Regioselective synthesis of functionalized 3,5-diketoesters and 2,4-diketosulfones by uncatalyzed condensation of 1-methoxy-1,3- bis(trimethylsilyloxy)-1,3-butadienes with α,β-unsaturated acid chlorides and sulfonyl chlorides

Article abstract of DOI:10.1039/b810151e

The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadienes with α,β-unsaturated and functionalized acid chlorides afforded a variety of 3,5-diketoesters which are not readily available by other methods. The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadiene with sulfonyl chlorides allows a direct synthesis of 2,4-diketosulfones. This journal is

Full text of DOI:10.1039/b810151e

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Regioselective synthesis of functionalized 3,5-diketoesters and
2,4-diketosulfones by uncatalyzed condensation of
1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadienes with
a,b-unsaturated acid chlorides and sulfonyl chlorides†
Thomas Rahn,a,b T. H. Tam Dang,a,b Anke Spannenberg,b Christine Fischerb and Peter Langer*a,b
Received 16th June 2008, Accepted 26th June 2008
First published as an Advance Article on the web 25th July 2008
DOI: 10.1039/b810151e
The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadienes with a,b-unsaturated and
functionalized acid chlorides afforded a variety of 3,5-diketoesters which are not readily available by
other methods. The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadiene with sulfonyl
chlorides allows a direct synthesis of 2,4-diketosulfones.
Introduction
1,3,5-Tricarbonyl derivatives and their higher homologues are of
considerable pharmacological relevance and occur in a variety
of natural products (polyketides). In addition, they are versatile
synthetic intermediates.1 Important syntheses of polyketides rely
on the condensation of 1,3-dicarbonyl dianions2 with carboxylic
acid derivatives.3–5 However, there are several drawbacks, such
as proton transfer and O-acylation. In addition, functionalized
substrates, such as a,b-unsaturated esters, cannot be successfully
used, due to various side-reactions (e.g. conjugate addition of
the dianion onto the double bond of the substrate). In fact,
the preparative scope is limited to substrates which tolerate the
presence of strong nucleophiles and bases. The employment of N-
acyl-2-methylaziridines6 and Weinreb amides7 allow some of these
Scheme
1
Possible mechanism of the reaction of 1-methoxy-1,3-
problems to be addressed.
bis(trimethylsilyloxy)-1,3-butadiene 1a with benzoyl chloride (2a).8 Con-
ditions: i: 1) CH2Cl2, −78 → 20 ◦C, 2) NaHCO3, H2O; keto : enol = 0 :
100.
Recently, we reported8 the condensation of 1,3-bis(silyl enol
ethers)9 with acid chlorides. This strategy provides a convenient
approach to several 1,3,5-tricarbonyl compounds under mild
conditions. In our previous paper8 we focussed on reactions of
1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadiene (1a), readily
available from methyl acetoacetate,10 with various simple aromatic
and aliphatic acid chlorides. For example, the reaction of 1a with
benzoyl chloride (2a) afforded 3,5-dioxoester 3a in good yield
(Scheme 1). Product 3a mainly exists in its enol tautomeric form.
The dashed line given in the structure of 3a indicates that there is
a fast equilibrium between two enolic forms. In fact, only one set
of signals is observed by NMR. This type of fast equilibrium is
also observed in case of acetylacetone.
of 1a onto the acid chloride. This step might be catalyzed by
the presence of a catalytic amount of HCl present in the acid
chloride (formed by its hydrolysis). The reaction works equally
well using commercially available (new bottle) or freshly distilled
2a. The yields significantly dropped when relatively old material
was employed. Due to the preparative utility of this reaction,
we studied its scope in more detail and the results of our
efforts are reported herein. The present study includes, for the
first time, the variation of the 1-methoxy-1,3-bis(silyloxy)-1,3-
butadiene and of the acid chloride (including unsaturated and
functionalized derivatives and sulfonic acid chlorides). Note, the
products reported herein are not available by direct reaction of
1,3-dicarbonyl dianions with carboxylic acid derivatives.
It is of note that it proved to be important that the reaction
was carried out in the absence of a Lewis acid. The formation
of 3a can be explained by attack of the terminal carbon atom
aInstitut fu¨r Chemie, Universita¨t Rostock, Albert-Einstein-Str. 3a, 18059,
Rostock, Germany. E-mail: peter.langer@uni-rostock.de; Fax: +49 381
49864112; Tel: +49 381 4986410
Results and discussion
Variation of the 1,3-bis(trimethylsilyloxy)-1,3-butadiene
bLeibniz-Institut fu¨r Katalyse e. V. an der Universita¨t Rostock, Albert-
Einstein-Str. 29a, 18059, Rostock, Germany
The reaction of benzoyl chloride (2a) with 1-alkoxy-1,3-
bis(silyloxy)-1,3-butadienes 1b and 1c, containing a substituent
located at the central carbon atom, afforded the 3,5-dioxoesters
† Electronic supplementary information (ESI) available: Full experimental
details. CCDC reference number 691729. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/b810151e
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Table 1 Synthesis of 1,3,5-tricarbonyl compounds 3b,c
Table 3 Synthesis of 6,7-unsaturated 3,5-dioxoesters 5a–m
a
5
R1
R2
R3
%
a
3
R1
R2
Keto : enol
%
a
b
c
d
e
f
g
h
i
H
H
H
H
H
H
H
H
H
H
H
Me
H
Ph
Ph
H
Me
H
H
H
H
H
H
H
H
H
H
H
71
63
17
37
35
30
20
14
13
30
30
71
47
b
c
Me
Et
Et
Me
87 : 13
67 : 33
43
50
4-MeC6H4
4-(MeO)C6H4
3,4-(MeO)2C6H3
3,4-(–OCH2O–)C6H3
4-FC6H4
3-ClC6H4
4-(O2N)C6H4
2-Furyl
a Yields of isolated products; the products contain benzoic acid which
could not be separated (see Experimental section) Conditions: i: CH2Cl2,
−78 → 20 ◦C, 2) NaHCO3, H2O.
Table 2 Synthesis of 1,3,5-tricarbonyl compounds 3d,e
j
k
l
2-Thienyl
Me
CH3CH CH
=
m
a Yields of isolated products; keto : enol = 0 : 100 for all products
Conditions: i: 1) CH2Cl2, −78 → 20 ◦C, 2) NaHCO3, H2O.
seems to be restricted to b-ketoester-derived and unsubstituted
1,3-bis(silyl enol ethers), such as 1a.
a
3
Ar
keto : enol
%
d
e
Ph
100 : 0
100 : 0
32
35
Variation of the acid chloride
4-(NO2)C6H4
a Yields of isolated products; the products contain benzoic or 4-
nitrobenzoic acid which could not be separated (see Experimental section)
Conditions: i: 1) CH2Cl2, −78 → 20 ◦C, 2) NaHCO3, H2O.
The reaction of 1,3-bis(silyloxy)-1,3-butadiene 1a with a,b-
unsaturated acid chlorides 4a–m afforded the 6,7-unsaturated
3,5-dioxoesters 5a–m (Table 3). All products exclusively exist in
their enol tautomeric form. Similar to compound 3a, a rapid
equilibrium between two enolic structures is present. Therefore,
only one set of signals is observed by NMR. The best yields
were obtained for phenyl- and methoxyphenyl-substituted acrylic
acid chlorides. Good yields were obtained also for 5l and 5m
which were prepared from 3-methylbutanoyl chloride and hexa-
2,4-dienoic acid chloride, respectively. To our surprise, the yields of
the products derived from aryl-substituted acrylic acid chlorides
very much depend on the type of the aryl group. Whereas a good
yield was obtained for products 5a,b (containing a phenyl group),
the yields dropped for electron-rich and (even more) for electron-
poor aryl groups.
In contrast, we have reported earlier that equally good yields
were obtained for the reaction of 1a with electron-rich and
electron-poor benzoyl chlorides. The yields dropped for steri-
cally encumbered acid chlorides. The reaction of 1a with 2-
fluorobenzoyl chloride (6), carried out for reasons of compari-
son, gave the 5-(2-fluorophenyl)-3,5-dioxoester 7 in good yield
(Scheme 2). The use of heterocyclic substrates has not been
studied in our previous report. The reaction of 1a with (thien-
2-yl)carboxylic chloride (8), carried out again for reasons of
comparison, afforded the 5-(thien-2-yl)-3,5-dioxoester 9 in good
yield (Scheme 3). These results show that the reaction of 1,3-
bis(silyloxy)-1,3-butadienes with a,b-unsaturated acid chlorides is
much more prone to slight changes of the substitution pattern
compared to the reaction with simple benzoyl chlorides. It is
noteworthy, that relatively good yields were obtained for products
3b and 3c, respectively (Table 1). However, a considerable amount
of benzoic acid could not be separated from the product. The
presence of benzoic acid might be explained by the instability of
the products which presumably undergo a retro-Claisen reaction
during silica gel chromatography or during the reaction. In
contrast to the unsubstituted diketoester 3a, products 3b,c mainly
exist in their keto forms.
The reaction of benzoyl chlorides 2a,b with 1-methoxy-
1,3-bis(silyloxy)-1,3-butadiene 1d, derived from methyl 3-
oxopentanoate, afforded 1,3,5-tricarbonyl compounds 3d and 3e.
The products again contained benzoic acid which could not be
separated (Table 2). The ethyl ester analogue of 3d has been
previously reported.6 Products 3d,e exclusively reside in their keto
form. This is not unexpected as the presence of a substituent
located between the two carbonyl groups of 1,3-diketones usually
results in a considerable increase of the amount of the keto
tautomer.
The reaction of 2a with 1-phenyl-1,3-bis(trimethylsilyloxy)-1,3-
butadiene and 2,4-bis(trimethylsilyloxy)-1,3-pentadiene, derived
from benzoylacetone and acetylacetone, respectively, proved to
be unsuccessful (no conversion). This is a result of the lower
reactivity of 1,3-diketone- compared to b-ketoester-derived 1,3-
bis(silyl enol ethers). Due to these limitations, the variation of
the 1,3-bis(silyloxy)-1,3-butadiene was not further studied. Taking
into account the results of our previous study in this field,8
the condensation of 1,3-bis(silyl enol ethers) with acid chlorides
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Table 4 Synthesis of 3-oxo-sulfonylesters 13a–p
Scheme 2 Synthesis of 5-(2-fluorophenyl)-3,5-dioxoester 9 Conditions: i:
1) CH2Cl2, −78 → 20 ◦C, 2) NaHCO3, H2O; keto : enol = 0 : 100.
13
R
keto : enol
% (13)a
a
b
c
d
e
f
g
h
j
Ph
60 : 40
78 : 22
60 : 40
67 : 33
60 : 40
33 : 67
60 : 40
75 : 25
60 : 40
55 : 45
60 : 40
50 : 50
55 : 45
55 : 45
100 : 0
100 : 0
100 : 0
61
87
99
38
17
89
78
33
61
20
6
14
6
12
10
20
15
4-MeC6H4
4-iPrC6H4
4-tBuC6H4
4-PhC6H4
4-(MeO)C6H4
3,4-(MeO)2C6H3
2-Naph
4-ClC6H4
4-FC6H4
2,5-Cl2C6H3
4-Cl-3-FC6H3
4-BrC6H4
4-(MeCO)C6H4
Me
Scheme 3 Synthesis of 5-(thien-2-yl)-3,5-dioxoester 9 Conditions: i: 1)
CH2Cl2, −78 → 20 ◦C, 2) NaHCO3, H2O; keto : enol = 0 : 100.
k
l
5l and 5m containing a methyl and a (prop-1-en-1-yl) group,
respectively.
m
n
o
p
q
r
Some years ago, we reported the synthesis of 3(2H)furanones
based on reactions of 1,3-bis(silyl enol ethers) with chloroacetyl
chloride.11 The reaction of 1,3-bis(silyloxy)-1,3-butadiene 1a with
3-chloropropanoyl chloride (10a) and 4-chlorobutanoyl chloride
(10b) proceeded with very good chemoselectivity and afforded the
x-chloro-3,5-dioxoesters 11a and 11b, respectively, in very good
yields (Scheme 4). It is of note that the reaction of the dianion
of methyl acetoacetate with 10a and 10b and their corresponding
ester derivatives failed. Compounds 7, 9, and 11a,b exclusively
exist in their enol tautomeric form.
nBu
nOct
a Yields of isolated products Conditions: i: 1) CH2Cl2, −78 → 20 ◦C, 2)
NaHCO3, H2O.
yields were again obtained when the reactions were carried out
in the absence of Lewis acid. The reaction of 1a with phenyl-
sulfonyl chloride (12a) and its alkyl-substituted derivatives 12b–
d afforded the 3-oxo-4-sulfonylesters 13a–d in good to excellent
yield (Table 4). In contrast, the yield of biphenyl derivative 13e
was rather low. The condensation of 1a with methoxy-substituted
phenylsulfonyl chlorides 12f,g gave products 13f,g in very good
yields. 3-Oxo-4-sulfonylester 13h was prepared in moderate yield
from 2-naphthylsulfonyl chloride. The reactions of 1a with 1-
naphthylsulfonyl chloride (12i) failed, presumably due to steric
reasons. The reaction of 1a with halogen-substituted phenyl-
sulfonyl chlorides gave the 3-oxo-4-sulfonylester 13j–n. Except
from 4-chlorophenyl-derivative 13j (61%), the yields were rather
low. The great difference between the yields of 4-chlorophenyl
and 4-bromophenyl derivatives 13j and 13n is surprising. The
results are reproducible but cannot convincingly be explained at
present. The individual quality of the sulfonyl chlorides may have
a considerable influence on the reactions. The reaction of 1a with
(4-acetylphenyl)sulfonyl chloride gave 13o, albeit, in low yield. The
arylsulfones 13a–o exist as mixtures of keto-enol-tautomers. The
condensation of 1a with alkylsulfonyl chlorides 12p–r afforded
products 13p–r in low yields. These products exclusively exist in
their keto form.
Scheme 4 Synthesis of 11a,b Conditions: i: 1) CH2Cl2, −78 → 20 ◦C, 2)
NaHCO3, H2O; keto : enol = 0 : 100 for both products.
The reaction of enolates with sulfonyl chlorides was previously
reported to result in chlorination rather than formation of
b-ketosulfones.12,13 b-Ketosulfones are available by reaction of
enolates with disulfides and subsequent oxidation of the sulfide
moiety.14 Kamigata et al. reported the synthesis of b-ketosulfones
by Ru(PPh3)2Cl2-catalyzed reaction of silyl enol ethers with
sulfonyl chlorides.15 However, the scope of this method is limited to
acetophenone-derived silyl enol ethers. Other reactions of silyl enol
ethers with sulfonyl chlorides have, to the best of our knowledge,
not been reported to date.
Our starting point was the reaction of the dianion of methyl
acetoacetate with tosyl chloride which resulted in the formation
of complex mixtures under various conditions. In contrast,
the reaction of 1,3-bis(silyloxy)-1,3-butadiene 1a with sulfonyl
chlorides proved to be, in principle, possible. However, the yields
strongly depended on the type of substrate employed. The best
The structures of all products were confirmed by spectroscopic
methods. The structure of 13j was independently confirmed by
X-ray crystal structure analysis (Fig. 1).†
Conclusions
In conclusion, we have reported the synthesis of 3-oxo-
5-hydroxy-hepta-4,6-dienoates by reaction of 1-methoxy-1,3-
bis(trimethylsilyloxy)-1,3-butadiene with a,b-unsaturated acid
chlorides. The reaction of 1-methoxy-1,3-bis(trimethylsilyloxy)-
1,3-butadiene with sulfonyl chlorides provides a convenient
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Methyl 3,5-dioxo-5-(thiazol-2-yl)pentanoate (9)
Starting with 8 (0.84 g, 5.76 mmol), CH2Cl2 (10 ml) and 1,3-
bis(silyl enol ether) 1a (3.00 g, 11.52 mmol), 9 was isolated as a
1
brownish oil (0.80 g, 61%). H-NMR (300 MHz, CDCl3, keto :
enol = 0 : 100): d = 3.43 (s, 2H, CH2), 3.77 (s, 3H, CH3), 6.15 (s,
1H, CH), 7.14 (dd, 3J = 5.0 Hz, 3J = 3.8 Hz, 1H, CH), 7.63 (dd,
3J = 5.0 Hz, J = 1.2 Hz, 1H, CH), 7.72 (dd, J = 3.8 Hz, J =
1.2 Hz, 1H, CH), 15.49 (s, 1H, OH). 13C-NMR (75 MHz, CDCl3):
d = 44.0 (CH2), 52.8 (CH3), 97.3, 128.7, 131.2, 133.3 (CH), 141.0
(C), 168.4, 181.4, 182.8 (CO). IR (neat, cm−1): m = 3106 (m), 3001
(w), 2953 (m), 2845 (w), 1742 (s), 1618 (s, br), 1519 (s), 1436 (s),
1412 (s), 1353 (m), 1272 (s, br), 1156 (m), 1084 (m), 1067 (m), 1015
(m), 948 (m), 861 (m), 789 (m), 727 (m). MS (EI, 70 eV) m/z = 226
(M+, 13.9), 194 (19.5), 166 (24.3), 153 (40.4), 111 (100), 69 (40.6).
HRMS (EI, 70 eV): calcd. for C10H10O4S (M+) 226.0294, found
226.0298.
4
3
4
Fig. 1 Ortep plot of 13j (50% probability level).
approach to 4-arylsulfonyl-3-ketobutanoates. It is worth noting
that the products reported herein are not available by direct reac-
tion of 1,3-dicarbonyl dianions with carboxylic acid derivatives.
Experimental section
Methyl 7-chloro-5-hydroxy-3-oxohept-4-enoate (11a)
General comments
Starting with 10a (0.55 ml, 5.76 mmol) dissolved in CH2Cl2 (10 ml)
and 1a (3.00 g, 11.52 mmol), 11a was isolated as a yellow oil (0.88 g,
74%). 1H-NMR (300 MHz, CDCl3, keto : enol = 0 : 100): d = 2.80
All solvents were dried by standard methods and all reactions
were carried out under an inert atmosphere. For 1H and 13C
NMR spectra the deuterated solvents indicated were used. Mass
spectrometric data (MS) were obtained by electron ionization (EI,
70 eV), chemical ionization (CI, H2O) or electrospray ionization
(ESI). For preparative scale chromatography, silica gel (60–
200 mesh) was used. Melting points are uncorrected.
3
(t, J = 6.6 Hz, 2H, CH2), 3.38 (s, 2H, CH2), 3.75 (s, 3H, CH3),
3.76–3.78 (m, 2H, CH2), 5.68 (s, 1H, CH), 14.93 (s, 1H, OH). 13C-
NMR (75 MHz, CDCl3): d = 39.4, 41.1, 44.8 (CH2), 52.8 (CH3),
101.2 (CH), 168.1, 186.4, 189.8 (CO). IR (neat, cm−1): m = 3002
(m), 2956 (s), 2848 (m), 1742 (s), 1617 (s, br), 1437 (s), 1407 (m),
1331 (s), 1263 (s), 1157 (s), 1015 (m), 922 (m), 785 (m, br). MS (EI,
70 eV) m/z = 206 (M+, 8.2), 174 (17.9), 146 (10.4), 143 (73.6), 139
(13.1), 135 (13.8), 133 (41.1), 116 (16.9), 111 (20.3), 101 (67.0), 97
(26.3), 93 (14.4), 91 (43.0), 84 (16.2), 69 (100). HRMS (EI, 70 eV):
calcd. for C8H11O4Cl (M+) 206.0340, found 206.0342.
General procedure for the synthesis of 3,5-dioxoalkanoates 3, 5, 7,
9, and 11
To a CH2Cl2 solution of 1 (2.0 equiv.) was slowly added the acid
chloride (1.0 equiv.) at −78 ◦C. The reaction mixture was slowly
warmed to 20 ◦C during 6 h and the solution was stirred at 20 ◦C
for further 6–8 h. To the solution was added a saturated aqueous
solution of NaHCO3 (20 mL). The organic and the aqueous layer
were separated and the latter was extracted with CH2Cl2 (3 ×
10 mL). The combined organic layers were dried (Na2SO4), filtered
and the filtrate was concentrated in vacuo. The residue was purified
by column chromatography (silica gel, n-heptane–EtOAc) to give
the respective products.
General procedure for the synthesis b,d-diketosulfones 13a–r
To a CH2Cl2 solution (10 mL) of 1,3-bis(silyl enol ether) 1a
(11.5 mmol) was added sulfonyl chloride 12a–r (5.8 mmol) at
−78 ◦C under argon atmosphere. The temperature of the reaction
mixture was allowed to rise to 20 ◦C during 14 h and, subsequently,
a saturated aqueous solution of NaHCO3 (20 mL) was added.
The organic layer was separated and extracted with CH2Cl2 (3 ×
20 mL). The combined organic layers were dried (Na2SO4), filtered
and the filtrate was concentrated in vacuo. The residue was purified
by column chromatography (silica gel, n-heptane : EtOAc =
10 : 1).
Methyl 5-hydroxy-7-phenyl-3-oxohepta-4,6-dienoate (5a)
Starting with 4a (0.96 g, 5.76 mmol) and 1a (3.00 g, 11.52 mmol),
dissolved in CH2Cl2 (10 ml), 5a was isolated as an orange oil
(1.01 g, 71%). 1H NMR (300 MHz, CDCl3, keto : enol = 0 : 100):
d = 3.46 (s, 2H, CH2), 3.75 (s, 3H, CH3), 5.76 (s, 1H, CH), 6.58 (d,
3J = 15.9 Hz, 1H, CH=CH), 7.37–7.54 (m, 5H, Ph), 7.63 (d, 3J =
15.9 Hz, 1H, CH=CH), 14.84 (s, 1H, OH). 13C NMR (75 MHz,
Methyl 3-oxo-4-(phenylsulfonyl)butanoate (13a)
Starting with 12a (1.02 g, 5.8 mmol) and 1a (3.00 g, 11.5 mmol),
dissolved in CH2Cl2 (10 mL), 13a was isolated as a yellow solid
(0.90 g, 61%), mp 62–64 ◦C. 1H-NMR (300 MHz, CDCl3, keto :
enol = 60:40): enol: d = 3.74 (s, 3H, OCH3), 3.94 (s, 2H, CH2),
5.19 (s, 1H, CH), 7.54–7.61 (m, 2H, Ar), 7.66–7.73 (m, 1H, Ar),
7.88–7.94 (m, 2H, Ar), 11.76 (s, 1H, OH); keto: d = 3.75 (s, 3H,
OCH3), 3.78, 4.37 (s, 2H, CH2), 7.54–7.61 (m, 2H, Ar), 7.66–7.73
(m, 1H, Ar), 7.88–7.94 (m, 2H, Ar). 13C-NMR (75 MHz, CDCl3):
enol: d = 52.0 (OCH3), 62.1 (CH2), 95.5 (CH), 128.6, 129.8, 134.9,
138.7 (Ar), 164.4, 172.4 (CO); keto: d = 49.6 (CH2), 53.0 (OCH3),
67.1 (CH2), 128.6, 129.6, 134.6, 138.8 (Ar), 167.2, 191.3 (CO). IR
=
CDCl3): d = 47.1 (CH2), 52.8 (CH3), 101.1 (CH), 122.4 (CH CH),
=
128.4, 129.3, 130.5 (Ph), 135.2 (C), 150.0 (CH CH), 168.3, 177.1,
192.9 (CO). IR (neat, cm−1): m = 3061 (m), 3027 (m), 2953 (m),
1742 (s), 1636 (s), 1584 (s, br), 1496 (m), 1437 (s), 1328 (s), 1261
(s), 1203 (m), 1129 (s), 1073 (m), 1017 (m), 973 (m), 945 (m), 931
(m), 867 (m), 770 (m). MS (CI, isobutane) m/z (%) = 247 ([M +
1]+, 100). Anal. calcd. for C14H14O4 (246.26): C, 68.28; H, 5.73.
Found: C, 68.20; H, 5.39%.
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(KBr, cm−1): m = 3439 (w), 3103 (s), 3068 (s), 2959 (s), 2911 (s),
2854 (s), 1747 (m), 1724 (m), 1587 (s), 1481 (s), 1446 (m), 1439
(s), 1409 (s), 1373 (s), 1339 (m), 1323 (m), 1264 (s), 1205 (m), 1154
(m), 1127 (s), 1090 (s), 1072 (s), 1057 (s), 1024 (s), 948 (s), 869 (s),
796 (s), 748 (s), 720 (s), 688 (s), 652 (s), 607 (s), 541 (s), 528 (s),
461 (s). MS (EI, 70 eV): m/z (%) = 256 (M+, 2), 225 (19), 224 (11),
192 (31), 183 (25), 174 (9), 160 (18), 141 (87), 135 (17), 125 (17),
118 (13), 115 (39), 101 (45), 94 (12), 91 (19), 78 (20), 77 (100), 74
(14), 69 (16), 59 (13), 51 (37), 43 (14). HRMS (EI, 70 eV): calcd
for C11H12O5S (M+) 256.0400, found: 256.0396. Anal. calcd. for
C11H12O5S (256.27): C 51.55, H 4.72, S 12.51; found: C 51.70, H
4.58, S 12.40%.
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Acknowledgements
Financial support from the State of Mecklenburg-Vorpommern is
gratefully acknowledged.
Notes and references
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3370 | Org. Biomol. Chem., 2008, 6, 3366–3370
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