Intracluster transmetalation of cuprates with stannanes

Article abstract of DOI:10.1039/a906399d

Alkylarylcuprates with intramolecularly tethered stannanes undergo an intracluster Cu(I)/Sn(IV) transmetalation to yield arylstannanes.

Full text of DOI:10.1039/a906399d

Intracluster transmetalation of cuprates with stannanes
Cristina Mateo, Diego J. Cárdenas, Belén Martín-Matute and Antonio M. Echavarren*
Departamento de Química Orgánica, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
E-mail: anton.echavarren@uam.es
Received (in Liverpool, UK) 5th August 1999, Accepted 13th September 1999
Alkylarylcuprates with intramolecularly tethered stannanes
undergo an intracluster CuI/SnIV transmetalation to yield
arylstannanes.
exchange reaction with [LiCuMe2·LiCN] (1a).5,6 Therefore, we
chose to study the reactivity of arylcuprates 3, synthesised by
reaction of aryl iodide 2 with 1 (Scheme 1 and Table 1). Upon
warming of the solution of 3a7 from 278 to 23 °C, arylstannane
4a was cleanly formed in high yield by an apparent intra-
molecular Cu/Sn transmetalation.8,9† A similar reaction was
observed with cuprates 3b–d formed in situ from aryl iodide 2
by reaction with the corresponding homocuprates 1b–d,
although yields were lower due to the slower iodine/copper
exchange reaction as compared with that of 1a. Stannane 4a was
also obtained by reaction of 2 with [LiCuMe2·LiI], although the
reaction was not so clean. Reaction of 2 with either MeLi or
BuLi (2 equiv. each) failed to give any of the rearranged
products 4a or 4b, instead yielding 5 after hydrolysis.
Arylstannanes 4 presumably arise by Cu/Sn transmetalation,
followed by reaction of the resulting cuprate with RI formed in
the first iodine/copper exchange process. Although a direct
intramolecular process on 3 appears to be forbidden due to
endocyclic restriction,10 the following experiment also excludes
a simple intermolecular pathway. Thus, treatment of a mixture
of stannane 5 and iodobenzene with 1a failed to give any of
ethers 6a,b and phenyltributylstannane.11 Similarly, no CuI/
SnIV exchange was observed between 5 and [LiCuPh2·LiCN]
(1d).
Transmetalation of diorganocuprates with alkenyltrialkylstan-
nanes allows for the selective synthesis of mixed organocu-
prates with concomitant formation of stable tetraalkylstannanes
[eqn. (1)].1 This method has been successfully extended to the
preparation of allyl cuprates.2 However, despite the synthetic
importance of this reaction1–3 little is known about its
mechanism.
We have been able to isolate the Pd/Sn and Pd/Si transmetala-
tion steps of the Stille and Hiyama coupling reactions,
respectively, by performing the reaction intramolecularly in a
system which was unable to reductively eliminate because of
the instability of the resulting organic product [eqn. (2)].4 We
decided to use a similar approach to study the Cu/Sn
transmetalation.
Recently, Sakamoto demonstrated that mixed arylmethylcu-
prates can be obtained from iodobenzenes by iodine–copper
On the other hand, treatment of a 1+1 mixture of 2 and 7 with
[Bu2CuLi·LiCN] led to a mixture of the four possible products
4b, 8a, 8b and 9.12 Although apparently puzzling, this cross-
over experiment can be readily explained if the usual dimeric
structure of the cuprates is taken into account (Scheme 2).13
Thus, reaction of cuprates 1 with the aryl iodides would furnish
Scheme 1
Table 1 Reaction of stannane 2 with cuprates 1a–d
Isolated
1 (equiv.)
R
Product
yield (%)
1a (1.1)
1a (2.0)
1b (1.6)
1b (2.0)
1c (1.5)
1c (2.0)
1d (1.2)
Me
Me
Bu
Bu
But
But
Ph
4a
4a
4b
4b
4c
4c
4d
96
38
40
50
37
26
43
Scheme 2
Chem. Commun., 1999, 2205–2206
This journal is © The Royal Society of Chemistry 1999
2205

dimer alkylarylcuprates 10,14 which could suffer a selective
intracluster transmetalation to afford mixed cuprate 11. Evi-
dence for the formation of species 11 was obtained by the
isolation of stannane 1215 in the reactions of 1b with 2,
presumably as a result of the hydrolysis of hemiketal 13
resulting from the oxidation of cuprate 11 (R = RA = Bu) by
oxygen. Final coupling of cuprates 11 with RI (R = Me, Bu,
But, Ph) formed in the first iodine/copper exchange reaction
accounts for the formation of products 4a–d (Scheme 1).
Thus the present study demonstrates that transmetalation of
stannanes with cuprates can proceed in an intracluster manner.
This is also the first example of transmetalation of alkyl-
stannanes with organocuprates. Similar transformations could
be conceived with organostannanes bonded to the lithium atoms
of cuprate dimers through the appropriate directing groups.
We are grateful to the DGES (Project PB97-0002-C2-02) for
support of this research and to the MEC for a predoctoral
fellowship to B. M.-M.
2 B. H. Lipshutz, R. Crow, S. H. Dimock, E. L. Ellsworth, R. A. J. Smith
and J. R. Behling, J. Am. Chem. Soc., 1990, 112, 4063.
3 M. Benecie and K. Khuong-Huu, Synlett, 1992, 266.
4 D. J. Cárdenas, C. Mateo and A. M. Echavarren, Angew. Chem., Int. Ed.
Engl., 1994, 33, 2445; C. Mateo, D. J. Cárdenas, C. Fernández-Rivas
and A. M. Echavarren, Chem. Eur. J., 1996, 2, 1596; C. Mateo, C.
Fernández-Rivas, A. M. Echavarren and D. J. Cárdenas, Organome-
tallics, 1997, 16, 1997; C. Mateo, C. Fernández-Rivas, D. J. Cárdenas
and A. M. Echavarren, Organometallics, 1998, 17, 3661.
5 Y. Kondo, T. Matsudaira, J. Sato, N. Murata and T. Sakamoto, Angew.
Chem., Int. Ed. Engl., 1996, 35, 736.,
6
For the structure of organocuprates generated from CuCN: N. Krause,
Angew. Chem., Int. Ed., 1999, 38, 79.
7 Formation of an arylcuprate intermediate was demonstrated by the
formation of o-allylphenol by treatment o-iodophenol allyl ether with 1a
(73% yield). For a similar rearrangement: J. Barluenga, R. Sanz and
F. J. Fañanás, Tetrahedron Lett., 1997, 38, 6103.
8 Best results were obtained with 1.1–1.5 equiv. of cuprate 1a. The use of
larger amounts led to lower yields of 4a, presumably as a result of the
early quenching of MeI by the excess 1a (ref. 5).
9 The mixed cuprates could not be prepared by the direct Sn/Cu exchange
from the o-substituted arylstannanes, probably due to steric hindrance.
Thus, no reaction was observed in the reaction of 1a or 1b with 2-(tri-n-
butylstannylmethoxy)phenyltri-n-butylstannane, while the reaction be-
tween phenyltri-n-butylstannane and 1b yields tetra-n-butylstanne (74%
isolated yield).
10 P. Beak, Acc. Chem. Res., 1992, 25, 215; M. L. Kurtzweil, D. Loo and
P. Beak, J. Am. Chem. Soc., 1993, 115, 421
11 The only new stannane was methyltributylstannane, resulting from the
selective transmetalation of 5 with [LiCuMePh·LiCN]. A similar
reaction with [LiCuBu2·LiCN] afforded Bu4Sn.
12 Determined by 1H NMR and GC-EI-MS analysis.
13 G. van Koten, S. L. James and J. T. B. H. Jastrzebski, Comprehensive
Organometallic Chemistry II, Pergamon, Oxford, 1995, vol. 3, ch. 2.
14 Coordination of the ethers to the lithium atoms is omitted for clarity in
Scheme 2. The arrows in 10 only indicate the group connectivity in the
rearranged product 11.
Notes and references
† Preparation of 4a: MeLi (1.6 M solution in hexanes, 0.93 ml, 1.49 mmol)
was added into a suspension of CuCN (66 mg, 0.74 mmol) in THF (4 ml)
at 278 °C. After stirring at 278 °C for 3 h, the light yellow solution was
treated with a solution of 2 (350 mg, 0.67 mmol) in THF (5 ml). The
resulting mixture was allowed to reach 23 °C over 17 h. A saturated NH4Cl–
NH3 buffered solution (pH = 8, 50 ml) and Et2O (100 ml) were then added.
After the usual extractive workup and chromatography (SiO2, hexanes) 4a
was obtained as a colorless oil (264 mg, 96%); dH(CDCl3, 200 MHz) 7.37
(dd, J 6.6, 1H), 7.32–7.24 (m, 1H), 6.94 (br t, J 7.1, 1H), 6.78 (br d, J 8.1,
1H), 3.99 (q, J 6.9, 2H), 1.65–1.12 (m, 15H), 1.08–0.99 (m, 6H), 0.92–0.84
(m, 9H); dC(CDCl3, 75 MHz) 163.09, 136.99 [2J(13C–Sn) 23], 130.24,
129.60, 120.7 [1J(13C–Sn) 40], 109.35 [2J(13C–Sn) 21], 62.92, 29.20
[3J(13C–Sn) 19], 27.42 [2J(13C–Sn) 58], 14.92, 13.70, 9.83 [1J(13C–119Sn)
333.3, 1J(13C–117Sn) 332.6]; m/z (EI) 411 (M+), 355 (100%) (Calc. for
C
20H36OSn: C, 58.42; H, 8.82. Found: 58.45; H, 9.15%).
15 Variable amounts of 12 and phenol, the product of protodestannylation
of 12, were obtained when oxygen was present before the aqueous
workup.
1
J. R. Behling, K. A. Babiak, J. S. Ng, A. L. Campbell, R. Moretti, M.
Koerner and B. H. Lipshutz, J. Am. Chem. Soc., 1988, 110, 2641. This
method has been successfully extended for the preparation of allyl
cuprates.
Communication 9/06399D
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Chem. Commun., 1999, 2205–2206