Total synthesis of (+)-gelsedine

Article abstract of DOI:10.1002/(SICI)1521-3773(19990802)38:15<2214::AID-ANIE2214>3.0.CO;2-V

A novel iodide-promoted, allene-terminated cyclization of an N- acyliminium ion, a stereoselective Heck spirocyclization, and a chemoselective demethylation at the nitrogen atom of an oxindole are the key transformations in the first total synthesis of th

Full text of DOI:10.1002/(SICI)1521-3773(19990802)38:15<2214::AID-ANIE2214>3.0.CO;2-V

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Total Synthesis of (‡)-Gelsedine
Winfred G. Beyersbergen
van Henegouwen,
O
•
H
HO
HO
O
a
b
Rutger M. Fieseler,
Floris P. J. T. Rutjes, and
Henk Hiemstra*
EtO
Ph
H2OC
CO2H
O
N
N
•
(S)-malic acid
–
O
I
Ph
4
Species of the plant genus Gelsemi-
um (Loganiaceae) constitute a rich
source of indole alkaloids with remark-
ably complex and diverse structures.[1]
Among these are gelsemine (1) and
gelsedine (2). Recently, we[2] and oth-
ers[3] have published total syntheses of
racemic gelsemine. Here we present
the first total synthesis of gelsedine in
enantiopure form. Our studies are
motivated by the challenging molecu-
lar architecture of the Gelsemium
alkaloids and by the interesting bio-
logical activity that some of these
natural products display. In fact, ex-
tracts from Gelsemium species have a
rich medicinal history, particularly in
China.[1]
c
RO
O
O
H
Ph
O
N
5
O
3
Ph
I
N
6: R = HCO
7: R = H
d
e
8: R = SiMe2tBu
O
5
f
tBuMe2SiO
Ph
tBuMe2SiO
Ph
OTf
N
N
OTf
O
O
9
10
Gelsedine (2) was isolated from
Carolina jasmine (Gelsemium semper-
virens) in 1953 by Schwarz and Mari-
on[4] and was later also found to occur
in G. elegans.[5] Its structure was eluci-
dated by Wenkert et al.[6] in 1962 on
the basis of a spectroscopic comparison
Scheme 1. Cyclization of 4. a) Reference [11]; b) NaI (20 equiv), HCO2H (0.2m), 858C, 18 h, 42% of
5 ‡ 34% of 6; c) HCO2H, 858C, 18 h; d) satd NH3 in MeOH, RT (room temperature), 15 min, 79%
over two steps; e) TBDMSCl (3 equiv), imidazole (4 equiv), DMAP (0.2 equiv), CH2Cl2, RT, 18 h,
96%; f) LiHMDS (1.5 equiv), THF, 788C, 0.5 h, then PhNTf2 (1.5 equiv), 788C !RT, 18 h, 45%
of 10. DMAP ˆ 4-(dimethylamino)pyridine, HMDS ˆ hexamethyldisilazane, TBDMS ˆ tert-butyldi-
methylsilyl, Tf ˆ trifluoromethanesulfonyl.
with its 11-methoxy analogue gelsemicine (3), whose structure
had already been determined in 1961 through X-ray crystal-
lography by Przybylska and Marion.[7]
raises additional problems, such as the introduction of the
ethyl substituent in the correct stereochemical sense and the
special functionalization of the seven-membered ring. Until
now, three groups have reported studies towards a total
synthesis of gelsedine.[8, 9] The elegant approach by Kende and
co-workers is particularly noteworthy, but the formation of
the undesired stereoisomer in the final spirocyclization step
has prevented real success.[9] Furthermore, in 1994 a semisyn-
thesis of gelsedine starting from koumidine was accomplished
by Takayama et al.[10] We now report the first totally chemical
synthesis of gelsedine based on the unique reaction sequence
of a novel iodide-promoted cyclization of an allene onto an
N-acyliminium ion followed by palladium-catalyzed carbon-
ylation and Heck spirocyclization. The synthesis starts with
inexpensive (S)-malic acid and leads to the enantiomer of
natural gelsedine.
Previously, we have reported an efficient five-step synthesis
of ethoxylactam 4 from (S)-malic acid, and cyclization of the
N-acyliminium ion of 4 in neat formic acid to bicyclic ketone 6
in 79% yield (Scheme 1).[11] Because a successful route to
gelsedine starting from ketone 6 requires functionalization at
C4, we tried to prepare vinyl triflate 9 from 6 via hydroxy
ketone 7 and silyl ether 8. However, we were unable to
generate 9 from 8; the regioisomer 10 was always the sole
product obtained.[12] We then considered the possibility of a
more direct and elegant pathway to arrive at vinyl iodide 5,
H
O
O
N
R
N
H
N
N
O
O
OMe
Me
1: gelsemine
2: gelsedine, R = H
3: gelsemicine, R = OMe
Being a minor constituent in Carolina jasmine, gelsedine
has not received as much attention as the parent alkaloid
gelsemine. From a synthetic point of view, both alkaloids
present the formidable challenge of a compact tricyclic
skeleton adorned with a spiro-oxindole moiety. Gelsedine
[*] Prof. Dr. H. Hiemstra, W. G. Beyersbergen van Henegouwen,
R. M. Fieseler, Dr. F. P. J. T. Rutjes
Laboratory of Organic Chemistry, Institute of Molecular Chemistry
University of Amsterdam
Nieuwe Achtergracht 129
1018 WS Amsterdam (The Netherlands)
Fax: (‡31)20-5255670
E-mail: henkh@org.chem.uva.nl
2214
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which is a synthetic equivalent of 9. The successful one-step
transformation of 4 into 5 appeared to be the key to success.
Cyclizations of allenes onto N-acyliminium ions are scarce
in the literature,[13] and iodide-promoted variants are un-
known, to the best of our knowledge. Overman and Brosius
have reported examples of the beneficial effect of iodide as a
powerful nucleophile in cationic cyclizations of alkenes.[14]
When allene 4 was dissolved in formic acid in the presence of
a large excess of sodium iodide and heated to 858C for 18 h,
we were delighted to find 5 as the main product in 42% yield
(Scheme 1, Table 1). In spite of extensive experimentation
for the Heck spirocyclization.[16] This reaction proceeded best
in acetonitrile in a sealed tube at 1208C. We obtained
oxindole 15 as the sole product with the desired spiroster-
eochemistry in 90% yield.[17]
The installation of the tetrahydropyran ring was the next
phase of the synthesis. Hydroboration of 15 with dicyclohex-
ylborane[18] gave exclusively the desired stereoisomer 16 in
79% yield (Table 1). Ring closure was effected by treatment
with Hg(O2CCF3) followed by addition of saturated aqueous
NaCl to produce chloromercurial 17 in excellent yield. Only
the six-membered ring ether was formed. After extensive
experimentation we found that demercuration was most
cleanly achieved by reduction with nBu3SnH[19] to furnish
18, which already features the complete skeleton of gelsedine.
Introduction of the ethyl moiety required prior reductive
removal of the benzyl group from the saturated lactam
nitrogen atom. However, to achieve this through reduction by
a dissolved metal, the oxindole ring would need protection as
the anion. Therefore, the oxindole methyl group should be
removed first. This latter chore was readily accomplished by
using a procedure which is known for removal of an N-methyl
group from an indole.[20] Treatment of 18 with dibenzoyl
peroxide followed by saturated NH3 in methanol gave 19 in a
remarkable 74% yield. Removal of the benzyl group now
proceeded smoothly to give the very polar compound 20.
The appropriate lactam carbonyl group was activated
towards Grignard addition by double protection with tert-
butoxycarbonyl (Boc) to give 21. Treatment of biscarbamate
21 with excess EtMgBr (6 equiv) gave the highly useful
hemiaminal 22 in a surprisingly efficient transformation. We
assume that attack of the Grignard reagent takes place on the
carbonyl moiety of the Boc group that is then removed (R2 in
21) because the oxindole carbonyl moiety is too sterically
hindered. Although 22 was stable at room temperature, it was
treated in crude form with trifluoroacetic acid (TFA) to
generate N-acyliminium ion 23, which was reduced in situ
with triethylsilane. On addition of more TFA the Boc group
was removed, and the TFA salt of desmethoxygelsedine (24)
was obtained in good yield (Table 1).[17]
Table 1. Selected physical properties of compounds 5, 16, and 24.
5: Rf ˆ 0.31 (EtOAc/petroleum ether (60 ± 80) 1/1); [a]2D2 ˆ ‡10.3 (c ˆ 1.0,
1
CHCl3); IR (thin film): nÄ ˆ 2920, 1735, 1682, 1495, 1446, 1165 cm
;
1H NMR (400 MHz, CDCl3): d ˆ 7.97 (s, 1H), 7.30 (m, 5H), 6.34 (s, 1H),
5.02 (s, 1H), 4.86 (d, J ˆ 15.3 Hz, 1H), 4.12 (d, J ˆ 15.3 Hz, 1H), 3.44 (t, J ˆ
3.3 Hz, 1H), 2.99 (d, J ˆ 18.7 Hz, 1H), 2.83 (d, J ˆ 18.9 Hz, 1H), 2.77 (s,
1H), 2.70 (d, J ˆ 18.5 Hz, 1H), 2.57 (d, J ˆ 18.5 Hz, 1H); 13C NMR
(100 MHz, CDCl3): d ˆ 173.0, 159.8, 137.3, 135.4, 128.7, 127.6, 127.5, 93.1,
75.4, 61.9, 45.8, 45.2, 44.2, 32.5; HR-MS (EI) calcd for C16H16INO3:
397.0174, found: 397.0146.
16: Rf ˆ 0.37 (CH2Cl2/acetone 1/1); m.p. 87 ± 898C; [a]D22
ˆ
13.4 (c ˆ 1.0,
CHCl3); IR (thin film): nÄ ˆ 3394, 2932, 1699, 1682, 1610, 1495, 1342,
1
1252 cm
;
1H NMR (400 MHz, CDCl3): d ˆ 7.26 (m, 7H), 7.07 (t, J ˆ
7.5 Hz, 1H), 6.81 (d, J ˆ 7.8 Hz, 1H), 6.00 (dd, J ˆ 9.1, 11.6 Hz, 1H), 5.33
(d, J ˆ 15.7 Hz, 1H), 5.20 (d, J ˆ 11.7 Hz, 1H), 4.07 (m, 2H), 3.86 (d, J ˆ
15.7 Hz, 1H), 3.78 (t, J ˆ 4.5 Hz, 1H), 3.26 (dd, J ˆ 6.8, 8.7 Hz, 1H), 3.19 (s,
3H), 2.77 (m, 1H), 2.30 (dd, J ˆ 4.3, 16.3 Hz, 1H), 2.21 (dd, J ˆ 1.6, 16.1 Hz,
1H); 13C NMR (100 MHz, CDCl3): d ˆ 176.6, 174.9, 142.2, 137.2, 135.1,
132.4, 128.5, 128.4, 128.2, 127.7, 127.2, 123.2, 123.0, 107.9, 59.3, 56.9, 55.3,
45.3, 45.1, 45.0, 32.7, 26.5; HR-MS (EI) calcd for C24H24N2O3: 370.1787,
found: 370.1787.
24: Rf ˆ 0.42 (CH2Cl2/MeOH 4:1); m.p. 110 ± 1128C; [a]2D2 ˆ ‡83.0 (c ˆ 1.0,
1
MeOH); IR (thin film): nÄ ˆ 2971, 1679, 1620, 1472, 1435, 1201, 1124 cm
;
1H NMR (400 MHz, CDCl3): d ˆ 11.5 (s, 1H), 11.3 (s, 1H), 9.32 (s, 1H), 7.33
(d, J ˆ 7.4 Hz, 1H), 7.24 (t, J ˆ 7.7 Hz, 1H), 7.06 (t, J ˆ 7.5 Hz, 1H), 6.95 (d,
J ˆ 7.7 Hz, 1H), 4.51 (s, 1H), 4.27 (m, 2H), 3.80 (s, 1H), 3.72 (d, J ˆ 6.5 Hz,
1H), 2.88 (s, 1H), 2.56 (s, 1H), 2.35 (dd, J ˆ 16.4, 3.4 Hz, 1H), 2.26 (d, J ˆ
15.5 Hz, 1H), 2.18 (m, 2H), 2.00 (m, 2H), 1.08 (t, J ˆ 7.5 Hz, 3H); 13C NMR
(100 MHz, CD3OD): d ˆ 184.2, 163.4 (q, J(C,F) ˆ 35.4 Hz), 141.5, 136.5,
129.9, 126.0, 124.4, 118.3 (q, J(C,F) ˆ 290.6 Hz), 111.5, 76.6, 66.4, 63.7, 61.3,
60.9, 40.9, 35.2, 32.0, 22.1, 20.6, 11.4; 19F NMR (282 MHz, CD3OD): d ˆ
77.4; HR-MS (EI) calcd for C18H22N2O2: 298.1682, found: 298.1679.
For the final stageÐthat is, the introduction of the
N-methoxy groupÐwe followed a procedure which was
especially designed for this purpose.[10, 21] Protection of the
amine in 24 with 2,2,2-trichloroethyl chloroformate gave 25,
and subsequent reduction of the oxindole carbonyl group with
borane afforded spiro-indoline 26. The oxidation of this
indoline (urea ´ H2O2, Na2WO4 ´ 2H2O, 10% aq MeOH)
proceeded rather slowly, but did produce 27 after subsequent
treatment with diazomethane. Deprotection of 27 with zinc in
acetic acid gave (‡)-gelsedine, which was identical to natural
( )-gelsedine[22] (1H (400 MHz) and 13C NMR spectroscopy
(100 MHz), high-resolution mass spectrometry (FAB)), ex-
(varying temperature, concentration, iodide source), we were
unable to prevent competitive attack of formic acid as a
nucleophile, and 6 (after unavoidable in situ hydrolysis of the
intermediate vinyl formate) was always obtained as a by-
product (34%). Iodide 5 was readily separated from 6 by flash
chromatography, so that sufficient quantities of 5 could be
obtained to proceed with the total synthesis of gelsedine.
The construction of the spiro-oxindole moiety onto 5
commenced with a Pd-catalyzed aminocarbonylation[15] to
give anilide 11 after subsequent deformylation (Scheme 2). To
render the molecular architecture more favorable for the
desired stereochemical course of the Heck spirocyclization,
we deemed an sp2-hybridized bridging carbon atom to be
desirable. The approach of the arylpalladium complex from
the exo direction would then be least sterically encumbered.
Therefore, alcohol 11 was first oxidized with PCC to ketone 12
and subjected to a Wittig reaction to provide 13 in good
overall yield. The nitrogen atom in anilide 13 was then
protected with a methyl group to give 14, which set the stage
cept for the optical rotation (synthetic (‡)-gelsedine: [a]D22
ˆ
‡120 (c ˆ 0.25, CHCl3); natural ( )-gelsedine: [a]D25
(c ˆ 1.35, CHCl3)).[4]
ˆ
159
In conclusion, we have successfully completed the first total
synthesis of (‡)-gelsedine in 21 steps from (S)-malic acid. This
synthetic endeavour produces a single enantiomer, proceeds
with complete stereoselectivity, and has brought forth a
number of novel transformations which may find further
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O
H
X
HO
N
O
O
O
a
b
Ph
Ph
N
N
R
N
H
Ph
I
N
Br
Br
O
O
O
5
11
12: X = O, R = H
13: X = CH2, R = H
14: X = CH2, R = Me
c
d
e
OH
g
f
O
Ph
Ph
N
N
Ph
N
N
N
N
Me
Me
Me
O
O
O
O
O
O
R
15
17: R = HgCl
18: R = H
16
h
i
m
Boc
R1
O
Boc
O
O
N
N
N
–
H
N
NH
NH
R2
O
OH
O
O
O
19: R1 = Bn, R2 = H
20: R1 = H, R2 = H
21: R1 = Boc, R2 = Boc
22
23
j
k
15
10
9
R1
–
H
O
TFA
O
N
q
O
n
H
N
HN
N
R2
NH
N
8
OMe
X
O
O
25: R1 = Troc, R2 = H, X = O
26: R1 = Troc, R2 = H, X = H2
27: R1 = Troc, R2 = OMe, X = O
o
p
24
ent-gelsedine
Scheme 2. Synthesis of ent-gelsedine. a) 1. o-Bromoaniline (3 equiv), Pd(OAc)2 (0.15 equiv), PPh3 (0.30 equiv), Et3N (5 equiv), CO (balloon), DMF, 408C,
20 h; 2. satd NH3 in MeOH, RT, 15 min, 64%; b) PCC (5 equiv), CH2Cl2, 408C, 24 h, 66%; c) Ph3PMeBr (2.5 equiv), nBuLi (1.6m in hexanes, 2.45 equiv),
THF, 08C, then 12, reflux, 18 h, 83%; d) MeI (2.5 equiv), NaH (3 equiv), THF, RT, 4.5 h, 78%; e) [Pd(PPh3)4] (0.2 equiv), Et3N (10 equiv), MeCN, sealed
tube, 1208C, 40 h, 90%; f) (Chx)2BH (2 equiv), THF, 08C, 2 h, then 3m NaOH/H2O2, 1 h, RT, 79%; g) Hg(O2CCF3)2 (2 equiv), THF, 5 h, then satd aq NaCl,
RT, 3 h, 88%; h) nBu3SnH (2.5 equiv), AIBN (0.1 equiv), toluene (0.5m of 17), RT!558C, 2 h, 80%; i) 1. (PhCO2)2 (2 equiv), CH2Cl2, sealed tube,
808C, 18 h; 2. satd NH3 in MeOH, RT, 20 h, 74%; j) Li (10 equiv), NH3, 788C, 30 min, then isoprene (25 equiv), 788C !RT, 79%; k) Boc2O (8 equiv),
DMAP (6 equiv), THF, RT, 4 h, 78%; l) EtMgBr (1m in THF, 6 equiv), THF, 78 !08C, 30 min, then satd aq NH4Cl; m) TFA (12 equiv), Et3SiH (8 equiv),
CH2Cl2, 08C !RT, 4 h, then extra TFA, RT, 18 h, 61% over two steps; n) TrocCl (2.2 equiv), pyridine, CH2Cl2, RT, 18 h, 67%; o) BH3 ´ SMe2 (20 equiv),
THF, 0 !708C, 18 h, then Me3NO (5 equiv), MeOH, reflux, 2 h, 72%; p) 1. urea ´ H2O2 (20 equiv), Na2WO4 ´ 2H2O (0.6 equiv), 10% aq MeOH, RT, 4 h;
2. CH2N2 (excess), Et2O, 1 h, 31% over two steps; q) Zn (40 equiv), AcOH, RT, 20 h, 84%. AIBN ˆ 2,2'-azobisisobutyronitrile, Boc ˆ tert-butoxycarbonyl,
Chx ˆ cyclohexyl, DMAP ˆ 4-(dimethylamino)pyridine, PCC ˆ pyridinium chlorochromate, TFA ˆ trifluoroacetic acid, TrocCl ˆ 2,2,2-trichloroethyl
chloroformate.
application. The unique combination of the iodide-promoted
cationic allene cyclization to produce a vinyl iodide and
palladium-catalyzed elaboration of the latter in carbonylation
and subsequent Heck chemistry has been the key to success.
In addition, methyl has shown to be a good protecting group
for the oxindole nitrogen atom. Finally, the fully chemo- and
stereoselective introduction of the ethyl group provides
another illustration of the powerful utility of N-acyliminium
ions as intermediates in modern synthesis.
Received: January 28, 1999
Revised version: April 6, 1999 [Z12971IE]
German version: Angew. Chem. 1999, 111, 2351 ± 2355
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Keywords: alkaloids ´ allenes ´ natural products ´ spiro
compounds ´ total synthesis
Coinage Metal Complexes of a Tellurium
Diimide: cis !trans Isomerization and Metal ±
Metal Interactions**
[1] Reviews on Gelsemium alkaloids: a) J. E. Saxton in The Alkaloids,
Vol. 8 (Ed.: R. H. F. Manske), Academic Press, New York, 1965,
pp. 93 ± 117; b) Z.-J. Liu, R.-R. Lu in The Alkaloids, Vol. 33 (Ed.: A.
Brossi), Academic Press, New York, 1988, pp. 83 ± 140; c) H. Takaya-
ma, S. Sakai in Studies in Natural Products Chemistry, Vol. 15 (Ed.: A.
Rahman), Elsevier, Amsterdam, 1995, pp. 465 ± 518.
Tristram Chivers,* Masood Parvez, and
Gabriele Schatte
The unique properties of inorganic polymers, especially
those with metal atoms in the backbone, provide an incentive
for the investigation of novel systems.[1] The versatile ligand
behavior of sulfur(iv) diimides encompasses s(N), s(N,N'),
and, less commonly, s(S) and p(N,S) bonding modes.[2]
[2] N. J. Newcombe, Y. Fang, R. J. Vijn, H. Hiemstra, W. N. Speckamp, J.
Chem. Soc. Chem. Commun. 1994, 767 ± 768.
[3] a) J. K. Dutton, R. W. Steel, A. S. Tasker, V. Popsavin, A. P. Johnson, J.
Chem. Soc. Chem. Commun. 1994, 765 ± 766; b) D. Kuzmich, S. C. Wu,
D.-C. Ha, C.-S. Lee, S. Ramesh, S. Atarashi, J.-K.Choi, D. J. Hart, J.
Am. Chem. Soc. 1994, 116, 6943 ± 6944; c) T. Fukuyama, L. Gang, J.
Am. Chem. Soc. 1996, 118, 7426 ± 7427; d) S. Atarashi, J.-K. Choi, D.-
C. Ha, D. J. Hart, D. Kuzmich, C.-S. Lee, S. Ramesh, S. C. Wu, J. Am.
Chem. Soc. 1997, 119, 6226 ± 6241.
[4] H. Schwarz, L. Marion, Can. J. Chem. 1953, 31, 958 ± 975.
[5] H. L. Jin, R. S. Xu, Acta Chim. Sinica 1982, 40, 1129 ± 1135.
[6] E. Wenkert, J. C. Orr, S. Garratt, J. H. Hansen, B. Wickberg, C. L.
Leicht, J. Org. Chem. 1962, 27, 4123 ± 4126.
[7] M. Przybylska, L. Marion, Can. J. Chem. 1961, 39, 2124 ± 2127.
[8] a) S. W. Baldwin, R. J. Doll, Tetrahedron Lett. 1979, 20, 3275 ± 3278;
b) N. K. Hamer, J. Chem. Soc. Chem. Commun. 1990, 102 ± 103.
[9] a) A. S. Kende, M. J. Luzzio, J. S. Mendoza, J. Org. Chem. 1990, 55,
918 ± 924; b) M. J. Luzzio, Dissertation, University of Rochester,
USA, 1987. We thank Professor A. S. Kende of the University of
Rochester for sending us a copy of this thesis.
The only known complex of
a
selenium(iv) diimide,
[3]
ˆ
ˆ
SnCl4(tBuN Se NtBu), displays s(N,N') chelation. Unlike
ˆ ˆ
their lighter congeners RN E NR (E ˆ S, Se), which adopt
monomeric structures with syn,syn or syn,anti conformations
in the solid state[4, 5] and gas phase,[6] tellurium diimides are
dimeric and form cis or trans isomers in the solid state.[7±9] The
cis isomer 1 is obtained with an endo,endo arrangement of
terminal tBu groups,[8] whereas in the trans isomers 2b and 2c
the terminal groups occupy exo positions with respect to the
[10] H. Takayama, Y. Tominaga, M. Kitajama, N. Aimi, S. Sakai, J. Org.
Chem. 1994, 59, 4381 ± 4385.
[11] W. G. Beyersbergen van Henegouwen, H. Hiemstra, J. Org. Chem.
1997, 62, 8862 ± 8867.
[12] More detailed information about these reactions will be provided in a
full paper.
[13] a) P. M. M. Nossin, W. N. Speckamp, Tetrahedron Lett. 1981, 22,
3289 ± 3292; b) P. M. M. Nossin, J. A. M. Hamersma, W. N. Speckamp,
Tetrahedron Lett. 1982, 23, 3807 ± 3810; c) P. M. M. Nossin, Disserta-
tion, University of Amsterdam, The Netherlands, 1983; for intermo-
lecular reactions of N-acyliminium ions with allenes, see d) R. L.
Danheiser, C. A. Kwasigroch, Y.-M. Tsai, J. Am. Chem. Soc. 1985, 107,
7233 ± 7235; e) J. S. Prasad, L. S. Liebeskind, Tetrahedron Lett. 1988,
29, 4257 ± 4260; f) W. F. J. Karstens, F. P. J. T. Rutjes, H. Hiemstra,
Tetrahedron Lett. 1997, 38, 6275 ± 6278.
[14] A. D. Brosius, L. E. Overman, J. Org. Chem. 1997, 62, 440 ± 441.
[15] S. Cacchi, E. Morera, G. Ortar, Tetrahedron Lett. 1985, 26, 1109 ± 1112.
[16] a) M. M. Abelman, T. Oh, L. E. Overman, J. Org. Chem. 1987, 52,
4130 ± 4133; b) A. Madin, L. E. Overman, Tetrahedron Lett. 1992, 33,
4859 ± 4862; c) A. Ashimori, B. Bachand, L. E. Overman, D. J. Poon, J.
Am. Chem. Soc. 1998, 120, 6477 ± 6487.
[17] The stereochemistry of the oxindole and ethyl group was proven
unambiguously in 24. Distinct NOEs between C10 and C15 protons
and C8 and C9 protons were observed.
[18] H. C. Brown, A. K. Mandal, S. U. Kulkarni, J. Org. Chem. 1977, 42,
1392 ± 1398.
[19] D. A. Evans, S. L. Bender, J. Morris, J. Am. Chem. Soc. 1988, 110,
2506 ± 2526.
[20] S. Nakatsuka, O. Asano, T. Goto, Heterocycles 1986, 24, 2791 ± 2792.
Te2N2 ring.[9] In solution 2b and 2c slowly convert into the
corresponding cis isomers.[9]
As part of our investigations of the coordination chemistry
of tellurium diimide dimers the generation of a polymer in
which ligands of type 2 are bridged by metal ions seemed
especially intriguing. We describe here the synthesis and
X-ray structures of 3 and 4, the first metal complexes of a
tellurium diimide dimer. The ligand 1 exhibits remarkably
‡
‡
different ligand behavior towards Cu and Ag . In particular,
‡
Cu promotes cis !trans isomerization (1 !2a) in the
formation of 3. In contrast, the dinuclear complex 4 with a
metal ± metal (d10 ± d10) interaction is produced in the pres-
‡
ence of Ag .
[Cu2L3](CF3SO3)2
[Ag2L2](CF3SO3)2
[Cu2L](CF3SO3)2
3
4
5
ˆ
ˆ
L ˆ tBuN Te(m-NtBu)2Te NtBu
Â
We thank Professor C. Szantay of the Technical University of
Complex 3 was obtained by a two-step process in which 5
was prepared from stoichiometric amounts of copper(i)
trifluoromethanesulfonate and 1.[10] Subsequently, 5 was
Budapest (Hungary) for drawing our attention to this article.
[21] a) S.-I. Murahashi, T. Oda, T. Sugahara, Y. Masui, J. Org. Chem. 1990,
55, 1744 ± 1749; b) M. Kitajima, H. Takayama, S. Sakai, J. Chem. Soc.
Perkin Trans. 1 1994, 1573 ± 1578.
[*] Prof. Dr. T. Chivers, Dr. M. Parvez, Dr. G. Schatte
Department of Chemistry
[22] We are very grateful to Professor H. Takayama of Chiba University
(Japan) for NMR spectra and a sample of ( )-gelsedine.
University of Calgary
Calgary, AB T2N1N4 (Canada)
Fax: (‡1)403-289-9488
E-mail: chivers@ucalgary.ca
[**] We gratefully acknowledge the Natural Sciences and Engineering
Research Council (Canada) for financial support.
Angew. Chem. Int. Ed. 1999, 38, No. 15
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