin instead of a costlier aldehyde as substrate is a challenging
task. Consequently some Pd catalyzed protocols have been
developed for this important functional group transformation.9
Recently Lahiri et al reported the iron catalyzed synthesis of
35 terminal acetals from olefins.10 Couple of nonꢀmetal catalyzed
methods have also been reported for the synthesis of terminal
acetals from olefins.11
(1.5 equiv)
O
Scheme 1
In view of the increased attention to design costꢀeffective,
environmentally benign and metalꢀfree chemical transformations.
55 Herein, we report a novel and efficient metalꢀfree protocol for the
synthesis of terminal acetals and esters from olefins using oxone
as an oxidising agent in presence of catalytic amount of iodine
(Scheme 1).
60 Table 1 Optimization for acetal and ester formationa
I2, Oxidant
O
Ph
1a
Ph
O
3a
HOCH2CH2OH
O
OH
Ph
I
2a
Entry
I2
Oxidant
(mmol)
Time
Yieldb (%)
(mmol)
2a
10
10
-
ꢀ
3a
49
84
1
2
3
4
5
6
7
8
0.1
0.1
0.1
0.1
0.1
1
0.5
1
0.1
0.1
0.1
0.1
Oxone (0.5)
Oxone (1)
Oxone (1.5)
Oxone (2.5)
Oxone (3)
Oxone (0.5)
Oxone (1.5)
Oxone (1.5)
H2O2 (1.5)
O2
24 h
24 h
1.3 h
24 h
24 h
1.3 h
1.3 h
1.3 h
24 h
24 h
24 h
24 h
95
12 (70)c
- (94)c
-
92
12
35
10
ꢀ
ꢀ
Over the last few years iodineꢀmediated reactions have been
increased dramatically due to its readily availablility, convenient,
40 relatively cheap and environmentally benign characteristics over
the toxic heavy metals or complex reagents.12 The use of oxone
85
61
ꢀ
ꢀ
ꢀ
9
10
11
TBHP (1.5)
ꢀ
ꢀ
aI&PC Division, bNCMS, cCentre for NMR, dCMM, CSIRꢀIICT,
Hyderabad 500 007, India. Eꢀmail: narendern33@yahoo.co.in.
45 † Electronic Supplementary Information (ESI) available: Experimental
procedures, 1H and 13C NMR spectra of all compounds. See
DOI: 10.1039/b000000x/
12
ꢀ
ꢀ
a
b
Styrene (2 mmol), Ethylene glycol (2 ml). Products were
c
characterized by NMR, mass spectra and quantified by GC. 2ꢀ
Hydroxyethylꢀ2ꢀphenylacetate (4a).
65
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Table 2 Synthesis of acetals form various olefinsa
Table 3 Synthesis of esters from various olefinsa
Yieldb (%)
94
Entry
Olefin
Time
(h)
Product
Yieldb
(%)
Entry
Olefin
Product
O
OH
1
1a
O
O
1
2
3
4
5
6
1.3
3.3
3
95
O
4a
O
1a
1b
1c
3a
3b
3c
OH
O
2
3
4
5
6
7
90
51
60
88
90
65
1b
1c
1d
1e
1f
O
90
76
89
95
94
O
4b
O
OH
OH
O
O
O
4c
O
O
O
O
O
3.3
5
O
O
4d
O
1d
1e
1f
3d
3e
OH
OH
O
O
Br
Cl
O
Br
Cl
Br
Cl
4e
O
O
O
6
O
4f
OH
3f
1g
O
O
Ph
Ph
OH
O
O
7
2.3
95
OH
OH
Ph
Ph
4g
Ph
1g
3g
O
OH
OH
8
9
ꢀ
1h
1i
O
O
O
O
4h
8
9
7
80
64
Ph Ph
Ph Ph
3h
O
1h
60
O
O
4i
1.3
a
25 Olefine (2 mmol), I2 (0.1 mmol), Oxone (3 mmol), Ethylene
glycol (2 ml), 24 h, r.t. Products were characterized by NMR,
3i
1i
b
a Olefine (2 mmol), I2 (0.1 mmol), Oxone (1.5 mmol), Ethylene
glycol (2 ml), r.t. b Products were characterized by NMR, mass
spectra and quantified by GC.
mass spectra and quantified by GC.
scope of this novel transformation with a variety of olefins and
30 results are summarized in Table 2. Various aryl alkenes
underwent the oxidative rearrangement to give the corresponding
cyclic acetals in good to excellent yields. Styrene produced the
respective terminal cyclic acetal with 95% yield in 1.3 h.
Whereas, relatively longer reaction time required for activating or
35 deactivating groups present on aromatic ring of styrene to provide
excellent yields of corresponding acetals. However, 2, 4ꢀdimethyl
styrene gave relatively lesser yield, probably due to steric
hindrance. Asymmetric and symmetric olefins also underwent
oxidative rearrangement and afforded good yields of the
40 corresponding acetals (entries 7 and 8, Table 2). It is worth
mentioning that in the case of cyclic olefin, ringꢀcontraction
product was observed (entry 9, Table 2).
5
Initially, we investigated the suitable reaction conditions for
direct acetalization of olefins (oxidative rearrangement) using
styrene as the model substrate. As seen in Table 1, a variety of
reaction conditions were employed to achieve the optimal
10 conditions. After screening of several oxidants, oxone is found to
have excellent activity and selectivity than other oxidants such as
H2O2, TBHP and O2 in the presence of iodine at room
temperature. Further styrene (2 mmol) was allowed to react with
different mole ratios of oxone (0.5, 1.0, 1.5, 2.5, 3.0) in the
15 presence of I2 (0.1, 0.5, 1.0). The results revealed that 2:1.5:0.1
mole ratio of styrene, oxone and I2 at room temperature shown to
be optimum reaction conditions for terminal acetalization. Acetal
was not observed in the absence of oxone, which indicate that it
plays a crucial role in formation of acetal (entry 12, Table 1).
20 With increasing the amount of oxone, formation of ester was
observed, 3 mmol of oxone is required for complete conversion
of olefin to ester (entry 5, Table 1).
After our success with the synthesis of terminal acetals from
olefins, we turned our attention to extending the scope of this
45 protocol to preparation of glycol mono esters. Formation of
glycol mono esters from variety of olefins (2 mmol) with
ethylene glycol (2 ml) using oxone (3 mmol) as an oxidant in
After optimizing the reaction conditions, we explored the
2
|
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presence of iodine was studied at room temperature (Table 3).
Styrene smoothly converted to the corresponding ester with
of glycol mono esters from olefins has also been introduced using
the same reagent system. To our knowledge, this is the first
excellent yield in 24 h. Styrene with a moderately activating 45 example for direct esterification of olefins at terminal carbon.
substituent i.e. methyl and moderately deactivating substituents
such as Cl, Br groups also furnished the corresponding esters
with high yield in 24 h. Whilst, highly activated styrene i.e. 4ꢀ
methoxystyrene afforded moderate yield. However, the sterically
hindered substrate i.e. 2,4ꢀdimethyl styrene yielded the respective
ester comparatively in lesser yield. In case of cisꢀstilbene ester
10 formation was not observed, probably due to the bulkyness of
phenyl groups. Cylohexene provided the ring contraction product
i.e 2ꢀhydroxyethyl cyclopentanecarboxylate in 60% yield.
Interestingly, ringꢀcontraction products were obtained when the
process is subjected to cyclic olefins. Further application of this
method to prepare acetals and esters using different nucleophiles
is currently underway in our laboratory.
5
50
M.A.K, M.N and M.M.R thanks the CSIR and P.S for UGC,
India for the fellowship.
Notes and references
1
T.W. Greene and P. G. M. Wuts, Protecting Groups in Organic
Synthesis, John Wiley and Sons, New York, 3rd edn, 1999.
O
O
O
-
OH
55
60
65
70
75
80
85
90
OH
-HI
O
HO
2
(a) H. Fujioka, A. Goto, K. Otake, O. Kubo, Y. Sawamaz and T.
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I
+
O
I+
2a
I
3a
-HI
2A
KHSO5
KHSO5 + 2HI
O
1A
OH
H
O
I2
OSO3K
KHSO4 + H2O
3A
O
3
4
5
OH
-KHSO4
1a
O
4a
Scheme 2
The plausible reaction mechanism for the formation of
15 acetals/esters is depicted in Scheme 2. It is assumed that
electrophilic addition of iodine onto the olefin to give a threeꢀ
membered cyclic iodonium ion intermediate (1A). It then
undergoes nucleophilic ring opening by ethylene glycol lead to
coꢀiodo intermediate
(2a). Further, oxone facilitates the
20 deiodination of 2a to give phenonium ion intermediate (2A) and
subsequent cyclization provides the corresponding cyclic acetal
6 (a) P. H. R. Silva, V. L. C. Goncolves and C. J. A. Mota, Bioresour.
Technol., 2010, 101, 6225; (b) H. Maarse, Volatile Compounds in
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7 (a) J. Tsuji, Palladium Reagents and Catalysts Innovations in Organic
Synthesis; John Wiley & Sons : New York, 1998; (b) P.M. Maitlis,
The Organic Chemistry of Palladium, Academic Press, New York
(1971), Vol 2, pp 77.
(
3a). Oxone converts the generated HI into I2 and then the
reaction cycle continues.14 In presence of oxone, 3a forms a
mixed peroxyacetal intermediate (3A), which further undergoes
25 rearrangement to yield ester by expelling potassium bisulfate.15
Initial support for this proposal was obtained by acetalization of
styreneꢀβ,βꢀd2, which gives a benzylic deuterated product. In situ
ESIꢀMS and 13C NMR experimental data also supports the
proposed mechanism. Further, computational studies at
30 B3LYP/6ꢀ31G* level, clearly demonstrate the propensity for Oꢀ
attack on αꢀC rather than on βꢀC in the phenonium ion
intermediate (see ESI for further details).
8
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9
The role of oxone in the deiodination of 2a was confirmed by
treating pure 2a with oxone in EG (Scheme 3, eqn 1).While,
35 formation of 3a was not observed when pure 2a stirred in EG or
treated with I2 in EG. Reaction of 3a with oxone in EG provided
the corresponding ester (4a) (Scheme 3, eqn 2).
95 10 A. D. Chowdhury and G. K. Lahiri, Chem. Commun., 2012, 48, 3448.
11 (a) M. Ochiai, K. Miyamoto, M. Shiro, T. Ozawa and K. Yamaguchi,
J. Am. Chem. Soc., 2003, 125, 13006; (b) M. S. Yusubov and G. A.
Zholobova, Russ. J. Org. Chem., 2001, 37, 1179.
OH
O
O
Oxone (1.5 mmol)
(1)
O
I
EG (2 ml), 2 h, r.t.
3a: 75%
12 P. T. Parvatkar, P. S. Parameswaran and S. G. Tilve, Chem. Eur. J.,
2a
100
2012, 18, 5460.
O
O
Oxone (1.5 mmol)
EG (2 ml), 24 h, r.t.
Scheme 3
OH
13 (a) B. Yu, A.ꢀH. Liu, L.ꢀN. He, B. Li, Z.ꢀF. Diao and Y.ꢀN. Li, Green
Chem., 2012, 14, 957; (b) G.ꢀW. Wang and J. Gao, Green Chem.,
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Chem., 2011, 76, 623; (d) J. N. Moorthy, K. Senapati, K. N. Parida,
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(2)
O
O
4a: 80%
3a
105
In conclusion, we have developed a remarkably mild, efficient
40 and selective metalꢀfree method for the synthesis of terminal
acetals from olefins using commercially available, safe, stable
and inexpensive reagents. A one pot protocol for the preparation
This journal is © The Royal Society of Chemistry [year]
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