N-thioaroylmorpholines in silica gel-water: An efficient system to access functionalized allylic thioesters from baylis-hillman bromides

Article abstract of DOI:10.1055/s-0030-1258476

A facile, one-pot synthesis of allylic thioesters starting from Baylis-Hillman (BH) bromides and N-thioaroylmorpholines is described. The synthesis is performed in a silica gel-water system without any additional catalyst or co-catalyst. The reaction path

Full text of DOI:10.1055/s-0030-1258476

PAPER
1261
N-Thioaroylmorpholines in Silica Gel–Water: An Efficient System to Access
Functionalized Allylic Thioesters from Baylis–Hillman Bromides
Functionalized
A
a
llylic
T
hioe
j
stersfr
e
omBaylis–
s
Hillma
n
B
h
romides Patel, Vishnu P. Srivastava, Lal Dhar S. Yadav*
Green Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad 211 002, India
Fax +91(532)2460533; E-mail: ldsyadav@hotmail.com
Received 29 December 2010
mations; such compounds have distinct chemical proper-
Abstract: A facile, one-pot synthesis of allylic thioesters starting
from Baylis–Hillman (BH) bromides and N-thioaroylmorpholines
is described. The synthesis is performed in a silica gel–water system
without any additional catalyst or co-catalyst. The reaction pathway
ties compared to their oxo-analogues.7–9 Unsaturated
thoiesters are well-known as interesting synthetic build-
ing blocks, and their utilization in asymmetric cycloaddi-
involves selective S-alkylation of N-thioaroylmorpholines via nu- tion, in peptide synthesis, and in natural product synthesis
are well-documented.10,11 Moreover, allylic thioesters
cleophilic displacement (SN2) with BH bromides, followed by hy-
drolysis to afford the corresponding thioesters. The present
serve as useful starting materials for the synthesis of allyl-
synthetic protocol avoids the application of malodorous sulfur com-
ic sulfides and their S-derivatized products, owing to the
pounds of limited accessibility such as thiols, and thioacids and
ease of hydrolysis of the former to the corresponding al-
their salts as reactants.
lylic thiols followed by facile alkylation, arylation, or het-
Key words: Baylis–Hillman adducts, aqueous medium, allylic
eroarylation.12
thioesters, nucleophilic displacement, green chemistry, regioselec-
tivity
Most preparations of thioesters employ either activated
acyl derivatives, such as acyl halides or anhydrides, with
thiols in the presence of a base, or the reaction of thioacids
and their salts with electrophilic reagents such as alkyl ha-
lides or Michael acceptors.13 Recently, some elegant ap-
proaches have been introduced to access thioesters that
avoids the application of unpleasant and noxious com-
pounds of limited accessibility such as thiols, thioacids
and their salts, as reactants.14 However, malodorous sulfur
compound free methodologies with which to access allyl-
ic thioesters has been rarely reported until now.14b Thus,
given the importance of allylic sulfur compounds,15 it is
highly desirable to develop an environmentally benign
protocol that provides efficient access to such a highly
useful family of organosulfur compounds. Herein,
Baylis–Hillman (BH) chemistry has been applied to ac-
complish this goal (Scheme 1).
The development of new synthetic methodologies has had
to undergo a paradigmatic shift due to increasingly tight
restrictions on the release of waste and toxic emissions, in
order to control environmental pollution. Thus, besides
the usual requisites of mildness and selectivity, the issue
of environmentally friendly reaction conditions has be-
come increasingly important in the design of alternate
synthetic routes for fine chemicals. In this context, the use
of micelles, microemulsions, surfactants, and other micro-
heterogeneous liquids as media for organic reactions in
water has gained considerable interest among synthetic
chemists. Silica gel is easily available, low cost, nontoxic,
and is of general use for chromatographic separation of
organic compounds. It plays an important role as a heter-
ogeneous catalyst in organic synthesis1 and can be viewed
as being analogous to microheterogeneous liquids. Thus,
the combination of silica gel and water, originally estab-
lished by Minakata and Komatsu,2 constitutes a powerful
organic reaction media that offers several advantages,
such as easy isolation of crude products, potential reuse of
the silica gel, and minimization of waste production.
EWG
S
EWG
SiO2–H2O
R
+
Ar
R
N
S
80 °C, 2 h
87–94%
Ar
Br
O
O
R = aryl, alkyl; EWG = COOMe, COMe
Scheme 1 One-pot synthesis of allylic thioesters using BH chemi-
The synthesis of organosulfur compounds, essentially
routes involving the carbon–sulfur bond formation, has at-
tracted much attention due to their occurrence in many
molecules that are of biological, pharmaceutical, and ma-
terial interest.3,4 Thioesters are protected thiols and repre-
sent a unique class of organosulfur compounds with
widespread application in drug discovery,5 industry,6 and
as key intermediates in various synthetic organic transfor-
stry
Among the leading ‘name’ reactions in organic synthesis,
the BH reaction16 has become a popular atom-economical
carbon–carbon bond-forming reaction that yields func-
tionalized allylic alcohols. Multifunctional allylic alco-
hols (BH adducts) could be readily transformed into
suitable leaving groups, such as acetate or bromide (com-
monly known as BH acetate or BH bromide), through
acetylation and bromination, respectively. The BH ace-
tates and bromides have been used as nucleophilic accep-
tors in many useful organic transformations, leading to the
SYNTHESIS 2011, No. 8, pp 1261–1266
x
x
.
x
x
.2
0
1
1
Advanced online publication: 14.03.2011
DOI: 10.1055/s-0030-1258476; Art ID: Z52910SS
© Georg Thieme Verlag Stuttgart · New York

1262
R. Patel et al.
PAPER
synthesis of trisubstituted alkenes and to a range of multi- We then turned our attention towards activated allylic ha-
functional molecules en route to heterocycles through a lides known as BH bromides 3, which are distinct from
nucleophilic displacement (SN2 or SN2¢) with various C-, benzyl halides both in structure and reactivity. The BH
N-, and O-centered nucleophiles.17 However, their exploi- bromides 3 are more prone to nucleophilic displacement
tation for generating sulfur-containing products with S- (SN2 and SN2¢) than the corresponding acetates 1 and these
centered nucleophiles has been limited and includes only were thus chosen as electrophilic substrates for the present
arenesulfinates,18 thiolates,19 thiocyanate anions,20 and study. At the outset, it was unclear whether S-alkylation
thiol acetic acid.21 Recently, we have reported a one-pot, of N-thioaroylmorpholines 2 with BH bromides 3 would
stereoselective synthesis of allyl dithiocarbamates involv- be effective in a silica gel–water system and whether it
ing nucleophilic displacement (SN2¢) of BH acetates by would follow the SN2 or SN2¢ pathway.
dithiocarbamate anions in water.22d
O
In a continuation of our recent interest in synthetic appli-
SN2'
COOMe
S
O
cations of BH adducts,22 we report herein a regioselective,
one-pot synthesis of hitherto unknown functionalized Z-
allylic thioesters from BH bromides using N-thioaroyl-
morpholines in a silica gel–water system without any ad-
ditional catalyst or co-catalyst (Scheme 1). We initiated
our experiment with BH acetate 1 as an electrophilic sub-
strate, which is known to undergo nucleophilic displace-
ment (SN2¢) with S-centered nucleophiles.18–21,22d
However, we could not obtain any product from the reac-
tion of BH acetate 1 and N-thioaroylmorpholine 2a under
the reaction conditions reported for S-alkylation of N-
thioaroylmorpholines with benzyl/alkyl halides14c
(Scheme 2). Instead of an S-alkylated product, isomerized
BH acetate 1¢ was obtained in 20% yield, along with start-
ing materials 1 and 2a.
N
COOMe
SN2
••
Br
Ph
SiO2
H2O
Ph
N
Ph
4a
Br
S
+
Ph
3a
2a
••
O
H
H
O
COOMe
COOMe
H
Ph
S
N
H
S
Ph
Ph
N
O
Br
O
–
Br
Ph
H
O
5a
H
5a'
Scheme 3 One-pot synthesis of allylic thioesters 5a in a silica gel–
water system
AcO
Ph
COOMe
Gratifyingly, we observed rapid S-alkylation of N-thio-
aroylmorpholine 2a through only SN2 type nucleophilic
displacement with BH bromide 3a in the silica gel–water
system. Thus, on stirring 2a (1 mmol) and 3a (1 mmol) in
the silica gel–water system at 80 °C for two hours, the cor-
responding allylic thioester 5a (94% isolated yield) was
obtained in the absence of any additional catalyst or co-
catalyst (Scheme 3). The temperature appears crucial, be-
cause the reaction did not take place appreciably even af-
ter stirring for 20 hours at room temperature. The
effectiveness of the reaction in the absence of silica gel
was also investigated; under these conditions, the reaction
proceeded sluggishly to give a poor yield (30%) of allylic
thioester 5a after stirring the reaction mixture for three
hours at 95 °C. Thus, the use of silica gel in water facili-
tates the reaction, presumably by enlargement of the sur-
face area available for reaction compared with that of the
interface in a conventional liquid–liquid biphasic system.
This is because the organic substrate is adsorbed onto the
silica through hydrophobic interactions between the sur-
face of the silica and the organic molecule.2 Encouraged
by this result, various other BH bromides 3 were treated
with a variety of N-thioaroyl morpholines 2 following the
same protocol. Table 1 summarizes our results, which
demonstrate the generality of the method by the success-
ful synthesis of variously functionalized allylic thioesters
5 in good to excellent yields (87–94%) with high regiose-
lectivity.
COOMe
OAc
1
DABCO, NaI, HTAB
H2O, 6 h, 95 °C
+
+ 1 + 2a
Ph
S
1'
N
2a
Ph
O
Scheme 2 Reaction of BH acetate 1 with N-thioaroylmorpholine 2a
in the presence of DABCO
This is consistent with the earlier observations that BH
acetate 1 isomerizes in the presence of 1,4-diazabicy-
clo[2.2.2]octane (DABCO),23 and that it fails to undergo a
nucleophilic displacement reaction with potassium thio-
cyanate (KSCN).24 Boeini and Kashan reported that the
hydrolysis of thiouronium salt 4a was catalyzed by
DABCO.14c We proposed the hypothesis that thiouronium
salt 4a would be hydrolyzed even in the absence of DABCO
and, indeed, this was found to be the case (Scheme 3).
The above points led us to develop a new, environmental-
ly benign system that would be a more economical and vi-
able approach that is able to facilitate S-alkylation of N-
thioaroylmorpholines with BH acetate 1. In this regard,
we chose to use a silica gel–water system to access the tar-
get allylic thioester 5a by treating BH acetate 1 with N-
thioaroylmorpholine 2a, in the absence of any additional
catalyst or co-catalyst, at 80 °C. Unfortunately, no reac-
tion took place even after prolonged stirring at 80–95 °C.
Synthesis 2011, No. 8, 1261–1266 © Thieme Stuttgart · New York

PAPER
Functionalized Allylic Thioesters from Baylis–Hillman Bromides
1263
eter.1H and 13C NMR spectra were recorded with a Bruker AVII 400
spectrometer in CDCl3 using TMS as internal reference. Mass (EI)
spectra were recorded with a JEOL D-300 mass spectrometer. Ele-
mental analyses were performed with a Carlo Erba 1108 microana-
lyzer or Elementar’s Vario EL III microanalyzer.
Table 1 Synthesis of Functionalized Allylic Thioesters 5a
EWG
O
EWG
Br
SiO2–H2O
80 °C
N
S
+
R
R
Ar
Ar
S
O
Synthesis of Allylic Thioesters 5; General Procedure
(Z)-3
(Z)-5
2
A mixture of N-thioaroylmorpholine 2 (1 mmol), BH bromide 3 (1
mmol), and silica gel 60–100 mesh (1 g) in H2O (5 mL) was stirred
at 80 °C for 2 h. After completion of the reaction (as indicated by
TLC), the reaction mixture was cooled to r.t. and filtered through
Celite. The filter cake was washed with EtOAc (3 × 5 mL) and the
organic phase was retained. The aqueous phase was extracted with
EtOAc (2 × 5 mL), and the combined organic extracts were dried
over MgSO4, filtered, and evaporated to afford the crude allylic
thioester 5, which was purified by silica gel column chromatogra-
phy (hexane–EtOAc, 8:2) to give the desired pure allylic thioester 5.
Compound R
Ar
Ph
EWG
Yield (%)b,c
5a
5b
5c
5d
5e
5f
Ph
Ph
Ph
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
CO2Me
COMe
COMe
COMe
COMe
COMe
COMe
COMe
94
89
92
90
93
94
87
91
89
90
94
88
90
92
2-naphthyl
4-ClC6H4
4-MeC6H4
4-biphenyl
Ph
2-ClC6H4
Ph
(Z)-Methyl 2-(Benzoylthiomethyl)-3-phenylacrylate (5a)
IR (neat): 1711, 1668, 1628, 1578, 1422, 1240, 1030, 760, 692 cm–1.
4-MeOC6H4
4-O2NC6H4
Ph
1H NMR (400 MHz, CDCl3): d = 3.85 (s, 3 H, OCH3), 4.26 (s, 2 H,
CH2S), 7.37–7.47 (m, 7 H, ArH), 7.58–7.60 (m, 1 H, ArH), 7.88 (s,
1 H, =CH), 7.97–8.00 (m, 2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 28.6, 52.2, 127.2, 128.4, 128.7,
129.1, 129.8, 130.2, 133.4, 134.9, 136.8, 141.4, 167.5, 191.9.
5g
5h
5i
Ph
Ph
4-ClC6H4
4-MeC6H4
2-MeOC6H4
4-i-PrC6H4
n-Pr
4-ClC6H4
4-MeC6H4
Ph
MS (EI): m/z = 312 [M]+.
5j
Anal. Calcd for C18H16O3S: C, 69.21; H, 5.16. Found: C, 69.49; H,
5.04.
5k
5l
Ph
(Z)-Methyl 2-[(2-Naphthoylthio)methyl]-3-phenylacrylate (5b)
IR (KBr): 1709, 1664, 1621, 1582, 1418, 1398, 1246, 1028, 884,
815, 730, 690 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.82 (s, 3 H, OCH3), 4.21 (s, 2 H,
CH2S), 7.35–7.43 (m, 5 H, ArH), 7.56–7.59 (m, 2 H, ArH), 7.86 (s,
1 H, =CH), 7.91 (t, J = 8.3 Hz, 2 H, ArH), 7.98 (d, J = 8.0 Hz, 1 H,
ArH), 8.03 (dd, J = 8.6, 1.5 Hz, 1 H, ArH), 8.56 (s, 1 H, ArH).
13C NMR (100 MHz, CDCl3): d = 28.9, 52.1, 123.4, 125.8, 127.1,
128.0, 128.4, 128.7, 129.0, 129.3, 129.7, 130.0, 130.6, 132.3, 134.1,
134.7, 135.8, 141.1, 167.7, 191.2.
5m
2-naphthyl
Ph
5n
n-Hept
a Reaction conditions: BH bromide 3 (1 mmol), N-thioaroylmorpho-
line 2 (1 mmol), silica gel–water (1 g in 5 mL) at 80 °C for 2 h. For
experimental procedure, see experimental section.
b Pure product after column chromatography.
c All compounds gave C, H and N analysis within 0.35% and satis-
factory spectral (IR, 1H NMR, 13C NMR and EIMS) data.
MS (EI): m/z = 362 [M]+.
In summary, we have described an expedient, green syn-
thetic protocol for the synthesis of densely functionalized
Z-allylic thioesters via selective S-alkylation of N-thio-
aroylmorpholines with BH bromides, followed by hydrol-
Anal. Calcd for C22H18O3S: C, 72.90; H, 5.01. Found: C, 72.14; H,
5.23.
(Z)-Methyl 2-[(4-Chlorobenzoylthio)methyl]-3-phenylacrylate
(5c)
ysis in
a silica gel–water system. The present
methodology avoids the need to handle unpleasant and
noxious thiols as well as corrosive acid chlorides. The ap-
proach requires no added catalyst or co-catalyst, and
needs only the use of distilled water in combination with CH2S), 7.31–7.36 (m, 5 H, ArH), 7.41–7.46 (m, 2 H, ArH), 7.88 (s,
easily available, inexpensive, and nontoxic silica gel. The
method offers several advantages, such as the ease of
crude product separation, potential catalyst reuse (SiO2),
and minimization of waste production.
IR (neat): 1713, 1670, 1630, 1578, 1426, 1240, 1028, 820, 764, 710
cm–1.
1H NMR (400 MHz, CDCl3): d = 3.84 (s, 3 H, OCH3), 4.28 (s, 2 H,
1 H, =CH), 7.95–7.98 (m, 2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 28.7, 52.2, 128.4, 128.8, 129.2,
129.8, 130.2, 134.3, 134.7, 133.1, 140.3, 141.2, 167.4, 189.6.
MS (EI): m/z = 346 [M]+, 348 [M + 2]+.
Anal. Calcd for C18H15ClO3S: C, 62.33; H, 4.36. Found: C, 61.98;
H, 4.39.
All starting materials, unless otherwise stated, were purchased as re-
agent grade and used without further purification. The requisite N-
thioaroylmorpholines 2, BH bromides 3, and BH acetate 1 were pre-
pared by a known method.25 Dry silica gel (Merck 60–100 mesh)
was used in the reaction. Column chromatography was carried out
over silica gel (Merck 100–200 mesh) and TLC was performed us-
ing silica gel GF254 (Merck) plates. Melting points were deter-
mined by the open glass capillary method and are uncorrected. IR
spectra were recorded with a Perkin–Elmer 993 IR spectrophotom-
(Z)-Methyl 3-(4-Chlorophenyl)-2-[(4-methylbenzoylthio)meth-
yl]acrylate (5d)
IR (KBr): 2968, 2922, 1710, 1662, 1621, 1580, 1428, 1237, 1094,
1028, 840 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.39 (s, 3 H, CH3), 3.81 (s, 3 H,
OCH3), 4.26 (s, 2 H, CH2S), 7.23 (d, J = 8.2 Hz, 2 H, ArH), 7.41 (d,
Synthesis 2011, No. 8, 1261–1266 © Thieme Stuttgart · New York

1264
R. Patel et al.
PAPER
J = 8.0 Hz, 2 H, ArH), 7.54 (d, J = 8.0 Hz, 2 H, ArH), 7.88 (s, 1 H,
=CH), 7.94 (d, J = 8.2 Hz, 2 H, ArH).
Anal. Calcd for C18H16O2S: C, 72.94; H, 5.44. Found: C, 72.69; H,
5.29.
13C NMR (100 MHz, CDCl3): d = 21.6, 28.7, 53.4, 127.2, 128.7,
(Z)-S-2-(4-Chlorobenzylidene)-3-oxobutyl 4-Chlorobenzothio-
ate (5i)
129.2, 129.6, 130.1, 133.2, 134.3, 135.1, 141.4, 144.3, 167.1, 191.2.
MS (EI): m/z = 360 [M]+, 362 [M + 2]+.
IR (KBr): 1678, 1664, 1628, 1590, 1420, 1242, 1094, 1036, 840
cm–1.
Anal. Calcd for C19H17ClO3S: C, 63.24; H, 4.75. Found: C, 63.19;
H, 4.81.
1H NMR (400 MHz, CDCl3): d = 2.49 (s, 3 H, CH3CO), 4.21 (s, 2 H,
CH2S), 7.32–7.46 (m, 6 H, ArH), 7.79 (s, 1 H, =CH), 7.95–7.98 (m,
2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 26.1, 30.2, 128.4, 128.8, 129.2,
130.9, 132.6, 135.1, 135.4, 135.8, 139.6, 140.8, 192.0, 197.3.
(Z)-Methyl 2-(Biphenylcarbonylthiomethyl)-3-phenylacrylate
(5e)
IR (KBr): 1714, 1671, 1629, 1580, 1430, 1240, 1098, 1024, 824,
760, 710 cm–1.
MS (EI): m/z = 364 [M]+, 366 [M + 2]+.
1H NMR (400 MHz, CDCl3): d = 3.81 (s, 3 H, OCH3), 4.26 (s, 2 H,
CH2S), 7.31–7.43 (m, 6 H, ArH), 7.50 (d, J = 7.4 Hz, 2 H, ArH),
7.64 (d, J = 7.4 Hz, 2 H, ArH), 7.71 (d, J = 8.3 Hz, 2 H, ArH), 7.88
(s, 1 H, =CH), 8.05 (d, J = 8.3 Hz, 2 H, ArH).
Anal. Calcd for C18H14Cl2O2S: C, 59.19; H, 3.86. Found: C, 59.41;
H, 3.78.
(Z)-S-2-(4-Methylbenzylidene)-3-oxobutyl 4-Methylbenzothio-
ate (5j)
13C NMR (100 MHz, CDCl3): d = 28.7, 52.4, 127.3, 127.8, 128.2,
128.6, 128.8, 129.1, 129.4, 129.7, 130.0, 130.3, 134.8, 139.8, 141.1,
146.2, 167.8, 191.8.
IR (neat): 2964, 2928, 1674, 1668, 1620, 1578, 1424, 1246, 1032,
856 cm–1.
MS (EI): m/z = 388 [M]+.
1H NMR (400 MHz, CDCl3): d = 2.36 (s, 3 H, CH3), 2.40 (s, 3 H,
CH3), 2.47 (s, 3 H, CH3CO), 4.20 (s, 2 H, CH2S), 7.23–7.26 (m,
4 H, ArH), 7.50–7.52 (d, J = 7.7 Hz, 2 H, ArH), 7.80 (s, 1 H, =CH),
7.92–7.94 (d, J = 8.2 Hz, 2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 21.4, 21.6, 26.2, 30.4, 127.4,
129.2, 129.7, 129.9, 131.5, 134.1, 135.3, 140.2, 140.5, 144.2, 191.5,
196.7.
Anal. Calcd for C24H20O3S: C, 74.20; H, 5.19. Found: C, 74.29; H,
5.11.
(Z)-Methyl 2-(Benzoylthiomethyl)-3-(4-methoxyphenyl)acry-
late (5f)
IR (neat): 1710, 1670, 1631, 1580, 1424, 1260, 1238, 1031, 831,
760, 714 cm–1.
MS (EI): m/z = 324 [M]+.
1H NMR (400 MHz, CDCl3): d = 3.82 (s, 3 H, OCH3), 3.88 (s, 3 H,
OCH3), 4.30 (s, 2 H, CH2S), 6.94 (d, J = 8.8 Hz, 2 H, ArH), 7.36 (d,
J = 8.8 Hz, 2 H, ArH), 7.42–7.48 (m, 2 H, ArH), 7.56–7.59 (m, 1 H,
ArH), 7.87 (s, 1 H, =CH), 7.97–8.01 (m, 2 H, ArH).
Anal. Calcd for C20H20O2S: C, 74.04; H, 6.21. Found: C, 73.71; H,
6.14.
(Z)-S-2-(2-Methoxybenzylidene)-3-oxobutyl Benzothioate (5k)
IR (KBr): 1672, 1664, 1620, 1582, 1420, 1236, 1028, 930, 860, 760
cm–1.
1H NMR (400 MHz, CDCl3): d = 2.51 (s, 3 H, CH3CO), 3.88 (s, 3 H,
OCH3), 4.16 (s, 2 H, CH2S), 6.94 (d, J = 8.3 Hz, 1 H, ArH), 7.06 (m,
1 H, ArH), 7.42–7.48 (m, 3 H, ArH), 7.59–7.61 (m, 1 H, ArH), 7.72
(d, J = 7.9 Hz, 1 H, ArH), 7.81 (s, 1 H, =CH), 7.94–7.98 (m, 2 H,
ArH).
13C NMR (100 MHz, CDCl3): d = 28.9, 52.1, 53.6, 114.1, 126.4,
127.6, 128.5, 129.0, 129.8, 130.4, 136.8, 141.6, 160.3, 167.9, 191.4.
MS (EI): m/z = 342 [M]+.
Anal. Calcd for C19H18O4S: C, 66.65; H, 5.30. Found: C, 66.80; H,
5.12.
(Z)-Methyl 2-(Benzoylthiomethyl)-3-(4-nitrophenyl)acrylate
(5g)
13C NMR (100 MHz, CDCl3): d = 26.3, 30.1, 55.6, 110.7, 120.8,
123.3, 128.4, 128.8, 129.6, 131.4, 135.2, 135.6, 139.5, 140.4, 157.8,
191.4, 197.1.
IR (KBr): 1718, 1672, 1624, 1576, 1520, 1424, 1342, 1264, 1232,
1036, 830, 756, 712 cm–1.
1H NMR (400 MHz, CDCl3): d = 3.86 (s, 3 H, OCH3), 4.30 (s, 2 H,
CH2S), 7.41–7.46 (m, 2 H, ArH), 7.54–7.58 (m, 3 H, ArH), 7.91 (s,
1 H, =CH), 7.97–8.01 (m, 2 H, ArH), 8.20 (d, J = 8.7 Hz, 2 H,
ArH).
MS (EI): m/z = 326 [M]+.
Anal. Calcd for C19H18O3S: C, 69.91; H, 5.56. Found: C, 70.09; H,
5.43.
13C NMR (100 MHz, CDCl3): d = 28.9, 52.7, 124.0, 127.3, 128.2,
(Z)-S-2-(4-Isopropylbenzylidene)-3-oxobutyl Benzothioate (5l)
IR (neat): 2960, 2927, 1672, 1669, 1626, 1576, 1430, 1248, 1040,
860, 730, 710 cm–1.
129.8, 130.8, 133.6, 136.8, 139.9, 141.7, 147.6, 165.6, 190.8.
MS (EI): m/z = 357 [M]+.
Anal. Calcd for C18H15NO5S: C, 60.49; H, 4.23; N, 3.92. Found: C,
60.30; H, 4.78; N, 3.81.
H NMR (400 MHz, CDCl3): d = 1.30 (d, J = 7.0 Hz, 6 H), 2.48 (s,
3 H, CH3CO), 2.97 (sept, J = 7.0 Hz, 1 H), 4.16 (s, 2 H, CH2S),
7.35–7.48 (m, 4 H, ArH), 7.54–7.59 (m, 3 H, ArH), 7.78 (s, 1 H,
=CH), 7.96–8.00 (m, 2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 23.7, 26.2, 30.1, 34.0, 127.2,
128.3, 128.8, 130.0, 131.6, 135.1, 135.4, 139.5, 140.6, 151.2, 191.8,
197.1.
(Z)-S-2-Benzylidene-3-oxobutyl Benzothioate (5h)
IR (neat): 1676, 1666, 1625, 1580, 1424, 1240, 1032, 760, 680 cm–1.
1H NMR (400 MHz, CDCl3): d = 2.50 (s, 3 H, CH3CO), 4.20 (s, 2 H,
CH2S), 7.34–7.45 (m, 7 H, ArH), 7.56–7.59 (m, 1 H, ArH), 7.76 (s,
1 H, =CH), 7.95–7.99 (m, 2 H, ArH).
13C NMR (100 MHz, CDCl3): d = 26.2, 30.2, 127.3, 128.1, 128.8,
129.4, 129.8, 133.6, 134.2, 135.2, 136.8, 140.6, 191.5, 197.1.
MS (EI): m/z = 338 [M]+.
Anal. Calcd for C21H22O2S: C, 74.52; H, 6.55. Found: C, 74.79; H,
6.49.
MS (EI): m/z = 296 [M]+.
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Functionalized Allylic Thioesters from Baylis–Hillman Bromides
1265
(Z)-S-2-Acetylhex-2-enyl Naphthalene-2-carbothioate (5m)
IR (KBr): 2973, 2928, 2854, 1686, 1664, 1621, 1588, 1416, 1242,
1032, 890, 820, 760, 714 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.98 (t, J = 7.5 Hz, 3 H), 1.52 (m,
2 H), 2.24–2.40 (m, 5 H), 3.89 (s, 2 H, CH2S), 6.89 (t, J = 7.6 Hz,
1 H, =CH), 7.53–7.56 (m, 2 H, ArH), 7.89 (t, J = 8.3 Hz, 2 H, ArH),
7.96 (d, J = 8.0 Hz, 1 H, ArH), 8.01 (dd, J = 8.6, 1.5 Hz, 1 H, ArH),
8.54 (s, 1 H, ArH).
Hammond, G. G.; Pompliano, D. L.; Epstein-Toney, J. H.
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125.9, 127.1, 128.6, 128.9, 129.2, 129.6, 132.4, 134.1, 135.4, 135.8,
146.2, 191.4, 196.9.
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MS (EI): m/z = 312 [M]+.
Anal. Calcd for C19H20O2S: 73.04; H, 6.45. Found: 72.88; H, 6.71.
(Z)-S-2-Acetyldec-2-enyl Benzothioate (5n)
IR (neat): 2980, 2926, 2852, 1686, 1669, 1626, 1590, 1420, 1240,
1034, 760, 714 cm–1.
1H NMR (400 MHz, CDCl3): d = 0.83 (t, J = 6.8 Hz, 3 H), 1.19–
1.51 (m, 10 H), 2.21–2.39 (m, 5 H), 3.91 (s, 2 H, CH2S), 6.87 (t,
J = 7.5 Hz, 1 H, =CH), 7.26–7.35 (m, 2 H, ArH), 7.54–7.58 (m,
1 H, ArH), 7.99–8.02 (m, 2 H, ArH).
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5909.
13C NMR (100 MHz, CDCl3): d = 13.9, 22.5, 25.4, 28.6, 28.9, 29.2,
29.4, 30.8, 31.6, 127.1, 128.6, 132.4, 135.6, 136.8, 146.6, 191.1,
196.7.
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MS (EI): m/z = 318 [M]+.
Anal. Calcd for C19H26O2S: C, 71.66; H, 8.23. Found: C, 71.41; H,
8.36.
Acknowledgment
We sincerely thank SAIF, Punjab University, Chandigarh, for pro-
viding microanalyses and spectra. One of us (V.P.S.) is grateful to
the CSIR, New Delhi, for the award of a Senior Research Fel-
lowship (SRF).
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