The conversion of stilbenols to stilbenethiols via N,N- dimethylthiocarbamates

Article abstract of DOI:10.1080/10426500500270016

A series of O-stilbenyl N,N-dimethylthiocarbamates has been prepared by the reaction of N,N-dimethylthiocarbamoyl chloride with stilbenols in the presence of DABCO and DMF. The thermal rearrangement of O-stilbenyl N,N- dimethylthiocarbamates into S-stilbe

Full text of DOI:10.1080/10426500500270016

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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The Conversion of Stilbenols
to Stilbenethiols via N,N-
Dimethylthiocarbamates
Zdzisława Nowakowska a
a Department of Chemistry , Adam Mickiewicz
University , Poznań, Poland
Published online: 15 Aug 2006.
To cite this article: Zdzisława Nowakowska (2006) The Conversion of Stilbenols to
Stilbenethiols via N,N-Dimethylthiocarbamates, Phosphorus, Sulfur, and Silicon and
the Related Elements, 181:4, 707-715, DOI: 10.1080/10426500500270016
To link to this article: http://dx.doi.org/10.1080/10426500500270016
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Phosphorus, Sulfur, and Silicon, 181:707–715, 2006
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500500270016
The Conversion of Stilbenols to Stilbenethiols via
N,N-Dimethylthiocarbamates
Zdzislawa Nowakowska
ꢀ
Department of Chemistry, Adam Mickiewicz University, Poznan´, Poland
A series of O-stilbenyl N,N-dimethylthiocarbamates has been prepared by the
reaction of N,N-dimethylthiocarbamoyl chloride with stilbenols in the pres-
ence of DABCO and DMF. The thermal rearrangement of O-stilbenyl N,N-
dimethylthiocarbamates into S-stilbenyl analogues has also been studied. The S-
stilbenyl N,N-dimethylthiocarbamates obtained have been converted into the cor-
responding stilbenethiols. Electron ionization mass spectral fragmentation of these
compounds has been studied. Fragmentation pathways have been proposed on the
basis of the accurate mass and metastable transition measurements.
Keywords EI-MS; Newman-Kwart rearrangement; stilbene
The thiol functionality is of prime importance in organic chemistry as
well as in biochemistry. The conversion of phenols into the correspond-
ing thiophenols is a very useful but not easy reaction. Since phenols
are readily converted into the corresponding O-aryl dialkylthiocarba-
mates in a high yield by treatment with N,Nꢀ-dialkylthiocarbamoyl chlo-
ride and S-aryl dialkylthiocarbamates and are readily hydrolyzed to
the corresponding aryl mercaptans, a general method is now available
for the conversion of phenols to thiophenols.1−7 The thermal rear-
rangement of O-aryl N,N-dimethylthiocarbamates to the S-aryl N,N-
dimethylthiocarbamates proceeds by an intramolecular nucleophilic
attack of the thiocarbonyl sulfur atom on the migrating aromating
ring with a four-membered cyclic transition state, according to the
Newman-Kwart rearrangement.1,3 The rates of the rearrangement
are much faster for the electron-withdrawing substituents than for
the electron-releasing substituents. Although the rearrangement of
many O-aryl dimethylthiocarbamates to the corresponding S-aryl com-
pounds was successful, the following O-aryl analogs did not yield the
Received March 16, 2005; accepted April 15, 2005.
Address correspondence to Zdzislawa Nowakowska, Adam Mickiewicz University,
ꢀ
Department of Chemistry, Grunwaldzka 6, Poznan´, 60-780 Poland. E-mail: zdzisian@
main.amu.edu.pl
707

708
Z. Nowakowska
S-aryl compounds: aminophenyl, hydroxyphenyl, acetoxyphenyl, and
acetylphenyl. In all these cases, decomposition set in well below the
temperature needed for rearrangement.1
Stilbenes make a class of naturally occurring substances of great
biological interest. Stilbenols isolated from different plants exhibit dif-
ferent pharmacological activity. They have been reported to exert es-
trogenic, fungistatic, antimicrobial, and antileukemic properties.8−13
Resveratrol (3,5,4ꢀ-trihydroxy-trans-stilbene), found in grapes and
wine, may play an active role in the prevention of heart disease and
cancer. It has also been reported to exert antiestrogenic, antiinflamma-
tory, antioxidant, and antiplatelet properties.
Although the reactions of the modifications of stilbenols as well as
mass spectral14−17 behavior of these compounds have been widely stud-
ied and interpreted, publications on mercapto analogues of these com-
pounds have been rather limited. Thiolate anions are nucleophiles of
theoretical and practical interest and are employed in a wide variety of
organic reactions. They are usually generated in a solution by the treat-
ment of the corresponding thiols with bases or sometimes by the basic
hydrolysis of precursors such as thiol esters or other sulfur-containing
compounds.
The purpose of this work is to establish an efficient and simple
method of preparation of stilbenethiols. This article also presents
mass spectrometric analyses of the obtained O-4-(and 4ꢀ-nitro-)stilbenyl
N,N-dimethylthiocarbamates 1 and 4, S-4-(and 4ꢀ-nitro-)stilbenyl N,N-
dimethylthiocarbamates 2 and 5, and 4-(and 4ꢀ-nitro-)stilbenethiols 3
and 6, under Electron Impact (EI) ionization conditions, as well as
metastable transitions and exact mass determinations of these com-
pounds. The objective was to establish fragmentation pathways that
may be of value in the structural determination of related compounds.
RESULTS AND DISCUSSION
O-stilbenyl N,N-dimethylthiocarbamates 1 and 4 used in the present
study were synthesized by a reaction of trans-4-hydroxystilbene or
trans-4ꢀ-nitro-4-hydroxystilbene with a commercially available N,N-
dimethylthiocarbamoyl chloride in the presence of DABCO in refluxing
dimethylformamide by the modifyed method of Newman and Karnes,1,7
(Scheme 1).
The thermal rearrangement of the products O-4-stilbenyl and O-
4-(4ꢀ-nitro-)stilbenyl N,N-dimethylthiocarbamates was investigated at
temperatures of 270◦C or 230◦C in the absence of any solvent under
a blanket of argon. The progress of the rearrangements was followed
by changes in the 1H NMR spectrum reflecting the transformation

The Conversion of Stilbenols to Stilbenethiols
709
SCHEME 1
of the two singlets assigned to the dimethylamino moiety of the
O-stilbenyl thiocarbamate in the 3.37–3.42 ppm region into a broad
singlet shifted upfield (to 3.02–3.05 ppm) assigned to the correspond-
ing moiety of the S-aryl carbamates. The rearrangement reactions were
confirmed by infrared spectra showing a disappearance of the strong
absorptions in the mid-1540 cm−1 and mid-1280 cm−1 regions, char-
acteristic of C S bonds. However, the EI-MS spectral analysis seems
to be the best way to check the extent of the rearrangement of O-aryl
N,N-dimethylthiocarbamates to the S-aryl N,N-dimethylthiocarbama-
tes. The lack of the m/z 88 ion peak [C3H6NS]+ in the mass spectrum

710
Z. Nowakowska
TABLE I Elemental Composition and Relative Intensities of the Ion
Peaks in the Spectra of 1–6 According to High-Resolution Data
Relative abundances %
Elemental
Ion
composition
m/z
1
2
3
4
5
6
C17H17NOS
283
212
328
257
256
211
224
179
240
195
178
165
152
139
115
88
38.0
—
—
—
—
—
—
—
—
3.5
6.6
13.8
8.5
3.6
4.2
100
—
26.2
—
—
—
—
5.8
—
—
—
—
8.0
6.6
5.2
2.5
2.7
—
100
—
4.3
—
100
—
—
—
16.3
—
45.8
—
—
57.2
11.5
12.1
4.2
4.6
—
—
—
19.8
—
—
16.4
—
—
—
—
—
1.6
—
2.1
14.0
3.0
4.5
2.5
92.0
—
—
—
5.9
—
1.2
—
—
—
—
—
—
—
—
100
4.2
—
1.1
—
C14H12
S
a
C17H16N2O3S
C14H11NO2S
C14H10NO2S
b1
b2
c1
c2
d1
d2
e
f
g
h
i
j
C14H11
S
C14H10NO2
C14H11
C14H10NO3
—
—
C14H11
14H10
C13H9
12H8
O
C
1.3
60.1
29.6
15.1
6.5
5.3
—
—
—
11.6
5.7
1.1
1.1
1.0
—
100
—
C
C11H7
C9H7
C3H6NS
C3H6NO
C2H2NS
C7H5
k
l
m
72
72
89
95.8
5.3
100
3.7
2.1
of the S-aryl derivatives 2 and 5 indicated that the rearrangement had
occurred with a 100% yield.
On basic hydrolysis with potassium hydroxide dissolved in methanol,
S-stilbenyl N,N-dimethylthiocarbamates afforded the corresponding
arylthiols in high yield. Thus, the conversion of stilbenols into the thio-
phenolic analogs via the three-step procedure was highly successful.
On the basis of low- and high-resolution electron-ionization as well
as B2/E linked scan mass spectra, the principal mass spectral fragmen-
tation routes of compounds 1–6 are interpreted as shown in Table I
and Scheme 2. The O-Csp2 or S-Csp2 bond cleavage appeared to be the
first step in the decomposition of the molecular ions in all compounds
investigated.
In 1, 2, 4, and 5 at the cleavage of S-Csp2 and O-Csp2 bonds the
N,N-dimethylthiocarbamoyl substituent and two pairs of complemen-
tary ions (b and k as well as d and j even-electron fragment ions)
are obtained. The molecular ions a of 1, 2, 4, and 5 readily loose
C14H10R1O· or C14H10R1S· radicals furnishing k or j even-electron frag-
ment ions. The charge-site initiated inductive cleavages (i) proceed
·
·
with the elimination of C(S) N(CH3)2 (1, 4) or C(O) N(CH3)2 (2,
5) radicals (even-electron fragment ions d1 or d2, and b1 or b2 are

The Conversion of Stilbenols to Stilbenethiols
711
Compound R1
R2
Compound
R1
R2
1
2
3
H
H
H
O C(S) N(CH3)2
S C(O) N(CH3)2
SH
4
5
6
NO2 O C(S) N(CH3)2
NO2 S C(O) N(CH3)2
NO2
SH
SCHEME 2 ∗Transitions checked by B2/E spectra of compounds 1–6.
obtained). The positive charge is stabilized more effectively on the
[C(S) N(CH3)2]+ (1, 4) and [C(O) N(CH3)2]+ (2, 5) than on the stil-
benyl fragment [C14H10OR1]+ (1, 4) and [C14H10SR1]+ (2, 5). Thus, for
1, 2, and 5, the peaks of the ions j and k are the base peaks of the
spectra. In the second step of the mass fragmentation of compounds
1 and 4, the CH4 molecule is eliminated from ions j, which leads to
the final ions l of m/z 72. This fragmentation pathway was confirmed
by metastable ion analyses and by exact mass measurements. In the
linked scan B2/E spectra of ion [72]+, only ion [88]+ was detected as its
parent ion.

712
Z. Nowakowska
In the processes of the mass decomposition of the molecular ions,
M+· a of 1–6 is also observed the Mc Lafferty rearrangement, with
a simultanous hydrogen transfer and elimination of R2H neutral
molecule. This decomposition produces the odd-electron fragment ion
e. In the case of 1–3, this ion is also formed by the inductive cleavage
of the Csp2-O or Csp2-S bond ·in the even-electron fragment ions d2 and
·
b2, with the ejection of the OH as well as SH radicals, respectively.
The appearance of odd-electron ions g could be explained in terms of
the elimination of C2H2 from odd-electron fragment ions e [C14H10]+·.
The even-electron fragment ions f [C13H9]+ situated at m/z 165 were
obtained by the elimination of the neutral molecule of formaldehyde
from the fragment ion d2 (1) or thioformaldehyde from fragment ions
b2 (2, 3). In the case of 4–6, ions f are als·o obtained by the successive
·
·
or simultaneous elimination of NO2 and CSH or COH radicals from
even-electron fragment ions b1 (m/z 256) or d1 (m/z 240).
The loss of the acethylene neutral molecule from the even-electron
fragment ions f of 2 and 3 involves the formation of the even-electron
fragment h (m/z 139). In the second step of the mass fragmentation,
ion f decomposes by the ejection of the neutral molecule of C4H2 (even-
electron fragment ion i is obtained). As follows from the B2/E linked-
scan spectra, the [C7H5]+ ion m at m/z 89 is formed from three parent
ions (even-electron ions c, h, and i).
In 3 and 6, the mass fragmentation begins with the elimination of
the ·SH radical. By this fragmentation route, the c1 and c2 even-electron
fragment ions are derived. These ions decompose further, giving even-
electron fragment ions m. For structures 3 and 6, the molecular ions
·
M
+•a (the base peaks in the mass spectra) lose also the H radical,
giving b1 or b2 even-electron fragment ions.
The UV/Vis spectra of all analyzed compounds 1–6 in chloroform con-
tain two or three bands; most characteristic is an absorption maximum
in the range of 314–319 nm (1–3) or 346–359 nm (4–6), and a second one
shifted towards shorter wavelengths of 241–257 nm (1–3) or 240–253
nm (4–6). The presence of two distinct maxima at ∼250 and ∼320 or
∼350 nm indicates typical π → π∗ transitions of the conjugated system,
which is corroborated by relatively high values of log ε.
The analysis of the IR spectra revealed (E)-configuration of the
(E)-ethylene bridge of the stilbene skeletone for all studied compounds
due to the presence of strong bands of out-of-plane trans olefinic
C-H bending vibrations between 963–971 cm−1. The IR spectra of
3 and 6 also show absorption bands of medium intensities in the
region of 2440–2560 cm−1, which have been assigned to the ν S-H
vibrations. In the case of the NO2 group, (4–6) gives intense absorption
for symmetrical (∼1340 cm−1) and antisymmetrical (∼1510 cm−1
)
streching vibrations.

The Conversion of Stilbenols to Stilbenethiols
713
EXPERIMENTAL SECTION
General Remarks
The melting points were determined on a Melt-Temp II melting point
apparatus and are uncorrected. Low- and high-resolution EI mass spec-
tra were recorded using an AMD-Intectra GmbH (Harpstedt) D-27243
Model 402 two-sector mass spectrometer (ionizing voltage 70 eV, ac-
celerating voltage 8 kV, resolution 1,000 for low-resolution and 10,000
for high-resolution mass spectra). Samples were introduced by a direct
insertion probe at a source temperature of ∼50◦C. The elemental compo-
sitions of all the ions discussed were determined by accurate mass mea-
surement using a peak matching method relative to perfluorokerosene.
All masses measured agreed with the compositions listed in column 2 of
Table I to within 2 ppm. The fragment ion spectra from the first field-
free region, recorded using linked scans at constant B2/E, with helium
as the collision gas at a pressure of 1.73 × 10−5 mbar with an ion source
temperature of 180◦C, ionization energy of 70 eV and an accelerating
voltage of 8 kV. Infrared spectra were recorded for KBr pellets on a
Bruker IFS 113 FT-IR spectrometer. 1H-NMR spectra were recorded on
a Varian Gemini VT 300 spectrometer at 300.075 MHz using TMS as an
internal standard, and (CD3)CO was used as a solvent. UV/VIS spectra
were recorded on a Specord UV/VIS spectrophotometer in chloroform
solution. Elemental analyses were performed on a Perkin-Elmer 240
CHN analyzer. All new compounds were analyzed for C, H, and N, and
the results were in an acceptable range.
General Procedure for the Preparation of O-4- (and
4ꢀ-Nitro-)stilbenyl N,N-Dimethylthiocarbamates
To a solution of trans-4-hydroxystilbene (9.80 g, 50 mmol) [or trans-
4ꢀ-nitro-4-hydroxystilbene (12.05 g, 50 mmol)] in dimethylformamide
(80 mL), single portions of 1,4-diazabicyclo[2.2.2]octane (DABCO)
(22.44 g, 200 mmol) and N,N-dimethylthiocarbamoyl chloride (12.36 g,
100 mmol) as solids were added. The resulting mixture was heated at
70◦C for 3 h. After cooling, the salt was filtered off. The mixture was
poured into 300 mL of ice-water and acidified to pH 3 with hydrochloric
acid. The precipitate formed was filtered off, washed with 100 mL of
water, and dried to yield a crude product. Recrystallization from a mix-
ture of ethanol and water (3:1) provided 12.03 g (85%) pure O-4-stilbenyl
N,N-dimethylthiocarbamate 1 and 14.27 g (87%) O-4-(4ꢀ-nitro-)stilbenyl
N,N-dimethylthiocarbamate 4.
1: m.p. 159–161◦C; IR (KBr): 1539, 1501, 1393, 1287, 1203, 1132,
967 cm−1; UV/Vis λmax/nm 257, 302, 314; 1H NMR 3.37 (3H, s, NCH3),

714
Z. Nowakowska
3.41 (3H, s, NCH3), 7.22 (1H, s, CHα), 7.26 (1H, s, CHβ). Elemental
Anal. Calcd. for C17H17NOS (283): C, 72.08; H, 6.05; N, 4.95. Found: C,
72.01; H, 6.03; N, 4.90.
4: m.p. 232–233◦C; IR (KBr): 1549, 1505, 1392, 1338, 1286, 969 cm−1
;
1
UV/Vis λmax/nm 253, 349; H NMR 3.38 (3H, s, NCH3), 3.42 (3H, s,
NCH3), 7.40 (1H, d, J = 16.5, CHα), 7.56 (1H, d, J = 16.5, CHβ). Ele-
mental anal. calcd. for C17H16N2O3S (328): C, 62.18; H, 4.91; N, 8.54.
Found: C, 62.08; H, 4.90; N, 8.51.
General Procedure for the Preparation of S-4- (and 4ꢀ-Nitro-)-
stilbenyl N,N-Dimethylthiocarbamates
O-4-stilbenyl N,N-dimethylthiocarbamate (5.66 g, 20 mmol) [or O-4-
(4ꢀ-nitro-)stilbenyl N,N-dimethylthiocarbamate (6.56 g, 20 mmol)] was
placed into a 100-mL flask equipped with a reflux condenser and ther-
mometer. The contents of the flask were maintained under argon for 0.5
h at 25◦C, and then the flask was immersed in a preheated oil bath and
heated at 270◦C for 1 or 230◦C for 4. The reaction was complete in 2 h,
yielding a single, clean rearranged product, S-4-(or 4ꢀ-nitro-)stilbenyl
N,N-dimethylthiocarbamate. Upon cooling of the reaction mixture, the
product crystallized in a quantitive yield. Recrystallization from a mix-
ture of ethanol and water (3:1) provided 12.03 g (85%) of pure S-4-
stilbenyl N,N-dimethylthiocarbamate 2 and 14.27 g (87%) of S-4-(4ꢀ-
nitro-)stilbenyl N,N-dimethylthiocarbamate 5.
2: m.p. 153–155◦C; IR (KBr): 1668, 1495, 1362, 1259, 1088, 963 cm−1
;
UV/Vis λmax/nm 241, 307, 319; 1H NMR 3.02 (6H, bs, N(CH3)2), 7.29 (2H,
s, CHα and CHβ). Elemental anal. calcd. for C17H17OSN (283): C, 72.08;
H, 6.05; N, 4.95. Found: C, 72.04; H, 6.03; N, 4.92.
5: m.p. 138–140◦C; IR (KBr): 1671, 1595, 1515, 1342, 1088, 971 cm−1
;
UV/Vis λmax/nm 241, 272, 346; 1H NMR 3.05 (6H, bs, N(CH3)2), 7.48 (1H,
d, J = 16.5, CHα), 7.57 (1H, d, J = 16.5, CHβ). Elemental anal. calcd.
for C17H16N2O3S (328): C, 62.18; H, 4.91; N, 8.54. Found: C, 62.03; H,
4.88; N, 8.50.
General Procedure for the Preparation of 4- (and 4ꢀ-Nitro-)-
stilbenethiols
To a solution of the S-4-stilbenyl N,N-dimethylthiocarbamate (5.66 g,
20 mmol) [or S-4-(4ꢀ-nitro-)stilbenyl N,N-dimethylthiocarbamate
(6.56 g, 20 mmol)] in tetrahydrofurane (90 mL), a portion of 10.5 mL
of a methanol solution of potassium hydroxide (2.53 g, 45 mmol) was
added. The reaction mixture was stirred at r.t. for 5 h and was then
poured onto icewater and acidified with 6.0 N hydrochloric acid to attain

The Conversion of Stilbenols to Stilbenethiols
715
a value of pH 3. The product was collected by filtration, washed with
100 mL of cold water, and recrystallized from ethanol and water (1:1) to
give 3.67 g (87%) of pure 4-stilbenethiol 3 and 4.27 g (83%) of 4ꢀ-nitro-
4-stilbenethiol 6.
3: m.p. 135–137◦C; IR (KBr): 2557, 1495, 1447, 1095, 969 cm−1
;
1
UV/Vis λmax/nm 241, 317; H NMR 4.36 (1H, s, SH), 7.20 (2H, s, CHα
and CHβ). Elemental anal. calcd. for C14H12S (212): C, 79.22; H, 5.70.
Found: C, 79.20; H, 5.58.
6: m.p. 120–122◦C; IR (KBr): 2447, 1584, 1507, 1336, 1103, 968 cm−1
;
1
UV/Vis λmax/nm 240, 276, 359; H NMR 4.49 (1H, s, SH), 7.39 (1H, d,
J = 16.4, CHα), 7.50 (1H, d, J = 16.5, CHβ). Elemental anal. calcd. for
C14H11NO2S (257): C, 65.36; H, 4.31; N, 5.45. Found: C, 65.34; H, 4.33;
N, 5.53.
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