Simple synthesis of β-acetoxy thiocyanates from oxiranes

Article abstract of DOI:10.1080/00397911.2010.494817

A convenient and simple method for the preparation of previously unknown β-acetoxy thiocyanates by regioselective ring opening of the corresponding oxiranes with thiocyanate anion followed by acetylation is described. The shorter reaction times, better yields of the products, and easy workup are the advantages of this methodology.

Full text of DOI:10.1080/00397911.2010.494817

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Simple Synthesis of β-Acetoxy
Thiocyanates from Oxiranes
Edyta Łukowska-Chojnacka a & Jan Plenkiewicz a
a Faculty of Chemistry, Institute of Biotechnology, Warsaw University
of Technology, Warsaw, Poland
Version of record first published: 02 May 2011.
To cite this article: Edyta Łukowska-Chojnacka & Jan Plenkiewicz (2011): Simple Synthesis of β-
Acetoxy Thiocyanates from Oxiranes, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 41:13, 1999-2006
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Synthetic Communications1, 41: 1999–2006, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.494817
SIMPLE SYNTHESIS OF b-ACETOXY THIOCYANATES
FROM OXIRANES
Edyta Łukowska-Chojnacka and Jan Plenkiewicz
Faculty of Chemistry, Institute of Biotechnology, Warsaw University of
Technology, Warsaw, Poland
GRAPHICAL ABSTRACT
Abstract A convenient and simple method for the preparation of previously unknown
b-acetoxy thiocyanates by regioselective ring opening of the corresponding oxiranes with
thiocyanate anion followed by acetylation is described. The shorter reaction times, better
yields of the products, and easy workup are the advantages of this methodology.
Keywords Acetate; acetylation; b-hydroxy thiocyanate; oxirane
INTRODUCTION
b-Hydroxy thiocyanates, known as intermediates in thiiranes synthesis, consti-
tute an interesting subclass of secondary alcohols and exhibit several modes of reac-
tivity. They can be prepared by three methods as reported in the literature. The first
one involves opening of cyclic sulfate with ammonium thiocyanate followed by
hydrolysis of the corresponding b-sulfate.[1,2] The second method consists of nucleo-
philic substitution of a bromine atom in bromohydrin[3–5] by a thiocyanate anion.
The last and the most frequently used is the ring opening of an oxirane with a thio-
cyanate anion. This method uses the addition of thiocyanic acid generated in situ at
low temperature[6,7] or thiocyanate salts in catalyst-free conditions[8] or in the pres-
ence of various catalysts, such as tetrabutylammonium fluoride,[9] titanium isoprop-
oxide,[10] triphenylphosphine–thiocyanogen (TPPT),[11] titanium, zinc, and gallium
chlorides,[12,13] triphenylphosphinepalladium,[14] crown ethers,[15] polyacrylo-
amides,[16] selectfluor,[17] 2-phenyl-2-(pyridyl)imidazolidine (PPI),[18] 2,6-bis[2-
(o-aminophenoxy)-methyl]-4-bromo-1-methoxybenzene (BABMB),[19] Schiff-base
metal (II) complexes,[20] metalloporphyrins,[21] or tetraarylporphyrins.[22] According
to the literature data,[6,23] b-hydroxy thiocyanates are not stable, and the presence of
Received April 23, 2010.
Address correspondence to Jan Plenkiewicz, Warsaw University of Technology, Faculty of
Chemistry, Institute of Biotechnology, Noakowskiego St. 3, 00-664 Warsaw, Poland. E-mail: plenki@
ch.pw.edu.pl
1999

2000
E. ŁUKOWSKA-CHOJNACKA AND J. PLENKIEWICZ
traces of hydroquinone or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) stabilize
them and slow down their rapid conversion into thiiranes. In recent papers,[24,25]
we have described a possibility of transforming b-hydroxy thiocyanates into appro-
priate acetates by reaction with acetyl chloride. In contrast to the corresponding
alcohols, the acetates were stable at room temperature and could be obtained with
satisfying yields. We have also proved that the acetates can be used as substrates
in lipase-catalyzed hydrolyses. As the result of kinetic enantiomers separation, the
enantiomerically enriched 1-substituted-3-thiocyanatopropan-2-ols and their acet-
ates were obtained. We have also found[25] that optically active 1-substituted-3-
thiocyanatopropan-2-yl acetates, similar to free alcohols, can be transformed into
corresponding thiiranes with retention of optical purity. These reactions were carried
out in two-phase aqueous LiOH=tetrahydrofuran (THF) system, and appropriate
thiiranes were obtained in a short time with high enantiomeric excesses and excellent
yields.
RESULTS AND DISCUSSION
Herein, we describe the simplified procedure for preparation of several new
b-hydroxy thiocyanate acetates 3. This procedure omits the laborious purification
step and can be performed almost as an one-pot synthesis. The compounds 3 were
obtained from the appropriate oxiranes 1 in a two-step reaction (Scheme 1). The first
step involved oxirane ring opening by ammonium thiocyanate in the presence of
crown ether as the catalyst. The reaction was carried out in acetonitrile under reflux.
Next, after filtration and evaporation of the acetonitrile, an excess of acetyl chloride
was added to crude b-hydroxy thiocyanate 2, and the mixture was refluxed for a few
hours, yielding the requested acetate 3.
The preparation of three groups of b-acetoxy thiocyanates, different from each
other in nature of substituent, were studied. At first, the ring opening of epoxides 1a, b
was investigated. The known epoxide 1a[26] was prepared from potassium
phthalimide and epichlorohydrin (66%), whereas epoxide 1b[27] from N-hydro-
xyphthalimide[28] and epibromohydrin (55%). In our experiments, 18-crown-6 was
Scheme 1. Synthesis of b-acetoxy thiocyanates from oxiranes.

SYNTHESIS OF b-ACETOXY THIOCYANATES
2001
used as the catalyst. We also checked the earlier[6] suggestion that addition of a trace
amount of hydroquinone stabilizes the formed b-hydroxy thiocyanates 2. The reac-
tions were carried out with and without the addition of hydroquinone. The progress
of the reaction was monitored by thin-layer chromatography (TLC), and the reac-
tion was stopped when the conversion reached 100%. Because of low stability, b-
hydroxy thiocyanates 2a, b were not isolated as free alcohols but immediately treated
with excess of acetyl chloride and refluxed for approximately 2.5 h. The acetates 3a, b
were purified and characterized by infrared (IR), 1H NMR, and 13C NMR as well as
by elemental analysis. As shown in Table 1, the presence of hydroquinone in the
reaction mixtures increase the yields of the acetates 3a, b.
In the same manner, the reaction was performed with other oxiranes 1c–g.
3-(N-Alkyl-N-phenylamino)propylene oxides 1c, d were prepared from the appropri-
ate chlorohydrins in cold 50% sodium hydroxide solution according to the described
Table 1. The yields of b-acetoxythiocyanates 3a–g obtained from oxiranes 1a–g
Entry
Ar
Yield (%)
a
63a=72
b
c
d
45a=56
74
79
e
f
66
62
72
g
aThe yields of acetates obtained without addition of hydroquinone.

2002
E. ŁUKOWSKA-CHOJNACKA AND J. PLENKIEWICZ
method[29] (82–87%). The starting 2-(arylsulfonylmethyl)oxiranes 1e–g were pre-
pared in excellent yields (84–95%) by oxidation of the corresponding arylsulfanylgly-
cidyl ethers with Oxone as the oxidant. The employed procedure was known,[30] but
we lowered the temperature of the reaction.
For oxiranes 1c–g, the reactions with ammonium thiocyanate were carried out
with addition of hydroquinone. In all cases, the crown ether–catalyzed reactions of
regioselective ring opening by ammonium thiocyanate led to only one product. The
results are summarized in Table 1.
CONCLUSIONS
In summary, we have presented a general method of synthesis of b-acetoxy
thiocyanates in a two-step reaction from appropriate oxiranes, ammonium thiocyan-
ate, and acetyl chloride. In all reactions, the attack of the nucleophile occurs prefer-
entially at the less-substituted oxirane carbon. Only acetates of secondary alcohols
were synthesized. We have observed a slight stabilizing influence of hydroquinone
on intermediate b-hydroxy thiocyanates. The conversion of these alcohols into the
corresponding acetates gave completely stable in room-temperature compounds.
Regardless of the substituent type, all acetates were obtained in a short time and with
excellent yields.
EXPERIMENTAL
1H (400 MHz) and 13C NMR (100-MHz) spectra were recorded on a Varian
Mercury 400 MHz spectrometer in CDCl3 solution. Chemical shifts (d) are reported
in parts per million (ppm); J values are given in hertz. Infrared (IR) spectra were
taken on a Carl Zeiss Specord M80 instrument. Elemental analyses were performed
on a CHNSCl=O Perkin-Elmer type 2400 instrument. The reactions were monitored
by thin-layer chromatograghy (TLC) on silica gel 60 plates (230–400 mesh). The
arylsulfanylglycidyl ethers were prepared in good yields (80–85%) from the
corresponding thiophenols and epichlorhydrin in NaOH=tetrahydrofuran (THF)
suspension according to the described[31] method. 1-Chloro-3-(N-alkyl-N-
phenylamino)propan-2-ols were synthesized[29] from the corresponding N-alkylani-
lines and epichlorohydrin in a MeOH=H2O solution under reflux conditions
(67–87%). Solvents, reagents, and chemicals were obtained from POCH, Merck,
Fluka, and Aldrich.
General Procedure for Oxidation of Arylsulfanylglycidyl Ethers to
2-(Arylsulfonylmethyl)oxiranes (1e–g)
A solution of appropriate arylsulfanylglycidyl ether (0.06 mol) in MeOH
(46 ml) was added dropwise to a stirred solution of Oxone (2KHSO5 Â
KHSO4 Â K2SO4, 0.12 mol, 73.77 g) in water (262 ml) at 3 ꢀC over 1 h. Next, the mix-
ture was stirred for 0.5 h at 3 ꢀC and then for 1 h at room temperature. The progress
of the reaction was monitored by TLC using CHCl3-MeOH (98:2 v=v) as the eluent.
After completion of the reaction, the precipitate was filtered off and washed
with CH2Cl2 (3 Â 50 ml). The organic layer was dried over anhydrous MgSO4 and

SYNTHESIS OF b-ACETOXY THIOCYANATES
2003
evaporated. Product 1e was purified by chromatography on a silica-gel column with
n-hexane–ethyl acetate (1:1 v=v) as the eluent, and products 1f, g were purified by
crystallization from toluene.
Selected Data for 1e–g
2-(Benzenesulfonylmethyl)oxirane (1e). Oil, yield 95%. 1H NMR: 2.42
(dd, 1H, CHCHaHb, JHaCH ¼ 2, JHaHb ¼ 4.8), 2.78 (dd, 1H, CHCHaHb, JHbCH ¼ 4),
3.24–3.36 (m, 3H, CH, SO2CH2), 7.57–7.96 (m, 5H, C6H5). 13C NMR: 45.72, 45.84,
1
59.39, 128.14, 129.34, 134.11, 139.06. The H NMR spectrum is identical with that
given in the literature.[32]
2-(4-Chlorobenzenesulfonylmethyl)oxirane (1f). Colorless crystals, mp
65–67 ꢀC, yield 84%. 1H NMR: 2.44 (dd, 1H, CHCHaHb, JHaCH ¼ 2.2, JHaHb ¼ 4.6),
2.79–2.81 (m, 1H, CHCHaHb), 3.22–3.37 (m, 3H, CH, SO2CH2), 7.54–7.90 (m, 4H,
C6H4). 13C NMR: 45.66, 45.74, 59.49, 129.66, 129.69, 137.55, 140.92.
2-(p-Toluenesulfonylmethyl)oxirane (1g). Colorless crystals, mp 50–51 ꢀC
(lit.[33] 51–53 ꢀC), yield 84%. 1H NMR: 2.43 (dd, 1H, CHCHaHb, JHaCH ¼ 2,
JHaHb ¼ 4.8), 2.46 (s, 3H, CH3), 2.77–2.79 (m, 1H, CHCHaHb), 3.23–3.34 (m, 3H,
CH, SO2CH2), 7.37–7.83(m, 4H, C6H4). 13C NMR: 21.67, 45.84, 45.87, 59.49,
1
128.18, 129.98, 136.15, 145.21. H NMR spectrum is identical with that given in
the literature.[33]
General Procedure for the Synthesis of b-Acetoxy Thiocyanates
(3a–g)
A solution of 18-crown-6 ether (0.1 mmol, 0.0264 g) in CH2Cl2 (5 mL) was
added to the mixture of an epoxide (10 mmol) and NH4SCN (10 mmol, 0.76 g) in
acetonitrile (30 mL), and the mixture was stirred under reflux. The progress of the
reaction was monitored by TLC, using ethyl acetate–cyclohexane–chloroform
(1:1:1 v=v) mixture as the eluent for epoxides 1a, b, n-hexane–ethyl acetate
(3:1 v=v) for epoxides 1c, d, and chloroform-methanol (98:2 v=v) for epoxides 1e–
g. After completion of the reaction, the solid was filtered off, and the solvent was
evaporated. The resulting crude mixture of product 2 was used as the substrate
in the synthesis of acetate 3 by adding an excess of acetyl chloride (25 mL) and stir-
ring the mixture for 2.5 h at reflux. After cooling to room temperature, traces of the
solid material were filtered off, and the filtrate was cooled in an ice bath and neutra-
lized to pH 7 with a K2CO3 solution. The products were extracted with CH2Cl2
(3 ꢁ 30 mL); the combined organic layers washed with water (3 ꢁ 50 mL), dried over
anhydrous MgSO4, and evaporated. Products 3a and 3b were purified by column
chromatography on a silica gel with ethyl acetate–cyclohexane–chloroform
(1:1:1 v=v) mixture as the eluent. For 3c and 3d n-hexane–ethyl acetate (10:1 v=v)
mixture was used as the eluent. Acetates 3e–g were purified by crystallization from
ethyl acetate.

2004
E. ŁUKOWSKA-CHOJNACKA AND J. PLENKIEWICZ
Selected Data
N-(2-Acetoxy-3-thiocyanatopropyl)phthalimide (3a). Colorless crystals,
1
mp 120–122 ꢀC, yield 72%. H NMR: 2.10 (s, 3H, CH3), 3.09 (dd, 1H, CHaHbSCN,
JHaCH ¼ 7.6, JHaHb ¼ 14.4), 3.27 (dd, 1H, CHaHbSCN, JHbCH ¼ 4), 3.94 (dd, 1H,
NCHcHd, JHcCH ¼ 4.6, JHcHd ¼ 14.8), 4.08 (dd, 1H, NCHcHd, JHdCH ¼ 4.4),
3.28–3.35 (m, 1H, CH), 7.74–7.87 (m, 4H, C6H4). 13C NMR: 20.64, 35.20, 38.97,
70.18, 111.66, 123.60, 131.60, 134.39, 168.11, 170.04. IR (nujol, cmꢁ1) 2150 (CN),
1695 (CO), 1730 (CO), 1768 (CO). Anal. calcd. for C14H12N2SO4: C, 55.26; H,
3.94; N, 9.21; S, 10.52. Found: C, 55.27; H, 4.00; N, 9.06; S, 10.52.
N-(2-Acetoxy-3-thiocyanatopropoxy)phthalimide (3b). Colorless crystals,
1
mp 69–71 ꢀC, yield 56%. H NMR: 2.13 (s, 3H, CH3), 3.47 (dd, 1H, CHaHbSCN,
JHaCH ¼ 6.4, JHaHb ¼ 14.4), 3.63 (dd, 1H, CHaHbSCN, JHbCH ¼ 4), 4.36–4.43 (m,
2H, NCH2), 5.35–5.40 (m, 1H, CH), 7.76–7.85 (m, 4H, C6H4). 13C NMR: 20.60,
33.92, 69.14, 75.88, 111.71, 123.79, 128.54, 134.84, 163.18, 169.89. IR (nujol, cmꢁ1
)
2150 (CN), 1730 (CO), 1740 (CO), 1782 (CO). Anal. calcd. for C14H12N2SO5: C,
52.50; H, 3.78; N, 8.75; S, 10.01. Found: C, 52.38; H, 3.83; N, 8.70; S, 10.10.
1-(N-Methyl-N-phenylamino)-3-thiocyanatopropan-2-yl acetate (3c).
1
Oil, yield 74%. H NMR: 2.06 (s, 3H, COCH3), 2.97 (s, 3H, NCH3), 3.12 (dd, 1H,
CHaHbSCN, JHaCH ¼ 6.8, JHaHb ¼ 14), 3.30 (dd, 1H, CHaHbSCN, JHbCH ¼ 3.6),
3.45 (dd, 1H, NCHcHdCH, JHcCH ¼ 6.8, JHcHd ¼ 14.8), 3.68 (dd, 1H, NCHcHdCH,
JHdCH ¼ 6.4), 5.40 (m, 1H, CH), 7.75–7.27 (m, 5H, C6H5). 13C NMR: 20.67,
35.52, 39.37, 54.39, 69.97, 111.80, 112.66, 117.66, 129.35, 148.77, 170.19. IR (film,
cmꢁ1) 2140 (CN), 1735 (CO). Anal. calcd. for C13H16N2SO2: C, 59.07; H, 6.10; N,
10.60; S, 12.13. Found: C, 58.99; H, 5.99; N, 10.63; S, 12.27.
1-(N-Ethyl-N-phenylamino)-3-thiocyanatopropan-2-yl acetate (3d). Oil,
1
yield 79%. H NMR: 1.14 (t, 3H, CH2CH3, J ¼ 7), 2.11 (s, 3H, COCH3), 3.14 (dd,
1H, CHaHbSCN, JHaCH ¼ 6.8, JHaHb ¼ 14), 3.25–3.53 (m, 4H, CHaHbSCN,
NCH2CH3, NCHcHdCH), 3.62 (dd, 1H, NCHcHdCH, JHdCH ¼ 6.4, JHdHc ¼ 15.2),
5.38 (m, 1H, CH), 6.74–7.27 (m, 5H, C6H5). 13C NMR: 11.54, 20.72, 35.49, 46.22,
51.79, 70.13, 111.90, 113.29, 117.59, 129.43, 147.37, 170.21. IR (film, cmꢁ1) 2150
(CN), 1740 (CO). Anal. calcd. for C14H18N2SO2: C, 60.41; H, 6.52; N, 10.06; S,
11.52. Found: C, 60.22; H, 6.43; N, 9.97; S, 11.63.
1-Benzenesulfonyl-3-thiocyanatopropan-2-yl acetate (3e). Yellow crys-
tals, mp 99–101 ꢀC, yield 66%. 1H NMR: 1.94 (s, 3H, CH3), 3.30 (dd, 1H,
CHaHbSCN), JHaCH ¼ 5.8, JHaHb ¼ 14.6), 3.48–3.61 (m, 3H, CHaHbSCN, SO2CH2),
5.46–5.51 (m, 1H, CH), 7.61–7.93 (m, 5H, C6H5). 13C NMR: 20.34, 36.63, 57.03,
66.70, 111.28, 128.04, 129.59, 134.40, 138.87, 169.47. IR (nujol, cmꢁ1) 2158 (CN),
1745 (CO). Anal. calcd. for C12H13NS2O4: C, 48.15; H, 4.38; N, 4.68; S, 21.42.
Found: C, 48.36; H, 4.40; N, 4.45; S, 21.51.
1-(4-Chlorobenzenesulfonyl)-3-thiocyanatopropan-2-yl acetate (3f).
1
Yellow crystals, mp 128–130 ꢀC, yield 62%. H NMR: 1.98 (s, 3H, CH3), 3.29 (dd,
1H, CHaHbSCN, JHaCH ¼ 5.8, JHaHb ¼ 14.6), 3.47–3.60 (m, 3H, CHaHbSCN,
SO2CH2), 5.45–5.51 (m, 1H, CH), 7.57–7.87 (m, 4H, C6H4). 13C NMR: 20.38,
36.59, 57.10, 66.58, 111.23, 129.57, 129.92, 137.22, 141.32, 169.47. IR (nujol,

SYNTHESIS OF b-ACETOXY THIOCYANATES
2005
cmꢁ1) 2160 (CN), 1755 (CO). Anal. calcd. for C12H12ClNS2O4: C, 43.18; H, 3.62; Cl,
10.62; N, 4.20; S, 19.21. Found: C, 43.29; H, 3.78; Cl, 10.84; N, 3.97; S, 19.37.
1-(p-Toluenesulfonyl)-3-thiocyanatopropan-2-yl acetate (3g). Yellow
crystals, mp 77–79 ꢀC, yield 76%. 1H NMR: 1.96 (s, 3H, CH3), 2.46 (s, 3H,
CH3C6H4), 3.29 (dd, 1H, CHaHbSCN, JHaCH ¼ 5.8, JHaHb ¼ 14.6), 3.48 (dd, 1H,
CHaHbSCN, JHbCH ¼ 6.6), 3.52–3.57 (m, 2H, SO2CH2), 5.44–5.49 (m, 1H, CH),
7.39–7.80 (m, 4H, C6H4). 13C NMR: 20.41, 20.67, 36.64, 57.07, 66.74, 111.36,
128.08, 130.21, 135.85, 145.62, 169.51. IR (nujol, cmꢁ1) 2148 (CN), 1750 (CO). Anal.
calcd. for C13H15NS2O4: C, 49.82; H, 4.82; N, 4.47; S, 20.46. Found: C, 49.81; H,
4.72; N, 4.40; S, 20.51.
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