Dilithium aryl cyanocuprates from butyl aryl tellurides

Article abstract of DOI:10.1016/j.tetlet.2004.04.062

Butyl aryl tellurides reacted with dilithium dimethyl cyanocuprate and with dilithium methyl(2-thienyl)cyanocuprate to give the corresponding dilithium aryl cyanocuprates, which were captured with enones leading to 4-aryl ketones in good yields.

Full text of DOI:10.1016/j.tetlet.2004.04.062

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 4473–4475
Dilithium aryl cyanocuprates from butyl aryl tellurides
*
~
Priscila Castelani, Silas Luque and Joao V. Comasseto
ꢀ
~
~
Instituto de Quımica, Universidade de Sao Paulo, Av. Prof. Lineu Prestes, 748, Cx.P. 26077, 05599-970 Sao Paulo, Brazil
Received 18 November 2003; revised 17 March 2004; accepted 13 April 2004
Abstract—Butyl aryl tellurides reacted with dilithium dimethyl cyanocuprate and with dilithium methyl(2-thienyl)cyanocuprate to
give the corresponding dilithium aryl cyanocuprates, which were captured with enones leading to 4-aryl ketones in good yields.
ꢀ 2004 Elsevier Ltd. All rights reserved.
The preparation of aryl organometallics continues to
attract the attention of the synthetic organic chemists.1;2
The direct deprotonation is a well established method,
specially for the preparation of organometallics with a
ortho-stabilizing group, through the DOM methodol-
ogy.1;3 The preparation of aryl organometallics with
other substitution patterns in the aromatic core (meta
and para), is still made by a metal (specially lithium)
halogen exchange.1 In the course of the last decade we4
and others5 have shown that the sp2-Te bond, mainly in
vinylic tellurides, are prone to tellurium–metal
exchange, giving the organometallic species in a short
reaction time and in high yield. Similar reactions
involving aromatic tellurides were much less studied.
Diphenyl telluride was transformed into phenyllithium
by reaction with n-butyllithium,5b telluroferrocenes were
transformed into lithioferrocenes in a similar way,6
butyl 2-pyridyl telluride was transmetallated with zin-
cates to give butyl 2-pyridylzincates,7 diaryltellurides
and diarylditellurides were transmetallated with diethyl-
zinc leading to ethylarylzinc, which on reaction with
copper cyanide gave arylcopper intermediates.8 On the
other hand, the direct telluration of aromatic activated
hydrocarbons is a long known reaction. In most cases,
the para-substituted isomer is the only product formed.9
The application of the tellurium–metal exchange meth-
odology to the aromatic tellurides prepared in this way10
would be an advantageous alternative to access para-
substituted organometallics (Scheme 1). In order to test
the viability to prepare directly aryl cyanocuprates from
Y
Y
Y
R1M
1) TeCl4
2) [H], RX
M
TeBu
Y = electron-donating group
Scheme 1.
aryl tellurides8 we reacted some butyl aryl tellurides with
easily prepared higher order dilithium cyanocuprates.
Initially we treated butyl phenyl telluride (1a) with dil-
ithium dimethyl cyanocuprate (2a) (Scheme 2).
Telluride 1a was added to a solution of 2a in THF at
room temperature and the reaction was monitored by
TLC. After 5 min telluride 1a was completely consumed.
Then cyclohexenone (4a) was added and after 40 min the
reaction was complete, leading to the 1,4-addition
product 5a in 84% isolated yield. The reaction with
butyl(p-phenoxyphenyl)telluride (1b) also occurred in
5 min at room temperature. Capture of 3b with cyclo-
hexenone gave 5b in 77% yield. Similar results were
O
O
LL1Cu(CN)Li2
2
ArL1Cu(CN)Li2
ArTeBu
1
THF, N2, r.t.
4
Ar
3
5
2a: L = L1 = Me
2b: L = Me; L1 = 2-Th
Keywords: Dilithium arylcyanocuprates; Butylaryltellurides.
* Corresponding author. Tel.: +55-11-3091-2176; fax: +55-11-3815-
5579; e-mail: jvcomass@iq.usp.br
Scheme 2.
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.04.062

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P. Castelani et al. / Tetrahedron Letters 45 (2004) 4473–4475
obtained when butyl(p-methoxyphenyl)telluride (1c) was
used to generate the cyanocuprate (Table 1, entry 3). In
this case, the tellurium–copper exchange reaction was
slower, requiring 10 min to consume 1c completely. The
reaction worked satisfactorily also with methyl vinyl
ketone (Table 1, entry 4).11 The dilithium p-phenoxy-
phenyl cyanocuprate showed to be unstable. By keeping
it at room temperature for 40 min and then adding
cyclohexenone, only a mixture of diphenyl ether, p-
methylphenyl ether and bis-(p-phenoxy)biphenyl was
isolated. In this way, it is recommended to add the
enone immediately after the consumption of the starting
telluride 1b.
(2b) (Table 1, entry 5). Addition of the enone 4c
(1 mmol) to the dilithium aryl cyanocuprate 3c (1 mmol),
followed by BF3ÆEt2O (1 mmol) at )78 ꢁC and then
stirring for 40 min at the same temperature, gave the 1,4-
addition product in 82% yield as a 2:1 diastereomeric
mixture (Table 1, entry 5, compounds 5e and 5f). The
same procedure was used in the reaction with mesityl
oxide leading to the 1,4-addition product 5g in 84% yield
(Table 1, entry 6).
In conclusion, the tellurium–copper exchange is a
straight forward way to prepare dilithium arylcyano-
cuprates, constituting an advantageous method to
access para-substituted organometallics.
Preliminary experiments using hindered enones with
dilithium dimethyl cyanocuprate showed that, besides
the addition of the aryl cyanocuprate to the enone, a
methyl transfer also occurred. In view of these results we
performed the reaction with R-(+)-pulegone (4c), using
the cuprate derived from butyl(p-methoxyphenyl)tellu-
ride (1c) and dilithium methyl(2-thienyl)cyanocuprate
Acknowledgements
The authors acknowledge the following agencies for
support: CNPq and FAPESP.
Table 1. Transmetallation/1,4 addition
Entry
Ar
L
L1
Enone
Product
Yield (%)d;e
O
O
1
Ph, 1aa
Me
Me
84
4a
O
O
5a
2
3
p-C6H5OC6H4, 1bb
Me
Me
Me
Me
4a
77
86
O
5b
p-CH3OC6H4, 1cc
4a
OCH3
5c
O
O
4b
O
4
1b
Me
Me
74
O
5d
OCH3
OCH3
O
O
5
6
1c
1b
Me
Me
2-Th
2-Th
82f
4c
5e
5f
O
O
O
84
4d
5g
a Transmetallation time: 5 min.
b Transmetallation time: 5 min.
c Transmetallation time: 10 min.
d Isolated yield.
e All products presented analytical data in accordance with the proposed structures.
f
1
The diastereomeric ratio was determined by H NMR. Compound 5e presented coupling constants consistent with a cis arrangement between the
two substituents, being the minor constituent of the mixture and the isomer 5f presented coupling constants compatible with a trans arrangement
constituting the major constituent of the mixture.

P. Castelani et al. / Tetrahedron Letters 45 (2004) 4473–4475
4475
ed.; Vol. E12b. Recently we found that the aromatic
electrophilic substitution of activated aromatics with
tellurium tetrachloride proceeds in high yield in a short
reaction time to give aryltellurium trichlorides by
performing the reaction without solvent. In this way, the
use of chlorinated solvents (CHCl3 and CCl4) and
benzene, traditionally used in these reactions9a;b was
banned. Only the p-substituted aryltellurium trichlorides
were formed.
References and notes
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tellurides by reduction with sodium borohydride followed
by alkylation: Chieffi, A.; Menezes, P. H.; Comasseto,
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11. Typical procedure for the transmetallation/1,4-addition
reaction: To a two necked round bottomed flask under
nitrogen was added CuCN (0.089 g, 1 mmol) in THF
(5 mL). To the suspension cooled to 78 ꢁC was added
MeLi (2 mL, from a 1 M solution in THF/cumene,
2 mmol). The mixture was warmed to room temperature
and then butyl(p-methoxyphenyl)telluride (1c, 0.29 g,
1 mmol) was added, monitoring by TLC. After 10 min 1c
was completely consumed. The reaction mixture was then
cooled again to )78 ꢁC and cyclohexenone (4a, 0.10 g,
1 mmol) was added. After 40 min stirring the mixture was
diluted with ethyl acetate (15 mL) and washed with a
mixture of ammonium chloride and ammonium hydroxide
(3:1) (4 · 20 mL). The organic phase was dried with
magnesium sulfate and the solvent was evaporated. The
residue was purified by column chromatography in silica
gel eluting with hexane/ethyl acetate (9:1). 3-(4-Methoxy-
phenyl)-cyclohexanone (CAS number 107203-08-7); yield:
1
0,17 g (86%). H NMR (CDCl3, 300 MHz) (ppm): 7.2–7.1
(m, 2H); 6.9–7.1 (m, 2H); 6.9–6.8 (m, 2H); 3.79 (s, 3H);
3.0–2.9 (m, 1H); 2.6–2.3 (m, 4H); 2.2–2.03 (m, 2H); 1.9–1.7
(m, 2H). 13C NMR (CDCl3, 75 MHz) d (ppm): 210.9;
158.2; 136.5; 127.4; 114.0; 55.2; 49.1; 43.9; 41.1; 32.9; 25.4.
LRMS m/e (rel int.): 204 (47) (Mþ); 161 (20); 147 (100);
134 (26); 91 (26); 42 (37). IR (film) (cmꢀ1): 2998, 2936,
2865, 2836, 1712, 1611, 1513, 1464, 1447, 1422, 1303, 1289,
1256, 1225, 1180, 1034, 829, 810, 545, 511.
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