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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
Foods and Beverages, Marcel Dekker Inc, New York, 1991
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
(a) D. F. Hunt and G. T. Rodeheaver, Tetrahedron Lett., 1972, 13,
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Hosokawa, T. Ohta, S. Kanayama and S.ꢀI. Murahashi, J. Org.
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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.,
2012, 14, 1125; (c) G. A. Molander and L. N. Cavalcanti, J. Org.
Chem., 2011, 76, 623; (d) J. N. Moorthy, K. Senapati, K. N. Parida,
S. Jhulki, K. Sooraj and N. N. Nair, J. Org. Chem., 2011, 76, 9593.
14 G. Lente, J. Kalmar, Z. Baranyai, A. Kun, I. Kek, D. Bajusz, M.
Takacs, L. Veres and I. Fabian, Inorg. Chem., 2009, 48, 1763.
15 B. R. Travis, M. Sivakumar, G. O. Hollist and B. Borhan, Org. Lett.,
2003, 5, 1031.
(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
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