A facile synthesis of β-oxothiolcarboxylates from α-oxoketenedithioacetals

Article abstract of DOI:10.1081/SCC-100104056

α-Oxoketenedithioacetals and alkenoyl ketenedithioacetals underwent facile, boron trifluoride etherate assisted partial hydrolysis in dioxane to afford β-oxothiolcarboxylates and γ,δ-unsaturated β-oxothiolcarboxylates, respectively, in good yields.

Full text of DOI:10.1081/SCC-100104056

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A FACILE SYNTHESIS OF β-
OXOTHIOLCARBOXYLATES
FROM α-
*
OXOKETENEDITHIOACETALS
a
b
Satheesh K. Nair & C. V. Asokan
a
School of Chemical Sciences, Mahatma Gandhi
University, Priyadarshini Hills P. O., Kottayam, 686
5
60, India
b
School of Chemical Sciences, Mahatma Gandhi
University, Priyadarshini Hills P. O., Kottayam, 686
60, India
5
Version of record first published: 02 Aug 2010
To cite this article: Satheesh K. Nair & C. V. Asokan (2001): A FACILE SYNTHESIS
*
OF β-OXOTHIOLCARBOXYLATES FROM α-OXOKETENEDITHIOACETALS , Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 31:10, 1453-1465
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SYNTHETIC COMMUNICATIONS, 31(10), 1453–1465 (2001)
A FACILE SYNTHESIS OF
b-OXOTHIOLCARBOXYLATES FROM
a-OXOKETENEDITHIOACETALS*
Satheesh K. Nair and C. V. Asokan{
School of Chemical Sciences, Mahatma Gandhi
University, Priyadarshini Hills P. O., Kottayam,
India 686 560
ABSTRACT
a-Oxoketenedithioacetals and alkenoyl ketenedithioacetals
underwent facile, boron trifluoride etherate assisted
partial hydrolysis in dioxane to afford b-oxothiolcarboxylates
and g,d-unsaturated b-oxothiolcarboxylates, respectively, in
good yields.
a-Oxoketenedithioacetals have been shown to be highly versatile inter-
mediates in organic synthesis. Their reductive or alkylative 1,3-carbonyl
1
–3
group transpositions proceed stereoselectively to give a,b-unsaturated
4
carboxylates and thiolcarbioxylates. a-Oxoketenedithioacetals are con-
sidered as protected b-keto esters or b-ketothiolesters and can be effectively
5
,6
transformed to b-ketoesters by acid catalyzed solvolysis.
In this
communication, we report a convenient procedure for their conversion
to b-ketothiolesters. This method has been found suitable for the prepara-
tion of g,d-unsaturated b-ketothiolesters as well.
*
Dedicated to the memory of Sajush.
Corresponding author.
{
1
453
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

1
454
NAIR AND ASOKAN
b-Ketothiolesters have been shown to be valuable synthons
for a variety of transformations. Besides the conventional reactions of
7
–9
b-ketoesters, they undergo facile transesterification reactions with various
heteronucleophiles and displacement of the alkylthio group with a-hydroxy
or a-amino carbonyl compounds, followed by cyclization, has been utilized
in the synthesis of substituted tetronic acids and tetramic acids, including
1
0–15
the naturally occurring fuligorubin A.
The methods currently available
for the preparation of b-ketothiolesters are (i) Claisen condensation of
1
6–19
aliphatic thiolesters;
acid half thiolester with acyl imidazoles; (iii) a dithiolester version of the
(ii) reaction of the magnesium salt of malonic
2
0
2
Dieckmann condensation; and (iv) the addition of sodium mercaptide to
1
2
2
diketene. The g,d-unsaturated b-ketothiolesters are usually prepared by
the Wadsworth-Emmons coupling reaction of t-butyl-4-diethylphosphono-
2
-oxobutanethioate with aldehydes or ketones. They are analogues of
3
3
Nazarov reagents, which are valuable four-carbon components in
2
4–27
Robinson annulation type reactions.
The benzoyl ketenedithioacetal 1a derived from acetophenone was
treated in non-nucleophilic solvents with different Lewis and protic acids
in the presence and absence of mercury salts. The methyl benzoyl thiolace-
tate 2a was formed in low yield under most of these conditions. However,
refluxing 1a in dioxane in the presence of an equivalent amount of boron
trifluoride etherate for 4–5h in dioxane followed by treatment with water
gave the thiolester 2a in 52% yield.
Similarly, other substituted benzoyl ketenedithioacetals 1b–e also gave
the substituted benzoyl thiolacetates 2b–e in moderate to good yields
(
Scheme 1, Table 1). The ketenedithioacetal 1f prepared from 2-acetylthio-
phene gave the corresponding thiolester 2f in 48% yield. Ketenedithioacetal
derived from cyclic ketones also underwent smooth conversion to the
respective b-ketothiolesters. Thus, the ketenedithoacetal 1g derived from
a-tetralone gave the thiolester 2g in nearly quantitative yield. The ketene-
dithioacetal 1h prepared from cyclohexanone gave a complex product
mixture under these conditions. Nevertheless, moderate yield of the thiol-
ꢀ
ester 2h was obtained on treatment of 1 h with BF Et O in dioxane at 25 C
2
3
Scheme 1.

b-OXOTHIOLCARBOXYLATES
Table 1. b-Oxothiolcarboxylates 2 Prepared
1455
a
1
,2
Substrate
Product
Yield (%)
a
Ar ¼ C
4-CH
4-ClC H
6
H
5
52
58
90
48
59
48
b
c
d
e
f
3
C
6
H
4
6
4
CH
4-BrC
2-thienyl
3 6 4
OC H
6
H
4
g
97
b
64
h
i
35
a
b
Yield of the isolated product; reaction was carried out at 25 C.
ꢀ
for 6 h, followed by work-up with water. The acetyl ketenedithioacetal 1i
also gave the methyl acetothiolacetatae 2i in 35% yield when the reaction
ꢀ
was carried out at 25 C.
The acid-catalyzed partial hydrolysis of ketenedithioacetals involves a
partially reversible protonation of the carbon-carbon double bond, followed
2
8–32
by hydration of the intermediate dithiocarbocation formed.
The Lewis-
acid assisted partial hydrolysis of acyl ketenedithioacetals could involve the
initial formation of a complex 3 with borontrifluoride etherate. Addition of
water to this complex during work-up to give 4, followed by loss of methyl-
thio group, would lead to the formation of b-oxothiolester 2 (Scheme 2).
We have extended the scope of this reaction to the preparation of
g,d-unsaturated b-oxothiolesters 6 as well (Scheme 3). Acyl ketenedithio-
acetals derived from aliphatic ketones such as acetone and ethyl methyl
ketone on Claisen-Schmidt condensation with aromatic aldehydes afford
3
3,34
5
the cinnamoyl ketene dithioacetal 5a was refluxed in dioxane, in the
-aryl-1,1-bis(methylthio)-3-oxo-1,4-pentadienes 5 in good yields.
When
presence of boron trifluoride etherate, the methyl cinnamoyl thiolacetate

1
456
NAIR AND ASOKAN
Scheme 2.
Scheme 3.
6
a was formed in 87% yield. Similarly, other substituted cinnamoyl ketene-
dithioacetals 5b–d also gave the respective thiolesters in good yields
Table 2). Similarly, the 1,1-bis(methylthio)-3-oxo-5-(2-thienyl)-1,4-penta-
(
dienone 5e and the methyl substituted cinnamoyl ketenedithioacetal 5f
also gave the respective g,d-unsaturated b-ketoesters 6e and 6f.
We have also examined the reaction with a polyenoyl ketenedithio-
acetal 7. The Claisen-Schmidt condensation of 5-aryl-2,4-pentadienaldehyde
with acetyl ketnedithioacetal gave 1,1-bis(methylthio)-3-oxo-9-phenyl-
1
,4,6,8-nonatetraene 7. Treatment of 7 with borontrifluoride etherate in
refluxing dioxane for 1.5h, followed by usual work-up, gave the thiolester
in 88% yield (Scheme 4).
8
Scheme 4.

b-OXOTHIOLCARBOXYLATES
Table 2. g,d-Unsaturated b-oxothilesters 6 Prepared
Substrate Product
1457
5
,6
Yield (%)
a
b
c
d
e
Ar=C
4-ClC H
6
H
5
87
92
65
70
90
6
4
4-NO
4-CH
2-thienyl
2 6 4
C H
3 6 4
C H
f
67
The proton NMR spectra of b-oxothiolesters prepared indicate that
they exist as a mixture of keto and enol tautomers in CDCl3.
g,d-Unsaturated b-ketothiolesters 6 and 8 exist mostly in the enol form.
In conclusion, we have developed a facile method for the partial
hydrolysis of a-oxoketenedithioacetals. The method is useful for the pre-
paration of starting from active methylene ketones in a two-step process.
g,d-Unsaturated b-ketothiolesters and conjugated polyenoyl thiolacetates
can also be prepared by this reaction in good yields.
EXPERIMENTAL
Melting points are uncorrected and were obtained on a Buch-530
melting point apparatus. IR spectra were recorded on a Schimadzu
1
13
IR-470 spectrometer. H and C NMR spectra were recorded on a Jeol
GX 90 or a Bruker WM 300 spectrometer with tetramethyl silane as the
internal standard. MS were obtained on a Finnigen-Mat 312 instrument.
Preparation of b-Oxothiolcarboxylates 2
To the acyl ketenedithioacetal 1 (10 mmol) in dioxane (30 mL), boron
trifluoride etherate (1.3 mL, 10 mmol) was added and the mixture
ꢀ
was refluxed for 2–4 h or stirred at 25 C (in the case of 1h and 1i) for 6 h.
The reaction mixture was then poured into cold water and was neutralized

1
458
NAIR AND ASOKAN
with saturated sodium bicarbonate solution. The mixture was extracted with
ether (3Â50 mL) and the combined organic layer was washed with water,
dried over anhydrous sodium sulphate, and the solvent removed under
vacuum. The residue was column chromatographed over silica gel (60–120
mesh) using hexane-ethyl acetate(50:1) as the eluent.
S-Methyl-3-oxo-3-phenylpropanethioate(2a)
Obtained as a pale yellow liquid, 1 g (52%), by the reaction of the
ketenedithioacetal 1a in refluxing dioxane for 4.5h, (keto:enol ¼ 47:53),
À1
IR(neat); ꢀ ¼ 1660, 1600(C ¼ O), 1560, 1480, 1440(C ¼ C) 1210 cm
.
1
H NMR(90 MHz, CDCl ) d ¼ 2.32(s, l.59H, SCH , enol), 2.40(s, 1.41H,
3
3
SCH , keto), 4.22(s, 0.94H, CH , keto), 6.11(s, 0.53H, vinylic, enol),
3
2
1
3
.20–8.10(m, 5H, arom), 13.19(s, 0.53H, OH, enol) ppm. C NMR
7
(
keto), 96.87(vinylic, enol)126.92, 128.43, 128.58, 131.44, 132.67, 133.59,
22.4 MHz, CDCl ) d ¼ 10.88(SCH , enol), 11.90(SCH , keto), 53.52(CH ,
3
3
3
2
1
35.83(arom, keto, and enol), 168.44(C-O, enol), 191.68, 192.19(C ¼ O,
þ
keto), 194.96(C ¼ O, enol) ppm. EIMS m/z l94(M , 7.2%), 146(49.3%),
1
C, 61.83; H, 5.19.
33(11.4%), 105(100%). Anal. found C, 61.36; H, 5.10; C H O S requires
10 10 2
S-Methyl-3-oxo-3-(4-methylphenyl)propanethioate(2b)
Obtained as a pale yellow liquid, 1.5g (58%), by the reaction of the
ketenedithioacetal 1b in refluxing dioxane for 4 h, (keto:enol ¼ 65:35),
À1
1
IR(neat); ꢀ ¼ 1678, 1600(C ¼ O), 1580, 1565(C ¼ C) 1215cm . H NMR
(
keto), 2.36(s, 3H, CH ) 4.13(s, 1.30H, CH , keto), 6.07(s, 0.35H, vinylic,
90 MHz, CDCl ) d ¼ 2.28(s, 1.05H, SCH , enol), 2.34(s, 1.95H, SCH ,
3 2
3
3
3
enol), 7.07–7.28(m, 2H, arom), 7.65(d, J ¼ 9Hz, 0.7H, arom), 7.82(d,
1
3
J ¼ 9Hz, 1.3H, arom), 13.22(s, 0.35H, OH, enol) ppm.
C NMR
22.4 MHz, CDCl ) d ¼ 10.88(SCH , enol), 11.87(SCH , keto), 21.32,
(
3
3
3
2
1
1.47(CH ) 53.46(CH , keto), 96.30(vinylic, enol), 126.26, 128.79, 129.24,
3 2
29.30, 129.84, 133.51, 142.16, 144.58(arom, keto, and enol), 168.74(C-O,
enol), 191.30, 192.31(C ¼ O, keto), 194.79(C ¼ O, enol) ppm. EIMS m/z
þ
2
08(M , 5.5%), 160(26.3%), 134(21.9%), 119(100%). Anal. found C,
3.44; H, 5.72; C H O S requires C, 61.77; H, 5.81.
6
11
12
2
S-Methyl-3-oxo-3-(4-chlorophenyl)propanethioate(2c)
Obtained as a pale yellow liquid, 2 g (90%), by the reaction of the
ketenedithioacetal 1c in refluxing dioxane for 1.5h exists as the enol form in

b-OXOTHIOLCARBOXYLATES
1459
ꢀ
ꢀ
CDCl (> 95%), m.p. 86 –87 C, IR(KBr); ꢀ ¼ 1680, 1625(C ¼ O), 1560,
3
À1
1
1
535, 1480, 1440(C ¼ C), 1390, 1210 cm
.
H NMR(90 MHz, CDCl )
3
d ¼ 2.39(s, 3H, SCH ), 6.08(s, 1H, vinylic, enol), 7.36(d, J ¼ 9Hz, 2H,
3
1
3
arom), 7.71(d, J ¼ 9Hz, 2H, arom), 13.18(s, 1H, OH, enol) ppm.
C
NMR (22.4 MHz, CDCl ) d ¼ 10.88(SCH , enol), 11.87(SCH , keto),
3
3
3
5
1
3.37(CH , keto), 96.84(vinylic, enol)127.39, 128.58, 128.79, 129.92,
2
31.00, 137.44(arom, keto, and enol), 166.89(C-O, enol), 194.84(C ¼ O,
þ
enol) ppm. EIMS m/z 228(M , 13.6%), 181(74.3%), 139(100%),
1
11(25.8%). Anal. found C, 52.26; H, 3.90; C H O ClS requires C,
10 9 2
5
2.52; H, 3.97.
S-Methyl-3-oxo-3-(4-methoxyphenyl)propanethioate(2d)
Obtained as a pale yellow liquid, l g (48%), by the reaction of the
ketenedithioacetal 1d in refluxing dioxane for 6 h (keto:enol ¼ 75:25),
À1
1
IR(neat); ꢀ ¼ 1650, 1595(C ¼ O), 1575, 1498(C ¼ C) 1220 cm
.
H
NMR(90 MHz, CDCl ) d ¼ 2.27(s, 0.75H, SCH , enol), 2.34(s, 2.25H,
3
3
SCH , keto), 3.80(s, 3H, OCH ), 4.07(s, 1.5H, CH , keto), 6.05(s, 0.25H,
3
3
2
vinylic, enol), 7.72(d, J ¼ 9Hz, 2H, arom), 7.71(d, J ¼ 9Hz, 2H, arom),
1
3
1
3.31(s, 0.25H, OH, enol) ppm.
d ¼ 10.55(SCH , enol), 11.57(SCH3,
5.04(OCH ), 95.19(vinylic, enol), 124.43, 127.77, 128.64, 130.73 (arom,
C NMR (22.4 MHz, CDCl )
3
keto),
53.07(CH2,
keto),
3
5
3
keto, and enol), 168.29(C-O, enol), 189.86, 192.19(C ¼ O, keto),
1
requires C, 58.85; H, 5.35.
94.22(C ¼ O, enol) ppm. Anal. found C, 58.62; H, 5.30; C H O S
1
1
12
3
S-Methyl-3-oxo-3-thienylpropanethioate(2e)
Obtained as pale yellow liquid, 0.96 g(48%), by the reaction
of ketenedithioacetal 1e in refluxing dioxane for 4 h (keto:enol ¼ 47:53),
À1
1
IR(neat); ꢀ ¼ 1650, 1615(C ¼ O), 1540, 1420(C ¼ C) 1215cm . H NMR
(
keto), 4.08(s, 1.86H, CH , keto), 5.95(s, 0.07H, vinylic, enol),
400 MHz, CDCl ) d ¼ 2.22(s, 2.79H, SCH , enol), 2.29(s, 0.21H, SCH ,
2
3
3
3
6
7
7
.89–7.02(m, 0.07H, arom, enol), 7.02–7.09(m, 0.93H, arom, keto),
.39–7.42(m, 0.07H, arom, enol), 7.45–7.51(m, 0.07H, arom, enol),
.58–7.62(m, 0.93H, arom, keto), 7.67–7.78(m, 0.93H, arom, keto) ppm.
C NMR (100.4 MHz, CDCl ) d ¼ 11.97(SCH , keto), 54.14(CH , keto),
1
3
3
3
2
9
1
5.88(vinylic, enol)128.00, 128.24, 128.57, 130.11, 133.73, 135.15, 136.41,
42.95(arom, keto, and enol), 163.33(C-O, enol), 184.04, 191.66(C ¼ O,
keto) ppm. Anal. found C, 47.88; H, 3.97; C H O S requires C, 47.98;
2 2
1
0
9
H, 4.03.

1
460
NAIR AND ASOKAN
S-Methyl-3,4-dihydro-1(2H)-napthalenone-2-thiocarboxylate(2f )
Obtained as a yellow solid, 2.14 g (97%), by the reaction of the
ketenedithioacetal 1f in refluxing dioxane for 2 h, exists as the enol form
ꢀ
in CDCl (>95%), m.p. 56–58 C, IR(KBr); ꢀ ¼ 3450, 1680, 1610(C ¼ O),
3
À1
1
1
550, 1445(C ¼ C), 1250, 1110 cm
.
H
NMR(90 MHz, CDCl )
3
d ¼ 2.38(s, 3H, SCH ), 2.52–2.95(m, 4H, CH ), 7.08–7.35(m, 3H, arom),
3
2
1
3
7
.72–7.90(m, 1H, arom), 13.40(s, 1H, OH, enol) ppm.
C NMR
(
22.4 MHz, CDCl ) d ¼ 11.06(SCH ), 21.29, 27.62(CH ), 61.21(CH, keto),
3
3
2
1
1
3
6
05.52(vinylic, enol), 126.52, 127.15, 129.51, 130.76, 138.40(arom),
62.59(C-O, enol), 196.10(C ¼ O), 194.96 ppm. EIMS m/z 220(M ,
þ
4.5%), 173(100%), 145(47%), 115(90.9%), 105(60.9%). Anal. found C,
5.22; H, 5.36; C H O S requires C, 65.37; H, 5.44.
12
12
2
S-Methyl cyclohexanone-2-thiolcarboxylate(2g)
Obtained as a pale yellow liquid, 1.10 g (64%), by the reaction of the
ketenedithioacetal 1g in refluxing dioxane for 5.5 h, exists as the enol
form (> 95%) in CDCl , IR(neat); ꢀ ¼ 1620(C ¼ O), 1560, 1440(C ¼ C),
3
1
À1
1
2
320, 1245, 1160 cm . H NMR(90 MHz, CDCl ) d ¼ 1.65(m, 4H, CH ),
3 2
3
2
1
.26(m, 7H, SCH and CH ), 13.05(s, 1H, OH, enol) ppm. C NMR
3
(
1
6
22.4 MHz, CDCl ) d ¼ 10.79(SCH ), 21.20, 22.28, 22.43, 29.08(CH ),
3
3
2
06.53(vinylic) 170.20(C-O), 196.87(C ¼ O) ppm. Anal. found C, 55.62; H,
.88; C H O S requires C, 55.79; H, 7.02.
1
0
10
2
S-Methyl-3-oxo-butanethioate(2h)
Obtained as a pale yellow liquid, 0.46 g (35%), by the reaction of the
ketenedithioacetal 1h in dioxane at room temperature for 5.5 h, exists as the
ketoform in CDCl (> 95%), IR(neat); ꢀ ¼ 1710, 1670(C ¼ O), 1640, 1550,
3
À1
1
1
(
210, 1090 cm . H NMR(90 MHz, CDCl )d ¼ 2.31(s, 1.3H, SCH ), 2.44
3 2 3
3
3
1
s, 3H, CH , keto), 3.78(s, 2H, CH ) ppm. C NMR(22.4 MHz, CDCl )
3
d ¼ 11.08(SCH , enol), 11.92(SCH , keto), 21.42(CH , enol), 29.32(CH ,
3
3
3
3
keto), 58.16(CH , keto), 100.78(vinylic, enol), 174.98(C-O, enol), 194.23
2
(
6
C ¼ O) ppm. Anal. found C, 45.36; H, 5.93; C H O S requires C, 45.44; H,
5
8
2
.10.
Preparation of g,d-Unsaturated b-Oxothiolcarboxylates, 6
To the alkenoyl ketenedithioacetals 5 (10 mmol) in dioxane, boron
trifluoride etherate (1.3 mL, 10 mmol) was added and the mixture was

b-OXOTHIOLCARBOXYLATES
1461
refluxed for 2–3 h. The reaction mixture was poured into cold water,
neutralized with saturated sodium bicarbonate solution, and extracted
with ether(3 Â 50 mL). The combined organic layer was washed with
water, dried over anhydrous sodium sulphate, and evaporated under
vacuum. The residue was column chromatographed over silica gel using
hexane ethylacetate(50:2) as the eluent.
S-Methyl-3-oxo-5-phenyl-4-pentenethioate(6a)
Obtained as a pale yellow solid, 1.91 g (87%), by the reaction of the
ketenedithioacetal 5a in refluxing dioxane for 2 h, (keto:enol ¼ 25:75), m.p.
ꢀ
ꢀ
5
1
3
0
6
6 –58 C, IR(KBr); ꢀ ¼ 3400, 1635(C ¼ O), 1580, 1440, 1415(C ¼ C), 1260,
À1
3 3
1
170, 1080 cm
.
H NMR(90 MHz, CDCl ) d ¼ 2.35(s, 3H, SCH ),
.91(s, 0.5H, CH , keto), 5.60(s, 0.75H, vinylic, enol), 6.40(d, J ¼ 16Hz,
2
.25H, vinylic, keto), 6.78(d, J ¼ 16Hz, 0.75H, vinylic, enol), 7.18–7.63(m,
1
3
H, arom and vinylic), 12.52(s, 0.75H, OH, enol) ppm.
C NMR
(
22.4 MHz, CDCl ) d ¼ 10.64(SCH , enol), l1.75(SCH , keto), 55.33(CH ,
3
3
3
2
keto), 101.10(vinylic, enol), 120.97, 124.73, 127.36, 128.25, 128.49, 128.61,
29.24, 130.58, 133.71, 134.85, 138.13, 144.57(arom and vinylic, keto, and
1
enol), 165.96(C-O, enol), 190.70, 191.92(C ¼ O, keto), 194.37(C ¼ O, enol)
þ
ppm. ELMS m/z 220(M , 19.8%), 173(79.9%), 131(100%), 115(15.3%),
03(50.4%). Anal. found C, 65.32; H, 5.46; C H O S requires C, 65.43;
10 10 2
1
H, 5.49.
S-Methyl-3-oxo-5-(4-chlorophenyl)-4-pentenethioate(6b)
Obtained as a pale yellow solid, 2.30 g (92%), by the reaction of the
ketenedithioacetal 5b in refluxing dioxane for 2 h, exists in the enol
ꢀ
ꢀ
À1
form(>95%), m.p. 122 –123 C, IR(KBr); ꢀ ¼ 1630(C ¼ O), 1580,
1
1
3
7
440(C ¼ C), 1260, 1080, 800 cm . H NMR(90 MHz, CDCl ) d ¼ 2.38(s,
3
H, SCH ), 5.59(s, 1H, vinylic, enol), 6.28(d, J ¼ 16Hz, 1H, vinylic),
3
.22–7.58(m, 5H, arom and vinylic), 12.49(s, 1H, OH, enol) ppm.
1
3
C NMR (22.4 MHz, CDCl ) d ¼ 11.00(SCH ), 101.64(vinylic), 121.87,
3
3
1
(
28.73, 129.06, 129.68, 133.71, 135.35, 136.96(arom and vinylic), 165.81
þ
C-O, enol), 194.87(C ¼ O) ppm. EIMS m/z 254(M , 12.1%), 207(58.5%),
1
4
65(100%), 137(28.5%), 127(3.9%), 75(26.8%). Anal. found C, 56.48; H,
.26; C H O ClS requires C, 56.58; H, 4.35.
1
2
11
2

1
462
NAIR AND ASOKAN
S-Methyl-3-oxo-5-(4-nitrophenyl)-4-pentenethioate(6c)
Obtained as a yellow solid, 1.73 g (65%), by the reaction of the
ketenedithioacetal 5c in refluxing dioxane for 3.5h, exists as the enol form
ꢀ
ꢀ
in CDCl (>95%), m.p. 159 –160 C, IR(KBr); ꢀ ¼ 1640(C ¼ O), 1600,
3
À1
1
1
3
7
515(C ¼ C) 1340, 1260 cm
.
H NMR(90 MHz, CDCl ) d ¼ 2.35(s,
3
H, SCH ), 5.67(s, 1H, vinylic), 6.46(d, J ¼ 16Hz, 1H, vinylic),
3
.10–8.10(m, 5H, arom and vinylic), 12.52(s, 1H, OH, enol) ppm. Anal.
found C, 54.26; H, 4.10; N, 5.28; C H NO S requires C, 54.33; H, 4.18;
1
2
11
4
N, 5.28.
S-Methyl-3-oxo-5-(4-methoxyphenyl)-4-pentenethioate(6d)
Obtained as a pale yellow solid, 1.75g (70%), by the reaction of the
ketenedithioacetal 5d in refluxing dioxane for 2.5h, (keto:enol ¼ 50:50), m.p.
ꢀ
ꢀ
8
1
3
6
2 –83 C, IR(KBr); ꢀ ¼ 1630(C ¼ O), 1580, 1550(C ¼ C) 1265, 1170,
À1
3 3
1
080 cm . H NMR(90 MHz, CDCl ) d ¼ 2.33(s, 3H, SCH ), 3.69–3.71(m,
H, OCH ), 3.82(s, 1H, CH , keto), 5.51(s, 0.5H, vinylic, enol),
3
2
.18(d, J ¼ 17Hz, 1H, vinylic), 6.90(d, J ¼ 9 Hz, 2H, arom), 7.28–7.58(m, 3H,
1
3
arom and vinylic), 12.50(s, 0.5H, OH, enol) ppm. C NMR (22.4 MHz,
CDCl3) d ¼ 10.70(SCH , enol), 11.84(SCH3, keto), 55.42(OCH3),
3
5
1
1
5.56(CH , keto), 100.48(vinylic, enol), 118.56, 122.55, 126.43, 127.69,
2
29.03, 130.16, 138.04, 144.63, 166.68(arom and vinylic, keto and enol),
60.68(C-O, enol), 190.70(C ¼ O, keto), 194.25(C ¼ O, enol) ppm. EIMS
þ
m/z 250(M , 27.4%), 203(64.1%), 161(100%), 133(41.2%), 131(8%).
Anal. found C, 62.28; H, 5.55; C H O S requires C, 62.38; H, 5.64.
1
3
14
3
S-Methyl-3-oxo-5-thienyl-4-pentenethioate(6e)
Obtained as a pale yellow solid, 2.03 g (90%), by the reaction of the
ketenedithioacetal 5e in refluxing dioxane for 2 h, exists as the enol form
ꢀ
ꢀ
in CDCl (>95%), m.p. 62 –63 C, IR(KBr); ꢀ ¼ 1625(C ¼ O), 1580, 1500,
3
À1
1
1
3
6
410(C ¼ C), 1265, 1215, 1080 cm . H NMR(90 MHz, CDCl ) d ¼ 2.30(s,
3
H, SCH ), 5.50(s, 1H, vinylic, enol), 6.l0(d, J ¼ 16 Hz, 1H, vinylic),
3
1
.92–7.78(m, 4H, arom and vinylic), 12.53(s, 1H, OH) ppm. C NMR
3
(
keto), 100.86(vinylic, enol), 120.02, 123.36, 127.42, 127.80, 128.10, 129.42,
22.4 MHz, CDCl ) d ¼ 10.70(SCH , enol), 11.78(SCH , keto), 55.40(CH ,
3
3
3
2
1
1
30.88, 132.16, 136.90, 139.08, 140.36(arom and vinylic, keto and enol),
65.64(C-O, enol), 190.07, 191.92(C ¼ O, keto), 194.19(C ¼ O, enol) ppm.

b-OXOTHIOLCARBOXYLATES
1463
þ
EIMS m/z 226(M , 12.6%), 179(47.1%), 137(100%), 123(7.6%). Anal.
found C, 52.97; H, 4.39; C H O S requires C, 53.07; H, 4.45.
1
0
10
2 2
S-Methyl-2-methyl-3-oxo-5-phenyl-4-pentenethioate(6f )
Obtained as a pale yellow solid, 1.57 g (67%), by the reaction of the
ketenedithioacetal 5f in refluxing dioxane for 2 h, exists as the enol form in
ꢀ
ꢀ
CDCl (>95%), m.p. 67 –68 C, IR(KBr); ꢀ ¼ 1630(C ¼ O), 1580, 1550,
3
À1
1
1
440(C ¼ C) 1260, 1210 cm . H NMR(90 MHz, CDCl ) d ¼ 2.10(s, 3H,
3
CH ), 2.34(s, 3H, SCH ), 6.85(d, J ¼ 16 Hz, 1H, vinylic), 7.28–7.72(m, 6H,
3 3
1
arom and vinylic), 13.50(s, 1H, OH, enol) ppm. C NMR (22.4 MHz,
3
CDCl ) d ¼ 11.51(CH ), 11.78(SCH ), 105.79 (vinylic), 127.63, 128.79,
3
3
3
1
1
28.91, 129.36, 135.80, 138.52, (arom and vinylic), 166.10(C-O, enol),
98.19(C ¼ O) ppm. EIMS m/z 234(M , 21.4%), 186(86.8%), 131(100%),
þ
1
C, 65.64; H, 6.02.
28(8.7%), 115(7.1%). Anal. found C, 66.56; H, 5.95; C H O S requires
1
3
14
2
S-Methyl-3-oxo-9-phenyl-4,6,8-nonatrienethioate(8)
Obtained as a pale yellow solid, 2.5g (88%), by the reaction of the
ketenedithioacetal 7 in refluxing dioxane for 1.5h, exists as the enol form in
ꢀ
ꢀ
CDCl (>95%), m.p. 108 –110 C, IR(KBr); ꢀ ¼ 3400(OH), 1635(C ¼ O),
3
À1
1
1
595, 1570, 1550(C ¼ C), 1080, 1000 cm . H NMR(300 MHz, CDCl )
3
3
d ¼ 2.29(s, 3H, SCH ), 5.43(s, 1H, vinylic), 5.74(d, J ¼ 15Hz, 1H, vinylic),
6
.30–6.84(m, 4H, vinylic), 7.10–7.36(m, 6H, arom and vinylic), 12.33
1
3
(
enol), 11.50(SCH , keto), 54.82(CH , keto), 100.15(vinylic, enol), 125.72,
s, 0.75H, OH) ppm. C NMR (75.47 MHz, CDCl ) d ¼ 10.02(SCH ,
3 2
3
3
1
1
27.34, 127.71, 127.98, 134.97, 138.23, 142.36(arom and vinylic),
65.37(C-O, enol), 190.01, 191.57(C ¼ O, keto), 193.54(C ¼ O, enol) ppm.
Anal. found C, 70.46; H, 5.83; C H O S requires C, 70.56; H, 5.92.
1
0
10
2
ACKNOWLEDGMENTS
We are indebted to DST and CSIR, Government of India, for
financial support (Research Projects SP/S1/G-24/91 and 01(1324)94).
SKN thanks UGC for a Junior Research Fellowship. We thank the direc-
tors of the Regional Sophisticated Instrumentation centers at IIT Madras,
NEHU Shillong, and CDRI Lucknow for providing spectral and analytical
data.

1
464
NAIR AND ASOKAN
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1
2
3
4
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9
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1
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2
2
2
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b-OXOTHIOLCARBOXYLATES
1465
3
0. Okuyama, T.; Kawao, S.; Fujiwara, W.; Fueno, T. J. Org. Chem. 1984,
9, 89.
4
1. Okuyama, T.; Kawao, S.; Fueno, T. J. Org. Chem. 1984, 49, 85 .
3
3
3
3
2. Okuyama, T. J. Am. Chem. Soc. 1984, 106, 7134.
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Received in the UK September 7, 1998