Synthesis of some 3-aryl-1H-isochromene-1-thiones

Article abstract of DOI:10.1002/jhet.5570450307

(Chemical Equation Presented) A rapid microwave-accelerated thionation of some 3-substitued isocoumarins to corresponding 1-thioisocoumarins was achieved employing Lawesson's reagent under solventless conditions.

Full text of DOI:10.1002/jhet.5570450307

May-Jun 2008
679
Synthesis of Some 3-Aryl-1H-isochromene-1-thiones
Aamer Saeed*and Zaman Ashraf
Department of Chemistry, Quaid-I-Azam University, Islamabad 45320, Pakistan.
Email: aamersaeed@yahoo.com
Received February 23, 2007
R
R
Lawesson's reagent
O
O
!W,1.2-3 min., 71-95 %
(2a-j)
(1a-j) R= -Aryl; -alkyl
O
S
A rapid microwave-accelerated thionation of some 3-substitued isocoumarins to corresponding 1-thio-
isocoumarins was achieved employing Lawesson’s reagent under solventless conditions.
J. Heterocyclic Chem., 45, 679 (2008).
INTRODUCTION
products. The 2,4-bis(p-methoxyphenyl)-1,3-dithiaphos-
phetane 2,4-disulfide (Lawesson’s reagent), has
frequently been used for the conversion of oxygen
functionalities into their thio analogues [21].
Conventional conversions require refluxing in dry
benzene or toluene for several hours (4-20) under dry
inert atmosphere using an excess of the reagent (1-3.0
molar equiv.) and despite these only poor yields (30-50
%) were obtained. It is possibly due to formation of side
products and decomposition of the reagent.
The use of microwaves in organic synthesis has now
become an area of paramount importance and of
considerable interest due to cleaner reactions, shorter
reaction times, and the ease of handling [22]. In
continuation of our interest towards synthesis of naturally
occurring isocoumarins and their synthetic analogues [23]
in this article, we wish to describe the microwave
accelerated thionation of a number of isocoumarins using
Lawesson’s reagent (Scheme 1). An easy access to 1-
thioanolgues of isocoumarins will be valuable for
evaluation of effect of substitution of oxygen by sulfur
atom on bioactivity.
Isocoumarins (1H-2-benzopyran-1-ones) are the
secondary metabolites of an extensive variety of fungi,
bacteria, higher plants, marine organisms and are also
among insect venoms and pheromones; exhibiting a wide
range of structural diversity and biological activities [1-3].
Important examples of natural bioactive isocoumarins
include the furoisocoumarin coriandrin phototoxic to
RNA-virus Sindbis virus, DNA-virus murine cytomegalo-
virus and HIV [4], thunberginol, phyllodulcin and
hydrangenol having differentiation inducing, antiallergic,
and immunomodulatory effects [5], ochratoxins A & B,
nephratoxic, hepatotoxic [6], hiburipyranone, cytotoxic
[7], duclauxin, antitumor [8], cytogenin and its synthetic
analogues antitumor, antidiabetic anticancer [9] and Sg17-
1-4, possessing potent cytotoxic activities [10].
Majority of the natural isocoumarins being of
polyketide origin are derived biogenetically from acetate-
polymalonate pathway, hence most of them possess a C-3
alkyl/aryl substituent. Although, more than two hundred
isocoumarins and dihydroisocoumarins have been isolated
and the number is still increasing dramatically,
1-thioisocoumarins are thus far unknown in nature. A
review of literature reveals that while, the thio analogues
RESULTS AND DISCUSSION.
The isocoumarins (1a-j) were synthesized according to
previously reported method [23]. An intimate mixture of
the isocoumarin with Lawesson’s reagent (0.5-0.6 equiv)
was irradiated in an alumina bath using a domestic
microwave oven. The progress of reaction was monitored
by analytical TLC every 30 s to establish the minimum
time necessary to complete the reaction. The successful
thionation was primarily indicated by appearance of a
visible yellowish spot on TLC having slightly higher Rf
value than the parent isocoumarin. The products were
of
a number of associated natural products viz.,
chromones, [11] flavones, [12] isoflavones [13] and
coumarins [14] have been prepared; the reports of
synthetic 1-thioisocoumarins (1H-isochromene-1-thiones)
are exceptional [15]. The various reagents and conditions
employed for thionation include phosphorus pentasulfide
in presence of base [16], hydrogen sulfide in the presence
of acid [17], bis-(tricyclohexyltin)sulfide with boron
trichloride [18] bis(trimethyl-silyl)sulfide with hydrated
cobalt chloride [19] and boron sulfide in refluxing
chloroform [20]. Most of these procedures require an
excess of reagents, use of anhydrous aromatic
hydrocarbon solvents, acidic or basic medium and
rigorously dry conditions, affording only modest yields of
1
further characterized by mp, IR, H and 13C NMR, mass
spectral and elemental analysis data. Accordingly,
absence of lactonic carbonyl absorption at 1700-1720 cm-1
and appearance of absorption at 1070-1250 cm-1 in the IR
spectra manifested the change from carbonyl to

680
A. Saeed and Z. Ashraf
Vol 45
1H NMR and the 13C NMR spectra were determined as CDCl3
solutions at 300 MHz and 100 MHz respectively, on a Bruker
AM-300 machine. FT IR spectra were recorded using an FTS
3000 MX spectrophotometer; Mass Spectra (EI, 70eV) on a GC-
MS instrument and elemental analyses with a LECO-183 CHNS
analyzer. The reactions were carried out in an unmodified
domestic microwave oven (MW 900 W, frequency 2450 MHz,
Power level 1, Dawlance, Pakistan). The analytical TLC was
carried out using recoated plated from Merck and thick layer
chromatography using silica gel from Merck.
General procedure for the conversion of isocoumarins into
1-1H-isochromene-1-thiones (2a–j). A homogenized mixture
of isocoumarin (1a-j) (1 mmol) and Lawesson’s reagent (0.5-0.6
mmol) was irradiated for 1.3-2-3 min in an alumina bath inside
the microwave oven (Table-1). The progress of the reaction was
followed by TLC examination using hexane/ethyl acetate (9:1).
On completion the reaction mixture was diluted with ethyl
acetate and subjected to thick layer chromatography using same
solvent system. Elution using ethyl acetate followed by
concentration afforded the products (2a–j) which crystallized on
standing as yellow needles or plates.
thiocarbonyl. In general, absorptions of protons H-4 of
isocoumarins range from δ 6.77 to 6.96, while the
absorption of the same protons in thioisocoumarins range
1
from δ 6.86 to 7.08 in the H NMR. A more pronounced
downfield shift of 13C absorption of carbons C-1, ranging
from 30 to 40 ppm was observed in the 13C NMR
(Table 1). The products were obtained in 71-95 % yields
in high purity. A variety of substituents on the phenyl ring
are well-tolerated, and the reaction leads to completion in
all the cases.
R
R
Lawesson's reagent
O
O
MW, 1.2-3 min., 71-95 %
O
S
(2a-j)
(1a-j)
R=
R= same as in 1a-j
1a=3-FC6H4
;
1b=4-FC6H4
1c=4-ClC6H4;
1e=3-IC6H4;
1d=2-BrC6H4
1f=2,4-DiClC6H312
1g=2-F-4-ClC6H3; 1h=4-MeOC6H4
1i=4-FC6H4 CH2; 1j=C15H31
3-(3-Fluorophenyl)-1H-isochromene-1-thione (2a). Rf =0.8
IR (KBr):=1190, 2980, 1615. 1H NMR δ 6.98 (1H, s, H-4), 8.34
(1H, s, H-2'), 7.66-7.75 (2H, m, H-4', H-5'), 7.62 (1H, d, J=2.1,
H-6'), 7.53 (2H, d, J=7.8, H-5, H-8), 7.44 (1H, dd, J=1.8, 2.1, H-
6), 7.15 (1H, dd, J=2.4, 2.4, H-7). 13C NMR δ102 (C-4), 112 (C-
4a), 120 (C-6’,C-5’), 126 (C-7), 129 (C-8), 130 (C-2’,C-4’), 134
(C-5), 135 (C-6), 137 (C-1’), 152 (C-8a), 162 (C-3’), 164 (C-3),
203 (C-1). MS (70eV): m/z (%)=256 (M+,100), 95 (48), 161
(67). Anal. Calcd. For C15H9OSF: C, 70.31; H, 3.51; S, 12.50.
Found. C, 70.25; H, 3.45; S, 11.45.
3-(4-Fluorophenyl)-1H-isochromene-1-thione (2b). Rf=0.6,
IR (KBr):=1195, 3020, 1590. 1H NMR δ 7.08 (1H, s, H-4), 8.73
(2H, d, J=7.8, H-3', H-5'), 7.97 (2H, d, J=3, H-2', H-6'), 7.72
(1H, d, J=1.2, H-5), 7.51 (3H, m, H-6,H-7,H-8), 13C NMR δ104
(C-4), 116 (C-4a), 127 (C-2’,C-6’), 129 (C-7), 130 (C-8,C-5),
132 (C-3’,C-5’), 135 (C-1’), 155 (C-8a), 162 (C-4’), 165 (C-3),
200 (C-1). MS (70eV): m/z (%)=256 (M+,100), 95 (38), 161
(52). Anal. Calcd. For C15H9OSF: C, 70.31; H, 3.51; S, 12.50.
Found. C, 70.19; H, 3.41; S, 11.41.
Scheme-1 Solvent-Free conversion of Isocoumarin into 1-thioisocoumarins
The generality of the conversion was indicated by
substrates bearing an aralkyl group (2i) on C-3 or a long
aliphatic chain (2j).
In conclusion, an environmentally benign one pot,
microwave-accelerated conversion of isocoumarins to
their 1-thio analogues is reported. The solvent-free
conversion shows several advantages over the
conventional method. These include short reaction times,
high yields and lack of side-product formation. In
addition, it avoids the need for essentially dry conditions,
toxic hydrocarbon solvents and acidic or basic media.
Furthermore, the work up is not necessary, since the crude
mixture can be directly subjected to chromatographic
purification.
3-(4-Chlorophenyl)-1H-isochromene-1-thione (2c). Rf=0.7,
1
EXPERIMENTAL
IR (KBr) 1171, 3025, 1615. H NMR δ 6.96 (1H,s, H-4), 7.85
(2H, d, J=1.8, H-3’,H-5’), 7.83 (2H, d, J=2.1, H-2’-H-6’), 7.75
(1H, d, J=1.5, H-5), 7.73 (1H, d, J=1.2, H-8), 7.40 (2H, m, H-6,
H-7). 13C NMR δ102 (C-4), 120 (C-4a), 126 (C-7), 128 (C-8),
Melting points were recorded using a digital Gallenkamp
(SANYO) model MPD BM 3.5 apparatus and are uncorrected.
Table 1 Physical and Analytical Data of Compounds 2a-j
Entry
Compd.
R
Mp
(oC)
Reaction
time
(min.)
Yield
(%)
1H NMR
δ (ppm) H-4 (s)
13C NMR
δ (ppm) C=X
1
2
1 X=O
2 X=S
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2g
2h
2i
3-FC6H4
4-FC6H4
4-ClC6H4
2-BrC6H4
3-IC6H4
2,4-DiClC6H3
2-Cl-4-FC6H3
4-MeOC6H4
4-FC6H4CH2
C15H31
109-113
138
128-130
Oil
116-118
123-125
129
109-111
65-67
32-33
1.50
2.0
2.2
1.20
2.30
1.50
1.30
2.20
2.0
78
95
89
81
71
74
81
91
93
87
6.10
6.40
6.01
6.2
6.34
6.21
6.35
5.90
5.93
6.24
6.98
7.08
6.96
6.89
6.97
7.03
6.97
6.86
7.01
6.27
164
161
161.3
163
163
162
161
162.5
162
163
203
200
195
194
197
208
200
203
176
201
9
10
2j
3.0
Recrystallization solvent: Ethyl acetate.

May-Jun 2008
An Expeditious, Solvent-Free Conversion of Isocoumarins into 1-Thioisocoumarins
681
129 (C-1’), 130 (C-2’,C-6’), 135 (C-3’,C-5’), 136 (C-5), 137 (C-
6), 152 (C-8a,), 152 (C-4’), 162 (C-3), 195 (C-1). MS (70eV):
m/z (%)=272.5 (M+,100), 111.5 (48), 161 (67). Anal. Calcd. For
C15H9OSCl: C, 66.05; H, 3.30; S, 11.74. Found. C, 65.76; H,
3.22; S, 11.66.
3-(2-Bromophenyl)-1H-isochromene-1-thione (2d). Rf=0.6,
IR (KBr):=1079, 3025, 1590; 1H NMR δ 6.89 (1H, s, H-4), 8.03
(1H, d, J= 2.4, H-3’), 7.61-7.69 (3H, m, H-4’,5’,6’), 7.30-7.40
(4H, m, H-5,6,7,8), 13C NMR δ107 (C-4), 113 (C-4a), 127 (C-7),
129 (C-8), 131 (C-5’), 132 (C-4’,C-6’), 133 (C-3’), 133.8 (C-1’),
134 (C-5), 136 (C-6), 141 (C-2’), 152 (C-8a), 164 (C-3), 194 (C-
1). MS (70eV): m/z (%)=316 (M+,100), 155 (52), 161 (68).
Anal. Calcd. For C15H9OSBr: C, 56.96; H, 2.84; S, 10.12. Found.
C, 56.87; H, 2.78; S, 10.05.
3-(Pentadecyl)-1H-isochromene-1-thione (2j). Rf=0.6 IR
1
(KBr):=1272, 3010, 1605. H NMR δ 6.27 (1H, s, H-4), 8.26
(1H, d, J=8.1, H-8), 7.66-7.68 (2H, m, H-6-H-7), 7.36 (1H, d,
J=7.8,H-5), 2.50 (2H, t, J=7.5,H-1'), 1.73 (2H, p, J=6.6,H-2'),
1.27-1.38 (24H, m, H-3'-H-14'), 0.89 (3H, t, J=5.4, H-15'). 13C
NMR δ10 (C-15’), 14 (C-14’), 22 (C-13’), 23 (C-12’), 26 (C-11’),
28 (C-10’), 29 (C-9’), 29 (C-8’), 29 (C-7’), 30 (C-6’), 31 (C-5’),
33 (C-4’), 38 (C-3’), 55 (C-2’), 68 (C-1’), 112 (C-4), 125 (C-4a),
128 (C-5), 129 (C-7), 132 (C-8), 137 (C-6), 158 (C-8a), 167 (C-
3), 201 (C-1). MS (70eV): m/z (%)=372 (M+,100), 211 (27), 161
(55), 43 (66). Anal. Calcd. For C24H36OS: C, 77.42; H, 9.67; S,
8.60. Found. C, 77.36; H, 9.59; S, 8.52.
REFERENCES
3-(3-Iodophenyl)-1H-isochromene-1-thione (2e). Rf=0.65,
IR (KBr):=1085, 3010, 1580; 1H NMR δ 6.97 (1H, s, H-4), 8.25
(1H, s, H-2'), 8.06 (1H, d, J=9, H-4'), 7.77 (1H, d, J=8.1, H-6'),
7.73 (1H, dd, J=4.8, 3.3, H-5'), 7.52-7.57 (4H, m, H-5-H-8). 13C
NMR δ 109 (C-4), 109 (C-4a), 112 (C-6’) 113 (C-5’), 125 (C-
1’), 128 (C-2’,C-4’), 130 (C-7), 132 (C-8), 135 (C-5), 137 (C-6),
152 (C-3’), 155 (C-8a), 158 (C-3), 197 (C-1); MS (70eV): m/z
(%)=364 (M+,100), 203 (48), 161 (67). Anal. Calcd. For
C15H9OSI: C, 49.45; H, 2.47; S, 8.79. Found. C, 49.37; H, 2.39;
S, 8.71.
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3-(2,4-Dichorophenyl)-1H-isochromene-1-thione (2f). Rf =
1
0.7 IR (KBr):=1128, 2970, 1620. H NMR δ 7.03 (1H, s, H-4),
7.80 (1H, d, J=0.9, H-3'), 7.74 (1H, d, J=13.2, H-5'), 7.71 (1H,
d, J=8.5,H-6'), 7.51-7.61 (4H, m, H-5-H-8). 13C NMR δ106 (C-
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(C-6), 131 (C-5’), 133 (C-1’), 135 (C-3’), 136 (C-8a), 137 (C-
2’,C-4’) 150 (C-3), 208 (C-1). MS (70eV): m/z (%)=307
(M+,100), 146 (52), 161 (62). Anal. Calcd. For C15H9OSCl2: C,
58.63; H, 2.60; S, 10.42. Found. C, 58.55; H, 2.52; S, 10.37.
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1
Rf=0.6 IR (KBr):=1275, 2990, 1595. HNMR δ 6.97 (1H, s, H-
4), 7.83 (1H, s, H-3’), 7.81 (1H, d, J=2.7 H-5’), 7.29 (1H, d,
J=2.4, H-6’), 7.28 (4H, m, H-5,6,7,8). 13C NMR δ 107 (C-4), 114
(C-4a), 127 (C-7), 129 (C-8), 130 (C-6’), 131 (C-1’), 132 (C-5’),
133 (C-3’), 134 (C-5), 135 (C-6), 153 (C-8a), 153 (C-2’) 161 (C-
4’), 164 (C-3), 200 (C-1). MS (70eV): m/z (%)=290.5 (M+,100),
129.5 (34), 161 (75). Anal. Calcd. For C15H9OSClF: C, 61.96; H,
2.75; S, 11.01. Found. C, 61.85; H, 2.68; S, 10.96.
3-(4-Methoxyphenyl)-1H-isochromene-1-thione (2h). Rf=
1
0.6 IR (KBr):=1205, 3015, 1575. H NMR δ 6.86 (1H, s, H-4),
7.85 (2H, d, J=2.1, H-3’,H-5’), 7.83 (2H, d, J=2.1, H-2’-H-6’),
7.74 (1H, d, J=1.5, H-5), 7.69 (1H, d, J=1.5, H-8), 7.40-7.50
(2H, m, H-6, H-7), 3.88 (3H, s, OCH3). 13C NMR δ 55.0 (CH3),
100 (C-4), 114 (C-4a), 126 (C-2’,C-6’), 127 (C-7), 128 (C-8),
129 (C-1’), 130 (C-3’,C-5’), 134 (C-5), 137 (C-6), 153 (C-8a),
161 (C-4’), 162 (C-3), 203 (C-1). MS (70eV): m/z (%)=268
(M+,100), 107 (72), 161 (63). Anal. Calcd. For C16H12O2S: C,
71.64; H, 4.47; S, 11.94. Found. C, 71.57; H, 4.39; S, 11.87.
3-(4-Fluorobenzyl)-1H-isochromene-1-thione (2i). Rf=0.6
IR (KBr):=1194, 2960, 1610. 1H NMR δ 7.01 (1H, s, H-4), 7.73
(2H, d, J = 3.1, H-3’,5’), 7.71 (2H, d, J=3.3 H-2’,H-6’), 7.30 (4H,
m, H-5,6,7,8), 3.64 (2H, s, CH2). 13C NMR δ 68 (CH2), 107
(C-4), 114 (C-4a), 127 (C-7), 129 (C-8), 130 (C-1’), 131
(C-2’,6’), 134 (C-3’,5’), 135 (C-5), 136 (C-6), 153 (C-8a), 164
(C-4’), 167 (C-3), 176 (C-1). MS (70eV): m/z (%)=270 (M+,
100), 109 (37), 161 (62). Anal. Calcd. For C16H11OSF: C, 71.11;
H, 4.07; S, 11.85. Found. C, 71.05; H, 4.01; S, 11.78.

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A. Saeed and Z. Ashraf
Vol 45
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