Diastereoselective O-vinylation of phenols using DMAD under mild reaction conditions

Article abstract of DOI:10.1080/00397910802219163

An efficient and straightforward pyridine-catalyzed method allowing selective O-vinylation of phenols with DMAD is reported. The reaction is diastereoselective and leads exclusively to (Z)-configuration in high yields. Copyright Taylor & Francis Group, LL

Full text of DOI:10.1080/00397910802219163

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Diastereoselective O-Vinylation
of Phenols using DMAD under
Mild Reaction Conditions
Ebrahim Kianmehr a , Katayoun Tabatabai a , Alireza
Abbasi a & Hamideh Shokouhi Mehr a
a School of Chemistry, University College of Science ,
University of Tehran , Tehran, Iran
Published online: 09 Sep 2008.
To cite this article: Ebrahim Kianmehr , Katayoun Tabatabai , Alireza Abbasi &
Hamideh Shokouhi Mehr (2008) Diastereoselective O-Vinylation of Phenols using DMAD
under Mild Reaction Conditions, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 38:15, 2529-2539, DOI:
10.1080/00397910802219163
To link to this article: http://dx.doi.org/10.1080/00397910802219163
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Synthetic Communications1, 38: 2529–2539, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802219163
Diastereoselective O-Vinylation of Phenols using
DMAD under Mild Reaction Conditions
Ebrahim Kianmehr, Katayoun Tabatabai, Alireza Abbasi, and
Hamideh Shokouhi Mehr
School of Chemistry, University College of Science, University of Tehran,
Tehran, Iran
Abstract: An efficient and straightforward pyridine-catalyzed method allowing
selective O-vinylation of phenols with DMAD is reported. The reaction is
diastereoselective and leads exclusively to (Z)-configuration in high yields.
Keywords: Diastereoselective, phenol, regioselective, vinylation
INTRODUCTION
Aryl vinyl ethers are valuable intermediates that can be used in a wide
array of chemical transformations.[1] They are involved in reactions such
as cycloaddition,[2] cyclopropanation,[3] metathesis reactions,[4] and
hydroformylation,[5] and they find applications in the synthesis of natural
product analogs,[6] biologically active molecules,[7] and the generation of
new polymeric materials.[8] The base-catalyzed reaction of phenols with
acetylene under high temperature and pressure was one of the first meth-
ods developed to synthesize this class of compounds.[9] The main routes
to form aryl vinyl ethers include alkylation of phenols with 1,2-dibromo-
ethane[10] or related compounds followed by dehydrohalogenation. The
new methods are based upon transition-metal-mediated coupling of
phenols with different vinyl sources.[11–14] However, the development of
general, mild, and stereoselective synthetic methodologies to provide
access to aryl vinyl ether derivatives is still required. The reaction of
Received in the U.K. August 25, 2007
Address correspondence to Ebrahim Kianmehr, School of Chemistry, University
College of Science, University of Tehran, Tehran. E-mail: kianmehr@khayam.
ut.ac.ir
2529

2530
E. Kianmehr et al.
nucleophiles with activated acetylenes for C-C or C-O bond formation is
of great significance in organic synthesis.[15–18,19b] In this work, pyridine-
catalyzed addition of phenols to dimethyl acetylenedicarboxylate
(DMAD) has been used to create C-O bonds and diastereoselective
synthesis of aryl vinyl ether derivatives under mild reaction conditions.
RESULTS AND DISCUSSION
Using pyridine as nucleophilic catalyst (20 mol%) under the optimized
reaction conditions, we examined the reaction of phenols (1 equiv.) with
DMAD (1 equiv.) in dry tetrahydrofurane (THF). The results are
summarized in Table 1. As can be seen from the table, the corresponding
products 2a–l are stereoselectively obtained in high yields with (Z)-config-
urations. The structures of products are determined by 1H NMR,
13C NMR, mass spectrometry, elemental analysis, and X-ray diffraction.
The X-ray crystal structure of 2g is shown in Fig. 1.
There are four molecules for the structure in the unit cell. Details
of the structure determination and refinement are described in the
Experimental section.
1
The HNMR spectrum of 1a exhibits three singlet signals identified
as methoxy groups (d ¼ 3.75, 3.79 ppm) and the vinylic proton
Table 1. O-Vinylation of substituted phenols by DMAD in the presence of
pyridine
Entry
Phenol
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
4-Chlorophenyl, 1a
3-Chlorophenyl, 1b
4-Methoxyphenyl, 1c
4-t-Butylphenyl, 1d
3-Nitrophenyl, 1e
4-Methyl, 1f
2,4-dichlorophenyl, 1g
Phenyl, 1h
2-t-Butyl-4-methylphenyl, 1i
4-Chloro-3-nitrophenyl, 1j
4-Chloro-3-methyl, 1k
4-Chloro-3,5-dimethyl, 1l
22
20
18
16
16
19
20
22
19
20
20
19
70
80
90
90
96
84
91
89
75
93
91
87
10
11
12

Diastereoselective O-Vinylation of Phenols
2531
Figure 1. Molecular structure of 2g, with 50% probability displacement
ellipsoids, H atoms with arbitrary radii.
(d ¼ 6.67 ppm). The aromatic protons appear at d ¼ 6.93–7.29 ppm. The
13CNMR spectrum of 2a shows 10 distinct resonances expected for the
structure. The spectral data of 2a–l are in agreement with the proposed
structures. A mechanistic rationalization for the reaction is provided in
Scheme 1.
Scheme 1. Proposal mechanism.

2532
E. Kianmehr et al.
The initially formed 1,3-dipole A is subsequently protonated by the
phenolic proton to produce B and the corresponding aryloxide ion C.
The aryloxide ion can add to the electrophilic carbon–carbon double
bond of B to provide a new zwittterion D, which can undergo a hydrogen
shift to provide E. Elimination of pyridine from E delivers the corres-
ponding aryl vinyl ether derivative. C-Vinylation, which might arise from
nucleophilic addition of C to B, was not observed. The diastereo
selectivity of the reaction may be explained using the resonance form
F. Steric and nonbonded interactions of the methoxy group with the
methoxycarbonyl and pyridine groups and probable intramolecular
ionic hydrogen bonding[20] may stabilize and dominate the formation
of conformation G, which leads to the (Z)-isomer under elimination.
In summary, we have developed a mild procedure for the preparation
of aryl vinyl ether derivatives through the reaction of the zwitterions
derived from pyridine and dimethyl acetylenedicarboxylate (DMAD)
with phenols in dry THF and under a nitrogen atmosphere. The reaction
is applicable to a variety of phenolic substrates and leads exclusively to
the (Z)-configuration of the O-vinylation products.
EXPERIMENTAL
1H NMR (500 MHz) and 13C NMR (125 MHz) spectra were recorded on a
Bruker DRX-500 NMR spectrometer using TMS as an internal standard.
MS spectra were carried out on an HP 5973 GC-MS instrument. IR spectra
were measured using a Shimadzu FTIR-4300. Elemental analyses were per-
formed at the Research Institute of Petroleum Industry. X-ray single-crystal
structure analysis was performed by means of Oxford Instruments Xcalibur,
equipped with a CCD detector (crystal-to-detector distance of 5.00 cm).
Chemicals were purchased from Merck and were used as received. Column
chromatography was performed on silica gel (0.063–0.200 mm, Merck).
X-ray Crystallography
Crystal structure determination of 2g (Fig. 1): data collections were made
at room temperature, by means of Oxford Instruments Xcalibur,
equipped with a CCD detector (crystal-to-detector distance of 5.00 cm).
The CrysAlis program packages were used for indexing and integrating
the single-crystal reflections. Absorption corrections were performed with
the programs X-RED and X-Shape. Symmetry equivalent reflections
were used to optimize the crystal shape and size. The structures were
solved by direct methods using SHELXS-97 and refined using full-matrix

Diastereoselective O-Vinylation of Phenols
2533
least-squares method on F2, SHELXL-97. All nonhydrogen atoms were
refined anisotropically.
General Procedure for the Preparation of Compound 1
Pyridine (48 mg, 0.6 mmol) was added to a solution of DMAD (566 mg,
4.0 mmol) and 1 (4.0 mmol) in dry THF (15 ml) under a nitrogen atmos-
phere, and the reaction mixture was stirred for 16–22 h at room tempera-
ture. The solvent was removed under vacuum and the residue on
chromatographic separation on a silica-gel column using hexane–
ethylacetate (90:10) gave the pure title compounds.
Data
Dimethyl (Z)-2-(4-chlorophenoxy)-2-butenedioate (2a)
White solid. Mp 69–70 ꢀC; IR (KBr) t=cmꢁ1: 3097, 2956, 1732, 1662,
1
1587, 1487, 1444, 1261, 1205, 1178, 1101 cmꢁ1. H NMR: d (ppm) 3.75
(3H, S, OMe), 3.79 (3H, S, OMe), 6.67 (1H, S, vinylic CH), 6.93 (2H,
d, J ¼ 8.9 Hz), 7.29 (2H, d, J ¼ 8.9 Hz). 13C NMR: d (ppm) 52.5
(OCH3), 53.5 (OCH3), 116.1 (CH), 117.9 (CH), 128.9 (C), 130.1 (CH),
=
=
149.8 (C), 155.6 (C), 162.7 (C O), 164.1 (C O). MS (EI, 70 ev) m=z
(%) 270 (Mþ , 29), 239 (37), 211 (100), 179 (7), 169 (26), 155 (6), 139
(6), 111 (20), 99 (10). Anal. calcd. for C12H11ClO5: C, 53.33; H, 4.11.
Found: C, 53.48; H, 4.21.
Dimethyl (Z)-2-(3-Chlorophenoxy)-2-butenedioate (2b)
White solid. Mp 74–75 ꢀC; IR (KBr) t=cmꢁ1: 3085, 1732, 1660, 1591,
1
1479, 1435, 1284, 1209, 1172, 1091, 1026 cmꢁ1. H NMR: d (ppm) 3.76
(3H, S, OMe), 3.80 (3H, S, OMe), 6.70 (1H, S, vinylic CH), 6.88 (1H,
dd, J ¼ 8.3 Hz, J ¼ 2.5 Hz), 7.00 (1H, t, J ¼ 2.2 Hz), 7.10 (1H, dd,
J ¼ 8.3 Hz, J ¼ 2.5 Hz), 7.26 (1H, t, J ¼ 8.1 Hz). 13C NMR: d (ppm)
52.5 (OCH3), 53.6 (OCH3), 114.7 (CH), 116.6 (CH), 117.0 (CH), 124.1
=
(CH), 130.9 (CH), 135.5 (C), 149.5 (C),þ157.5 (C), 162.7 (C O), 164.0
=
(C O). MS (EI, 70 ev) m=z (%) 270 (M , 34), 239 (24), 211 (100), 196
(11), 169 (31), 169 (26), 128 (14), 139 (6), 111 (34), 99 (18). Anal. calcd.
for C12H11ClO5: C, 53.33; H, 4.11. Found: C, 53.45; H, 4.02.
Dimethyl (Z)-2-(4-Methoxyphenoxy)-2-butenedioate (2c)
Light green oil. IR (KBr) t=cmꢁ1: 3103, 2954, 1714, 1658, 1606, 1500,
1
1480, 1437, 1267, 1203, 1180, 1103 cmꢁ1. H NMR : d (ppm) 3.74 (3H,

2534
E. Kianmehr et al.
S, OMe), 3.75 (3H, S, OMe), 3.79 (3H, S, OMe), 6.54 (1H, S, vinylic CH),
6.85 (2H, d, J ¼ 8.8 Hz), 6.94 (2H, d, J ¼ 8.6 Hz). 13C NMR: d (ppm)
52.3 (OCH3), 53.3 (OCH3), 56.0 (OCH3), 114.4 (CH), 115.1 (CH),
117.8 (CH), 150.8 (C), 150.8 (C), 156.2 (C), 163.2 (C ¼ O), 164.4
þ
=
(C O). MS (EI, 70 ev) m=z (%) 266 (M , 81), 235 (16), 207 (100), 192
(7), 165 (4), 150 (7), 123 (14), 95 (9). Anal. calcd. for C13H14O6: C,
58.63; H, 5.30. Found: C, 58.49; H, 5.19.
Dimethyl (Z)-2-[(4-tert-Butyl)phenoxy]-2-butenedioate (2d)
Light yellow oil. IR (KBr) t=cmꢁ1: 3089, 2958, 1728, 1660, 1602, 1505,
1461, 1436, 1365, 1282, 1203, 1176, 1114, 1022 cmꢁ1. 1H NMR: d
(ppm) 1.29 (9H, S, 3CH3), 3.65 (3H, S, OMe), 3.69 (3H, S, OMe), 6.57
(1H, S, vinylic CH), 6.88 (2H, d, J ¼ 8.7 Hz), 7.30 (2H, d, J ¼ 8.7 Hz).
13C NMR: d (ppm) 31.8 (CH3), 34.6 (C), 52.2 (OCH3), 53.2 (OCH3),
115.1 (CH), 115.9 (CH), 126.8 (CH), 146.4 (C), 150.4 (C),þ154.7 (C),
=
=
163.0 (C O), 164.2 (C O). MS (EI, 70 ev) m=z (%) 292 (M , 28), 277
(100), 233 (3), 205 (13), 177 (32), 149 (74), 121 (16), 91 (21). Anal. calcd.
for C16H20O5: C, 65.72; H, 6.90. Found: C, 65.91; H, 6.99.
Dimethyl (Z)-2-(3-Nitrophenoxy)-2-butenedioate (2e)
White solid. Mp 88–89 ꢀC. IR (KBr) t=cmꢁ1: 3089, 2950, 1726, 1662,
1
1614, 1533, 1479, 1440, 1384, 1288, 1226, 1176, 1107 cmꢁ1. H NMR: d
(ppm) 3.77 (3H, S, OMe), 3.84 (3H, S, OMe), 6.82 (1H, S, vinylic CH),
7.36 (1H, dd, J ¼ 8.2 Hz, J ¼ 2.4 Hz), 7.54 (1H, t, J ¼ 8.2 Hz), 7.80
(1H, t, J ¼ 2.3 Hz), 8.0 (1H, dd, J ¼ 8.1 Hz, J ¼ 2.0 Hz). 13C NMR: d
(ppm) 52.6 (OCH3), 53.8 (OCH3), 111.4 (CH), 117.8 (CH), 118.7 (CH),
=
122.9 (CH), 130.8 (CH), 148.9 (C), 149.6 (C), 157.5 (C), 162.3 (C O),
þ
=
163.7 (C O). MS (EI, 70 ev) m=z (%) 281 (M , 5), 250 (17), 222 (100),
204 (4), 176 (39), 146 (4), 108 (7), 92 (11). Anal. calcd. for C12H11NO7:
C, 51.24; H, 3.94. Found: C, 51.45; H, 3.91.
Dimethyl (Z)-2-(4-Methylphenoxy)-2-butenedioate (2f)[20b]
White solid; mp 62–63 ꢀC. IR (KBr) t=cmꢁ1: 2982, 1735, 1656, 1600,
1
1508, 1440, 1369, 1259, 1203, 1174, 1103 cmꢁ1. H NMR: d (ppm) 2.34
(3H, S, CH3), 3.75 (3H, S, OMe), 3.77 (3H, S, OMe), 6.60 (1H, S, vinylic
CH), 6.90 (2H, d, J ¼ 8.4 Hz), 7.14 (2H, d, J ¼ 8.2 Hz). 13C NMR: d
(ppm) 21.1 (CH3), 52.4 (OCH3), 53.4 (OCH3), 114.9 (CH), 116.3 (CH),
=
=
130.6 (CH), 133.4 (C), 150.6 (C), 154.2 (C), 163.2 (C O), 164.6 (C O).
MS (EI, 70 ev): m=z (%) 250 (Mþ , 39), 219 (20), 191 (100), 176 (10),
149 (29), 134 (16), 108 (9), 91 (44). Anal. calcd. for C13H14O5: C,
62.38; H, 5.64. Found: C, 62.30; H, 5.76.

Diastereoselective O-Vinylation of Phenols
2535
Dimethyl (Z)-2-(2,4-Dichlorophenoxy)-2-butenedioate (2 g)
White solid; mp 60–61 ꢀC. IR (KBr) t=cmꢁ1: 3089, 2954, 1720, 1660,
1
1579, 1481, 1440, 1361, 1286, 1207, 1178, 1099, 1018 cmꢁ1. H NMR: d
(ppm) 3.75 (3H, S, OMe), 3.80 (3H, S, OMe), 6.71 (1H, S, vinylic CH),
6.79 (1H, d, J ¼ 8.7 Hz), 7.17 (1H, dd, J ¼ 8.7 Hz, J ¼ 2.5 Hz), 7.46
(1H, d, J ¼ 2.5 Hz). 13C NMR: d (ppm) 52.7 (OCH3), 53.7 (OCH3),
116.3 (CH), 117.4 (CH), 124.8 (C), 128.0 (C), 129.2 (C), 130.9 (CH),
=
=
149.4 (C), 151.6 (C), 162.2 (C O), 163.8 (C O). MS (EI, 70 ev) m=z
(%) 304 (Mþ , 15), 273 (12), 245 (100), 188 (4), 162 (9), 133 (9), 109
(12), 69 (34). Anal. calcd. for C12H10Cl2O5: C, 47.37; H, 3.32. Found:
C, 47.30; H, 3.38.
X-ray Structure Determination of 2 g
Empirical formula C12H10Cl2O5; formula weight 305.10; colorless needle;
crystal dimensions 0.2 ꢂ 0.02 ꢂ 0.02 mm; monoclinic; primitive; space
˚
˚
group P21=c; lattice parameters a ¼ 4.6975(13) A, b ¼ 11.030(3) A, c ¼
o
3
˚
˚
26.285(8) A, b ¼ 95.57(3) , V ¼ 1355.5(7) A , Z ¼ 4; qcalcd ¼ 1.495
g cmꢁ3; F000 ¼ 624; m(Mo Ka) ¼ 0.71073 cmꢁ1; 2hmax ¼ 51o; number of
reflections measured total: 8569, unique: 2524 (Rint ¼ 0.1151); number
of observations [I > 2r(I)] 776; R1 ¼ 0.0371; wR2 ¼ 0.0650.
Dimethyl (Z)-2-Phenoxy-2-butenedioate (2 h)[19a,c]
White solid; mp 74–75 ꢀC. IR (KBr) t=cmꢁ1: 3043, 2984, 1728, 1665,
1593, 1492, 1436, 1357, 1275, 1203, 1176, 1103 cmꢁ1. 1H NMR: d
(ppm) 3.64 (3H, S, OMe), 3.66 (3H, S, OMe), 6.60 (1H, S, vinylic CH),
6.94 (2H, d, J ¼ 8.4 Hz), 7.03 (1H, t, J ¼ 7.3 Hz), 7.27 (2H, t, J ¼
7.6 Hz).13C NMR: d (ppm) 52.2 (OCH3), 53.3 (OCH3), 115.5 (CH), 116.5
=
(CH), 123.7 (CH), 130.0 (CH), 150.2 (C), 157.0 (C), 162.9 (C O), 164.1
=
(C O). Anal. calcd. for C12H12O5: C, 61.00; H, 5.12. Found: C, 61.14;
H, 5.14.
Dimethyl (Z)-2-[(2-tert-Butyl)-4-methylphenoxy]-2-butenedioate (2i)
Light yellow oil, IR (KBr) t=cmꢁ1: 3089, 2954, 1731, 1649, 1606, 1492,
1
1434, 1363, 1263, 1205, 1174, 1109 cmꢁ1. H NMR: d (ppm) 1.49 (3H,
S, CH3), 1.56 (9H, S, 3CH3), 3.78 (3H, S, OMe), 3.79 (3H, S, OMe),
6.57 (1H, d, J ¼ 8.1 Hz), 6.60 (1H, S, vinylic CH), 6.96 (1H, dd,

2536
E. Kianmehr et al.
J ¼ 8.1 Hz, J ¼ 1.8 Hz), 7.26 (1H, d, J ¼ 1.7 Hz). 13C NMR: d (ppm) 21.4
(CH3), 30.3 (3CH3), 35.2 (C), 52.3 (OCH3), 53.3 (OCH3), 114.1 (CH),
114.6 (CH), 127.6 (CH), 128.8 (CH), 132.8 (C), 138.2 (C), 150.3 (C),
=
=
153.6 (C), 163.3 (C O), 164.8 (C O). MS (EI, 70 ev) m=z (%) 306
(Mþ , 100), 291 (15), 259 (34), 247 (44), 227 (51), 217 (75), 199 (73),
191 (85), 171 (44), 159 (13), 149 (26), 115 (26), 105 (29), 91 (31). Anal.
calcd. for C17H22O5: C, 66.63; H, 7.24. Found: C, 66.54; H, 7.16.
Dimethyl (Z)-2-(4-Chloro-3-nitrophenoxy)-2-butenedioate (1j)
White solid; mp 72–73 ꢀC. IR (KBr) t=cmꢁ1: 3111, 2950, 1730, 1660,
1
1602, 1537, 1477, 1438, 1361, 1271, 1203, 1178, 1101 cmꢁ1. H NMR: d
(ppm) 3.77 (3H, S, OMe), 3.82 (3H, S, OMe), 6.80 (1H, S, vinylic CH),
7.18 (1H, dd, J ¼ 8.9 Hz, J ¼ 2.9 Hz), 7.49 (1H, d, J ¼ 2.9 Hz), 7.52
(1H, d, J ¼ 8.9 Hz). 13C NMR: d (ppm) 52.7 (OCH3), 53.9 (OCH3),
113.7 (CH), 118.2 (CH), 121.6 (C), 121.6 (CH), 133.2 (CH), 148.4 (C),
=
=
148.5 (C), 155.7 (C), 162.0 (C O), 163.5 (C O). MS (EI, 70 ev) m=z
(%) 315(Mþ , 13), 284 (16), 256 (100), 210 (39), 173 (36), 127 (13), 115
(24), 99 (33). Anal. calcd. for C12H10ClNO7: C, 45.71; H, 3.20. Found:
C, 45.58; H, 3.26.
Dimethyl (Z)-2-(4-Chloro-3-methylphenoxy)-2-butenedioate (2 k)
Light yellow oil. IR (KBr) t=cmꢁ1: 3087, 2954, 1730, 1660, 1596, 1479,
1
1435, 1380, 1274, 1234, 1163, 1130, 1105 cmꢁ1. H NMR: d (ppm) 2.33
(3H, S, CH3), 3.78 (3H, S, OMe), 3.80 (3H, S, OMe), 6.66 (1H, S, vinylic
CH), 6.74 (1H, dd, J ¼ 8.7 Hz, J ¼ 2.9 Hz), 6.88 (1H, d, J ¼ 2.9 Hz), 7.26
(1H, d, J ¼ 8.7 Hz). 13C NMR: d (ppm) 20.6 (CH3), 52.8 (OCH3), 53.7
(OCH3), 115.1 (CH), 115.5 (CH), 119.1 (CH), 129.4 (C), 130.3 (CH),
=
=
138.2 (C), 150.3 (C), 155.2 (C), 163.1 (C O), 164.9 (C O). MS (EI,
70 ev): m=z (%) ¼ 284 (Mþ , 29), 253 (12), 225 (100), 183 (12), 168 (8),
142 (7), 125 (14), 89 (23), 77 (16). Anal. calcd. for C13H13ClO5: C,
54.92; H, 4.61. Found: C, 54.98; H, 4.71.
Dimethyl (Z)-2-(4-Chloro-3,5-dimethylphenoxy)-2-butenedioate (2 l)
White solid; mp 79–80 ꢀC. IR (KBr) t=cmꢁ1: 3097, 2954, 1743, 1660,
1
1589, 1469, 1438, 1377, 1307, 1263, 1203, 1155, 1105 cmꢁ1. H NMR: d
(ppm) 2.37 (6H, S, 2CH3), 3.77 (3H, S, OMe), 3.80 (3H, S, OMe), 6.65
(1H, S, vinylic CH), 6.73 (2H, S, CH). 13C NMR: d (ppm) 21.3
(2CH3), 52.5 (OCH3), 53.5 (OCH3), 115.9 (CH), 116.2 (CH), 129.5 (C),

Diastereoselective O-Vinylation of Phenols
2537
=
=
138.1 (C), 150.0 (C), 154.7 (C), 163.0 (C O), 164.3 (C O). MS (EI, 70 ev)
m=z (%) 298 (Mþ , 35), 267 (11), 239 (100), 203 (33), 139 (8), 103 (20), 91
(12), 77 (19). Anal. calcd. for C14H15ClO5: C, 56.36; H, 5.07. Found: C,
56.52; H, 4.99.
ACKNOWLEDGMENT
We thank Gernot Boche, Philipps-Marburg University, for helpful advice
with this work and Karol Gajewski for providing us access to some
articles. Financial support from the University of Tehran is gratefully
acknowledged.
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John Wiley & Sons: New York, 1989; (b) Diaz-Requejo, M.; Disalvo, D.;
Brookhart, M. Synthesis of 1,2-diheteroatom-substituted alkenes via
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