Catalyst-free efficient regioselective ring opening of oxiranes with thioacids in water

Article abstract of DOI:10.1080/00397911.2010.491172

Epoxide ring opening with thioacetic acid and thiobenzoic acid was investigated in the presence of water under catalyst-free conditions. This green and simple process gave an excellent yield. With simple decanting, the products were obtained in high purit

Full text of DOI:10.1080/00397911.2010.491172

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Catalyst-Free Efficient Regioselective
Ring Opening of Oxiranes with Thioacids
in Water
Azim Ziyaei Halimehjani a , Aazam Jalali a , Maryam Khalesi a ,
Akram Ashouri a & Katayoun Marjani a
a Faculty of Chemistry, Tarbiat Moallem University, Tehran, Iran
Published online: 20 Apr 2011.
To cite this article: Azim Ziyaei Halimehjani , Aazam Jalali , Maryam Khalesi , Akram Ashouri
& Katayoun Marjani (2011) Catalyst-Free Efficient Regioselective Ring Opening of Oxiranes with
Thioacids in Water, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 41:11, 1638-1643, DOI: 10.1080/00397911.2010.491172
To link to this article: http://dx.doi.org/10.1080/00397911.2010.491172
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Synthetic Communications1, 41: 1638–1643, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.491172
CATALYST-FREE EFFICIENT REGIOSELECTIVE RING
OPENING OF OXIRANES WITH THIOACIDS IN WATER
Azim Ziyaei Halimehjani, Aazam Jalali, Maryam Khalesi,
Akram Ashouri, and Katayoun Marjani
Faculty of Chemistry, Tarbiat Moallem University, Tehran, Iran
GRAPHICAL ABSTRACT
Abstract Epoxide ring opening with thioacetic acid and thiobenzoic acid was investigated in
the presence of water under catalyst-free conditions. This green and simple process gave an
excellent yield. With simple decanting, the products were obtained in high purity and on a
large scale. In this process, alkyl halide and ester cleavage were not observed.
Keywords Epoxide; ring opening; thioacids; water
INTRODUCTION
The use of aqueous media in organic reactions offers significant environmental
advantages and has attracted a great deal of interest because water is nontoxic and
nonflammable, has a high heat capacity, and is relatively inexpensive. Since the use
of water for acceleration of Diels–Alder reaction by Breslow,[1] considerable atten-
tion has been directed toward the development of organic reactions in water. Besides
the Diels–Alder reaction, water was used in many useful organic reactions, even with
water-sensitive materials.[2] Also, catalyst-free reactions are completely in com-
pliance with the philosophy of green chemistry by reducing the hazardous materials
and in some cases by reducing the number of steps needed for the extraction and
purification of the products.
Epoxides play important roles in organic synthesis because their nucleophilic
ring-opening reactions leads to 1,2-difunctional systems with regioselectivity. There
are several reports in this area with different nucleophiles such as alcohols, thiols,
Received September 26, 2009.
Address correspondence to Azim Ziyaei Halimehjani, Faculty of Chemistry, Tarbiat Moallem
University, P. O. Box 11465-9516, Tehran 11365, Iran. E-mail: ziyaei@tmu.ac.ir
1638

EPOXIDE RING OPENING OF OXIRANES
1639
amines, azides, and halides.[3] Although epoxide ring opening with thiols has been
well documented to prepare b-hydroxy sulfids, valuable intermediates for construct-
ing both synthetic pharmaceuticals and naturally occurring substances,[4] there are
only a few reports on the synthesis of b-hydroxy thioesters in literature by this
method in the presence of mineral or organic bases, alumina, and b-cyclodextrin.[5]
b-Hydroxy thioesters can be easily converted to b-hydroxy thiols with hydrolysis.[6]
Usually b-hydroxy thiols were synthesized with the epoxide ring opening by nucleo-
philic attack of H2S and Na2S.[7] The reported methods suffer from drawbacks
such as H2S odor, long reaction time, use of high pressure, and double thiolysis of
epoxides. Also, reaction of thioacids with alkyl halides in the presence of epoxide
in basic media is another limitation of the reported methods. Consequently, efficient
and practical thiolysis of 1,2-epoxides remains a daunting challenge to contemporary
organic chemistry. Recently, our research was focused on the catalyst-free synthesis
of organic compounds in water[8] or solvent-free[9] conditions. In continuation of
our interest, here we report the catalyst-free and regioselective ring opening of 1,2-
epoxides with thioacids in water.
RESULTS AND DISCUSSION
Sirinivas et al. have reported that the reaction of thioacids with epoxides does
not proceed in the absence of b-CD in water.[5b] Against this claim, we have shown that
the reaction was completed in water in the absence of catalyst with vigorous stirring.
The reaction conditions were optimized by investigation of the reaction of thio-
acetic acid and thiobenzoic acid with 2,3-epoxypropyl phenyl ether (Scheme 1). For
this purpose, different solvents such as H2O, tetra hydro furan (THF), ether, acetone,
dimethyl formamide (DMF), CH2Cl2, acetonitrile, ethanol, and methanol were used,
and we have found that the reaction was completed in water with higher yield.
After optimization of the reaction conditions, the efficiency of the process was
checked with the reaction of thioacetic and thiobenzoic acids with different oxiranes.
The results are summarized in Table 1. As is shown in Table 1, all 1,2-epoxides gave
excellent yield with thioacids. Also, diepoxide (entries 11 and 12) were used as sub-
strate in this reaction and gave excellent yields. The reaction of 2,3-epoxypropyl
methacrylate with thioacetic acid gave both Michael adduct and b-hydroxy thioester.
The reaction of epiclorohydrin and epibromohydrin with thiobenzoic acid gave
only b-hydroxy thioester without carbon–halide bond cleavage. Reaction of styrene
epoxide with thioacids gave SN2-like products in good yield.
The reaction of epichlorohydrin and epibromohydrin with thioacetic acid gave
b-hydroxy thioester 1 as the only product at room temperature while at 30–35 oC, and
both b-hydroxy thioester 1 and acyl transfer product 2 were obtained (Scheme 2). The
ratio of 1 to 2 was obtained by comparing the area of -CH peaks in 1H NMR spectra.
Scheme 1. Epoxide ring opening with thioacids in water at room temperature.

1640
A. Z. HALIMEHJANI ET AL.
Table 1. Epoxide ring opening with thioacids in water at room temperature
Entry
Epoxide
Thioacid
Product
Yield (%)a
1
2
CH3COSH
C6H5COSH
88
85
3
4
CH3COSH
C6H5COSH
95 (83)b
100
5
6
CH3COSH
C6H5COSH
93 (79)b
100 (85)b
7
8
CH3COSH
C6H5COSH
100 (69)b
96
9
10
CH3COSH
C6H5COSH
100
100
11
12
CH3COSH
C6H5COSH
96 (80)b
100
13
14
CH3COSH
C6H5COSH
73(27)c
—
15
16
C6H5COSH
C6H5COSH
100
100
17
18
CH3COSH
C6H5COSH
66
60
19
20
CH3COSH
C6H5COSH
85
70
21
22
CH3COSH
C6H5COSH
89
100
aIsolated yields.
bIsolated yield for large-scale synthesis.
cThe yield in parentheses refers to the Michael adduct.
b-Hydroxy thiol was also prepared in situ via epoxide ring opening with
thioacetic acid and then hydrolysis of the product in 63% isolated yields (Scheme 3).
In conclusion, we have shown a catalyst-free method for the synthesis of
b-hydroxyl thioesters with the reaction of epoxides and thioacids in water. This
method is simple and green and gives high yields of products without use of any

EPOXIDE RING OPENING OF OXIRANES
1641
Scheme 2. Epoxide ring opening with acyl transfer reaction.
Scheme 3. In situ epoxide ring opening and hydrolysis of thioester.
catalyst or organic solvents. It is notable that in large-scale synthesis, the product
can be extracted by simple decanting and purified by distillation, which is completely
in compliance with the green chemistry goal of doing the reactions in water.[10] The
ester and alkyl halide cleavage was not observed in this method.
EXPERIMENTAL
All reactions were carried out in an atmosphere of air. All chemicals and sol-
vents except water (tap water) were purchased from Merck or Fluka and used as
1
received. The H and 13C NMR spectra were recorded on 300-MHz spectrometers.
General Procedure
In a round-bottomed flask equipped with a magnet, the epoxide (5 mmol),
water (10 mL), and thioacid (5.5 mmol) were added. After vigorous stirring for
10 h, the oily product was extracted by ethyl acetate, washed with 2 M aqueous
solution of NaHCO3, and evaporated to give a pure product in most of the cases.
Further purifications have been done by column chromatography (silica gel; ethyl
1
acetate=n-hexane; 2:8). The products were characterized by infrared and H and
13C NMR spectroscopy. It is notable that on large scale no solvent was required
for extraction, and decanting of the oily product is sufficient.
Spectroscopic Data for Selected Compounds
Table 1, Entry 3. 1H NMR (300 MHz, CDCl3) d (ppm) 3.83 (1H, m),
3.43–3.59 (2H, m), 3.33 (1H, dd, J ¼ 9.4 and 6.5 Hz), 2.97–3.12 (2H, m), 2.80
(1H, br s, -OH), 2.31 (3H, s), 1.12 (6H, d, J ¼ 6.0 Hz). 13C NMR (300 MHz, CDCl3)
d (ppm) 196.0, 72.2, 70.5, 69.6, 32.3, 30.4, 21.9. MS (EI): m=z ¼ 191 (M-1), 159, 99,
89, 73, 57, 43 (100).

1642
A. Z. HALIMEHJANI ET AL.
Table 1, Entry 7. 1H NMR (300 MHz, CDCl3) d (ppm) 5.81 (1H, dd, J ¼ 10.5
and 6.2 Hz), 5.08–5.21 (2H, m), 3.93 (2H, d, J ¼ 4.7 Hz), 3.81 (1H, m), 3.32–3.41 (2H,
m), 3.13 (1H, br s, -OH), 2.91–3.05 (2H, m), 2.27 (3H, s). 13C NMR (300 MHz,
CDCl3) d (ppm) 196.2, 134.8, 117.6, 73.1, 72.6, 69.8, 32.8, 30.8. MS (EI):
m=z ¼ 189 (M-1), 157, 149, 129, 103, 97, 73, 59, 55, 43 (100), 41.
Table 1, Entry 11. 13H NMR (300 MHz, CDCl3) d (ppm) 3.63 (2H, m),
3.04–2.77 (6H, m), 2.26 (6H, s), 1.42–1.33 (8H, m). 13C NMR (300 MHz, CDCl3)
d (ppm) 196.4, 69.3, 35.8, 35.7, 30.4, 20.9. MS (EI): m=z ¼ 295 (M þ 1), 277 (100),
259, 235, 217, 187, 175, 141, 127, 43.
Scheme 2, Compound 1(x ¼ cl). 1H NMR (300 MHz, CDCl3) d (ppm) 3.93
(1H, t, J ¼ 5.5 Hz), 3.61 (1H, dd, J ¼ 11.3 and 4.4 Hz), 3.54 (1H, dd, J ¼ 11.3 and
5.9 Hz), 3.40 (1H, br s, -OH), 3.04–3.15 (2H, m), 2.34 (3H, s). 13C NMR
(300 MHz, CDCl3) d (ppm) 196.5, 70.8, 48.4, 33.3, 30.8. MS (EI): m=z ¼ 167 (M ꢀ 1),
149, 135, 119, 103, 91, 79, 59, 43 (100).
Typical Procedure for Large Scale Synthesis
Thioacetic acid (15.4 mL, 218 mmol) was added to a stirred solution of 2,3-
epoxy propyl isopropyl ether (25 mL, 198 mmol) in water (100 mL), and the reaction
mixture was vigorously stirred at room temperature for 10 h. At completion, the
organic layer was separated and washed with 2 M aqueous solution of NaHCO3
(two times) to remove unreacted thioacetic acid. Then, the organic phase was evapo-
rated under reduced pressure to remove excess of epoxide. The product was obtained
in 83% isolated yield.
ACKNOWLEDGMENT
Many thanks go to the Faculty of Chemistry of Tarbiat Moallem University
for supporting this work.
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