Versatile synthesis of α-substituted taurines from nitroolefins

Article abstract of DOI:10.1007/s00726-010-0655-7

A series of 1-substituted and 1,1-disubstituted taurines were synthesized from nitroolefins via the Michael addition with sodium ethylxanthate, oxidation with performic acid, and reduction with hydrogen in the presence of palladium on carbon powder. The current route is a versatile and salt-free method for synthesis of both aliphatic and aromatic 1-substituted and 1,1-disubstituted taurines. Springer-Verlag 2010.

Full text of DOI:10.1007/s00726-010-0655-7

Amino Acids (2011) 41:195–203
DOI 10.1007/s00726-010-0655-7
ORIGINAL ARTICLE
Versatile synthesis of a-substituted taurines from nitroolefins
•
Chuanxiang Xu Jiaxi Xu
Received: 25 February 2010 / Accepted: 4 June 2010 / Published online: 12 June 2010
Ó Springer-Verlag 2010
Abstract A series of 1-substituted and 1,1-disubstituted
taurines were synthesized from nitroolefins via the Michael
addition with sodium ethylxanthate, oxidation with per-
formic acid, and reduction with hydrogen in the presence
of palladium on carbon powder. The current route is a
versatile and salt-free method for synthesis of both ali-
phatic and aromatic 1-substituted and 1,1-disubstituted
taurines.
used as enzyme inhibitors because of their tetrahedrally
structural properties (Carson et al. 1997; de Bont et al.
1999; Gennari et al. 1998; Xu 2003). Recently, much
attention has been paid to the synthesis of substituted
taurines for the investigation of biological activities and
structure–activity relationships and for discovery of
new peptidomimetic drugs (Liebowitz et al. 1987, 1988;
Lombardini and Liebowitz 1988).
Although several methods for synthesis of substituted
taurines have been developed (Cordero et al. 2002;
Enders et al. 2009; Hu et al. 2007; Wang et al. 2008; Xu
2002, 2003; Zhang et al. 2008), the efficient synthetic
methods for 1-mono- and 1,1-disubstituted taurines are
still scarce. They include addition of sulfite to nitroolefins
and the subsequent reduction (Gold et al. 1951); the
Mitsunobu reaction of N-protected vicinal amino sec-
ondary alcohols with thiolacetic acid and oxidation with
performic acid (Lowik and Liskamp 2000; Moree et al.
1995; Xu and Xu 2004; Xu et al. 2005); the nucleophilic
ring-opening reaction of aliphatic thiiranes with ammonia/
amines and subsequent oxidation with performic acid
(Huang et al. 2005, 2006; Yu et al. 2009); direct nucle-
ophilic ring-opening reaction of aromatic 2,2-disubstituted
aziridines (Chen et al. 2009b); the cyclization of vicinal
amino secondary alcohols with carbon disulfide to thia-
zolidine-2-thiones and subsequent oxidation with perfor-
mic acid (Chen et al. 2009a). However, desalinization in
the method of the direct addition of sulfite to nitroolefins
and the subsequent reduction is a tedious process for
water-soluble taurines. The methods with aziridines and
thiiranes as starting materials are only limited to aromatic
1,1-disubstituted taurines, and aliphatic 1-mono and 1,1-
disubstituted taurines, respectively. Moreover, vicinal
amino secondary alcohols are lacking of commercially
available chemicals in the method of the oxidation of
Keywords Amino acid Á Aminoalkanesulfonic acid Á
Nitroolefin Á Synthesis Á Taurine Á Xanthate
Introduction
Taurine is the simplest 2-aminoalkanesulfonic acid, found
more than 200 years ago, and has been widely used in
nutrition and medical fields (Gupta et al. 2005). Substituted
taurines were isolated from red alga and shellfishes during
the past century (Wickberg 1957). They have also been
found in many mammalian tissues and are involved in
various important physiological processes (Huxtable 1992).
It has been demonstrated clearly that taurine and its cyclic
analogs show different effects on ATP-dependent calcium
ion uptake and protein phosphorylation in rat retina
(Liebowitz et al. 1987, 1988; Lombardini and Liebowitz
1988). On the other hand, during the past three decades,
aminoalkanesulfonic acid derivatives have been widely
C. Xu Á J. Xu (&)
State Key Laboratory of Chemical Resource Engineering,
Department of Organic Chemistry, Faculty of Science,
Beijing University of Chemical Technology,
Beijing 100029, People’s Republic of China
e-mail: jxxu@mail.buct.edu.cn
123

196
C. Xu, J. Xu
thiazolidine-2-thiones. O-Ethyl S-(2-nitroalkyl) dithiocar-
bonates could be considered as linear analogs of
thiazolidine-2-thiones (Fig. 1) and can be oxidized to
2-nitroalkanesulfonic acids, precursors of substituted tau-
rines. The dithiocarbonates can be prepared readily from
nitroolefins. Moreover, nitroolefins are commercially
available or are prepared conveniently from aldehydes
and nitroalkanes (Kumaran and Kulkarni 1994) or olefins
(Fryszkowska et al. 2008). Oxidation of the dithiocar-
bonates with performic acid and the subsequent palla-
nitroolefins are identical to those previously reported in the
literature.
Preparation of O-ethyl S-(2-nitroalkyl) dithiocarbonates
3 (general procedure)
O-Ethyl S-(2-nitroalkyl) dithiocarbonates 3 were prepared
from nitroolefins and sodium ethylxanthate according to
the literature method (Ouvry et al. 2003).
To a stirred nitroolefin (10 mmol) in 20 mL of acetic acid
was added portionwise sodium ethylxanthate (2.88 g,
20 mmol) in an ice–water bath at 0–5°C. After addition, the
resulting mixture was further stirred for 3–4 h. Water
(20 mL) was added and the reaction mixture was extracted
with dichloromethane (3 9 20 mL). The combined organic
phase was washed with saturated aqueous bicarbonate, and
brine, and dried over anhydrous sodium sulfate. After
removal of solvent under reduced pressure, the residue was
purified on a silica gel column with a mixture of petroleum
ether and ethyl acetate (30:1 to 50:1, v/v) as an eluentto afford
yellowish oil O-ethyl S-(2-nitroalkyl) dithiocarbonate 3.
dium-catalyzed reduction is
a salt-free method for
synthesis of 1-mono- and 1,1-disubstituted taurines.
Herein, we describe the versatile route to the synthesis
of aliphatic and aromatic 1-mono- and 1,1-disubstituted
taurines from nitroolefins.
Materials and methods
Melting points were measured on a Yanaco MP-500
1
melting point apparatus and are uncorrected. H NMR and
13C NMR spectra were recorded on Varian Mercury 200
(200 MHz), Mercury Plus 300 (300 MHz), or Bruker (500
or 600 MHz) spectrometer in CDCl3 with TMS as an
internal standard, in D2O (with HCO2H as an internal
standard for 13C NMR spectra), in DMSO-d6, or in 85%
formic acid (Chen and Xu 2009). Mass spectra were
obtained on a Bruker ESQUIRE*LCTM ESI ion trap mass
spectrometer. High resolution mass spectrometry (HRMS)
data were carried out on an Agilent LC/MSD TOF mass
spectrometer. IR spectra were determined on a Nicolet
5700 FT-IR spectrometer. Nitroolefins 2a–h were prepared
from aldehydes with nitromethane under the catalysis of
triethylamine in satisfactory to good yields according to the
literature method (Kumaran and Kulkarni 1994). Nitro-
olefin 2i was prepared from butanone with nitromethane
via a one-pot and two step method in a satisfactory yield by
the reported method (Jang et al. 2003). Nitroolefins 2j–l
were prepared from olefins with sodium nitrite under the
catalysis of ceric ammonium nitrate (CAN) in satisfactory
to good yields by the reported method (Fryszkowska et al.
2008). Sodium ethylxanthate was prepared from ethanol
and carbon disulfide in the presence of sodium hydroxide
(Zhang et al. 2002). The analytical data of all known
O-Ethyl S-(2-nitro-1-phenylethyl) dithiocarbonate (3a)
Yellowish oil, yield: 88%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 1.44 (t,
J = 7.2 Hz, 3H, CH3), 4.68 (q, J = 7.2 Hz, 2H, CH2), 4.91
(dd, J = 10.2, 13.2 Hz, 1H in CH2N), 5.08 (dd, J = 5.1,
13.2 Hz, 1H in CH2N), 5.47 (dd, J = 5.1, 10.2 Hz, 1H,
CHS), 7.33–7.37 (m, 5H, Ar).
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.6, 50.3, 70.7,
77.5, 127.9, 129.0, 129.2, 134.3, 210.5.
IR (mmax, cm-1) 3,021.7, 2,978.3, 1,555.7 (NO2), 1,373.3
(NO2), 1,232.1 (COC), 1,110.9 (COC), 1,044.7 (C=S),
697.8.
HRMS (ESI) Calcd. for C11H13NNaO3S2 m/z: 294.0234
[M ? Na]?; Found 294.0213.
O-Ethyl S-[1-(4-methylphenyl)-2-nitroethyl]
dithiocarbonate (3b)
Yellowish oil, yield: 84%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 1.43 (t, J =
7.2 Hz, 3H, CH3), 2.33 (s, 3H, CH3), 4.67 (q, J = 7.2 Hz,
2H, CH2), 4.88 (dd, J = 10.2, 13.2 Hz, 1H in CH2N), 5.06
(dd, J = 5.3, 13.2 Hz, 1H in CH2N), 5.43 (dd, J = 5.3,
10.2 Hz, 1H, CHS), 7.16 (d, J = 8.1 Hz, 2H, ArH), 7.22
(d, J = 8.1 Hz, 2H, ArH).
S
S
S
OEt
NH
S
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.6, 21.1, 50.1,
70.6, 77.6, 127.8, 129.9, 131.1, 140.0, 210.8.
IR (mmax, cm-1) 3,021.7, 2,973.9, 2,921.7, 1,555.6
(NO2), 1,373.1 (NO2), 1,230.8 (COC), 1,111.4 (COC),
1,046.0 (C=S), 787.0, 673.9.
R1
NO2
R1
R2
R2
Fig. 1 O-Ethyl S-(2-nitroalkyl) dithiocarbonates and thiazolidine-2-
thiones
123

Versatile synthesis of a-substituted taurines from nitroolefins
197
O-Ethyl S-(2-methyl-1-nitromethylpropyl) dithiocarbonate
(3f)
HRMS (ESI) Calcd. for C12H15NNaO3S2 m/z: 308.0385
[M ? Na]?; Found 308.0371.
Yellowish oil, yield: 80%.
O-Ethyl S-[1-(4-chlorophenyl)-2-nitroethyl]
dithiocarbonate (3c)
1H NMR (CDCl3, 300 MHz) (d, ppm) 1.02 (d,
J = 6.8 Hz, 3H, CH3), 1.11 (d, J = 6.8 Hz, 3H, CH3),
1.45 (t, J = 7.1 Hz, 3H, CH3), 2.16 (dqq, J = 4.1, 6.8,
6.8 Hz, 1H, CH), 4.41 (ddd, J = 4.1, 6.3, 8.1 Hz, 1H,
CHS), 4.65 (dd, J = 8.1, 13.1 Hz, 1H in CH2N), 4.66 (q,
J = 7.1 Hz, 2H, CH2), 4.72 (dd, J = 6.3, 13.1 Hz, 1H in
CH2N).
Yellowish oil, yield: 79%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 1.43 (t,
J = 7.1 Hz, 3H, CH3), 4.66 (q, J = 7.1 Hz, 2H, CH2), 4.86
(dd, J = 10.3, 13.4 Hz, 1H in CH2N), 5.06 (dd, J = 5.3,
13.4 Hz, 1H in CH2N), 5.44 (dd, J = 5.3, 10.3 Hz, 1H,
CHS), 7.29 (d, J = 8.7 Hz, 2H, ArH), 7.34 (d, J = 8.7 Hz,
2H, ArH).
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.6, 18.3, 20.1,
29.1, 53.6, 70.6, 76.2, 211.6.
IR (mmax, cm-1) 2,972.7, 2,882.4, 1,555.5 (NO2),
1,465.1, 1,377.7 (NO2), 1,230.9 (COC), 1,109.5 (COC),
1,047.4 (C=S), 810.2, 728.4, 674.7.
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.6, 49.6, 70.9,
77.3, 129.3, 130.2, 132.9, 134.9, 210.0.
IR (mmax, cm-1) 3,026.1, 2,982.6, 2,930.4, 1,555.9
(NO2), 1,372.7 (NO2), 1,232.7 (COC), 1,044.5 (COC),
1,043.5 (C=S), 852.2, 817.4, 787.0.
HRMS (ESI) Calcd. for C8H15NNaO3S2 m/z: 260.0385
[M ? Na]?; Found 260.0375.
HRMS (ESI) Calcd. for C11H12NClNaO3S2 m/z:
327.9839 [M ? Na]?; Found 327.9829.
O-Ethyl S-(1-nitromethylpentyl) dithiocarbonate (3g)
O-Ethyl S-[1-(3-chlorophenyl)-2-nitroethyl]
dithiocarbonate (3d)
Yellowish oil, yield: 52%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 0.91 (t,
J = 7.1 Hz, 3H, CH3), 1.26–1.39 (m, 4H, 2CH2), 1.44 (t,
J = 7.1 Hz, 3H, CH3), 1.66–1.87 (m, 2H, CH2), 4.30 (ddt,
J = 4.7, 8.5, 9.2 Hz, 1H, CHS), 4.54 (dd, J = 8.5,
13.0 Hz, 1H in CH2N), 4.66 (q, J = 7.1 Hz, 2H, CH2),
4.78 (dd, J = 4.7, 13.0 Hz, 1H in CH2N).
Yellowish oil, yield: 82%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 1.43 (t,
J = 7.1 Hz, 3H, CH3), 4.67 (q, J = 7.1 Hz, 2H, CH2), 4.87
(dd, J = 10.0, 13.5 Hz, 1H in CH2N), 5.09 (dd, J = 5.4,
13.5 Hz, 1H in CH2N), 5.44 (dd, J = 5.4, 10.3 Hz, 1H,
CHS), 7.22–7.26 (m, 1H, ArH), 7.29–7.32 (m, 2H, ArH),
7.36 (s, 1H, ArH).
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.69, 13.71,
22.2, 28.6, 30.3, 47.2, 70.5, 77.8, 211.8.
IR (mmax, cm-1) 2,958.4, 2,931.6, 2,861.0, 1,563.5,
1,556.8 (NO2), 1,463.5, 1,455.4, 1,373.3 (NO2), 1,223.5
(COC), 1,111.1 (COC), 1,049.3 (C=S).
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.6, 49.7, 70.9,
77.2, 126.1, 128.2, 129.2, 130.4, 135.0, 136.6, 209.9.
IR (mmax, cm-1) 3,062.8, 2,984.4, 2,937.3, 1,556.8
(NO2), 1,372.3 (NO2), 1,227.1 (COC), 1,110.6 (COC),
1,043.6 (C=S), 881.5, 777.9, 692.8.
HRMS (ESI) Calcd. for C9H18NO3S2 m/z: 252.0722
[M ? H]?; Found 252.0716.
HRMS (ESI) Calcd. for C11H13NClO3S2 m/z: 306.0019
[M ? H]?; Found 306.0010.
O-Ethyl S-(1-nitromethylhexyl) dithiocarbonate (3h)
Yellowish oil, yield: 68%.
O-Ethyl S-(1-cyclohexyl-2-nitroethyl) dithiocarbonate (3e)
1H NMR (CDCl3, 300 MHz) (d, ppm) 0.89 (t,
J = 6.9 Hz, 3H), 1.29–1.38 (m, 6H, 3CH2), 1.44 (t,
J = 7.1 Hz, 3H, CH3), 1.65–1.86 (m, 2H, CH2), 4.30 (ddt,
J = 4.8, 8.4, 9.2 Hz, 1H, CHS), 4.54 (dd, J = 8.4,
13.0 Hz, 1H in CH2N), 4.66 (q, J = 7.1 Hz, 2H, CH2),
4.78 (dd, J = 4.8, 13.0 Hz, 1H in CH2N).
Yellowish oil, yield: 72%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 0.99–1.35 (m,
5H), 1.44 (t, J = 7.2 Hz, 3H, CH3), 1.66–1.88 (m, 6H,
3CH2), 4.37 (ddd, J = 4.3, 7.0, 7.0 Hz, 1H in CHS), 4.66
(q, J = 7.2 Hz, 2H, CH2), 4.60–4.76 (m, 2H, CH2N).
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.7, 25.86,
25.94, 26.0, 29.2, 30.5, 38.9, 53.0, 70.6, 75.9, 212.0.
IR (mmax, cm-1) 2,982.6, 2,913.9, 2,854.7, 1,560.8
(NO2), 1,448.9, 1,376.9 (NO2), 1,224.3 (COC), 1,147.2
(COC), 1,056.7 (C=S), 891.2, 673.3.
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.7, 13.9, 22.3,
26.2, 30.6, 31.2, 47.2, 70.5, 77.8, 211.9.
IR (mmax, cm-1) 2,957.5, 2,930.1, 2,859.8, 1,563.3
(NO2), 1,463.3, 1,374.3 (NO2), 1,223.3 (COC), 1,111.7
(COC), 1,049.8 (C=S).
HRMS (ESI) Calcd. for C10H20NO3NaS2 m/z: 288.0699
[M ? Na]?; Found 288.0692.
HRMS (ESI) Calcd. for C11H20NO3S2 m/z: 278.0879
[M ? H]?; Found 278.0868.
123

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C. Xu, J. Xu
O-Ethyl S-(1-methyl-1-nitromethylethyl) dithiocarbonate
(3i)
(6 mL) was added dropwise 30% H2O2 (1.2 mL) in an ice–
water bath at 0°C. The resulting mixture was stirred
overnight and allowed to warm to room temperature. After
addition of 20 mL of water the solution was washed with
dichloromethane to remove organic impurities. After con-
centration, colorless needle crystals 2-nitro-1-phenyletha-
nesulfonic acid (4a) was afforded by crystallization from
chloroform.
Yellowish oil, yield: 48%.
1H NMR (CDCl3, 600 MHz) (d, ppm) 1.05 (t,
J = 7.4 Hz, 3H, CH3), 1.50 (t, J = 7.1 Hz, 3H, CH3 in
EtO), 1.57 (s, 3H, CH3), 1.79 (dq, J = 7.3, 14.6 Hz, 1H in
CH2), 2.07 (dq, J = 7.3, 14.6 Hz, 1H in CH2), 4.70 (q,
J = 7.1 Hz, 2H, CH2), 4.91 (d, J = 11.0 Hz, 1H in CH2N),
4.99 (d, J = 11.0 Hz, 1H in CH2N).
2-Nitro-1-phenylethane-1-sulfonic acid 4a
13C NMR (CDCl3, 50.3 MHz) (d, ppm) 8.4, 13.5, 22.5,
30.1, 55.5, 70.0, 81.7, 210.5.
IR (mmax, cm-1) 3,675.0, 2,988.8, 2,971.4, 1,553.4
(NO2), 1,393.8 (NO2), 1,241.5 (COC), 1,074.6 (COC),
1,051.1 (C=S).
Colorless needle crystals, mp 162–164°C, yield 80%.
1H NMR (D2O, 300 MHz) (d, ppm) 4.80 (dd, J = 6.3,
8.7 Hz, 1H, CHS), 5.03 (dd, J = 8.7, 13.8 Hz, 1H in
CH2N), 5.190 (dd, J = 6.3, 13.8 Hz, 1H in CH2N), 7.27–
7.34 (m, 5H, ArH).
13C NMR (HCO2H, 75.5 MHz) (d, ppm) 63.2, 75.2,
129.0, 129.2, 129.3, 131.9.
HRMS (ESI) Calcd. for C8H16NO3S2 m/z: 238.0566
[M ? H]?; Found 238.0561.
IR (mmax, cm-1) 3,021.7, 2,978.3, 1,555.7 (NO2), 1,373.3
(NO2), 1,213.2 (SO3), 1,182.4 (SO3), 1,031.7 (SO3), 803.2.
HRMS (ESI) Calcd. for C8H9NNaO5S m/z: 254.0094
[M ? Na]?; Found 254.0088.
O-Ethyl S-(1-methyl-2-nitro-1-phenylethyl)
dithiocarbonate (3k)
Yellowish oil, yield: 40%.
1H NMR (CDCl3, 200 MHz) (d, ppm) 1.28 (t,
J = 7.2 Hz, 3H), 2.16 (s, 3H, CH3), 4.55 (q, J = 7.2 Hz,
2H, CH2), 5.19 (d, J = 12.0 Hz, 1H in CH2), 5.31 (d,
J = 12.0 Hz, 1H in CH2), 7.30–7.52 (m, 5H, ArH).
13C NMR (CDCl3, 50.3 MHz) (d, ppm) 13.3, 24.5, 56.9,
70.0, 82.6, 126.4, 128.4, 128.8, 138.9, 209.5.
IR (mmax, cm-1) 3,108.8, 3,061.9, 2,988.3, 1,553.3
(NO2), 1,398.6 (NO2), 1,238.1 (COC), 1,113.2 (COC),
1,038.1 (C=S).
Synthesis of 1-substituted taurines 5 O-ethyl
S-(2-nitroalkyl) dithiocarbonates 3 (oxidation
and subsequent hydrogenation) (general procedure)
To a stirred solution of O-ethyl S-(2-nitroalkyl) dithiocar-
bonate 3 (10 mmol) in 98% formic acid (6 mL) was added
dropwise 30% H2O2 (1.2 mL) in an ice–water bath at 0°C.
The resulting mixture was stirred overnight and allowed to
warm to room temperature. After addition of 20 mL of
water the solution was washed with dichloromethane to
remove organic impurities. After concentration, 2-nitroal-
kanesulfonic acid 4 was obtained. It was used directly in
the subsequent hydrogenation without further purification.
2-Nitroalkanesulfonic acid 4 prepared above was dis-
solved in MeOH (10 mL), and 10% Pd on carbon powder
(30 mg) was added. The suspension was stirred under the
atmosphere of hydrogen at RT overnight. 20 mL of
methanol was added to dissolve the precipitate. The cata-
lyst was removed by filtration through a filter paper and
was washed twice with formic acid (5 mL). After evapo-
ration of the solvent the crude product was purified by
recrystallization from methanol or a mixture of methanol
and diethyl ether to afford colorless crystals.
HRMS (ESI) Calcd. for C12H15NNaO3S2 m/z: 308.0386
[M ? Na]?; Found 308.0383.
O-Ethyl S-(2-nitro-1,1-diphenylethyl) dithiocarbonate (3l)
Yellowish oil, yield: 5%.
1H NMR (CDCl3, 300 MHz) (d, ppm) 1.33 (t,
J = 7.0 Hz, 3H, CH3), 4.33 (q, J = 7.0 Hz, 2H, CH2), 5.42
(s, 2H, CH2), 7.25–7.47 (m, 10H, ArH).
13C NMR (CDCl3, 75.5 MHz) (d, ppm) 13.4, 64.1, 71.4,
82.0, 128.2, 128.4, 128.9, 138.7, 209.5.
IR (mmax, cm-1) 3,020.1, 2,976.4, 1,554.3 (NO2), 1,372.5
(NO2), 1,230.0 (COC), 1,110.9 (COC), 1,044.4 (C=S).
HRMS (ESI) Calcd. for C17H17NNaO3S2 m/z: 370.0542
[M ? Na]?; Found 370.0536.
Oxidation of O-Ethyl S-(2-nitro-1-phenylethyl)
dithiocarbonate (3a) to 2-nitro-1-phenylethanesulfonic
acid (4a)
2-Amino-1-phenylethane-1-sulfonic acid 5a
Colorless crystals, yield: 58%. m.p. 352°C (dec.). Lit.
(Heath and Piggott 1947) m.p. 358–360°C (dec.).
1H NMR (D2O, 200 MHz) (d, ppm): 3.54 (dd, J = 8.4,
13.3 Hz, 1H in CH2N), 3.76 (dd, J = 6.8, 13.3 Hz, 1H in
To a stirred solution of O-ethyl S-(2-nitro-1-phenylethyl)
dithiocarbonate (3a) (2.71 g, 10 mmol) in 98% formic acid
123

Versatile synthesis of a-substituted taurines from nitroolefins
199
2-Amino-1-cyclohexylethane-1-sulfonic acid 5e
Colorless crystals, yield: 87%. m.p. 322°C (dec.).
CH2N), 4.27 (dd, J = 6.8, 8.4 Hz, 1H, CHS), 7.38 (s, 5H,
ArH).
13C NMR (D2O, 50 MHz) (d, ppm): 40.7, 63.4, 129.7,
129.9, 132.7, 132.7.
1H NMR (D2O, 300 MHz) (d, ppm) 1.01–1.23 (m, 6H,
3CH2), 1.51–1.64 (m, 4H, 2CH2), 1.79–1.89 (m, 1H, CH),
2.80–2.86 (m, 1H, CHS), 3.15–3.52 (m, 2H, CH2N),
13C NMR (DMSO-d6, 50 MHz) (d, ppm) 26.2, 26.3,
27.3, 31.1, 31.3, 36.9, 37.4, 60.9.
13C NMR (DMSO-d6, 50 MHz) (d, ppm): 40.9, 61.5,
127.2, 127.9, 129.0, 136.1.
HRMS (ESI) Calcd. for C8H12NO3S2 m/z: 202.0532
[M ? Na]?; Found 202.0524.
13C NMR (D2O, 50 MHz) (d, ppm) 25.4, 25.6, 26.0,
27.3, 31.2, 37.4, 38.3, 62.5.
IR (mmax, cm-1) 3,422.9 (NH3?), 3,177.6 (NH3?),
2,932.3, 2,864.7, 2,371.2, 1,624.1, 1,452.1, 1,215.2 (SO3-),
1,167.3, 1,034.8 (SO3-), 738.7, 609.0.
2-Amino-1-(4-methylphenyl)ethane-1-sulfonic acid 5b
Colorless crystals, yield: 60%. m.p. 339–342°C (dec.).
1H NMR (D2O, 300 MHz) (d, ppm) 2.24 (s, 3H, CH3),
3.49 (dd, J = 8.4, 13.3 Hz, 1H in CH2N), 3.71 (dd,
J = 6.8, 13.3 Hz, 1H in CH2N), 4.21 (dd, J = 6.8, 8.4 Hz,
1H, CHS), 7.19 (d, J = 8.4 Hz, 2H, ArH), 7.24 (d,
J = 8.4 Hz, 2H, ArH).
13C NMR (D2O, 75.5 MHz) (d, ppm) 20.9, 40.8, 63.1,
129.5, 129.6, 130.3, 140.3.
IR (mmax, cm-1) 3,014.1 (NH3?), 2,960.5, 1,632.5,
1,491.5, 1,215.2 (SO3-), 1,184.2 (SO3-), 1,032.0 (SO3-),
806.4.
HRMS (ESI) Calcd. for C8H18NO3S m/z: 208.1001
[M ? H]?; Found 208.1001.
1-Amino-3-methylbutane-2-sulfonic acid 5f
Colorless crystals, yield: 64%. m.p. 338–340°C (dec.).
1H NMR (D2O, 300 MHz) (d, ppm) 0.89 (d,
J = 7.0 Hz, 3H, CH3), 0.97 (d, J = 7.0 Hz, 3H, CH3), 2.22
(dqq, J = 3.3, 7.0, 7.0 Hz, 1H, CH), 2.87 (ddd, J = 2.9,
3.3, 10.1 Hz, 1H, CHS), 3.18 (dd, J = 10.1, 13.8 Hz, 1H in
CH2N), 3.26 (dd, J = 2.9, 13.8 Hz, 1H in CH2N).
13C NMR (D2O, 75.5 MHz) (d, ppm) 17.1, 21.1, 28.0,
37.4, 62.8.
IR (mmax, cm-1) 3,095.9 (NH3?), 2,937.9 (NH3?),
1,598.7, 1,508.5, 1,212.4 (SO3-), 1,153.2, 1,102.4, 1,023.5
(SO3-).
HRMS (ESI) Calcd. for C9H14NO3NS m/z: 216.0688
[M ? Na]?; Found 216.0687.
2-Amino-1-(4-chlorophenyl)ethane-1-sulfonic acid 5c
Colorless crystals, yield: 67%. m.p. 342°C (dec.).
1H NMR (D2O, 300 MHz) (d, ppm) 3.47 (dd, J = 8.7,
13.4 Hz, 1H in CH2N), 3.76 (dd, J = 6.9, 13.4 Hz, 1H in
CH2N), 4.27 (dd, J = 6.9, 8.4 Hz, 1H, CHS), 7.38 (m, 4H,
ArH).
HRMS (ESI) Calcd. for C5H14NO3S m/z: 168.0688
[M ? H]?; Found 168.0690.
13C NMR (D2O, 75.5 MHz) (d, ppm) 41.1, 61.9, 129.2,
129.4, 130.9, 134.9.
1-Aminohexane-2-sulfonic acid 5g
IR (mmax, cm-1) 3,015.8 (NH3?), 1,634.4, 1,493.2,
1,209.7 (SO3-), 1,180.8, 1,036.3 (SO3-), 799.2.
HRMS (ESI) Calcd. for C8H10ClNNaO3S m/z: 257.9962
[M ? H]?; Found 257.9953.
Colorless crystals, yield: 69%. m.p. 335°C (dec.). Lit.
(Chen et al. 2009a) m.p. 335°C (dec.).
1H NMR (D2O, 300 MHz) (d, ppm) 0.73 (t,
J = 7.0 Hz, 3H, CH3), 1.08–1.40 (m, 5H in 3CH2), 1.68–
1.81 (m, 1H in CH2), 2.90 (m, 1H, CHS), 3.03–3.22
(m, 2H, CH2N).
2-Amino-1-(3-chlorophenyl)ethane-1-sulfonic acid 5d
13C NMR (D2O, 75.5 MHz) (d, ppm) 13.7, 22.4, 27.8,
28.6, 39.8, 57.5.
IR (mmax, cm-1) 3,422.9 (NH3?), 3,140.0 (NH3?),
2,949.2, 2,867.5, 1,626.9 (NH3?), 1,508.5, 1,237.8 (SO3-),
1,158.8, 1,043.2 (SO3-), 738.7, 609.0.
Colorless crystals, yield: 59%. m.p. 331–334°C (dec.)
1H NMR (D2O, 300 MHz) (d, ppm) 3.47 (dd, J = 8.4,
13.2 Hz, 1H in CH2N), 3.68 (dd, J = 6.6, 13.2 Hz, 1H in
CH2N), 4.20 (dd, J = 6.6, 8.4 Hz, 1H, CHS), 7.31 (s, 4H,
ArH).
13C NMR (D2O, 75.5 MHz) (d, ppm) 40.8, 63.4, 129.7,
129.9, 130.0, 132.7.
1-Aminoheptane-2-sulfonic acid 5h
IR (mmax, cm-1) 3,016.9 (NH3?), 1,635.3, 1,494.4,
1,206.8 (SO3-), 1,172.9, 1,139.1, 1,026.3 (SO3-), 755.6,
685.2.
Colorless crystals, yield: 66%. m.p. 329–331°C.
1H NMR (D2O, 300 MHz) (d, ppm) 0.77 (t, J = 6.9 Hz,
3H, CH3), 1.17–1.30 (m, 4H, 2 CH2), 1.30–1.52 (m, 3H in
2CH2), 1.70–1.90 (m, 1H in CH2), 2.90–3.03 (m, 1H,
CHS), 3.07–3.32 (m, 2H, CH2N).
HRMS (ESI) Calcd. for C8H10ClNNaO3S m/z: 257.9962
[M ? H]?; Found 257.9955.
123

200
C. Xu, J. Xu
13C NMR (D2O, 75.5 MHz) (d, ppm) 13.9, 22.3, 26.1,
28.1, 31.3, 39.8, 57.5.
IR (mmax, cm-1) 3,135.3 (NH3?), 3,093.0 (NH3?),
2,968.9, 2,967.5, 1,601.5, 1,502.8, 1,235.0 (NH3?),
1,156.0, 1,031.9 (NH3?), 885.3, 738.7, 603.4.
HRMS (ESI) Calcd for C7H17NNaO3S m/z: 218.0821
[M ? Na]?; Found 218.0813.
1994). They underwent Michael addition with sodium
ethylxanthate to give rise to O-ethyl S-(2-nitroalkyl) di-
thiocarbonates according to the reported method (Ouvry
et al. 2003). The oxidation of the dithiocarbonates with
performic acid was investigated with dithiocarbonate 3a as
a model substrate. Initially, dithiocarbonate 3a was added
to performic acid generated in situ from 88% formic acid
and 30% hydrogen peroxide; the yield of 2-nitroalkane-
sulfonic acid 4a was generally low and nitroolefin 2a was
produced as byproduct. This revealed that retro Michael
addition occurred. When the dithiocarbonate was first
dissolved in formic acid and then hydrogen peroxide was
added into the resulting solution, the amount of the nitro-
olefin decreased in the reaction mixture and the yield of the
desired product was improved. The oxidation conditions
were further optimized. The results are summarized in
Table 1. The yield depended on the concentration of per-
formic acid. High concentration generally gave high yields
(Table 1, entry 1 vs. entry 2, entry 5 vs. entry 4). On the
other hand, high reaction temperature decreased the yield
(Table 1, entry 5 vs. entry 6). Although the yield was
increased in 88% formic acid when the crude product
re-subjected to oxidation conditions (Table 1, entry 2 vs.
entry 3), the same operation did not improve the yield
significantly in 98% formic acid. The optimal oxidative
conditions are that the dithiocarbonate was oxidized in
98% formic acid at 0°C. The obtained 2-nitroalkanesulf-
onic acids were reduced in methanol in excellent yields
with hydrogen in the presence of palladium on carbon
powder. To improve the overall yields, we tried to reduce
2-nitroalkanesulfonic acids without purification because
some nitroalkanesulfonic acids were lost in the recrystal-
lization purification. After reduction, filtration, and con-
centration, the residue was dissolved in water. The aqueous
solution was washed with dichloromethane to remove
organic impurities easily. The results clearly indicate that
1-Amino-2-methylbutane-2-sulfonic acid 5i
Colorless crystals, yield: 71%. m.p. 323–325°C.
1H NMR (D2O, 300 MHz) (d, ppm) 0.89 (t, J = 7.6 Hz,
3H, CH3), 1.25 (s, 3H, CH3), 1.69 (dq, J = 14.4, 7.6 Hz,
1H in CH2), 1.78 (dq, J = 14.4, 7.6 Hz, 1H in CH2), 3.15
(d, J = 15.1 Hz, 1H in CH2N), 3.21 (d, J = 15.1 Hz, 1H in
CH2N).
13C NMR (D2O, 125 MHz) (d, ppm) 7.1, 16.6, 25.6,
42.8, 58.0.
IR (mmax, cm-1) 3,150.0 (NH3?), 3,095.1 (NH3?),
2,974.4, 1,623.5, 1,504.3, 1,213.9 (NH3?), 1,183.3, 1,038.2
(NH3?), 684.3.
HRMS (ESI) Calcd. for C5H14NO3S m/z: 168.0689
[M ? H]?; Found 168.0680.
1-Amino-2-phenylpropane-2-sulfonic acid 5k
Colorless crystals, yield: 70%. m.p. 285–287°C (dec.). Lit.
(Chen et al. 2009b) m.p. 285–287°C (dec.).
1H NMR (D2O, 200 MHz) (d, ppm) 1.67 (s, 3H, CH3),
3.51 (d, J = 13.3 Hz, 1H in CH2N), 3.68 (d, J = 13.3 Hz,
1H in CH2N), 7.20–7.37 (m, 3H, ArH), 7.39–7.47 (m, 2H,
ArH).
13C NMR (D2O, 75 MHz) (d, ppm) 18.2, 44.7, 61.6,
129.9, 128.8, 128.9, 134.8.
2-Amino-1,1-diphenylethane-1-sulfonic acid 5l
Colorless crystals, yield: 69%. m.p. 196–198°C (dec.). Lit.
(Chen et al. 2009b) m.p. 196–198°C (dec.).
1H NMR (D2O, 300 MHz) (d, ppm) 3.70 (s, 2H, CH2),
7.11–7.27 (m, 10H, ArH).
13C NMR (D2O, 75 MHz) (d, ppm) 49.4, 75.8, 126.0,
128.5, 128.9, 143.1.
Table 1 Optimized oxidation of dithiocarbonate 3a
Entry Solvent
Volume (mL) Temperature (°C) Yield (%)
1
2
3
4
5
6
88% HCO2H
6
88% HCO2H 12
88% HCO2H 12
98% HCO2H 12
0
56
48
67a
62
80
61
0
0
0
98% HCO2H
98% HCO2H
6
6
0
Results and discussion
60–70
To a solution of 0.271 g (0.01 mol) O-ethyl S-(2-nitro-1-phenylethyl)
dithiocarbonate (3a) in formic acid was added dropwise 30% H2O2
(1.2 mL). The resulting mixture was stirred overnight. After addition
of 20 mL of water, the solution was washed with dichloromethane to
remove organic impurities. After concentration, 2-nitro-1-pheny-
lethanesulfonic acid was obtained
Nitroolefins can be prepared conveniently from nitro-
methane with aldehydes (Kumaran and Kulkarni 1994) or
ketones (Jang et al. 2003), or olefins (Fryszkowska et al.
2008). A series of 1-nitro-1-alkenes were prepared from
nitromethane and aldehydes in satisfactory to good yields
according to reported methods (Kumaran and Kulkarni
a
Double oxidations were conducted
123

Versatile synthesis of a-substituted taurines from nitroolefins
201
the overall yields were improved (Scheme 1). A series of
1-substituted taurines were obtained in satisfactory to good
overall yields (Table 2, entries 1–8).
that steric hindrance plays an important role in the Michael
addition step. The prepared dithiocarbonates 3i,k,l were
oxidized and reduced under similar conditions to afford
1,1-disubstituted taurines 5i,k,l in satisfactory yields
(Scheme 2, Table 2, entries 9, 11 and 12).
After the success in the synthesis of aliphatic and aro-
matic 1-substituted taurines, we decided to extend the
method to prepare 1,1-disubstituted taurines, especially
aromatic 1,1-disubstituted taurines because it was reported
to be synthesized in very low yields from the direct
nucleophilic ring-opening reaction of aromatic 2,2-disub-
stituted aziridines with sodium bisulphate (Chen et al.
2009b). Aliphatic 1-nitro-2,2-geminal disubstituted olefin
2i was prepared from butanone with nitromethane (Jang
et al. 2003). 1-Nitro-2,2-geminal disubstituted olefins 2j–l
were prepared from 2,4,4-trimethyl-1-pentene, a-methyl-
styrene, and 1,1-diphenylethene, respectively, with sodium
nitrite under the catalysis of CAN (Fryszkowska et al.
2008). They underwent the similar Michael addition with
lower yields possibly due to more steric hindrance com-
pared to monosubstituted nitroolefins. More steric 1-nitro-
2,2-diphenylethene 2l gave rise to the product with only
5% yield. For the most steric 2,4,4-trimethyl-1-nitro-1-
pentene 2j, no adduct was observed. The results revealed
Comparison with the previous method for the synthesis
of 1-mono- and 1,1-disubstituted taurines with thiiranes as
starting materials (Yu et al. 2009), which limits to the
synthesis of 1-alkyl and 1,1-dialkyl taurines; the synthetic
method for 1,1-disubstituted taurines from 2,2-disubsti-
tuted aziridines, only suitable for the aromatic 1,1-disub-
stituted taurines with low yields (Chen et al. 2009b), the
current method can be used to prepare not only aliphatic,
but also aromatic 1-mono- and 1,1-disubstituted taurines.
Although more steric geminal disubstituted nitroolefins do
not work very well in the current strategy, the method is
quite practical and versatile for less steric nitroolefins.
S
Ph
MeNO2, BnSH
O
NO2
H2NCH2CH2NH2, MeCN
6i
1i
1) H2O2, ClCH2CH2Cl
0 oC to RT
S
2) reflux
S
O
EtO
SNa
NaOH
R1
NO2
R1
+ CH3NO2
NaNO2
R1
1a-h
H
EtO
SNa
NO2
R1
R2
R2
HOAc
2a-h
CAN
7j-l
2i-l
HOAc
S
S
H2, Pd/C
MeOH
H2O2
HCO2H
SO3H H2, Pd/C
MeOH
SO3H
R1 R2
4i,k,l
H2O2
SO3H
SO3H
R1 R2
S
OEt
NO2
S
OEt
O2N
O2N
H2N
H2N
R1
NO2
R1
4a-h
R1
5a-h
HCO2H
R1
R2
5i,k,l
3a-h
3i,k,l
a: R1 = Ph; b: R1 = 4-MePh; c: R1 = 4-ClPh; d: R1 = 3-ClPh;
e: R1 = cHex; f: R1 = CHMe2; g: R1 = n-Bu; h: R1 = n-Am
i: R1 = Me, R2 = Et; j: R1 = Me, R2 = CH2CMe3;
k: R1 = Me, R2 = Ph; l: R1 = R2 = Ph
Scheme 1 Synthesis of 1-substituted taurines
Scheme 2 Synthesis of 1,1-disubstituted taurines
Table 2 Synthesis of taurines
Entry
R1
R2
Dithiocarbonate 3
Yield (%)
Taurine 5
Yield (%)a
from dithiocarbonates 3
1
Ph
3a
3b
3c
3d
3e
3f
88
84
79
82
71
80
52
68
48
0
5a
5b
5c
5d
5e
5f
58
60
67
59
87
64
69
66
71
–
2
4-MePh
4-ClPh
3-ClPh
cHex
CHMe2
Bun
3
4
5
6
7
3g
3h
3i
5g
5h
5i
8
Amn
9
Me
Et
10
11
Me
CH2CMe3
3j
5j
Me
Ph
Ph
3k
3l
54
5
5k
5l
71
69
12
Ph
a
From dithiocarbonates 3
123

202
C. Xu, J. Xu
S
S
+SH
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