Efficient synthesis of new sulfur macrocyclic diamides

Article abstract of DOI:10.1055/s-2004-815957

Some new sulfur macrocyclic diamides and tetraamides were obtained via a simple and convenient method. This method consists of reacting a dicarboxylic acid dichloride with the appropriate diamine in dichloromethane. The cyclization does not require high dilution technique or template effect and the expected dilactams were obtained in high yields.

Full text of DOI:10.1055/s-2004-815957

600
PAPER
Efficient Synthesis of New Sulfur Macrocyclic Diamides
Efficient
S
ynthesis
a
of
N
ew Su
s
lfur
M
acr
h
ocyclic
D
ia
m
e
ides m Sharghi,* Zahra Paziraee
Department of Chemistry, College of Science, Shiraz University, Shiraz 71454, I. R. Iran
E-mail: shashem@chem.susc.ac.ir
Received 22 December 2003; revised 3 January 2004
various double-activation methods18,19 and by a series of
consecutive ‘Zipper- type’ reactions.20 In most of these
methods the macrocyclic lactams and polylactams are ob-
tained by cyclization of a polyfunctional, linear precursor
Abstract: Some new sulfur macrocyclic diamides and tetraamides
were obtained via a simple and convenient method. This method
consists of reacting a dicarboxylic acid dichloride with the appropri-
ate diamine in dichloromethane. The cyclization does not require
high dilution technique or template effect and the expected dilac- to a ring product. The high dilution technique is however,
tams were obtained in high yields.
inconvenient as it requires a simultaneous addition of the
diamine and diacid dichloride to a large volume of solvent
over an extended period of time. Morphy et al.21 and Jurc-
zak et al.22 have reported that, consistent with the earlier
findings of Tabushi et al.23 that no high dilution technique
was required for the reaction of dimethyl malonates with
, -diamines to form cyclic diamides. These facts pro-
moted us to study and apply similar approaches and from
these results an appropriate method was used for the syn-
thesis of new sulfur macrocyclic diamides (5–12;
Scheme 1).
Key words: sulfur macrocyclic diamides, diamine, dicarboxylic
acid dichloride
Macrocyclic polyethers (‘crown-ethers’) are well known
for their complexation properties towards alkali and alka-
line-earth metal ions. A quite remarkable selectivity can
be achieved by changing the number and types of donor
atoms and the size of the internal cavity of the ligands.1–3
Many different modifications of the crowns have been
made to enhance their cation-complexing properties.
Some of these modifications involve the use of alkyl sub-
stituents, aromatic sub-cyclic units, nitrogen and/or sulfur
atoms substituted for oxygen in the macro-ring and some
other changes which provide crowns with unique com-
plexing properties.4–10 Nitrogen and sulfur, naturally, are
particularly interesting heterodonor atoms to investigate,
and various studies were carried out with a series of oligo-
oxa, oligo-aza or oligo-sulfur macrocycles in the last de-
cade. Oxathio crown ethers, indeed, have been exploited
for their ability to extract and transport heavy metal
ions.11–15
Treatment of thia-salicylic acid (1) with potassium hy-
droxide in ethanol under reflux, gave the yellow solid of
thia-salicylate salt 2 in 95% yield. Nucleophilic displace-
ment of 1,2-diethylene glycol dibromide with thia-salicy-
late 2, provides the acyclic sulfur dicarboxylic acid 3 as
white crystals in 90% yield.
In the next step, compound 3 was treated with thionyl
chloride and gave dicarboxylic acid dichloride 4 in 85%
yield. The cyclization between compound 4 and diamine
14b at first, was performed by the following high dilution
method.13 A solution of 4 in dichloromethane (200 mL)
and a solution of diamine 14b and triethylamine in dichlo-
romethane (200 mL) were added dropwise over 5 hours
into dichloromethane (1.5 L) at 0 °C. This was then stirred
for 3 hours giving macrocyclic diamide 6 in 12% yield.
However when the reaction time was shortened to 15 min-
utes, and triethylamine and diamine (14b) in dichlo-
romethane (10 mL) were added dropwise to a solution of
4 in dichloromethane (10 mL) diamide 6 was obtained in,
a much improved 75% yield. This result clearly indicates
that, cyclization of compound 4 with diamine 14b does
not need a high dilution method. Additionally, the cycliza-
tion was carried out with fast addition of a mixture of di-
amine 14b and triethylamine in dichloromethane (10 mL)
into a solution of compound 4 in dichloromethane (10
mL) over 5 minutes with vigorous stirring at 0 ºC and then
the mixture was stirred at room temperature for 15 min-
utes to give compound 6 in even better yields of 95%
yield. A low reaction time was observed for this macrocy-
clization reaction (15 mins). When this method was used
at room temperature without triethylamine, the same re-
sult was obtained.
Now, in continuing the synthesis of different modified
crown ethers, herein, we report new studies on sulfur mac-
rocyclic diamides, notably the synthetic routes and the
structures of the target molecules that were intended to in-
clude two/three benzo-condensed systems, containing
some additional structural feature such as a mixed set of
S-, O-, pyridine and amide groups.
Numerous studies have been devoted to the preparation of
different macrocyclic polylactams from diamines and di-
acids. Preparing sulfur macrocyclic polylactams from di-
amines and activated diacids requires
a
direct
condensation reaction to form ring products over poly-
mers. In an attempt to achieve this goal, there is a need for
simple methods to prepare multifunctional crowns from
inexpensive and available starting materials. Many differ-
ent cyclization procedures have been developed; earlier
high dilution techniques16,17 have been complemented by
SYNTHESIS 2004, No. 4, pp 0600–0604
x
x
.
x
x
.2
0
0
4
Advanced online publication: 09.02.2004
DOI: 10.1055/s-2004-815957; Art ID: Z18203SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Efficient Synthesis of New Sulfur Macrocyclic Diamides
601
COO-K+
S-K+
COOH
SH
COOH HOOC
KOH
EtOH, Reflux
BrCH2CH2OCH2CH2Br
S
S
O
(1)
(2)
(3)
NH
X
X
NH
O
O
H2N
14a - g
NH2
COCl
ClOC
C
C
SOCl2, 50-60 o
C
7-8 h
CH2Cl2,fast addition
S
O
S
S
O
S
(4)
(14a) H2N(CH2)2NH2
(14b) H2N(CH2)3NH2
(14c) H2N(CH2)6NH2
(5-12)
(14d) 4-Methyl 3,5-diamino benzene
(14e) 2,6-Diamino pyridine
(14f) Ethyl 3,4-diaminobenzoate
(14g) Ethyl 3,5-diamino benzoate
Scheme 1
In a preliminary study, the effect of some solvents on the however a decrease in macrocyclization yield occurred.
yield of the macrocyclization reaction was investigated All the presented cyclization reactions proceed efficiently
with formation of sulfur macrocyclic diamide 6 as a mod- under vigorous stirring conditions as well as fast addition
el reaction (Table 1).
of reactants, in a properely selected solvent. The course of
the reaction is assumed to depend on the occurrence of
self-assembly phenomena,26 which is probably stimulated
by a properly selected solvent, and the yields are im-
proved by application of high speed stirring and fast addi-
tion reactions.
Table 1 clearly indicates, CH2Cl2 is a suitable solvent for
this macrocyclization reaction.
Compounds 5–12 were readily obtained by reacting the
compound 4 with appropriate diamine derivatives in high
yields (Table 2).
The structure proposed for the sulfur macrocyclic com-
pounds are consistent with data derived from IR, 1HNMR,
13C NMR, UV-Vis, and MS spectra, along with elemental
analysis.
It should be mentioned, the fast addition of diamine 14e
on dicarboxylic acid dichloride 4 in various solvents gave
a mixture of products. After column chromatography both
monomeric compound 9 [1:1], and dimeric compound 10
[2:2] were isolated in 75% and 15% yields, respectively.
(Figure 1) (Table 2, entries 4 and 5)
The fast addition method for the preparation of sulfur
macrocyclic diamides has the following advantages:
(i) Synthetic versatility – prepare even or odd membered
dilactams.
Also for comparison of the conformational effects, we re-
acted dicarboxylic acid dichloride 4 with diamine 14c. In
contrast to fairly high yields of dilactams 5 and 6, reaction (ii) High yields of cyclization without additional external
of 4 with 14c in CH2Cl2, gave dilactam 7 with 21 ring at- cyclization factors (such as high dilution approach or tem-
oms in 55% yield. These properties provide a measure of plate effect).
steric control and predictability in ligand design (Table 2,
entry 3).
(iii) Ease of purification.
(iv) Short reaction time.
These results clearly indicate that the cyclization of dicar-
boxylic acid dichlorides with diamines does not need high
dilution method. The question arises as to whether vigor-
Petroleum ether used had a bp 60–80 °C.
ous stirring and fast addition of reactant are indispensable
for enforcing the cyclization of these substrates. To check
this assumption the same reactions were performed under
the modified conditions of slow addition and stirring,
Thia-salicylic Acid Salt 1
KOH (11.2 g, 20 mmol) in EtOH (200 mL) were placed in a 500 mL
two necked flask fitted with stirrer and reflux condenser, and re-
fluxed for 30 min. Then thia salicylic acid (15.4 g, 10 mmol) was
Table 1 Solvent Effects in Macrocyclization Reaction Between Diamine 14b and Dicarboxylic Acid Dichloride 4
Solvent
Acetone
CH2Cl2
CHCl3
CH3CN
DMSO
Et2O
EtOAc
THF
CH2Cl2/
EtOAc
Yield (%)
60
95
15
50
20
35
15
26
20
15
20
70
15
50
15
75
15
Time (min) 15
Synthesis 2004, No. 4, 600–604 © Thieme Stuttgart · New York

602
H. Sharghi, Z. Paziraee
PAPER
X
NH
NH
S
O
O
C
C
S
O
(5-12)
CH3
(5) X= -(CH2)2-
(8)
X=
O
O
C
C
C
S
O
S
NH
N
NH
(6)
(7)
(9) X=
(11) X=
(12) X=
X=-(CH2)3-
X=-(CH2)6-
N
N
COOCH2CH3
NH
NH
C
S
O
S
O
O
COOCH2CH3
(10)
Figure 1
Table 2 Cyclization Yields and Physical Properties of Macrocyclic Dilactames 5–12
c
Entry
Starting
Materials
Dilactam Time/
(min)
Yield
(%)a
Melting Point (°C)
1H NMR,
1
2
4
14a
5
15
63
175–177
(CH2Cl2)
3.40 (t, 4 H, CH2), 3.57 (m, 4 H, CH2S), 3.77(m, 4 H,
CH2O), 3.51(s, 2 H, NH), 6.8–7.9(m, 8 H, ArH)
4
14b
6
3
95
210–212
(CH2Cl2)
1.60 (m, 2 H, CH2), 1.95(t, 4 H, CH2), 3.03 (t, 4 H , CH2S),
3.55 (m, 4 H, CH2O), 4.28 (s, 2 H, NH), 7.19–7.60 (m, 8 H,
ArH)
3
4
14c
7
20
55
150–152
(CH2Cl2)
1.10–1.56 (m, 12 H, CH2), 3.13–3.22 (m, 4 H, CH2S),
3.72–3.78 (m, 4 H, CH2O), 3.91 (s, 2 H, NH), 7.14–7.91
(m, 8 H, ArH)
4
5
6
7
4
14d
8
9
5
5
73
75
15
80
240–242 (CH2Cl2)
2.33 (s, 3 H, CH3), 3.22 (m, 4 H, CH2S), 3.78 (m, 4 H,
CH2O), 7.26–8.03 (m, 11 H, ArH), 10.04 (s, 2 H, NH)
4
14e
228–230
(acetone– CH2Cl2)
3.18–3.22 (m, 4 H, CH2S), 3.67–3.7 (m, 4 H, CH2O), 7.32–
8.32 (m, 11 H, Ar), 10.18 (s, 2 H, NH)d
4
14e
10
11
5
178-180
(acetone–CH2Cl2)
3.22 (m, 8 H, CH2S), 3.68 (m, 8 H, CH2O), 6.66–8.32 (m,
22 H, Ar), 10.56 (s, 4 H, NH)d
4
20
196–198
(EtOAc–CH2Cl2)
1.41 (t, 3 H, CH3), 3.17 (m, 4 H, CH2S), 3.74 (m, 4 H,
CH2O), 4.38 (m, 2 H, CH2), 6.96–8.8 (m, 11 H, Ar), 9.85
(s, 2 H, NH)
14fb
8
4
14g
12
20
75
205–208
(EtOAc– CH2Cl2)
1.41 (t, 3 H, CH3), 3.15 (m, 4 H, CH2S), 3.62 (m, 4 H,
CH2O), 4.36 (m, 2 H, CH2), 6.72–8.50 (m, 11 H, Ar), 10.10
(s, 2 H, NH).
a Isolated yield.
b Ref.24,25
c 1H NMR were recorded at 250 MHz in CDCl3 unless otherwise stated.
d 1H NMR were recorded in DMSO.
Synthesis 2004, No. 4, 600–604 © Thieme Stuttgart · New York

PAPER
Efficient Synthesis of New Sulfur Macrocyclic Diamides
UV (CHCl3): max () = 260.3 (2626), 310.3 (449).
603
added dropwise and refluxed for 3–5 h. Then the mixture was
cooled and the precipitate filtrated to give the yellowish-green salt
of thia salicylic acid in 95% yield.
1,15-Diaza-3,4;12,13-dibenzo-8-oxa-5,11-dithiacycloune-
icosane-2,14-dione (7)
Sulfur Dicarboxylic Acid 3
IR (KBr): 715, 1057, 1251, 1434, 1463, 1710, 2931, 2954, 3473
Potassium thia-salicylate (1), (0.77g, 5 mmol) and diethylene glycol
dibromide (1.16 g, 2.5 mmol) in DMF (10 mL) was heated under re-
flux for 15 min (precipitation of KBr occured). The solvent was then
removed in vacuum and the remaining material was washed with
water (20 mL) and recrystallized from dil. EtOH to give colorless
crystals of diacid 3 in 90% yield; mp 182–184 ºC.
cm–1.
13C NMR (CDCl3, 62.9 MHz): = 30.08, 31.00, 31.94, 52.51,
69.53, 76.96, 124.53, 126.10, 131.69, 132.79.
MS: m/z (%) = 458.2 (M+), 194, 181, 167 (100), 152, 135, 109, 91,
69, 59, 50, 45.
UV (CHCl3): max ( ) = 260.3 (2302), 323.0 (1139).
IR (KBr): 698, 732, 914, 1114, 1272, 1413, 1465, 1562, 1693, 2958
cm–1.
1, 15-Diaza-3,4;12,13-dibenzo-16,18-(o-methylbenzo)-8-oxa-
5,11-dithiacyclooctadecane-2,14-dione (8)
IR (KBr): 748, 1105, 1253, 1315, 1525, 1633, 1604, 1658, 2864,
2929, 3278 cm–1.
13C NMR (CDCl3, 62.9 MHz): = 29.75, 30.08, 70.14, 76.89,
77.40, 77.90, 88.60, 119.99, 128.93, 131.70, 134.91, 158.32.
1H NMR (DMSO, 250 MHz): = 3.11 (m, 4 H, CH2S), 3.43 (m, 4
H, CH2O), 7.18–8.04 (m, 8 H, ArH), 13.05 (s, 2 H, COOH).
13C NMR (DMSO, 62.9 MHz): = 30.81, 68.27, 123.89, 125.56,
128.51, 130.78, 139.60, 167.44.
MS: m/z (%) = 378 (M+, 0.1), 180, 153 (100), 137, 109, 97, 77, 69,
63, 45.
MS: m/z (%) = 464 (M+, 13.5), 283, 256, 225, 208, 163, 148, 137,
UV (EtOH): max ( ) = 230.3 (2460), 261.9 (2186), 316.7 (856).
120, 56, 43 (100).
UV (CHCl3): max ( ) = 249 (1817).
Sulfur Dicarboxylic Acid Dichloride 4
Sulfur dicarboxylic acid 3, (9.45 g, 0.025 mol) was heated in SO2Cl2
(50 mL) for 8 h at 50–60 ºC. The SO2Cl2was evaporated from the
solution at low temperature and the residue was crystallized from
petroleum ether to give 4 as a yellow cream solid in 85% yield;
mp 82–87 ºC.
1,15-Diaza-3,4;12,13-dibenzo-8-oxa-16,18-pyridine-5,1-dithia-
cyclooctadecane-2,14-dione (9)
IR (KBr): 695, 763, 1195, 1280, 1452, 1570, 1666, 2827, 3315cm–1.
13C NMR (DMSO, 62.9 MHz): = 34.64, 38.87–40.88, 68.77,
77.51, 110.84, 126.94, 128.80, 130.95, 133.95, 138.25, 140.60,
150.27, 167.23.
MS: m/z (%) = 451 (M+, 5.9), 406, 377, 288, 163, 151, 137, 121,
109, 96, 83, 68, 57, 43(100).
IR (neat): 648, 657, 860, 1189, 1195, 1431, 1554, 1585, 1575, 2370,
3420 cm–1.
1H NMR (CDCl3, 250 MHz): = 3.26 (m, 4 H, CH2S) 3.75 (m, 4 H,
CH2O), 7.23–8.31 (m, 8 H).
13C NMR (CDCl3, 62.9 MHz): = 32.22, 69.35, 124.88, 126.14,
130.72, 134.77, 135.57,136.07.
UV (CHCl3): max ( ) = 250.6 (2809), 300.7 (2769).
Compound 10
IR (KBr): 740, 1047, 1110, 1257, 1415, 1465, 1562, 1677, 2987,
3035 cm–1.
13C NMR (DMSO, 62.9 MHz): = 35.44, 69.57, 78.51, 111.00,
128.04,129.60, 131.05, 134.15, 139.95, 141.01, 151.17, 169.23.
MS: m/z = 902 (M+), 552, 550, 538, 524, 451, 406, 364, 304,
239,193, 172 (100), 143, 109, 94, 77, 43.
Synthesis of Macrocyclic Diamides (5–12); General Procedure
A solution of diamine (2 mmol) in anhyd solvent (10 mL) was add-
ed quickly to a vigorously stirred solution of dicarboxylic acid
dichloride (2 mmol) in anhyd solvent at r.t. The mixture was stirred
for a further 5–20 min and then was washed with NaHCO3 (2 × 10
mL) and water (2 × 10 mL). The organic layer was dried over
MgSO4 and the solvent was evaporated to give a solid product. The
crude product was purified by column chromatography (petroleum
ether–EtOAc).
UV (CHCl3): max ( ) = 246.4 (2010), 307.7 (1255).
1, 15-Diaza-3,4;12,13-dibenzo-16,18-(p-ethylbenzoato)-8-oxa-
5,11-dithiacyclooctadecane-2,14-dione (11)
IR (KBr): 695, 897, 1115, 1475, 1600, 1654, 1712, 2878, 3255
cm–1.
13C NMR (CDCl3, 62.9 MHz): = 6.81, 14.76, 61.64, 67.61, 76.90,
77.9, 119.24, 129.32, 131.41, 135.81, 154.55, 164.38.
1,15-Diaza-3,4;12,13-dibenzo-8-oxa-5,11-dithiacycloheptade-
cane-2,14-dione (5)
IR (KBr): 746, 1105, 1429, 1541, 1645, 3269 cm–1.
13C NMR (CDCl3, 62.9 MHz): = 35.5, 45.0, 71.1, 126.7, 127.5,
132.1, 167.9.
MS: m/z (%) = 402 (M+, 2.5), 384, 35, 206, 192, 164, 136, 109, 91,
MS: m/z = 522 (M+,2.9), 477, 314, 236, 206, 180, 163, 137, 108, 83,
68, 57, 43 (100).
56 (100).
UV (CHCl3): max ( ) = 242.9 (831), 306.6 (474).
UV (CHCl3): max ( ) = 255.7 (750), 302.7 (532).
1,15-Diaza-3,4;12,13-dibenzo-16,18-(m-ethylbenzoato)-8-oxa-5,
11-dithiacyclooctadecane-2,14-dione (12)
IR (KBr): 667, 1020, 1205, 1217, 1228, 1365, 1726, 2858, 3280
cm–1.
13C NMR (CDCl3, 62.9 MHz): = 6.51, 13.76, 63.54, 68.61, 76.90,
79.9, 119.14, 128.32, 132.41, 136.81, 155.55, 167.38.
1,15-Diaza-3,4;12,13-dibenzo-8-oxa-5,11-dithiacyclooctade-
cane-2,14-dione (6)
IR (KBr): 686, 748, 862, 929, 1001, 1296, 1467, 1643, 2916, 3276
cm–1.
13C NMR (CDCl3, 62.9 MHz): = 32.15, 36.43, 69.1, 76.9, 127.73,
128.88, 130.82, 130.019, 162.86.
MS: m/z (%) = 416 (M+, 1.7), 398, 365, 220, 192, 164, 136, 109, 91,
MS: m/z (%) = 522 (M+, 4.7), 477, 314, 235, 206, 181, 163, 137,
108, 82, 68, 57, 43 (100).
56 (100).
UV (CHCl3): max ( ) = 244 (961), 307.4 (479).
Synthesis 2004, No. 4, 600–604 © Thieme Stuttgart · New York

604
H. Sharghi, Z. Paziraee
PAPER
(11) Chang, C. A.; Rowland, M. E. Inorg. Chem. 1983, 22, 3866.
(12) (a) Arnaud-Neu, F.; Spiess, B.; Schwing-Weill, M. J. Helv.
Chim. Acta 1977, 60, 2633. (b) Spiess, B.; Arnaud-Neu, F.;
Schwing-Weill, M. J. Helv. Chim. Acta 1979, 62, 1531.
(13) Holdt, H. J. Pure Appl. Chem. 1993, 65, 477.
(14) Sibert, J. W.; Lange, S. J.; Williams, D. J.; Barret, A. G. M.;
Hoffman, B. M. Inorg. Chem. 1995, 34, 2300.
(15) Blake, A. J.; Reid, G.; Schröder, M. J. Chem. Soc., Chem.
Commun. 1992, 1074.
Acknowledgment
We gratefully acknowledge the support of this work by the Shiraz
University Research Council.
References
(1) Delgado, R.; Frausto Da Silva, J. J. R.; Candida, T. A.; Vaz,
M. Polyhedron 1987, 6, 29.
(16) Stetter, H.; Marx, J. Ann 1957, 607, 519.
(17) Pellisard, D.; Louis, R. Tetrahedran Lett. 1972, 4589.
(18) Ogura, H.; Takeda, K. Heterocycles 1981, 15, 467.
(19) Fujita, E. Pure Appl. Chem. 1981, 53, 1141.
(20) Karmer, U.; Goggisberg, A.; Hesce, M.; Schmid, H. Angew.
Chem., Int. Ed. Engl. 1977, 16, 861.
(2) Lindoy, L. F.; Lip, H. C.; Power, L. F.; Rea, J. H. Inorg.
Chem. 1976, 15, 1724.
(3) (a) Armstrong, L. G.; Lindoy, L. F.; McPartlin, M.; Mockler,
G. M.; Tasker, P. A. Inorg. Chem. 1977, 16, 1665.
(b) Adam, K. R.; Lindoy, L. F.; Lip, H. C.; Rea, J. H. J.
Chem. Soc., Dalton Trans. 1981, 74.
(21) Morphy, R. J.; Parker, D.; Alexander, R.; Bains, A.; Carne,
A. F.; Eaton, M. A.; Millican, A.; Philipps, A.; Rhind, S. K.;
Tetmas, R.; Weatherby, D. J. Chem. Soc., Chem. Commun.
1988, 156.
(22) Jurczak, J.; Kasprzyh, S.; Stanaski, P.; Stankiewicz, T.;
Lipkowski, P. Tetrahedron 1993, 49, 1478.
(4) McDaniel, C. W.; Bradshaw, J. S.; Izatt, R. M. Heterocycles
1990, 30, 665.
(5) Krakowiak, K. E.; Bradshaw, J. S.; Izatt, R. M. J. Org.
Chem. 1990, 55, 3364.
(6) Shamsipur, M.; Ghiasvand, A.; Sharghi, H. Int. J. Environ.
Anal. Chem. 2002, 82, 23.
(23) (a) Tabushi, I.; Tanguchi, Y.; Kado, H. Tetrahedron Lett.
1977, 35, 1049. (b) Tabushi, I.; Okino, H.; Kuroda, Y.
Tetrahedron 1976, 4339.
(24) Sharghi, H.; Hosseini Sarvari, M. Synthesis 2003, 879.
(25) Sharghi, H.; Hosseini Sarvari, M. Tetrahedron 2003, 59,
3627.
(7) Javanbakht, M.; Ganjali, M. R.; Sharghi, H.; Eshghi, H.;
Shamsipur, M. Electroanalysis 1999, 11, 81.
(8) (a) Su, A. C. L.; Weiher, J. F. Inorg. Chem. 1968, 7, 176.
(b) Knochel, A.; Klimes, J.; Oehler, J.; Rudolph, G. Inorg.
Chem. Lett. 1975, 11, 787.
(9) Lindoy, L. F. Chem. Soc. Rev. 1975, 4, 421.
(10) (a) Kluiber, R. W.; Sasso, G. Inorg. Chim. Acta 1970, 4,
226. (b) Alcock, N. W.; Liles, D. C.; McPartlin, M.; Tasker,
P. A. J. Chem. Soc., Chem. Commun. 1974, 727. (c) Drew,
M. G. B.; BinOthman, A. H.; McFall, S. G.; Mcllroy, P. D.
A.; Nelson, S. M. J. Chem. Soc., Dalton Trans. 1977, 1173.
(26) Jurczack, J.; Dstaszewski, R.; Sahnski, P.; Stankiewicz, T.
Tetrahedron 1993, 49, 1471.
Synthesis 2004, No. 4, 600–604 © Thieme Stuttgart · New York