Selective synthesis of dihalo-substituted unsaturated carboxylic acids and derivatives

Article abstract of DOI:10.1055/s-2007-966043

A selective one-pot procedure was developed for the production of E-dihalo-substituted α,β-unsaturated alkenoic acids and derivatives from the corresponding α,β-unsaturated alkynoic acids. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-966043

1724
PAPER
Selective Synthesis of Dihalo-Substituted Unsaturated Carboxylic Acids and
Derivatives
D
ihalo-Substit
a
uted
U
nsa
t
n
C
arbo
d
xylic
A
cids
a
nd Deri
i
vativesne Langle,a Samuel Inack Ngi,b Elsa Anselmi,b Mohamed Abarbri,b Jérôme Thibonnet,b Alain Duchêne*b
a
Laboratoire Groupe SUCRES, Unité Mixte 7565 CNRS, Université Henri Poincaré-Nancy 1, B.P. 239, 54506 Nancy-Vandoeuvre,
France
b
Laboratoire de Synthèse et Physicochimie Organique et Thérapeutique, Faculté des Sciences et Techniques de Tours, Parc de Granmont,
37200 Tours, France
Fax +33(2)47367073; E-mail: alain.duchene@univ-tours.fr
Received 22 December 2006
The best results in terms of selectivity were obtained at
0 °C for the addition of iodine monochloride or -bromide
to propiolic acid (Table 1, entries 1 and 3), and at 35 °C
for the addition of iodine monochloride or -bromide to
tetrolic acid (Table 1, entries 2 and 4). We also tried to
isomerize acids 1–4 into the corresponding Z-acids by
heating, addition of iodine, or irradiation with a UV lamp;
only the irradiation method resulted in the following inter-
esting isomerization results: 1 (Z/E, 82:18, after 12 h), 2
(Z/E, 49:51, after 10 h), 3 (Z/E, 90:10, after 14 h; pure Z-
acid obtained by crystallization), and 4 (Z/E, 30:70, after
8 h).
Abstract: A selective one-pot procedure was developed for the pro-
duction of E-dihalo-substituted a,b-unsaturated alkenoic acids and
derivatives from the corresponding a,b-unsaturated alkynoic acids.
Key words: a,b-unsaturated acids, carboxylic acids, a,b-dihalo-
substituted acrylic acids, halogenation, addition reactions
Functionalized 1,2-dihaloalk-1-enes are useful intermedi-
ates in substitution reactions and in direct coupling reac-
tions for forming new carbon–carbon bonds involving
organolithium, organocopper, organozinc, organotin, or
palladium cross-coupling reactions. 1,2-Diiodoalkenes
can be prepared by a variety of methods, such as alumina-
or Florisil-assisted iodination of alkynes,1 direct addition
of iodine (or bromine) to alkynes,2 and the use of electro-
positive iodonium (or bromonium) species in the presence
of iodonium ions.3 Iodine monochloride or monobromide
is usually used as an intermediate to produce iodoalkene,
as, for example, in the classical methodology for the trans-
formation of vinylsilane into vinyl iodide or to synthesize
unsymmetrical 2,3-dihaloalk-2-en-1-ols or 2,3-dihaloalk-
2-enoates.4
The application of these reactions was extended to other
alk-2-ynoic acids and derivatives (Scheme 2, Table 2).
X'
O
O
solvent, X-X'
R1
R2
R2
time, temperature
R1
X
5–16
Scheme 2 Synthesis of 2,3-dihaloalk-2-enoic acids and derivatives
In all cases, under the various conditions shown in
Table 2, these additions were regio- and stereoselective,
resulting from trans addition at the triple bond of the start-
ing alk-2-ynoic acid, and the E/Z ratio was always in favor
of the E-isomer. In the case of unsymmetrical dihalogens,
the iodine atom was always in the a-position relative to
the carbonyl group. It should be noted that stannyl esters
and amides (Table 2, entries 5, 10, and 11) provided the
same selectivity. Some stereoisomerically pure E-isomers
were obtained by crystallization, but this resulted in de-
creased yield. Interestingly, in all cases no cyclization
product leading to a four-membered-ring product was ob-
tained.
We recently demonstrated the use of iodovinylic acids as
a flexible method for the stereoselective synthesis of poly-
enes containing natural products such as retinoic and ret-
inoid acids. In view of the surprising scarcity of literature
reports on the synthesis of dihaloalkenoic acids,5 we re-
port here the efficient synthesis of (E)- or (Z)-dihaloalk-
enoic acids or derivatives.
We first studied the effects of the reaction conditions on
the selectivity in the addition of iodine monochloride or
-bromide to propiolic and tetrolic acid in diethyl ether
(Scheme 1, Table 1).
O
(Br or)Cl
R
O
I-Cl (or I-Br), Et2O
time, temperature
To confirm the E-structure of some 2,3-dihaloalk-2-enoic
acids, X-ray analysis was performed on compounds 6
(Figure 1), 10 (Figure 2), 11, and 16.
OH
R = H, Me
OH
R
I
In conclusion, we report here a new synthetic method for
the synthesis of symmetrical and unsymmetrical a,b-di-
haloacrylic acids and derivatives. The reactivity of these
new compounds is currently under investigation in our
laboratory.
Scheme 1 Synthesis of 2,3-dihaloalk-2-enoic acids
SYNTHESIS 2007, No. 11, pp 1724–1728
x
x.
x
x
.
2
0
0
7
Advanced online publication: 02.05.2007
DOI: 10.1055/s-2007-966043; Art ID: Z27106SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Dihalo-Substituted Unsaturated Carboxylic Acids and Derivatives
1725
Table 1 Addition of Iodine Monochloride or Iodine Monobromide to Propiolic or Tetrolic Acida
Entry
1
R
H
IX
Temp (°C)
0
Time (h)
12
Product
E/Z ratio
Yield (%)
Cl
CO2H
ICl
98:2b,c
55
48
62
50
I
1
Cl
CO2H
2
3
4
Me
H
ICl
IBr
IBr
35
0
12
18
14
97:3
I
2
Br
CO2H
>99:1
98:2b
I
3
4
Br
CO2H
Me
35
I
a See Scheme 1 for corresponding reaction.
b The crude product was contaminated with the corresponding dichloro or diiodo acid.6
c Compound 1 must be used as soon as possible and kept away from light.
Figure 1 ORTEP drawing and labeling scheme for 6 (ellipsoids are
set at 50% probability)
Figure 2 ORTEP drawing and labeling scheme for 10 (ellipsoids
are set at 50% probability)
mol) in Et2O (25 mL) was added dropwise over 10 min while the re-
action mixture was vigorously stirred. After the addition, the result-
ing soln was stirred for an additional 15 h while being cooled in the
ice bath. The reaction mixture was quenched by dropwise addition
of aq sat. NaHSO3 soln (30 mL). The layers were separated, and the
aqueous layer was extracted with CH2Cl2 (4 × 25 mL). The com-
bined organic layers were washed with aq sat. NaCl soln (25 mL),
dried (MgSO4), filtered, and concentrated under reduced pressure;
this gave 2 as colorless crystals. The crude product was recrystal-
lized from a minimum amount of CH2Cl2; this yielded pure 2.
All reactions were carried out under an inert atmosphere (argon or
N2). Flash chromatography was performed on silica gel (Merck,
230–400 mesh). 1H (200 MHz) and 13C (50.3 MHz) NMR spectra
were recorded on a Bruker AC 200 NMR spectrometer; CDCl3 was
used as solvent, and the chemical shifts d are reported relative to
CDCl3 (dH = 7.25, dC = 77.0). Mass spectra were obtained on a
Hewlett Packard (engine 5989A) in the GC/MS (70 eV) mode or di-
rect injection mode. IR spectra were recorded on a Perkin Elmer
1600 series FTIR spectrophotometer.
(E)-3-Chloro-2-iodobut-2-enoic Acid (2); Typical Procedure
A 100-mL, three-necked, round-bottomed flask protected from
light, equipped with a magnetic stirrer, reflux condenser fitted with
an argon inlet adapter, thermometer, and pressure-equalizing drop-
ping funnel, was charged with tetrolic acid (5 g, 0.06 mol) and Et2O
(15 mL). The mixture was cooled with an ice–salt bath to –5 °C, and
maintained under an argon atmosphere. A soln of ICl (12.2 g, 0.075
Yield: 7.03 g (48%); mp 73–75 °C.
IR (KBr): 3100–2600, 3087, 1698, 1592, 1273 cm–1.
1H NMR (200 MHz, CDCl3): d (E-isomer) = 2.54 (s, 3 H), 11.60 (br
s, 1 H); d (Z-isomer, 3%) = 2.78 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 31.4, 80.9, 138.8, 170.5.
Synthesis 2007, No. 11, 1724–1728 © Thieme Stuttgart · New York

1726
S. Langle et al.
PAPER
Table 2 Addition of Dihalogens to Alk-2-ynoic Acidsa
Entry
1
R1
R2
X–X¢
Temp (°C) Time (h) Solvent
Product
E/Z ratio
Yieldb (%)
80
Br
CO2H
Br
Me
OH
Br2
–5
–5
–5
35
35
35
35
25
35
0
0.2
0.5
4
MeOH
none
CHCl3
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
Et2O
>99:1
5
Br
CO2H
Br
2
3
CH2OMe OH
Br2
Br2
I2
>99:1
91:9
87
MeO
6
Br
CO2H
Br
n-C5H11
OH
97
n-C5H11
7
I
CO2H
4
H
OH
12
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
98:2
68
H
I
8
I
CONHBz
I
5
Me
NHBz
OH
I2
12
18
18
12
18
12
12
12
70
Me
9
CO2H
I
I
6
Me
I2
85
Me
10
I
CO2H
7
CH2OMe OH
I2
84
MeO
I
11
I
CO2H
I
8
n-C5H11
OH
I2
95
n-C5H11
12
I
CO2H
9
Ph
OH
I2
80
Ph
13
Cl
I
CO2SnBu3
I
10
11
12
H
OSnBu3
OSnBu3
ICl
ICl
ICl
55
H
14
Cl
CO2SnBu3
Me
35
–5
98:2
50
I
15
Cl
CO2H
I
CH2OMe OH
87:13
47 (88c)
MeO
16
a See Scheme 2 for corresponding reaction.
b Isolated yield after crystallization.
c Yield estimated by NMR.
MS (EI, 70 eV): m/z (%) = 248 (18) [M + 2], 246 (55) [M+], 211
(31), 210 (48), 127 (24), 84 (12), 83 (39), 73 (15), 67 (26), 55 (26),
49 (18), 45 (20), 39 (100), 38 (37), 37 (24).
(E)-3-Chloro-2-iodoprop-2-enoic Acid (1)
Mp 67–69 °C.
IR (KBr): 3250–2600, 3047, 1685, 1600, 1257 cm–1.
Anal. Calcd for C4H4ClIO2: C, 19.50; H, 1.64. Found: C, 19.49; H,
1.69.
1H NMR (200 MHz, CDCl3): d (E-isomer) = 7.28 (s, 1 H), 11.40 (br
s, 1 H); d (Z-isomer, 2%) = 8.11 (s, 1 H).
13C NMR (50 MHz, CDCl3): d = 84.8, 133.6, 168.4.
Synthesis 2007, No. 11, 1724–1728 © Thieme Stuttgart · New York

PAPER
Dihalo-Substituted Unsaturated Carboxylic Acids and Derivatives
1727
MS (EI, 70 eV): m/z (%) = 234 (6) [M + 2], 232 (23) [M+], 197 (15),
152 (10), 127 (36), 107 (10), 105 (20), 61 (19), 60 (11), 53 (24), 50
(17), 45 (22), 44 (100), 42 (11).
MS (EI, 70 eV): m/z (%) = 300 (4) [M + 2], 220 (14), 219 (14), 179
(14), 177 (16), 165 (11), 163 (13), 139 (15), 121 (13), 111 (17), 97
(13), 95 (25), 94 (10), 93 (68), 81 (30), 79 (16), 67 (28), 66 (12), 65
(10), 57 (22), 56 (13), 55 (45), 53 (18), 51 (15), 44 (16), 43 (37), 42
(10), 41 (100), 39 (55), 38 (12).
13C NMR: 91.6, 133.0, 169.3.
Anal. Calcd for C3H2ClIO2: C, 15.50; H, 0.87. Found: C, 15.62; H,
0.95.
Anal. Calcd for C8H12Br2O2: C, 32.03; H, 4.03. Found: C, 32.14; H,
4.13.
(E)-3-Bromo-2-iodoprop-2-enoic Acid (3)
Mp 63–65 °C.
IR (KBr): 3200–2600, 3063, 1691, 1624, 1215 cm–1.
1H NMR (200 MHz, CDCl3): d (E-isomer) = 7.49 (s, 1 H), 11.66 (br
s, 1 H); d (Z-isomer, 1%) = 8.61 (s, 1 H).
(E)-2,3-Diiodoprop-2-enoic Acid (8)2a
Mp 104–106 °C.
IR (KBr): 3100–2600, 3054, 1701, 1545 cm–1.
1H NMR (200 MHz, CDCl3): d = 8.09 (s, 1 H), 11.70 (br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 85.9, 91.9, 169.3.
13C NMR (50 MHz, CDCl3): d = 84.1, 118.6, 168.3.
MS (EI, 70 eV): m/z (%) = 324 (73) [M+], 254, 36), 197 (71), 153
(28), 152 (22), 127 (88), 69 (28), 53 (100).
MS (EI, 70 eV): m/z (%) = 234 (1) [M – 44], 232 (1) [M – 44], 152
(100), 127 (32), 44 (56).
Anal. Calcd for C3H2I2O2: C, 11.13; H, 0.62. Found: C, 11.22; H,
0.66.
Anal. Calcd for C3H2BrIO2: C, 13.01; H, 0.73. Found: C, 12.89; H,
0.79.
(E)-N-Benzyl-2,3-diiodobut-2-enamide (9)
Mp 104–105 °C.
IR (KBr): 3418, 3053, 1654 cm–1.
1H NMR (200 MHz, CDCl3): d = 2.65 (s, 3 H), 4.53 (s, 1 H), 4.56
(s, 1 H), 5.85 (br s, 1 H), 7.33–7.40 (m, 5 H).
13C NMR (50 MHz, CDCl3): d = 38.7, 44.5, 89.3, 96.2, 128.2,
128.6, 129.2, 137.6, 168.2 (C1).
(E)-3-Bromo-2-iodobut-2-enoic Acid (4)
Mp 102–104 °C.
IR (KBr): 3200–2600, 3074, 1680, 1623, 1282 cm–1.
1H NMR (200 MHz, CDCl3): d (E-isomer) = 2.66 (s, 3 H), 11.3 (br
s, 1 H); d (Z-isomer, 2%) = 2.87 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 34.0, 81.2, 125.9, 171.2.
MS (EI, 70 eV): m/z (%) = 292 (20) [M+], 290 (20), 211 (81), 127
(11), 84 (13), 83 (14), 67 (23), 55 (23), 45 (13), 43 (10), 39 (100),
38 (29), 37 (16).
MS (EI, 70 eV): m/z (%) = 428 (4) [M + 1], 300 (61), 254 (43), 174
(17), 173 (99), 172 (23), 144 (11), 130 (34), 129 (27), 127 (32), 115
(14), 106 (37), 104 (13), 91 (100), 19 (19), 77 (26), 67 (66), 65 (27),
51 (23), 39 (64), 38 (16).
Anal. Calcd for C4H4BrIO2: C, 16.52; H, 1.39. Found: C, 16.63; H,
1.46.
Anal. Calcd for C11H11I2NO: C, 30.94; H, 2.60; N, 3.28. Found: C,
31.06; H, 2.70; N, 3.35.
(E)-2,3-Dibromobut-2-enoic Acid (5)
Mp 81–83 °C.
IR (KBr) : 3400–2300, 1690, 1599, 1273 cm–1.
(E)-2,3-Diiodobut-2-enoic Acid (10)
Mp 113–115 °C.
1H NMR (200 MHz, CDCl3): d = 2.58 (s, 3 H), 11.32 (br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 37.0, 116.8, 125.2, 169.2.
MS (EI, 70 eV): m/z (%) = 244 (16) [M+], 165 (41), 163 (44), 84
IR (KBr): 3300–2700, 1719, 1625, 1445, 1384, 1235 cm–1.
1H NMR (200 MHz, CDCl3): d = 2.75 (s, 3 H), 9.50 (br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 40.2, 84.6, 100.2, 171.6.
MS (EI, 70 eV): m/z (%) = 338 (22) [M+], 254 (39), 211 (61), 127
(34), 84 (19), 67 (40), 55 (19), 40 (12), 39 (100), 38 (30), 37 (18).
(39), 67 (32), 55 (11), 44 (40), 40 (38), 39 (100), 38 (40), 37 (27).
Anal. Calcd for C4H4Br2O2: C, 19.70; H, 1.65. Found: C, 19.79; H,
1.69.
Anal. Calcd for C4H4I2O2: C, 14.22; H, 1.19. Found: C, 14.15; H,
1.24.
(E)-2,3-Dibromo-4-methoxybut-2-enoic Acid (6)
Mp 66–68 °C.
IR (KBr): 3670–2280, 1723, 1623, 1451, 1258 cm–1.
1H NMR (200 MHz, CDCl3): d = 3.43 (s, 3 H), 4.44 (s, 2 H), 9.9 (br
s, 1 H).
(E)-2,3-Diiodo-4-methoxybut-2-enoic Acid (11)
Mp 84–86 °C.
IR (KBr): 3684–2303, 1715, 1445, 1360, 1230 cm–1.
1H NMR (200 MHz, CDCl3): d = 3.41 (s, 3 H), 4.28 (s, 2 H), 10.30
(s, 1 H).
13C NMR (50 MHz, CDCl3): d = 58.2, 74.6, 109.6, 125.6, 166.9.
13C NMR (50 MHz, CDCl3): d = 57.9, 81.4, 84.4, 103.8, 169.9.
MS (EI, 70 eV): m/z (%) = 368 (1) [M+], 254 (100), 127 (14), 39
MS (EI, 70 eV): m/z (%) = 274 (8) [M + 2], 195 (63), 193 (61), 163
(100), 161 (95), 53 (10), 45 (47), 39 (32), 38 (22), 37 (11).
Anal. Calcd for C5H6Br2O3: C, 21.92; H, 2.21. Found: C, 21.98; H,
2.33.
(11).
Anal. Calcd for C5H6I2O3: C, 16.32; H, 1.64. Found: C, 16.45; H,
1.60.
(E)-2,3-Dibromooct-2-enoic Acid (7)
IR (neat): 3714–2274, 1718, 1628, 1466, 1381, 1259 cm–1.
(E)-2,3-Diiodooct-2-enoic Acid (12)
1H NMR (200 MHz, CDCl3): d = 0.92 (t, J = 7.5 Hz, 3 H), 1.28–
1.37 (m, 4 H), 1.61–1.67 (m, 2 H), 2.77 (t, J = 7.5 Hz, 2 H), 10.90
(br s, 1 H).
13C NMR (50 MHz, CDCl3): d = 13.8, 22.3, 26.6, 30.5, 41.4, 106.1,
130.8, 168.6.
IR (neat): 3692–2397, 1703, 1606, 1455, 1383, 1255 cm–1.
1H NMR (200 MHz, CDCl3): d = 0.91 (t, J = 7.5 Hz, 3 H), 1.30–
1.37 (m, 4 H), 1.54–1.60 (m, 2 H), 2.75 (t, J = 7.4 Hz, 2 H), 10.60
(br s, 1 H).
Synthesis 2007, No. 11, 1724–1728 © Thieme Stuttgart · New York

1728
S. Langle et al.
PAPER
13C NMR (50 MHz, CDCl3): d = 13.9, 22.3, 27.5, 30.2, 49.2, 82.7,
reflections. Data reductions were performed with the DENZO-
SMN software.8 An empirical absorption correction was applied to
each data set based on the symmetry-equivalent reflections using
the SORTAV program.9 Structures were resolved with either
SIR9210 or SHELXS-9711 and refined with the SHELXL-97 pro-
gram.12 The hydrogen atoms were placed in geometrically idealized
positions and constrained to ride on their parent atoms. Crystallo-
graphic data for the structural analysis have been deposited with the
Cambridge Crystallographic Data Center, CCDC, under nos.
615418 (compound 6), 615417 (compound 10), 615415 (compound
11), and 615419 (compound 16). Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: +44(1223)336033; e-mail:
deposit@ccdc.cam.ac.uk or www.http://www.ccdc.cam.ac.uk].
107.4, 171.0.
MS (EI, 70 eV): m/z (%) = 394 (0.1) [M+], 254 (100), 127 (29), 95
(12), 67 (17), 55 (22), 51 (12), 49 (22), 43 (14), 41 (41), 39 (29), 35
(13).
Anal. Calcd for C8H12I2O2: C, 24.39; H, 3.07. Found: C, 24.32; H,
3.14.
(E)-2,3-Diiodo-3-phenylprop-2-enoic Acid (13)
Mp 173–175 °C.
IR (KBr): 3300–2600, 3055, 1720, 1660, 1603, 1586, 1485, 1391,
1220 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.28–7.46 (m, 5 H), 11.30 (br s, 1
H).
13C NMR (50 MHz, CDCl3): d = 85.6, 99.7, 128.1 (2 C), 129.0 (2
C), 129.6, 145.8, 169.7.
Acknowledgment
We thank MENRT for providing financial support, and the ‘Service
d’analyse chimique du vivant de Tours’ for recording NMR and
mass spectra, and the ‘Laboratoire de Cristallochimie’ of Marseille
University for X-ray diffraction analysis.
Anal. Calcd for C9H6I2O2: C, 27.03; H, 1.51. Found: C, 26.91; H,
1.58.
Tributylstannyl (E)-3-Chloro-2-iodoprop-2-enoate (14)
Mp 58–60 °C.
IR (KBr): 2956, 2921, 2854, 1611, 1586, 1461 cm–1.
References
1H NMR (200 MHz, CDCl3): d (E-isomer) = 0.94 (t, J = 7.1 Hz, 9
H), 1.15–1.55 (m, 12 H), 1.6–1.9 (m, 6 H), 6.87 (s, 1 H); d (Z-iso-
mer, 2%) = 7.83 (s, 1 H).
13C NMR (50 MHz, CDCl3): d = 14.2, 17.6 (3 C, 1JSn-C = 332–349
Hz), 27.6 (3 C, 3JSn-C = 62 Hz), 28.3 (3 C, 2JSn-C = 21 Hz), 89.6, 126,
167.7.
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MS (EI, 70 eV): m/z (%) = 465 (80) [M – 57], 359 (47), 305 (38),
269 (45), 247 (33), 177 (27), 153 (14), 127 (17), 121 (24), 119 (19),
105 (15), 57 (67), 53 (32), 45 (10), 41 (100), 39 (28).
Tributylstannyl (E)-3-Chloro-2-iodobut-2-enoate (15)
Mp 80–82 °C.
(3) (a) Lemay, A.; Vulic, K.; Ogilvie, W. J. Org. Chem. 2006,
71, 3615. (b) Berthelot, J.; Fournier, M. Can. J. Chem. 1986,
64, 603.
IR (KBr): 2956, 2922, 2861, 2854, 1602, 1545, 1469 cm–1.
1H NMR (200 MHz, CDCl3): d = 0.95 (t, J = 7.1 Hz, 9 H), 1.2–1.85
(m, 18 H), 2.46 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 14.2 (3 C), 17.5 (3 C, 1JSn-C = 333–
349 Hz), 27.6 (3 C, 3JSn-C = 62 Hz), 28.2 (3 C, 2JSn-C = 22 Hz), 30.1,
85.2, 132.1, 170.
(4) (a) Rossi, R.; Bellina, F.; Carpita, A.; Gori, R. Gazz. Chim.
Ital. 1995, 125, 381. (b) Rossi, R.; Bellina, F.; Carpita, A.;
Mazzarella, F. Tetrahedron 1996, 52, 4095. (c) Rossi, R.;
Bellina, F.; Mannina, L. Tetrahedron Lett. 1998, 39, 3017.
(5) (a) Henaff, N.; Stewart, S. K.; Whiting, A. Tetrahedron Lett.
1997, 38, 4525. (b) Henaff, N.; Whiting, A. J. Chem. Soc.,
Perkin Trans. 1 2000, 395. (c) Bellina, F.; Colzi, F.;
Mannina, L.; Rossi, R.; Viel, S. J. Org. Chem. 2003, 68,
10175.
(E)-3-Chloro-2-iodo-4-methoxybut-2-enoic Acid (16)
Mp 60–62 °C.
IR (KBr): 3681–2370, 1716, 1450, 1359, 1255 cm–1.
1H NMR (200 MHz, CDCl3): d = 3.44 (s, 3 H), 4.44 (s, 2 H), 11.1
(s, 1 H).
(6) (a) Andersson, K. Chem. Scr. 1972, 2, 113. (b) Andersson,
K. Chem. Scr. 1972, 2, 117.
(7) Castro, C. E.; Gaughan, E. J.; Owsley, D. C. J. Org. Chem.
1965, 30, 587.
(8) Otwinowsky, Z.; Minor, W. In Methods in Enzymology:
Macromolecular Crystallography, Part A, Vol. 276; Carter,
C. W. Jr.; Sweet, R. M., Eds.; Academic Press: New York,
1997, 307–326.
13C NMR (50 MHz, CDCl3): d = 58.2, 76.6, 82.4, 135.8, 168.6.
MS (EI, 70 eV): m/z (%) = 278 (4) [M + 2], 276 (15) [M+], 241 (51),
209 (62), 128 (13), 127 (24), 117 (20), 113 (30), 84 (21), 73 (10), 69
(44), 66 (10), 61 (14), 55 (25), 53 (21), 45 (98), 44 (57), 42 (17), 41
(40), 40 (18), 39 (100), 38 (49), 37 (23), 36 (26).
(9) Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421.
(10) Altamore, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi,
A.; Burla, M. C.; Polidori, G.; Camalli, M. J. Appl.
Crystallogr. 1994, 27, 435.
Anal. Calcd for C5H6ClIO3: C, 21.72; H, 2.19. Found: C, 21.78; H,
2.11.
X-ray Crystallography
(11) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(12) Sheldrick, G. M. SHELXL-97, Program for the Refinement
of Crystal Structures; University of Göttingen: Göttingen,
Germany, 1997.
Suitable single crystals of 6, 10, 11, and 16 were mounted on a glass
fiber. Data collection was carried out at r.t. on a Bruker-Nonius
Kappa CCD diffractometer equipped with graphite-monochromat-
ed Mo(Ka) radiation (l = 0.71073 Å). Cell parameters were re-
trieved and refined using DENZO-SMN software7 on all
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