One-pot synthesis of 3-hydroxymaleic anhydrides by cyclization of 1,1-bis(trimethylsilyloxy)ketene acetals with oxalyl chloride

Article abstract of DOI:10.1016/j.tet.2007.01.026

Functionalized 3-hydroxymaleic anhydrides were prepared by cyclization of 1,1-bis(trimethylsilyloxy)ketene acetals with oxalyl chloride.

Full text of DOI:10.1016/j.tet.2007.01.026

Tetrahedron 63 (2007) 2647–2656
One-pot synthesis of 3-hydroxymaleic anhydrides by cyclization of
1,1-bis(trimethylsilyloxy)ketene acetals with oxalyl chloride
c
b
a,b,
Sven Rotzoll,a,b Ehsan Ullah,a,b Helmar Gorls, Christine Fischer and Peter Langer
*
€
aInstitut fu€r Chemie, Universita€t Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
bLeibniz-Institut fu€r Katalyse e. V. an der Universita€t Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
cInstitut fu€r Anorganische und Analytische Chemie, Universita€t Jena, August-Bebel-Str. 2, 07740 Jena, Germany
Received 7 December 2006; accepted 16 January 2007
Available online 20 January 2007
Abstract—Functionalized 3-hydroxymaleic anhydrides were prepared by cyclization of 1,1-bis(trimethylsilyloxy)ketene acetals with oxalyl
chloride.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
enol ethers7 with oxalyl chloride.8 The cyclization of 1,3-
bis(silyl enol ethers)9 with oxalyl chloride provides a conve-
nient access to g-alkylidenebutenolides.10 Recently, we
reported a new method for the synthesis of 3-hydroxymaleic
anhydrides by one-pot cyclization of 1,1-bis(trimethylsilyl-
oxy)ketene acetals with oxalyl chloride.11 Herein, we report
full details of these studies. With regard to our preliminary
communication,11 we considerably extended the preparative
scope.
Functionalized maleic anhydrides represent important syn-
thetic building blocks,1 which have been employed, for
example, in the synthesis of g-alkylidenebutenolides,2a–c
maleimides,2d 5-alkylidene-5H-pyrrol-2-ones,2d numerous
carba- and heterocycles (by [4+2], [3+2], and [2+2] cycload-
dition reactions),3 functionalized 3-alkanoylacrylic acids
and naphthoquinones (by Friedel–Crafts acylations of maleic
anhydrides), 4-alkylidenebutane-1,3-diones (by reaction
with enolates),4a and various a,b-unsaturated carbonyl com-
pounds (by reaction with nucleophiles).4b Substituted maleic
anhydrides are available by Michael reaction of nucleophiles
with parent maleic anhydride and subsequent halogenation
and elimination,4c or by TiCl4/N(nBu)3 mediated reaction
of a-ketoesters with alkanoic acid anhydrides.5 The conden-
sation of ethyl propionate with diethyl oxalate and sub-
sequent methylation afforded 2-methoxy-3-methylmaleic
anhydride.6a 3-Methoxy-4-arylmaleic anhydrides are avail-
able by condensation of arylacetonitriles with diethyl oxa-
late, methylation and subsequent treatment with acid.6b
Notably, whereas 3,4-dihydroxymaleic anhydride,6c 3,4-
diacetoxymaleic anhydride,6d,e and 3,4-dimethoxymaleic
anhydride6f are known for a long time, methods for the syn-
thesis of unsymmetrical 3-hydroxyanhydrides have only
scarcely been reported.
2. Results and discussion
The 1,1-bis(trimethylsilyloxy)ketene acetals 2a–x were pre-
pared, according to known procedures,12 in two steps. The
reaction of the carboxylic acid with pyridine, 1,1,1,3,3,3-
hexamethyldisilazane (HMDS), and trimethylchlorosilane
afforded the trimethylsilyl carboxylates 1a–x (52–92%
yield). The latter were deprotonated by lithium-1,1,1,3,3,3-
hexamethyldisilazide and subsequently silylated to give the
1,1-bis(trimethylsilyloxy)ketene acetals 2a–x (47–94%
yield). The reaction of 2a–x with oxalyl chloride, in
the presence of trimethylsilyl-trifluoromethanesulfonate
(Me3SiOTf), afforded the 3-hydroxymaleic anhydrides 3a–x
in 20–73% yield (Scheme 1, Table 1). The formation of 3
can be explained by Me3SiOTf mediated attack of the carbon
atom of 2 onto oxalyl chloride and subsequent cyclizationvia
the oxygen atom. The best yields were obtained when the
Lewis acid Me3SiOTf (0.5 equiv) was employed. The yields
dropped when the amount of Lewis acid was reduced.
Oxalyl chloride represents an important building block for
the synthesis of O-heterocycles. For example, 2,3-dihydro-
furan-2,3-diones have been prepared by cyclization of silyl
The preparative scope was studied. The cyclization of oxalyl
chloride with 1,1-bis(trimethylsilyloxy)ketene acetals 2a–k,
prepared from various alkanoic acids, afforded the alkyl-
substituted 3-hydroxymaleic anhydrides 3a–k. The products
were generally isolated in moderate to good yields (except
Keywords: Anhydrides; Cyclizations; Ketene acetals; Oxalyl chloride; Silyl
enol ethers.
* Corresponding author. Tel.: +49 381 4986410; fax: +49 381 4986412;
e-mail: peter.langer@uni-rostock.de
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.01.026

2648
S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
O
O
a
R
R
R
OSiMe3
1a-x
OH
b
O
Cl
O
O
O
O
OSiMe3
Cl
c
HO
OSiMe3
2a-x
R
3a-x
Scheme 1. Synthesis of 3a–x. Reagents and conditions: (a) (1) pyridine
(0.5 mL per 10 mmol of 1, THF (1 mL per 10 mmol of 1), 0 ꢀC, 30 min;
(2) H[N(SiMe3)2] (1.0 equiv), Me3SiCl (0.5 equiv), 0/20 ꢀC, 12 h; (b)
(1) Li[N(SiMe3)2] (1.25 equiv), THF, 15 min, ꢁ78 ꢀC; (2) Me3SiCl
(1.5 equiv), ꢁ78/20 ꢀC, 12 h; (c) Me3SiOTf (0.5 equiv), CH2Cl2,
ꢁ78/20 ꢀC, 12 h, then 20 ꢀC, 3 h.
Figure 1. ORTEP plot of 3o. The thermal ellipsoids of 50% probability are
shown for the non-hydrogen atoms.
Table 1. Products and yields
for all compounds; in addition, elemental analyses could
not be obtained. However, the purity and identity was clearly
shown for all derivatives by H NMR. The structure of an-
hydrides 3 was established by spectroscopic methods. The
structure of 3o was independently confirmed by X-ray crys-
tal structure analysis (Fig. 1).13
3
R
1a (%)
2a (%)
3a (%)
1
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
Me
Et
n-Pr
n-Pent
n-Oct
n-Dodec
t-Bu
cHex
(cPent)CH2
(cHex)(CH2)2
Ph2CH
Ph
4-MeC6H4
4-ClC6H4
4-FC6H4
4-MeO(C6H4)
3,4-(MeO)2(C6H3)
4-PhC6H4
Thien-2-yl
MeO
54
66
80
74
78
89
61
80
84
89
91
92
83
77
83
78
85
84
96
53
72
69
84
52
62
70
74
75
64
94
92
87
85
78
92
92
87
86
91
83
70
88
83
53
92
47
86
82
20
36
42
50
56
71
17
60
62
63
30
70
73
65
53
70
45
57
62
53
50
40
50
20
In conclusion, a variety of functionalized 3-hydroxymaleic
anhydrides were prepared by cyclization of 1,1-bis(tri-
methylsilyloxy)ketene acetals with oxalyl chloride.
3. Experimental section
3.1. General
All solvents were dried by standard methods and all reac-
1
tions were carried out under inert atmosphere. For H and
t
13C NMR spectra (1H NMR: 300, 600 MHz; 13C NMR:
75, 150 MHz), the deuterated solvents indicated were
used. Mass spectrometry (MS) data were obtained by using
the electron ionization (70 eV), chemical ionization (CI,
H2O), or electrospray (ESI) techniques. For preparative
scale chromatography, silica gel (60–200 mesh) was used.
u
v
w
x
PhO
BnO
PhS
Allyl
a
Yields of isolated products.
for 3a, 3g, and 3k). The low yield of 3g and 3k can be ex-
plained by steric hindrance of the tert-butyl and the diphe-
nylmethyl groups, respectively. The ketene acetals 2l–r
were prepared from various arylacetic acids. The cyclization
of 2l–r with oxalyl chloride afforded the aryl-substituted 3-
hydroxymaleic anhydrides 3l–r in moderate to good yields.
The cyclization of oxalyl chloride with 2s, prepared from (2-
thienyl)acetic acid, gave the thienyl-substituted anhydride
3s. The methoxy-, phenyloxy-, and benzyloxy-substituted
3-hydroxymaleic anhydrides 3t–v were prepared from 1,1-
bis(trimethylsilyloxy)ketene acetals 1t–v. The cyclization
of oxalyl chloride with silyl ketene acetal 2w, prepared
from (thiophenoxy)acetic acid, afforded the thiophenoxy-
substituted maleic anhydride 3w. Allyl-substituted anhy-
dride 3x was prepared, albeit in low yield, from silyl ketene
acetal 1x (which is available from pent-4-enoic acid).
3.2. Typical procedure for the preparation of
2-substituted trimethylsilylacetates (1a–x)
3.2.1. Trimethylsilyl propionate (1a). To a stirred solution
of propionic acid (5.00 g, 67.56 mmol) in THF (6.7 mL) and
pyridine (3.4 mL) at 0 ꢀC was added HMDS (14.0 mL,
67.56 mmol), followed by dropwise addition of Me3SiCl
(4.24 mL, 33.78 mmol). After stirring the solution for
12 h, hexane (10 mL) was added to the mixture and the so-
lution was filtered under argon. The solvent was removed
under reduced pressure to give 1a (5.30 g, 54%) as colorless
oil. The spectroscopic data are in accordance with the data
provided in the literature.12a 1H NMR (300 MHz, CDCl3):
3
3
d¼2.26 (q, 2H, J¼7.5 Hz, CH2), 1.04 (t, 3H, J¼7.5 Hz,
CH3), 0.22 (s, 9H, SiMe3).
3.2.2. Trimethylsilyl butyrate (1b). Starting with butyric
acid (5.00 g, 56.80 mmol), HMDS (11.8 mL, 56.80 mmol),
Me3SiCl (3.8 mL, 28.40 mmol), THF (5.7 mL), and
Due to the unstable character of silyl esters 1 and silyl ketene
acetals 2, 13C NMR and MS spectra could not be obtained

S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
2649
pyridine (2.9 mL), 1b (6.00 g, 66%) was isolated as color-
less oil. The obtained spectroscopic data are in accordance
with the data provided in the literature.12e 1H NMR
(300 MHz, CDCl3): d¼2.22 (t, 2H, 3J¼7.5 Hz, CH2),
(3.6 mL, 28.13 mmol), THF (5.6 mL), and pyridine
(2.8 mL), 1i (10.15 g, 84%) was isolated as yellowish oil.
1H NMR (250 MHz, CDCl3): d¼2.25 (m, 2H, CH2), 1.67–
1.74 (m, 3H, CH, CH2), 1.44–1.60 (m, 6H, CH2), 1.00–
1.08 (m, 2H, CH2), 0.22 (s, 9H, SiMe3).
3
1.58–1.53 (m, 2H, CH2), 0.88 (t, 3H, J¼7.5 Hz, CH3),
0.22 (s, 9H, SiMe3).
3.2.10. Trimethylsilyl 4-(cyclohexyl)butyrate (1j). Start-
ing with 4-cyclohexylbutyric acid (5.00 g, 29.39 mmol),
HMDS (6.1 mL, 29.39 mmol), Me3SiCl (1.9 mL,
14.69 mmol), THF (2.9 mL), and pyridine (1.5 mL), 1j
(6.33 g, 89%) was isolated as yellowish oil. 1H NMR
3.2.3. Trimethylsilyl pentanoate (1c). Starting with penta-
noic acid (5.00 g, 49.00 mmol), HMDS (10.2 mL,
49.00 mmol), Me3SiCl (3.1 mL, 24.50 mmol), THF
(4.9 mL), and pyridine (2.5 mL), 1c (6.80 g, 80%) was iso-
lated as colorless oil. 1H NMR (300 MHz, CDCl3):
3
(250 MHz, CDCl3): d¼2.21 (t, 2H, J¼7.3 Hz, CH), 1.51–
3
d¼2.28 (t, 2H, J¼7.2 Hz, CH2), 1.61–1.51 (m, 2H, CH2),
1.67 (m, 5H, CH, CH2), 1.09–1.22 (m, 6H, CH2), 0.80–
0.85 (m, 4H, CH2), 0.22 (s, 9H, SiMe3).
3
1.36–1.25 (m, 2H, CH2), 0.89 (t, 3H, J¼7.5 Hz, CH3),
0.27 (s, 9H, SiMe3).
3.2.11. Trimethylsilyl 3,3-diphenylpropionate (1k). Start-
ing with 3,3-diphenylpropionic acid (7.00 g, 30.93 mmol),
HMDS (6.4 mL, 30.93 mmol), Me3SiCl (2.0 mL,
15.47 mmol), THF (3.1 mL), and pyridine (1.5 mL), 1k
(8.40 g, 91%) was isolated as colorless oil. 1H NMR
(250 MHz, CDCl3): d¼7.14–7.31 (m, 10H, Ph), 4.49 (t,
3.2.4. Trimethylsilyl heptanoate (1d). Starting with hepta-
noic acid (5.00 g, 43.04 mmol), HMDS (9.0 mL,
43.04 mmol), Me3SiCl (2.7 mL, 21.52 mmol), THF
(4.3 mL), and pyridine (2.2 mL), 1d (6.00 g, 74%) was iso-
lated as colorless oil. 1H NMR (300 MHz, CDCl3): d¼2.27
(t, 2H, 3J¼7.5 Hz, CH2), 1.60–1.55 (m, 4H, CH2), 1.32–1.26
3
3
1H, J¼8.0 Hz, CH), 3.05 (d, 2H, J¼8.0 Hz, CH2), 0.12
3
(m, 4H, CH2), 0.86 (t, 3H, J¼7.5 Hz, CH3), 0.27 (s, 9H,
(s, 9H, SiMe3).
SiMe3).
3.2.12. Trimethylsilyl 2-phenylacetate (1l). Starting with
phenylacetic acid (5.00 g, 36.72 mmol), HMDS (7.63 mL,
36.72 mmol), Me3SiCl (2.3 mL, 18.36 mmol), THF
(3.6 mL), and pyridine (1.8 mL), 1l (7.05 g, 92%) was iso-
lated as yellow oil. The obtained spectroscopic data are in
accordance with the data provided in the literature.12a 1H
NMR (300 MHz, CDCl3): d¼7.17–7.09 (m, 5H, Ph), 3.46
(s, 2H, CH2), 0.12 (s, 9H, SiMe3).
3.2.5. Trimethylsilyl decanoate (1e). Starting with dec-
anoic acid (5.00 g, 29.02 mmol), HMDS (6.0 mL,
29.02 mmol), Me3SiCl (1.8 mL, 14.51 mmol), THF
(3.0 mL), and pyridine (1.5 mL), 1e (5.20 g, 78%) was iso-
lated as colorless oil. 1H NMR (300 MHz, CDCl3):
d¼2.28 (t, 2H, J¼7.5 Hz, CH2), 1.58 (t, 2H, J¼7.5 Hz,
CH2), 1.26 (br s, 12H, CH2), 0.87 (t, 3H, 3J¼7.5 Hz, CH3),
0.27 (s, 9H, SiMe3).
3
3
3.2.13. Trimethylsilyl 2-(4-tolyl)acetate (1m). Starting
with p-tolylacetic acid (5.00 g, 33.30 mmol), HMDS
(6.9 mL, 33.30 mmol), Me3SiCl (2.1 mL, 16.65 mmol),
THF (3.3 mL), and pyridine (1.7 mL), 1m (6.15 g, 83%)
3.2.6. Trimethylsilyl tetradecanoate (1f). Starting with
tetradecanoic acid (7.00 g, 30.65 mmol), HMDS (6.3 mL,
30.65 mmol), Me3SiCl (2.0 mL, 15.33 mmol), THF
(3.1 mL), and pyridine (1.5 mL), 1f (8.19 g, 89%) was iso-
lated as yellowish oil. 1H NMR (250 MHz, CDCl3):
1
was isolated as yellow oil. H NMR (300 MHz, CDCl3):
3
3
d¼7.33 (d, 2H, J¼6.7 Hz, Ar), 7.08 (d, 2H, J¼8.1 Hz,
Ar), 3.78 (s, 1H, CH2), 2.27 (s, 3H, CH3), 0.29 (s, 9H,
SiMe3).
3
d¼2.23 (t, 2H, J¼7.6 Hz, CH2), 1.49–1.56 (m, 2H, CH2),
1.20 (m, 20H, CH2), 0.83 (t, 3H, 3J¼7.0 Hz, CH3), 0.22 (s,
9H, SiMe3).
3.2.14. Trimethylsilyl 2-(4-chlorophenyl)acetate (1n).
Starting with (4-chlorophenyl)acetic acid (5.00 g,
29.30 mmol), HMDS (6.1 mL, 29.30 mmol), Me3SiCl
(1.8 mL, 14.65 mmol), THF (3.0 mL), and pyridine
3.2.7. Trimethylsilyl 3,3-dimethylbutanoate (1g). Starting
with 3,3-dimethylbutyric acid (7.30 g, 62.84 mmol), HMDS
(13.0 mL, 62.84 mmol), Me3SiCl (4.0 mL, 31.42 mmol),
THF (6.2 mL), and pyridine (3.1 mL), 1g (7.21 g, 61%)
was isolated as yellow oil. The obtained spectroscopic data
are in accordance with the data provided by the literature.12d
1H NMR (250 MHz, CDCl3): d¼2.03 (s, 2H, CH2), 0.82 (s,
9H, CH3), 0.13 (s, 9H, SiMe3).
1
(1.5 mL), 1n (5.50 g, 77%) was isolated as yellow oil. H
NMR (300 MHz, CDCl3): d¼7.25–7.08 (m, 4H, Ar), 3.51
(s, 2H, CH2), 0.25 (s, 9H, SiMe3).
3.2.15. Trimethylsilyl 2-(4-fluorophenyl)acetate (1o).
Starting with (4-fluorophenyl)acetic acid (6.00 g,
38.93 mmol), HMDS (8.1 mL, 38.93 mmol), Me3SiCl
(2.5 mL, 19.46 mmol), THF (3.9 mL), and pyridine
(2.0 mL), 1o (7.29 g, 83%) was isolated as colorless oil.
1H NMR (250 MHz, CDCl3): d¼7.03–7.11 (m, 2H, Ar),
6.80–6.90 (m, 2H, Ar), 3.44 (s, 2H, CH2), 0.12 (s, 9H,
SiMe3).
3.2.8. Trimethylsilyl 2-(cyclohexyl)acetate (1h). Starting
with cyclohexylacetic acid (10.00 g, 70.32 mmol), HMDS
(14.6 mL, 70.32 mmol), Me3SiCl (4.5 mL, 35.16 mmol),
THF (7.0 mL), and pyridine (3.5 mL), 1h (12.06 g, 80%)
was isolated as yellowish oil. 1H NMR (250 MHz,
3
CDCl3): d¼2.11 (d, 2H, J¼6.7 Hz, CH2), 1.63–1.77 (m,
6H, CH/CH2), 0.83–1.32 (m, 5H, CH2), 0.22 (s, 9H, SiMe3).
3.2.16. Trimethylsilyl 2-(4-methoxyphenyl)acetate (1p).
Starting with (4-methoxyphenyl)acetic acid (5.00 g,
30.09 mmol), HMDS (6.3 mL, 30.09 mmol), Me3SiCl
(1.9 mL, 15.04 mmol), THF (3.0 mL), and pyridine
3.2.9. Trimethylsilyl 3-(cyclopropyl)propionate (1i).
Starting with 3-cyclopropylpropionic acid (8.00 g,
56.25 mmol), HMDS (11.6 mL, 56.25 mmol), Me3SiCl

2650
S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
1
(1.5 mL), 1p (5.60 g, 78%) was isolated as yellow oil. H
NMR (250 MHz, CDCl3): d¼7.09 (d, 2H, J¼8.5 Hz, Ar),
literature.12f 1H NMR (250 MHz, CDCl3): d¼7.10–7.34
3
(m, 5H, PhH), 3.55 (s, 2H, CH2), 0.17 (s, 9H, SiMe3).
3
6.76 (d, 2H, J¼8.5 Hz, Ar), 3.70 (s, 3H, OCH3), 3.46 (s,
2H, CH2), 0.18 (s, 9H, SiMe3).
3.2.24. Trimethylsilyl 2-allylacetate (1x). Starting with
pent-4-enoic acid (2.00 g, 19.40 mmol), HMDS (4.0 mL,
19.40 mmol), Me3SiCl (1.2 mL, 9.70 mmol), THF
(1.9 mL), and pyridine (1.0 mL), 1x (1.73 g, 52%) was iso-
lated as colorless oil. 1H NMR (300 MHz, CDCl3):
d¼5.87–5.78 (m, 1H, CH), 5.08–4.97 (m, 2H, CH2), 2.44–
2.31 (m, 4H, CH2), 0.28 (s, 9H, SiMe3).
3.2.17. Trimethylsilyl 2-(3,4-dimethoxyphenyl)acetate
(1q). Starting with (3,4-dimethoxyphenyl)acetic acid
(5.00 g, 25.48 mmol), HMDS (5.3 mL, 25.48 mmol),
Me3SiCl (1.6 mL, 12.74 mmol), THF (2.6 mL), and pyri-
dine (1.3 mL), 1q (5.80 g, 85%) was isolated as yellow oil.
1H NMR (300 MHz, CDCl3): d¼6.80 (br s, 3H, Ar), 3.85
(s, 3H, OCH3), 3.84 (s, 3H, OCH3), 3.53 (s, 2H, CH2),
0.25 (s, 9H, SiMe3).
3.3. Typical procedure for the preparation of
1,1-bis(trimethylsilyloxy)ketene acetals (2a–x)
3.2.18. Trimethylsilyl 2-(4-biphenyl)acetate (1r). Starting
with (4-biphenyl)acetic acid (8.00 g, 37.69 mmol), HMDS
(7.8 mL, 37.69 mmol), Me3SiCl (2.4 mL, 18.85 mmol),
THF (3.8 mL), and pyridine (1.9 mL), 1r (8.97 g, 84%)
was isolated as yellowish solid (mp 38 ꢀC). 1H NMR
(250 MHz, CDCl3): d¼7.38–7.45 (m, 4H, Ph/Ar), 7.13–
7.30 (m, 5H, Ph/Ar), 3.51 (s, 2H, CH2), 0.15 (s, 9H, SiMe3).
3.3.1. 2-Methyl-1,1-bis(trimethylsilyloxy)ethene (2a). To
a solution of HMDS (7.1 mL, 34.25 mmol) in THF
(28.0 mL) was dropwise added n-BuLi (13.7 mL, 2.5 M
solution in hexane, 34.25 mmol) at 0 ꢀC. After stirring for
30 min at 45 ꢀC, the mixture was cooled to ꢁ78 ꢀC, stirred
for 20 min at ꢁ78 ꢀC and, subsequently, 1a (4.00 g,
27.40 mmol) was slowly added. The reaction mixture was
stirred for 15 min at ꢁ78 ꢀC. Subsequently, Me3SiCl
(5.2 mL, 41.10 mmol) was dropwise added to the solution.
After holding the solution at ꢁ78 ꢀC for additional 15 min,
the solution was allowed to warm-up overnight. The solvent
was removed under reduced pressure and the filtration of the
residue through a sintered glass funnel under argon atmo-
sphere gave 2a (3.70 g, 62%). The obtained spectroscopic
data are in accordance with the data provided in the litera-
ture.12a 1H NMR (300 MHz, CDCl3): d¼3.51–3.42 (m,
1H, CH), 1.47 (d, 3H, 3J¼6.6 Hz, CH3), 0.20 (s, 18H,
SiMe3).
3.2.19. Trimethylsilyl 2-(thien-2-yl)acetate (1s). Starting
with (thien-2-yl)acetic acid (7.00 g, 49.24 mmol), HMDS
(10.1 mL, 49.24 mmol), Me3SiCl (3.1 mL, 24.62 mmol),
THF (4.9 mL), and pyridine (2.5 mL), 1s (10.13 g, 96%)
1
was isolated as yellow oil. H NMR (250 MHz, CDCl3):
d¼7.13 (dd, 1H, 3J¼4.9, 5.2 Hz, Hetar), 6.83–6.90 (m, 2H,
Hetar), 3.77 (s, 2H, CH2), 0.24 (s, 9H, SiMe3).
3.2.20. Trimethylsilyl 2-methoxyacetate (1t). Starting with
methoxyacetic acid (5.00 g, 50.97 mmol), HMDS (10.6 mL,
50.97 mmol), Me3SiCl (3.2 mL, 25.48 mmol), THF
(6.0 mL), and pyridine (3.0 mL), 1t (4.40 g, 53%) was iso-
lated as colorless oil. The obtained spectroscopic data are
in accordance with the data provided in the literature.12b
1H NMR (300 MHz, CDCl3): d¼3.94 (s, 2H, CH2), 3.40
(s, 3H, OCH3), 0.27 (s, 9H, SiMe3).
3.3.2. 2-Ethyl-1,1-bis(trimethylsilyloxy)ethene (2b).
Starting with 1b (5.90 g, 36.87 mmol), HMDS (9.6 mL,
46.08 mmol), n-BuLi (18.4 mL, 46.08 mmol), Me3SiCl
(8.7 mL, 55.30 mmol), and THF (37.0 mL), 2b (6.00 g,
70%) was isolated as colorless oil. The obtained spectro-
scopic data are in accordance with the data provided in the
literature.12g 1H NMR (300 MHz, CDCl3): d¼3.57 (t, 1H,
3J¼7.2 Hz, CH), 1.97–1.90 (m, 2H, CH3), 0.91 (t, 3H,
3J¼7.5 Hz, CH3), 0.20 (s, 18H, SiMe3).
3.2.21. Trimethylsilyl 2-(phenoxy)acetate (1u). Starting
with phenoxyacetic acid (5.00 g, 32.90 mmol), HMDS
(6.8 mL, 32.90 mmol), Me3SiCl (2.1 mL, 16.44 mmol),
THF (3.3 mL), and pyridine (1.6 mL), 1u (5.30 g, 72%)
1
was isolated as yellow oil. H NMR (300 MHz, CDCl3):
d¼7.17–7.09 (m, 5H, Ph), 3.46 (s, 2H, CH2), 0.12 (s, 9H,
3.3.3. 2-Propyl-1,1-bis(trimethylsilyloxy)ethene (2c).
Starting with 1c (6.73 g, 38.67 mmol), HMDS (10.1 mL,
48.33 mmol), n-BuLi (19.3 mL, 48.33 mmol), Me3SiCl
(6.9 mL, 55.00 mmol), and THF (39.0 mL), 2c (7.05 g,
SiMe3).
1
3.2.22. Trimethylsilyl 2-(benzyloxy)acetate (1v). Starting
with (benzyloxy)acetic acid (2.00 g, 11.44 mmol), HMDS
(2.4 mL, 11.44 mmol), Me3SiCl (0.7 mL, 5.72 mmol),
THF (1.1 mL), and pyridine (0.6 mL), 1v (1.88 g, 69%)
was isolated as colorless oil. The obtained spectroscopic
data are in accordance with the data provided in the litera-
ture.12c 1H NMR (300 MHz, CDCl3): d¼7.37–7.25 (m,
5H, Ph), 4.63 (s, 2H, OCH2), 4.06 (s, 2H, CH2), 0.31 (s,
9H, SiMe3).
74%) was isolated as colorless oil. H NMR (300 MHz,
CDCl3): d¼3.55 (t, 1H, 3J¼7.2 Hz, CH), 1.31 (q, 2H,
3
3J¼7.2 Hz, J¼14.4 Hz, CH2), 1.34–1.27 (m, 2H, CH2),
0.88 (t, 3H, 3J¼7.3 Hz, CH3), 0.28 (s, 18H, SiMe3).
3.3.4. 2-Pentyl-1,1-bis(trimethylsilyloxy)ethene (2d).
Starting with 1d (5.00 g, 24.70 mmol), HMDS (6.4 mL,
30.88 mmol), n-BuLi (12.4 mL, 30.88 mmol), Me3SiCl
(4.6 mL, 37.05 mmol), and THF (25.0 mL), 2d (5.10 g,
1
75%) was isolated as colorless oil. H NMR (300 MHz,
3.2.23. Trimethylsilyl 2-(thiophenoxy)acetate (1w). Start-
ing with (thiophenoxy)acetic acid (8.00 g, 47.56 mmol),
HMDS (9.8 mL, 47.56 mmol), Me3SiCl (3.0 mL,
23.78 mmol), THF (4.7 mL), and pyridine (2.4 mL), 1w
(9.56 g, 84%) was isolated as yellow oil. The spectroscopic
data are in accordance with the data provided in the
CDCl3): d¼3.55 (t, 1H, 3J¼7.2 Hz, CH), 1.92–1.89 (m,
2H, CH2), 1.33–1.26 (m, 6H, CH2), 0.88 (t, 3H,
3J¼7.3 Hz, CH3), 0.28 (s, 18H, SiMe3).
3.3.5. 2-Octyl-1,1-bis(trimethylsilyloxy)ethene (2e). Start-
ing with 1e (5.05 g, 22.17 mmol), HMDS (5.8 mL,

S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
2651
27.71 mmol), n-BuLi (11.1 mL, 27.71 mmol), Me3SiCl
(4.2 mL, 33.25 mmol), and THF (23.0 mL), 2e (4.50 g,
64%) was isolated as colorless oil. H NMR (300 MHz,
(61), 73 (72). HRMS (EI): calcd for C16H34O2Si2 ([M]+)
314.20918, found 314.209123.
1
CDCl3): d¼3.54 (t, 1H, 3J¼7.2 Hz, CH), 1.41–1.27 (m,
3.3.11. 2-Benzhydryl-1,1-bis(trimethylsilyloxy)ethene
(2k). Starting with 1k (8.40 g, 35.53 mmol), HMDS
(9.2 mL, 44.41 mmol), n-BuLi (17.8 mL, 44.41 mmol),
Me3SiCl (6.8 mL, 53.29 mmol), and THF (36.0 mL), 2k
(12.13 g, 92%) was isolated as colorless oil. 1H NMR
(250 MHz, CDCl3): d¼7.02–7.11 (m, 10H, Ph), 4.84 (d,
3
2H, CH2), 1.26 (br s, 12H, CH2), 0.88 (t, 3H, J¼7.3 Hz,
CH3), 0.20 (s, 9H, SiMe3), 0.18 (s, 9H, SiMe3).
3.3.6. 2-Dodecyl-1,1-bis(trimethylsilyloxy)ethene (2f).
Starting with 1f (8.19 g, 27.25 mmol), HMDS (7.0 mL,
34.06 mmol), n-BuLi (13.6 mL, 34.06 mmol), and Me3SiCl
(5.2 mL, 40.88 mmol), and THF (27.0 mL), 2f (9.51 g, 94%)
3
3
1H, J¼9.2 Hz, CH), 4.06 (d, 1H, J¼9.2 Hz, CH), 0.17
(s, 9H, SiMe3), 0.06 (s, 9H, SiMe3). 13C NMR (75 MHz,
CDCl3): d¼151.2 (COSi), 146.7 (CPh), 128.7, 126.1
(CHPh), 87.7 (CH), 47.7 (CHPh2), 0.9, 0.5 (SiMe3). MS
(EI, 70 eV): m/z (%)¼370 ([M]+, 82), 293 (31), 207 (24),
180 (100), 167 (99), 147 (55), 131 (44), 73 (69). HRMS
(EI): calcd for C28H30O2Si2 ([M]+) 370.17788, found
370.177791.
1
was isolated as yellow oil. H NMR (250 MHz, CDCl3):
3
d¼3.54 (t, 1H, J¼7.3 Hz, CH), 1.65–1.95 (m, 2H, CH2),
1.26 (m, 20H, CH2), 0.87 (t, 3H, 3J¼6.4 Hz, CH3), 0.18 (s,
9H, SiMe3), 0.05 (s, 9H, SiMe3). 13C NMR (75 MHz,
CDCl3): d¼150.3 (COSi), 83.7 (CH), 32.0, 30.7, 29.8,
29.8, 29.8, 29.6, 29.5, 29.3, 25.0, 22.8 (CH2), 14.1 (CH3),
2.7, 0.6 (SiMe3).
3.3.12. 2-Phenyl-1,1-bis(trimethylsilyloxy)ethene (2l).
Starting with 1l (6.87 g, 32.02 mmol), HMDS (8.6 mL,
41.28 mmol), n-BuLi (16.5 mL, 41.28 mmol), Me3SiCl
(6.2 mL, 49.53 mmol), and THF (34.0 mL), 2l (8.50 g,
92%) was isolated as yellow oil. The obtained spectroscopic
data are in accordance with the data provided in the litera-
ture.12a 1H NMR (300 MHz, CDCl3): d¼7.35–7.31 (m,
1H, Ph), 7.18–7.12 (m, 2H, Ph), 6.96–6.90 (m, 2H, Ph),
4.55 (s, 1H, CH), 0.24 (s, 18H, SiMe3).
3.3.7. 2-(tert-Butyl)-1,1-bis(trimethylsilyloxy)ethene (2g).
Starting with 1g (7.21 g, 38.28 mmol), HMDS (9.9 mL,
47.85 mmol), n-BuLi (19.1 mL, 47.85 mmol), Me3SiCl
(7.3 mL, 57.42 mmol), and THF (38.0 mL), 2g (9.16 g,
92%) was isolated as colorless oil. The obtained spectro-
scopic data are in accordance with the data provided in the
literature.12a 1H NMR (250 MHz, CDCl3): d¼3.32 (s, 1H,
CH), 0.82 (s, 9H, CH3), 0.17 (s, 9H, SiMe3), 0.14 (s, 9H,
SiMe3).
3.3.13. 2-(p-Tolyl)-1,1-bis(trimethylsilyloxy)ethene (2m).
Starting with 1m (6.10 g, 27.43 mmol), HMDS (7.1 mL,
34.28 mmol), n-BuLi (13.7 mL, 34.28 mmol), Me3SiCl
(5.2 mL, 41.14 mmol), and THF (27.0 mL), 2m (7.00 g,
87%) was isolated as yellow oil. 1H NMR (300 MHz,
CDCl3): d¼7.28 (d, 2H, 3J¼8.4 Hz, Ar), 7.02 (d, 2H,
3J¼7.8 Hz, Ar), 4.58 (s, 1H, CH2), 2.27 (s, 3H, CH3), 0.29
(s, 9H, SiMe3), 0.25 (s, 9H, SiMe3).
3.3.8. 2-Cyclohexyl-1,1-bis(trimethylsilyloxy)ethene (2h).
Starting with 1h (12.07 g, 56.30 mmol), HMDS (14.6 mL,
70.35 mmol), n-BuLi (28.1 mL, 70.35 mmol), Me3SiCl
(10.8 mL, 84.40 mmol), and THF (56.0 mL), 2h (14.07 g,
87%) was isolated as yellow oil. 1H NMR (250 MHz,
3
CDCl3): d¼3.42 (d, 2H, J¼8.8 Hz), 1.97–2.12 (m, 1H,
CH), 1.51–1.62 (m, 5H, CH2), 0.86–1.29 (m, 5H, CH2),
0.15 (s, 9H, SiMe3), 0.14 (s, 9H, SiMe3). 13C NMR
(75 MHz, CDCl3): d¼149.2 (COSi), 90.8, 34.8 (CH), 34.5,
26.6, 26.5 (CH2), 0.8, 0.4 (SiMe3).
3.3.14. 2-(4-Chlorophenyl)-1,1-bis(trimethylsilyloxy)-
ethene (2n). Starting with 1n (5.00 g, 20.60 mmol), HMDS
(5.4 mL, 25.75 mmol), n-BuLi (10.3 mL, 25.75 mmol),
Me3SiCl (3.9 mL, 30.90 mmol), and THF (21.0 mL), 2n
(5.60 g, 86%) was isolated as yellow oil. 1H NMR
(300 MHz, CDCl3): d¼7.25–7.08 (m, 4H, Ar), 4.48 (s, 1H,
CH), 0.25 (s, 9H, SiMe3), 0.24 (s, 9H, SiMe3).
3.3.9. 2-(Cyclopentyl)-1,1-bis(trimethylsilyloxy)ethene
(2i). Starting with 1i (10.15 g, 47.35 mmol), HMDS
(12.2 mL, 59.18 mmol), n-BuLi (23.7 mL, 59.18 mmol),
Me3SiCl (9.1 mL, 71.03 mmol), and THF (47.0 mL), 2i
(11.52 g, 85%) was isolated as yellowish oil. 1H NMR
3
(250 MHz, CDCl3): d¼3.51 (t, 1H, J¼7.0 Hz, CH), 1.83–
3.3.15. 2-(4-Fluorophenyl)-1,1-bis(trimethylsilyloxy)-
ethene (2o). Starting with 1o (7.29 g, 32.20 mmol), HMDS
(8.3 mL, 40.25 mmol), n-BuLi (16.1 mL, 40.25 mmol),
Me3SiCl (6.2 mL, 48.30 mmol), and THF (32.0 mL), 2o
(8.79 g, 91%) was isolated as yellowish oil. 1H NMR
(250 MHz, CDCl3): d¼7.25–7.30 (m, 2H, Ar), 6.81–6.88
(m, 2H, Ar), 4.52 (s, 1H, CH), 0.26 (s, 9H, SiMe3), 0.12
(s, 9H, SiMe3). 13C NMR (75 MHz, CDCl3): d¼159.2 (d,
1JF,C¼242.3 Hz, FCAr), 151.1 (COSi), 132.8 (CAr), 126.9
1.89 (m, 2H, CH2), 1.41–1.74 (m, 7H, CH, CH2), 1.04–
1.11 (m, 2H, CH2), 0.16 (s, 9H, SiMe3), 0.13 (s, 9H,
SiMe3). 13C NMR (75 MHz, CDCl3): d¼149.9 (COSi),
82.4, 40.7 (CH), 32.0, 30.7, 24.9 (CH2), 0.8, 0.4 (SiMe3).
3.3.10. 2-(Cyclohexylethyl)-1,1-bis(trimethylsilyloxy)-
ethene (2j). Starting with 1j (6.33 g, 26.11 mmol), HMDS
(6.8 mL, 32.64 mmol), n-BuLi (13.1 mL, 32.64 mmol),
Me3SiCl (5.0 mL, 39.16 mmol), and THF (26.0 mL), 2j
(6.42 g, 78%) was isolated as yellowish oil. 1H NMR
3
2
(d, JF,C¼6.8 Hz, CHAr), 114.2 (d, JF,C¼21.1 Hz, CHAr),
83.8 (CH), 0.8, 0.4 (SiMe3). MS (EI, 70 eV): m/z (%)¼298
([M]+, 27), 197 (23), 147 (35), 136 (100). HRMS (EI): calcd
for C14H23FO2Si2 ([M]+) 298.12151, found 298.121185.
3
(250 MHz, CDCl3): d¼3.47 (t, 1H, J¼7.3 Hz, CH), 1.55–
1.90 (m, 7H, CH, CH2), 1.09–1.19 (m, 6H, CH2), 0.77–
0.86 (m, 2H, CH2), 0.16 (s, 9H, SiMe3), 0.12 (s, 9H,
SiMe3). 13C NMR (75 MHz, CDCl3): d¼150.3 (COSi),
84.0 (CH), 38.6 (CH2), 37.1 (CH), 33.4, 27.0, 26.9, 22.5
(CH2), 0.9, 0.4 (SiMe3). MS (EI, 70 eV): m/z (%)¼314
([M]+, 5), 299 (11), 271 (19), 217 (100), 204 (12), 147
3.3.16. 2-(4-Methoxyphenyl)-1,1-bis(trimethylsilyloxy)-
ethene (2p). Starting with 1p (5.50 g, 23.07 mmol), HMDS
(6.0 mL, 28.84 mmol), n-BuLi (11.5 mL, 28.84 mmol),
Me3SiCl (5.4 mL, 43.26 mmol), and THF (23.0 mL), 2p

2652
S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
(6.00 g, 83%) was isolated as yellow oil. The obtained spec-
troscopic data are in accordance with the data provided in the
literature.12h 1H NMR (300 MHz, CDCl3): d¼7.26 (d, 2H,
28.97 mmol), n-BuLi (11.6 mL, 28.97 mmol), Me3SiCl
(5.5 mL, 43.45 mmol), and THF (29.0 mL), 2u (8.50 g,
92%) was isolated as yellow oil. The obtained spectroscopic
data are in accordance with the data provided in the litera-
ture.12g 1H NMR (300 MHz, CDCl3): d¼7.35–7.31 (m,
1H, Ph), 7.18–7.12 (m, 2H, Ph), 6.96–6.90 (m, 2H, Ph),
4.55 (s, 1H, CH), 0.24 (s, 18H, SiMe3).
3
3J¼8.8 Hz, Ar), 6.73 (d, 2H, J¼8.6 Hz, Ar), 4.52 (s, 1H,
CH2), 3.68 (s, 3H, OCH3), 0.24 (s, 9H, SiMe3), 0.21 (s,
9H, SiMe3). 13C NMR (75 MHz, CDCl3): d¼158.8 (CAr),
151.0 (COSi), 130.1 (CAr), 127.0, 113.8 (CHAr), 84.8
(CH), 55.3 (OCH3), 0.7, 0.4 (SiMe3). MS (EI, 70 eV): m/z
(%)¼310 ([M]+, 39), 267 (6), 238 (6), 209 (20), 179 (14),
148 (100), 120 (20). HRMS (EI): calcd for C15H26O3Si2
([M]+) 310.14150, found 310.14146.
3.3.22. 2-Benzyloxy-1,1-bis(trimethylsilyloxy)ethene
(2v). Starting with 1v (1.86 g, 7.81 mmol), HMDS
(2.0 mL, 9.77 mmol), n-BuLi (3.9 mL, 9.77 mmol), Me3SiCl
(1.5 mL, 11.72 mmol), and THF (8.0 mL), 2v (1.14 g, 47%)
was isolated as colorless oil. The obtained spectroscopic data
are in accordance with the data provided in the literature.12c
1H NMR (300 MHz, CDCl3): d¼7.38–7.33 (m, 5H, Ph), 5.35
(s, 1H, CH), 4.63 (s, 2H, CH2), 0.24 (s, 18H, SiMe3).
3.3.17. 2-(3,4-Dimethoxyphenyl)-1,1-bis(trimethylsilyl-
oxy)ethene (2q). Starting with 1q (5.67 g, 21.15 mmol),
HMDS (5.5 mL, 26.44 mmol), n-BuLi (10.6 mL,
26.44 mmol), Me3SiCl (4.0 mL, 31.72 mmol), and THF
1
(21.0 mL), 2q (5.00 g, 70%) was isolated as yellow oil. H
NMR (300 MHz, CDCl3): d¼7.21–7.15 (m, 1H, Ar), 6.80–
6.78 (m, 2H, Ar), 4.57 (s, 1H, CH), 3.88 (s, 3H, OCH3),
3.85 (s, 3H, OCH3), 0.29 (s, 18H, SiMe3). 13C NMR
(75 MHz, CDCl3): d¼151.1 (COSi), 148.9, 145.5, 130.6
(CAr), 118.6, 111.3, 109.4 (CHAr), 84.8 (CH), 56.0, 55.6
(OCH3), 1.0, 0.4 (SiMe3).
3.3.23. 2-Thiophenyl-1,1-bis(trimethylsilyloxy)ethene
(2w). Starting with 1w (9.56 g, 39.76 mmol), HMDS
(10.3 mL, 49.70 mmol), n-BuLi (19.9 mL, 49.70 mmol),
Me3SiCl (10.8 mL, 59.64 mmol), and THF (39.0 mL), 2w
(10.66 g, 86%) was isolated as yellow oil. The obtained
spectroscopic data are in accordance with the data provided
in the literature.12f 1H NMR (250 MHz, CDCl3): d¼6.94–
7.21 (m, 5H, Ph), 4.31 (s, 1H, CH), 0.22 (s, 9H, SiMe3),
0.19 (s, 9H, SiMe3). 13C NMR (75 MHz, CDCl3): d¼158.8
(COSi), 140.4 (CPh), 128.5, 125.5, 124.3 (CHPh), 70.1
(CH), 0.9, 0.4 (SiMe3).
3.3.18. 2-(4-Biphenyl)-1,1-bis(trimethylsilyloxy)ethene
(2r). Starting with 1r (8.97 g, 31.54 mmol), HMDS
(8.2 mL, 39.42 mmol), n-BuLi (15.8 mL, 39.42 mmol),
Me3SiCl (6.0 mL, 47.31 mmol), and THF (32.0 mL), 2r
(9.88 g, 88%) was isolated as yellow oil. 1H NMR
(250 MHz, CDCl3): d¼7.13–7.53 (m, 9H, Ph/Ar), 4.60 (s,
1H, CH), 0.22 (s, 9H, SiMe3), 0.12 (s, 9H, SiMe3). 13C
NMR (75 MHz, CDCl3): d¼151.7 (COSi), 140.7, 136.1,
135.4 (CAr), 128.7, 127.3, 127.1, 126.6, 126.5 (CHAr), 84.3
(CH), 0.7, 0.3 (SiMe3). MS (EI, 70 eV): m/z (%)¼356
([M]+, 16), 284 (66), 269 (35), 240 (44), 194 (32), 165
(36), 73 (100). HRMS (EI): calcd for C20H28O2Si2 ([M]+)
356.16223, found 356.162565.
3.3.24. 1,1-Bis(trimethylsilyloxy)penta-1,4-diene (2x).
Starting with 1x (1.71 g, 9.94 mmol), HMDS (2.6 mL,
12.42 mmol), n-BuLi (4.0 mL, 9.94 mmol), Me3SiCl
(1.9 mL, 14.91 mmol), and THF (10.0 mL), 2x (2.00 g,
82%) was isolated as colorless oil. The obtained spectro-
scopic data are in accordance with the data provided in the
literature.12i 1H NMR (300 MHz, CDCl3): d¼5.83–5.74
(m, 1H, CH), 5.01–4.84 (m, 2H, ]CH2), 3.57 (t, 1H,
3
3J¼7.3 Hz, CH), 2.05 (t, 2H, J¼2.4 Hz, CH2), 0.20 (s,
3.3.19. 2-(Thien-2-yl)-1,1-bis(trimethylsilyloxy)ethene
(2s). Starting with 1s (10.55 g, 49.20 mmol), HMDS
(12.7 mL, 61.50 mmol), n-BuLi (24.6 mL, 61.50 mmol),
Me3SiCl (9.4 mL, 73.80 mmol), and THF (49.0 mL), 2s
(11.37 g, 83%) was isolated as yellow oil. 1H NMR
(250 MHz, CDCl3): d¼6.97–7.00 (m, 1H, Hetar), 6.89 (dd,
1H, 3J¼5.2, 4.9 Hz, Hetar), 6.70–6.73 (m, 1H, Hetar), 4.99
(s, 1H, CH), 0.32 (s, 9H, SiMe3), 0.18 (s, 9H, SiMe3). 13C
NMR (75 MHz, CDCl3): d¼151.2 (COSi), 140.8 (CHetar),
126.0, 120.7, 120.4 (CHHetar), 81.2 (CH), 2.5, 0.6 (SiMe3).
MS (EI, 70 eV): m/z (%)¼286 ([M]+, 22), 185 (98), 147
(32), 124 (61), 73 (100). HRMS (EI): calcd for
C18H22O2SSi2 ([M]+) 286.08736, found 286.086880.
18H, SiMe3).
3.4. Typical procedure for the preparation of substituted
hydroxymaleic anhydrides (3a–x)
3.4.1. 3-Hydroxy-4-methylmaleic anhydride (3a). To
a CH2Cl2 solution (22.0 mL) of oxalyl chloride (0.252 g,
2.80 mmol) and of 2a (0.500 g, 2.15 mmol) was added
CH2Cl2 solution (5 mL) of TMSOTf (0.19 mL,
1.07 mmol) at ꢁ78 ꢀC. The temperature of the solution
was allowed to rise to 20 ꢀC during 12 h. After stirring for
3 h at 20 ꢀC, an aqueous solution of HCl (10%) was added.
The organic and the aqueous layer were separated and the
latter was extracted three times with CH2Cl2. The combined
organic layers were dried (Na2SO4), filtered, and the solvent
of the filtrate was removed in vacuo. The residue was puri-
fied by chromatography (silica gel, hexane/EtOAc) to give
3.3.20. 2-Methoxy-1,1-bis(trimethylsilyloxy)ethene (2t).
Starting with 1t (4.36 g, 26.91 mmol), HMDS (7.0 mL,
33.64 mmol), n-BuLi (13.5 mL, 33.64 mmol), Me3SiCl
(5.1 mL, 40.36 mmol), and THF (27.0 mL), 2t (4.00 g,
53%) was isolated as colorless oil. The obtained spectro-
scopic data are in accordance with the data provided in the
literature.12g 1H NMR (300 MHz, CDCl3): d¼5.26 (s, 1H,
CH), 3.43 (s, 3H, OCH3), 0.22 (s, 18H, SiMe3).
1
3a (68 mg, 20%) as a colorless oil. H NMR (300 MHz,
CDCl3): d¼1.96 (s, 3H, CH3). 13C NMR (75 MHz,
CDCl3): d¼165.7, 163.6 (CO), 152.6 (COH), 111.9 (C),
6.9 (CH3). IR (neat, cmꢁ1): ~n ¼ 3430 (br), 2959 (m), 1729
(s), 1666 (s), 1614 (m), 1378 (m), 1239 (m), 1090 (m). MS
(EI, 70 eV): m/z (%)¼128 ([M]+, 34), 100 (28), 83 (100),
55 (96), 27 (56). Anal. Calcd for C5H4O4 (128.08): C,
46.89; H, 3.15. Found: C, 47.02; H, 3.33.
3.3.21. 2-Phenoxy-1,1-bis(trimethylsilyloxy)ethene (2u).
Starting with 1u (5.20 g, 23.18 mmol), HMDS (6.0 mL,

S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
2653
3.4.2. 3-Ethyl-4-hydroxymaleic anhydride (3b). Starting
with 2b (0.500 g, 2.15 mmol), oxalyl chloride (0.251 g,
2.80 mmol), and TMSOTf (0.19 mL, 1.07 mmol), 3b
(0.100 g, 36%) was isolated as yellow oil. 1H NMR
(300 MHz, CDCl3): d¼6.78 (s, 1H, OH), 2.40 (q, 2H,
3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol), 3f
(0.544 g, 71%) was isolated as a colorless solid; mp 98 ꢀC.
1H NMR (250 MHz, (CD3)2CO): d¼2.40 (t, 2H,
3J¼7.3 Hz, CH2), 1.61 (m, 2H, CH2), 1.19–1.45 (m, 18H,
3
CH2), 0.91 (t, 3H, J¼6.4 Hz, CH3). 13C NMR (75 MHz,
3
3J¼7.5 Hz, CH2), 1.20 (t, 3H, J¼7.5 Hz, CH3). 13C NMR
(CD3)2CO): d¼166.3, 163.0 (CO), 154.0 (COH), 114.8
(C), 32.2, 30.2, 30.0, 29.9, 29.7, 29.6, 28.9, 28.7, 27.6,
22.9, 21.9 (CH2), 14.0 (CH3). IR (KBr, cmꢁ1): ~n ¼ 3353
(m), 1849 (m), 1790 (s), 1705 (s), 1275 (m), 1254 (m),
1231 (m). MS (EI, 70 eV): m/z (%)¼282 ([M]+, 9), 254
(40), 209 (17), 155 (25), 113 (100). Anal. Calcd for
C16H26O4 (284.38): C, 68.06; H, 9.28. Found: C, 67.73; H,
9.40.
(75 MHz, CDCl3): d¼165.2, 163.6 (CO), 151.8 (COH),
116.9 (C), 15.6 (CH2), 11.4 (CH3). IR (KBr, cmꢁ1):
~n ¼ 3440 (br), 2979 (w), 1766 (s), 1699 (s), 1398 (m),
1255 (m), 1167 (w), 899 (w). MS (EI, 70 eV): m/z
(%)¼142 (M+, 25), 113 (14), 97 (100), 70 (58), 55 (24),
41 (37), 28 (36). Anal. Calcd for C6H6O4 (142.11): C,
50.71; H, 4.26. Found: C, 50.90; H, 4.39.
3.4.3. 3-Hydroxy-4-propylmaleic anhydride (3c). Starting
with 2c (0.500 g, 2.03 mmol), oxalyl chloride (0.231 g,
2.64 mmol), and TMSOTf (0.18 mL, 1.01 mmol), 3c
(0.132 g, 42%) was isolated as yellow oil. 1H NMR
3.4.7. 3-tert-Butyl-4-hydroxymaleic anhydride (3g). Start-
ing with 2g (0.651 g, 2.50 mmol), oxalyl chloride (0.413 g,
3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol), 3g
(0.070 g, 17%) was isolated as colorless oil. 1H NMR
(250 MHz, (CD3)2CO): d¼1.21 (s, 9H, CH3). 13C NMR
(75 MHz, (CD3)2CO): d¼164.2, 162.5 (CO), 151.7 (COH),
118.8 (C), 46.3 (CMe3), 31.4 (CH3). IR (Nujol, cmꢁ1): ~n ¼
3353 (br, m), 3057 (br, m), 1845 (m), 1773 (s), 1757 (br, s),
1684 (br, s), 1472 (br, s), 1116 (s). MS (EI, 70 eV): m/z
(%)¼170 ([M]+, 1), 127 (100), 109 (59), 97 (73), 39 (58).
HRMS (ESI): calcd for C8H9O4 ([MꢁH]ꢁ) 169.0506, found:
169.0498.
3
(300 MHz, (CD3)2CO): d¼3.59 (t, 2H, J¼7.2 Hz, CH2),
3
3
2.85 (sext, 2H, J¼7.8 Hz, CH2), 2.20 (t, 3H, J¼7.2 Hz,
CH3). 13C NMR (75 MHz, (CD3)2CO): d¼167.4, 164.0
(CO), 155.1 (COH), 115.7 (C), 24.9, 22.0 (CH2), 14.6
(CH3). IR (KBr, cmꢁ1): ~n ¼ 3355 (br), 2935 (w), 2875
(m), 1771 (s), 1701 (s), 1393 (s), 1233 (s), 1167 (s), 909
(s), 750 (w). MS (EI, 70 eV): m/z (%)¼156 ([M]+, 14),
110 (78), 97 (27), 83 (19), 70 (23), 55 (51), 41 (40), 28
(100). Anal. Calcd for C7H8O4 (156.14): C, 53.85; H,
5.16. Found: C, 53.35; H, 6.00.
3.4.8. 3-Cyclohexyl-4-hydroxymaleic anhydride (3h).
Starting with 2h (0.716 g, 2.50 mmol), oxalyl chloride
(0.413 g, 3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol),
3h (0.292 g, 60%) was isolated as a colorless solid; mp
3.4.4. 3-Hydroxy-4-pentylmaleic anhydride (3d). Starting
with 2d (0.500 g, 1.82 mmol), oxalyl chloride (1.180 g,
2.37 mmol), and TMSOTf (0.16 mL, 0.91 mmol), 3d
(0.168 g, 50%) was isolated as colorless oil. 1H NMR
(300 MHz, (CD3)2CO): d¼11.35 (s, 1H, OH), 2.32 (t, 2H,
3J¼7.2 Hz, CH2), 1.59–1.51 (m, 2H, CH2), 1.36–1.26 (m,
4H, CH2), 0.96 (t, 3H, 3J¼7.2 Hz, CH3). 13C NMR
(75 MHz, (CD3)2CO): d¼167.4, 164.0 (CO), 155.0 (COH),
115.8 (C), 32.7, 28.3, 23.6, 22.9 (CH2), 14.9 (CH3). IR
(KBr, cmꢁ1): ~n ¼ 3356 (br), 2923 (s), 1775 (s), 1703 (s),
1394 (s), 1207 (s), 749 (m). MS (EI, 70 eV): m/z (%)¼184
([M]+, 2), 156 (10), 139 (27), 128 (50), 112 (66), 100 (34),
85 (26), 55 (50), 43 (100), 29 (50). Anal. Calcd for
C9H12O4 (184.19): C, 58.69; H, 6.57. Found: C, 58.90; H,
7.02.
1
88 ꢀC. H NMR (250 MHz, (CD3)2CO): d¼2.52–2.64 (m,
1H, CH), 1.68–2.09 (m, 6H, CH2), 1.25–1.45 (m, 4H,
CH2). 13C NMR (75 MHz, (CD3)2CO): d¼166.6, 164.2
(CO), 154.1 (COH), 119.1 (C), 34.9 (CH), 31.0, 27.3, 26.9
(CH2). IR (KBr, cmꢁ1): ~n ¼ 3558 (m), 3451 (m), 2667 (br,
s), 1834 (m), 1756 (s), 1687 (s), 934 (m). MS (EI, 70 eV):
m/z (%)¼196 ([M]+, 33), 178 (18), 124 (23), 81 (62), 150
(100). HRMS (EI): calcd for C10H12O4 ([M]+) 196.0730,
found 196.0729.
3.4.9. 3-(Cyclopentylmethyl)-4-hydroxymaleic anhy-
dride (3i). Starting with 2i (0.716 g, 2.50 mmol), oxalyl
chloride (0.413 g, 3.25 mmol), and TMSOTf (0.14 mL,
0.75 mmol), 3i (0.303 g, 62%) was isolated as colorless
oil. 1H NMR (250 MHz, (CD3)2CO): d¼2.37 (d, 2H,
3J¼3.8 Hz, CH2), 2.14–2.24 (m, 1H, CH), 1.45–1.83 (m,
6H, CH2), 1.19–1.26 (m, 2H, CH2). 13C NMR (75 MHz,
(CD3)2CO): d¼166.6, 163.2 (CO), 154.4 (COH), 114.6
(C), 39.2 (CH), 32.7, 27.7, 25.2 (CH2). IR (KBr, cmꢁ1): ~n ¼
3441 (m), 3351 (s), 2953 (s), 2868 (m), 1844 (s), 1774 (s),
1703 (s), 1443 (m), 1394 (s). MS (EI, 70 eV): m/z
(%)¼196 ([M]+, 1), 178 (3), 161 (13), 147 (12), 128 (100),
100 (55). HRMS (ESI): calcd for C10H11O4 ([MꢁH]ꢁ)
195.06573, found 195.06702.
3.4.5. 3-Hydroxy-4-octylmaleic anhydride (3e). Starting
with 2e (0.500 g, 1.58 mmol), oxalyl chloride (0.258 g,
2.97 mmol), and TMSOTf (0.21 mL, 1.14 mmol), 3e
(0.200 g, 56%) was isolated as colorless solid; mp 87 ꢀC.
1H NMR (300 MHz, (CD3)2CO): d¼11.18 (s, 1H, OH),
3
2.36 (t, 2H, J¼7.2 Hz, CH2), 1.61–1.17 (m, 12H, CH2),
0.89 (t, 3H, 3J¼7.2 Hz, CH3). 13C NMR (75 MHz,
(CD3)2CO): d¼166.7, 163.4 (CO), 154.3 (COH), 115.4
(C), 32.5, 29.9, 28.0, 23.3, 22.3 (CH2), 14.3 (CH3). IR
(KBr, cmꢁ1): ~n ¼ 3358 (s), 2924 (s), 2854 (m), 1780 (s),
1705 (s), 1397 (s), 903 (m), 750 (m). MS (EI, 70 eV): m/z
(%)¼226 ([M]+, 7), 198 (16), 180 (17), 155 (34), 128 (57),
112 (60), 57 (79), 43 (89), 41 (100), 28 (98). Anal. Calcd
for C12H18O4 (226.27): C, 63.70; H, 8.02. Found: C,
63.33; H, 7.85.
3.4.10. 3-(Cyclohexylethyl)-4-hydroxymaleic anhydride
(3j). Starting with 2j (0.787 g, 2.50 mmol), oxalyl chloride
(0.413 g, 3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol),
3j (0.354 g, 63%) was isolated as a colorless solid; mp
87 ꢀC. 1H NMR (250 MHz, (CD3)2CO): d¼2.37 (t, 2H,
3J¼7.5 Hz, CH2), 1.61–1.80 (m, 5H, CH, CH2), 1.41–1.50
(m, 2H, CH2), 1.13–1.32 (m, 4H, CH2), 0.85–0.98 (m, 2H,
3.4.6. 3-Dodecyl-4-hydroxymaleic anhydride (3f). Start-
ing with 2f (0.932 g, 2.50 mmol), oxalyl chloride (0.413 g,

2654
S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
CH2). 13C NMR (75 MHz, (CD3)2CO): d¼166.5, 163.3
(CO), 154.4 (COH), 114.6 (C), 37.7 (CH), 35.1, 33.4,
26.9, 26.6, 19.5 (CH2). IR (KBr, cmꢁ1): ~n ¼ 3349 (s),
3261 (m), 2926 (s), 2852 (m), 1839 (m), 1779 (br, s), 1708
(s), 1456 (m), 1391 (s). MS (CI pos.): m/z (%)¼225
([M+H]+, 100). Anal. Calcd for C12H16O4 (284.38): C,
64.27; H, 7.19. Found: C, 64.44; H, 9.31.
3.4.15. 4-(4-Fluorophenyl)-3-hydroxymaleic anhydride
(3o). Starting with 2o (0.746 g, 2.50 mmol), oxalyl chloride
(0.413 g, 3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol),
3o (0.232 g, 45%) was isolated as colorless solid; mp
1
115 ꢀC. H NMR (500.13 MHz, (CD3)2CO): d¼10.9 (br,
4
1H, OH); 8.12 (m, 2H, JF,H¼5.5 Hz, o-Ph), 7.27 (m, 2H,
3JF,H¼9.0 Hz, m-Ph). 13C NMR (125.8 MHz, (CD3)2CO):
1
d¼165.3, 160.0 (C-1, C-4), 163.6 (d, JF,C¼249.3 Hz,
3.4.11. 3-Benzhydryl-4-hydroxymaleic anhydride (3k).
Starting with 2k (0.927 g, 2.50 mmol), oxalyl chloride
(0.413 g, 3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol),
p-Ph), 152.6 (d, 6JF,C¼1.5 Hz, C-2); 131.3 (d, 3JF,C¼8.4 Hz,
o-Ph), 125.4 (d, 4JF,C¼3.4 Hz, i-Ph), 116.4 (d,
2JF,C¼22.0 Hz, m-Ph); 110.3 (C-3). 19F NMR (235 MHz):
d¼ꢁ111.8 (p-CF). IR (KBr, cmꢁ1): ~n ¼ 3308 (br, s), 1843
(m), 1773 (br, s), 1676 (m), 1606 (m), 1514 (m), 1419 (w),
1392 (br, s). MS (EI, 70 eV): m/z (%)¼208 ([M]+, 34), 180
(100), 163 (12), 135 (45), 107 (89). HRMS (EI): calcd for
C10H5FO4 ([M]+) 208.0166, found: 208.0168.
1
3k (0.212 g, 30%) was isolated as colorless oil. H NMR
(250 MHz, (CD3)2CO): d¼7.27–7.37 (m, 10H, Ph), 5.43
(s, 1H, CH). 13C NMR (62.5 MHz, (CD3)2CO): d¼165.9,
163.0 (CO), 155.0 (COH), 140.8 (CPh), 129.2, 128.8, 127.3
(CHPh), 114.8 (C), 45.5 (CH). IR (neat, cmꢁ1): ~n ¼ 3596
(w), 3062 (m), 3029 (m), 2633 (br, m), 1849 (s), 1763 (s),
909 (s). MS (EI, 70 eV): m/z (%)¼280 ([M]+, 59), 262 (9),
252 (34), 235 (50), 167 (100). HRMS (EI): calcd for
C17H12O4 ([M]+) 280.0730, found: 280.0729.
3.4.16. 3-Hydroxy-4-(4-methoxyphenyl)maleic anhy-
dride (3p). Starting with 2p (0.500 g, 1.61 mmol), oxalyl
chloride (0.180 g, 2.10 mmol), and TMSOTf (0.15 mL,
0.80 mmol), 3p (0.190 g, 53%) was isolated as yellow solid;
1
3.4.12. 3-Hydroxyphenylmaleic anhydride (3l). Starting
with 2l (0.500 g, 1.8 mmol), oxalyl chloride (0.20 mL,
2.3 mmol), and TMSOTf (0.16 mL, 0.9 mmol), 3l
(240 mg, 70%) was isolated as a yellow solid; mp 164 ꢀC.
1H NMR (300 MHz, CDCl3): d¼7.42–7.50 (m, 3H, Ph),
8.05–8.08 (m, 2H, Ph). 13C NMR (75 MHz, CDCl3):
d¼163.5, 163.4 (CO), 149.4 (COH), 130.3, 129.1, 128.8
(CHPh), 126.9 (CPh), 112.0 (C). IR (neat, cmꢁ1): ~n ¼ 3244
(s), 3123 (w), 1840 (s), 1760 (s), 1673 (s), 1393 (s), 1262
(s), 939 (s), 762 (s). MS (EI, 70 eV): m/z (%)¼190 ([M]+,
43), 162 (100), 145 (22), 118 (27), 105 (15), 89 (81), 77
(8). Anal. Calcd for C10H6O4 (190.15): C, 63.16; H, 3.18.
Found: C, 62.87; H, 3.63.
mp 115 ꢀC. H NMR (300 MHz, (CD3)2CO): d¼8.07–8.02
(m, 2H, Ar), 7.07–7.02 (m, 2H, Ar), 3.85 (s, 3H, OCH3).
13C NMR (75 MHz, (CD3)2CO): d¼165.8, 163.6, 161.2
(CO), 151.8 (COH), 131.3, 130.6 (CHAr), 121.7 (C),
115.0, 114.6 (CHAr), 111.1 (C), 55.8 (OCH3). IR (KBr,
cmꢁ1): ~n ¼ 3484 (br), 2927 (m), 1761 (s), 1604 (s), 1515
(s), 1251 (s), 1028 (m), 836 (m). MS (EI, 70 eV): m/z
(%)¼220 ([M]+, 43), 192 (100), 135 (64), 121 (85), 77
(36), 51 (45), 28 (50). Anal. Calcd for C11H8O5 (220.18):
C, 60.00; H, 3.66. Found: C, 59.95; H, 4.17.
3.4.17. 4-(3,4-Dimethoxyphenyl)-3-hydroxymaleic anhy-
dride (3q). Starting with 2q (0.500 g, 1.47 mmol), oxalyl
chloride (0.161 g, 1.91 mmol), and TMSOTf (0.14 mL,
0.17 mmol), 3e (0.261 g, 70%) was isolated as yellow solid;
3.4.13. 3-Hydroxy-4-(4-tolyl)maleic anhydride (3m).
Starting with 2m (0.501 g, 1.70 mmol), oxalyl chloride
(0.192 g, 2.21 mmol), and TMSOTf (0.15 mL, 0.85 mmol),
3b (0.253 g, 73%) was isolated as brown solid; mp 102 ꢀC.
1H NMR (300 MHz, (CD3)2CO): d¼7.95 (d, 2H,
1
mp 214 ꢀC. H NMR (300 MHz, (CD3)2CO): d¼7.72–7.68
(m, 2H, Ar), 7.07 (t, 1H, 3J¼8.4 Hz, Ar), 3.87 (s, 6H,
OCH3). 13C NMR (75 MHz, (CD3)2CO): d¼166.2, 163.9
(CO), 151.9 (COH), 151.7, 150.7 (CAr), 123.4 (CHAr),
122.8 (CAr), 113.1, 113.1 (CHAr), 112.2 (C), 56.7, 56.7
(OCH3). IR (KBr, cmꢁ1): ~n ¼ 3401 (s), 2927 (m), 1765
(s), 1714 (s), 1242 (s), 1022 (s), 915 (m), 822 (m). MS (EI,
70 eV): m/z (%)¼250 ([M]+, 46), 220 (100), 207 (18), 148
(20), 77 (10), 28 (33). Anal. Calcd for C12H10O6 (250.20):
C, 57.60; H, 4.03. Found: C, 58.01; H, 3.72.
3
3J¼8.4 Hz, Ar), 7.30 (d, 2H, J¼8.4 Hz, Ar), 2.29 (s, 3H,
CH3). 13C NMR (75 MHz, (CD3)2CO): d¼166.0, 163.9
(CO), 153.0 (COH), 140.7 (CAr), 130.7, 129.6 (CHAr),
126.8 (CAr), 111.9 (C), 22.0 (CH3). IR (KBr, cmꢁ1):
~n ¼ 3455 (br), 2925 (w), 1767 (s), 1680 (m), 1387 (s),
1173 (w), 825 (w). MS (EI, 70 eV): m/z (%)¼204 ([M]+,
36), 176 (76), 149 (31), 131 (30), 105 (100), 77 (40), 51
(18), 28 (10). Anal. Calcd for C11H8O4 (204.18): C, 64.71;
H, 3.95. Found: C, 65.00; H, 4.01.
3.4.18. 4-(4-Biphenyl)-3-hydroxymaleic anhydride (3r).
Starting with 2r (0.892 g, 2.50 mmol), oxalyl chloride
(0.413 g, 3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol),
3r (0.379 g, 57%) was isolated as yellowish solid; mp
3.4.14. 4-(4-Chlorophenyl)-3-hydroxymaleic anhydride
(3n). Starting with 2n (0.500 g, 1.60 mmol), oxalyl chloride
(1.042 g, 2.0 mmol), and TMSOTf (0.14 mL, 0.80 mmol),
3n (0.230 g, 65%) was isolated as yellow solid; mp
1
180 ꢀC. H NMR (250 MHz, (CD3)2CO): d¼8.31 (d, 2H,
3J¼8.5 Hz, Ph/Ar), 7.58–7.64 (m, 4H, Ph/Ar), 7.37–7.44
(m, 2H, Ph/Ar), 7.27–7.34 (m, 1H, Ph/Ar). 13C NMR
(75 MHz, (CD3)2CO): d¼177.5, 168.0 (CO), 150.3 (COH),
141.7, 139.4, 131.8 (C), 129.9, 128.2, 127.7, 127.7, 127.4
(CHAr). IR (Nujol, cmꢁ1): ~n ¼ 1810 (br, s), 1733 (br, m),
1620 (br, s), 1300 (br, m), 1240 (m), 1181 (m), 1077 (w).
HRMS (ESI): calcd for C16H9O4 ([MꢁH]ꢁ) 265.0506,
found: 265.0622.
1
150 ꢀC. H NMR (300 MHz, (CD3)2CO): d¼8.09 (d, 2H,
3
3J¼2.4 Hz, Ar), 7.55 (d, 2H, J¼7.2 Hz, Ar). 13C NMR
(75 MHz, (CD3)2CO): d¼165.9, 163.6 (CO), 154.2 (COH),
135.9, 135.5 (CAr), 132.5, 131.2, 130.3, 129.8 (CHAr),
110.6 (C). IR (KBr, cmꢁ1): ~n ¼ 3319 (s), 3100 (w), 1755
(s), 1697 (s), 1388 (s), 1092 (m), 864 (m). MS (EI, 70 eV):
m/z (%)¼224 ([M]+, 36), 196 (100), 151 (32), 125 (57), 89
(52), 63 (24), 28 (10). Anal. Calcd for C10H5ClO4
(224.60): C, 53.48; H, 2.24. Found: C, 53.29; H, 2.56.
3.4.19. 3-Hydroxy-4-(thien-2-yl)maleic anhydride (3s).
Starting with 2s (0.716 g, 2.50 mmol), oxalyl chloride

S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
2655
(0.413 g, 3.25 mmol), and TMSOTf (0.14 mL, 0.75 mmol),
3s (0.305 g, 62%) was isolated as yellowish solid; mp
HRMS (ESI): calcd for C10H5O4 ([MꢁH]ꢁ) 220.9914,
found: 220.9925.
1
151 ꢀC. H NMR (250 MHz, (CD3)2CO): d¼7.88 (dd, 1H,
4
3
3J¼3.7 Hz, J¼1.2 Hz, Hetar), 7.77 (dd, 1H, J¼5.2 Hz,
3.4.24. 3-Allyl-4-hydroxymaleic anhydride (3x). Starting
with 2x (1.900 g, 7.78 mmol), oxalyl chloride (5.061 g,
10.12 mmol), and TMSOTf (0.70 mL, 3.90 mmol), 3x
(0.134 g, 20%) was isolated as yellow oil. 1H NMR
4J¼1.2 Hz, Hetar), 7.27 (dd, 1H, J¼5.2 Hz, J¼3.7 Hz,
Hetar). 13C NMR (62.5 MHz, (CD3)2CO): d¼165.2, 163.4
(CO), 150.3 (COH), 130.4, 130.1 (CHHetar), 130.0 (CHetar),
129.0 (CHHetar), 109.3 (C). IR (Nujol, cmꢁ1): ~n ¼ 3182
(br, m), 3109 (m), 1829 (m), 1758 (s), 1676 (m), 1277 (s),
1230 (m). MS (CI pos.): m/z (%)¼197 ([M+H]+, 100).
HRMS (CI, neg.): calcd for C8H3O4S ([MꢁH]ꢁ)
194.9747, found: 194.9750.
3
3
3
(300 MHz, (CD3)2CO): d¼5.82 (q, 1H, J¼10.2 Hz, CH),
3
3
5.17 (d, 2H, Jtrans¼17 Hz, Jgem¼2 Hz, 1H, CH), 5.01 (d,
3
3
2H, Jcis¼12 Hz, Jgem¼2 Hz, 1H, CH). 13C NMR
(75 MHz, (CD3)2CO): d¼166.4, 163.4 (CO), 155.1 (COH),
133.3 (CH), 117.1 (CH), 112.2 (C), 26.3 (CH2). IR (KBr,
cmꢁ1): ~n ¼ 3344 (Br), 2982 (m), 1769 (s), 1673 (m), 1227
(m), 923 (m), 759 (m). MS (EI, 70 eV): m/z (%)¼154
([M]+, 17), 108 (60), 107 (89), 83 (50), 55 (100), 27 (50).
Anal. Calcd for C7H6O4 (154.12): C, 54.55; H, 3.92. Found:
C, 54.92; H, 4.01.
3.4.20. 3-Hydroxy-4-methoxymaleic anhydride (3t).
Starting with 2t (0.500 g, 2.13 mmol), oxalyl chloride
(0.252 g, 2.77 mmol), and TMSOTf (0.19 mL, 1.06 mmol),
3t (0.159 g, 53%) was isolated as yellow oil. 1H NMR
(300 MHz, (CD3)2CO): d¼4.10 (s, 3H, OCH3). 13C NMR
(75 MHz, (CD3)2CO): d¼163.5, 162.4 (CO), 153.3 (COH),
133.6 (C), 60.0 (OCH3). IR (neat, cmꢁ1): ~n ¼ 3436 (br),
2966 (m), 1773 (s), 1714 (s), 1353 (s), 1155 (s), 917 (w).
MS (EI, 70 eV): m/z (%)¼144 ([M]+, 3), 118 (6), 89 (7),
73 (14), 59 (23), 45 (100), 29 (77), 28 (21). Anal. Calcd
for C5H4O5 (144.08): C, 41.68; H, 2.80. Found: C, 41.80;
H, 3.20.
Acknowledgements
Financial support by the Degussa Stiftung (scholarship for
S.R.) is gratefully acknowledged.
References and notes
3.4.21. 3-Hydroxy-4-phenoxymaleic anhydride (3u).
Starting with 2u (0.500 g, 1.69 mmol), oxalyl chloride
(0.192 g, 2.19 mmol), and TMSOTf (0.15 mL, 0.84 mmol),
3u (0.178 g, 50%) was isolated as colorless solid; mp
164 ꢀC. 1H NMR (300 MHz, (CD3)2CO): d¼8.67–8.60 (m,
2H, Ph), 8.49–8.38 (m, 3H, Ph). 13C NMR (75 MHz,
(CD3)2CO): d¼162.6, 162.3 (CO), 157.1 (COH), 143.8,
133.1 (C), 131.3, 125.4, 117.8 (CHPh). IR (KBr, cmꢁ1): ~n ¼
3220 (br), 2960 (w), 1766 (s), 1721 (s), 1489 (s), 1381 (s),
1198 (s), 930 (s). MS (EI, 70 eV): m/z (%)¼206 ([M]+, 6),
180 (35), 151 (36), 107 (47), 105 (54), 77 (100), 51 (33),
28 (10). Anal. Calcd for C10H6O5 (206.15): C, 58.26; H,
2.93. Found: C, 58.00; H, 3.02.
1. Reagents for Organic Synthesis; Paquette, L. A., Ed.; Wiley:
Chichester, UK, 1995; p 3207.
2. (a) Knight, D. W.; Pattenden, G. J. Chem. Soc., Perkin Trans. 1
1979, 62; (b) Ingham, C. F.; Massy-Westropp, R. A.; Reynolds,
G. D.; Thorpe, W. D. Aust. J. Chem. 1975, 28, 2499; (c) Massy-
Westropp, R. A.; Price, M. F. Aust. J. Chem. 1980, 33, 333; (d)
James, G. D.; Mills, S. D.; Pattenden, G. J. Chem. Soc., Perkin
Trans. 1 1993, 2581.
3. (a) Danishefsky, S. J.; Kitahara, T.; Schuda, P. F.; Golob, D.;
Dynak, J.; Stevens, R. V. Org. Synth. 1983, 61, 147; (b)
Kloetzel, M. C. Org. React. 1948, 4, 1; (c) Alder, K. Neuere
Methoden der Pra€parativen Organischen Chemie; Foerst, W.,
Ed.; Chemie: Berlin, 1953; Part 2; (d) See also: Dauben,
W. G.; Kessel, C. R.; Takemura, K. H. J. Org. Chem. 1985,
50, 2576; (e) Kozikowski, A. P.; Huie, E.; Springer, J. P.
J. Am. Chem. Soc. 1982, 104, 2059.
4. (a) Murray, W. V.; Wachter, M. P. J. Org. Chem. 1990, 55,
3424; (b) Jacobi, P.; Blum, C. A.; DeShimone, R. W.;
Udodong, U. E. S. J. Am. Chem. Soc. 1991, 113, 5384; (c)
Kaydos, J. A.; Smith, D. L. J. Org. Chem. 1983, 48, 1096.
5. Kishorebabu, N.; Periasamy, M. Tetrahedron Lett. 2006, 47,
2107.
6. (a) Schreiber, J. Liebigs Ann. 1947, 2, 84; (b) Edwards, R. L.;
Gill, M. J. Chem. Soc., Perkin Trans. 1 1973, 1538; (c) Nef.
Justus Liebigs Ann. Chem. 1910, 376, 115; (d) Yalpani, M.;
Wilke, G. Chem. Ber. 1985, 118, 661; (e) Goodwin, S.;
Witkop, B. J. Am. Chem. Soc. 1954, 76, 5599; (f) Stachel,
H.-D.; Schachtner, J.; Seidel, J. Z. Naturforsch. B 1996, 51, 409.
7. For a review of silyl enol ethers, see: Brownbridge, P. Synthesis
1983, 85.
3.4.22. 3-Hydroxy-4-benzyloxymaleic anhydride (3v).
Starting with 2v (0.500 g, 1.61 mmol), oxalyl chloride
(1.051 g, 2.10 mmol), and TMSOTf (0.14 mL, 0.80 mmol),
1
3n (0.145 g, 40%) was isolated as colorless oil. H NMR
(300 MHz, (CD3)2CO): d¼7.49–7.34 (m, 5H, Ph), 5.46
(s, 2H, CH2). 13C NMR (75 MHz, (CD3)2CO): d¼163.4,
162.6 (CO), 137.6, 136.8 (C), 130.1, 130.0, 129.9, 129.8,
129.7 (CH), 128.0 (C), 74.6 (CH2). IR (KBr, cmꢁ1):
~n ¼ 3428 (br), 3035 (w), 1747 (s), 1208 (m), 743 (m),
699 (m). MS (EI, 70 eV): m/z (%)¼220 ([M]+, 1), 107
(4), 91 (100), 66 (14), 39 (6), 29 (6). Anal. Calcd for
C11H8O5 (220.18): C, 60.00; H, 3.66. Found: C, 59.69;
H, 3.20.
3.4.23. 3-Hydroxy-4-thiophenoxymaleic anhydride (3w).
Starting with 2w (0.782 g, 2.50 mmol), oxalyl chloride
(0.413 g,
0.75 mmol), 3w (0.277 g, 50%) was isolated as yellow
3.25 mmol),
and
TMSOTf
(0.14 mL,
8. (a) Murai, S.; Hasegawa, K.; Sonoda, N. Angew. Chem. 1975,
87, 668; Angew. Chem., Int. Ed. Engl. 1975, 14, 636; (b)
Kappe, C. O.; Kollenz, G.; Wentrup, C. Heterocycles 1994,
38, 779.
9. For a review of 1,3-bis(silyl enol ethers), see: Langer, P.
Synthesis 2002, 441.
1
oil. H NMR (250 MHz, (CD3)2CO): d¼7.06–7.57 (br m,
5H, Ph). 13C NMR (75 MHz, (CD3)2CO): d¼172.1,
167.8, 167.0, 138.8 (C), 128.9, 126.3, 125.0 (CHPh). IR
(KBr, cmꢁ1): ~n ¼ 3419 (br, m), 3058 (m), 1829 (m),
1696 (m), 1618 (s), 1480 (m), 1439 (m), 1402 (m).

2656
S. Rotzoll et al. / Tetrahedron 63 (2007) 2647–2656
10. (a) Langer, P.; Schneider, T.; Stoll, M. Chem.—Eur. J. 2000, 6,
3204; (b) For palladium-catalyzed functionalizations, see:
1738; (f) Hoppe, H.-W.; Kaiser, M.; Mueller, D.; Welzel, P.
Tetrahedron 1987, 43, 2045; (g) Emde, H.; Simchen, G.
Liebigs Ann. Chem. 1983, 5, 816; (h) Rubottom, G.-M.;
Marrero, R. J. Org. Chem. 1975, 40, 3783; (i) Rudler, H.;
Denise, B.; Xu, Y.; Parlier, A.; Vaissermann, J. Eur. J. Org.
Chem. 2005, 17, 3724.
€
Langer, P.; Eckardt, T.; Schneider, T.; Gobel, C.; Herbst-
Irmer, R. J. Org. Chem. 2001, 66, 2222; (c) Ahmed, Z.;
Langer, P. J. Org. Chem. 2004, 69, 3753.
11. Ullah, E.; Langer, P. Synlett 2004, 2782.
12. For the synthesis of 1,1-bis(trimethylsilyloxy)ketene acetals,
see: (a) Ainsworth, C.; Kuo, Y.-N. J. Organomet. Chem.
1972, 46, 73; (b) Wissner, A. J. Org. Chem. 1979, 44, 4617;
(c) Takai, K.; Heathcock, C. H. J. Org. Chem. 1985, 50,
3247; (d) Pola., et al. Collect. Czech. Chem. Commun. 1977,
42, 1540; (e) Washburne, S., et al. J. Org. Chem. 1972, 37,
13. CCDC-616698 contains all crystallographic details of this pub-
lication and is available free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html or can be ordered from the following
address: Cambridge Crystallographic Data Centre, 12 Union
Road, GB-Cambridge CB21EZ; fax: +44 1223 336 033;
deposit@ccdc.cam.ac.uk.