Azzena et al.
JOCArticle
SCHEME 5. Selectivity in the Reaction of Ether 15 with vic-
Diorganometals 2b and 2g
that, however, function under homogeneous and mild
reaction conditions.
4. Experimental Section
Equilibration Reactions. To 10 mL of a 0.1 M solution of a
diorganometal 2 (1 mmol), chilled at the temperature reported in
Table 1, was added a solution of the appropriate diarylalkene 1
(1 mmol) dissolved in 3 mL of dry THF. After stirring at the
temperature and for the time reported in Table 1, the mixture
was quenched by slow dropwise addition of H2O (15 mL), the
cold bath was removed, and THF was evaporated in vacuo. The
resulting mixture was extracted with CH2Cl2 (3 ꢀ 10 mL), then
the organic phases were collected, washed with H2O (1 ꢀ 10 mL)
and brine (10 mL), and dried (Na2SO4). After evaporation of the
solvent, the resulting mixture were analyzed by 1H NMR and/or
GC-MS. Reaction products 3a,23 3e,24 3f,25 and 3g26 were
characterized by comparison with literature data, while com-
pounds 3b-d were characterized by comparison with commer-
cially available samples.
SCHEME 6. Selectivity in the Reduction of Ethers 14 and 15
with vic-Diorganometals 2b and 2g
afforded triphenylmethane 11 in less than 10% yield (by 1H
NMR spectroscopy analysis), thus supporting the remark-
able effectiveness of 1,2-diaryl-1,2-disodiumethanes as acti-
vated forms of the alkali metal.
To test the versatility of our detritylation procedure, we
investigated the reactivity of ether 12 toward dianions 2b and
2g (Scheme 5). In agreement with the above-reported find-
ings, reduction of ether 12 with an excess (1.6 equiv) of the
most powerful diorganometal reductant, 2g, led to the
expected detritylation product, 13, in almost quantita-
tive yield. Conversely, no reaction of ether 12 with a less reactive
dianion, such as 2b, was observed.
Finally, we investigated the reduction of 10,11-dibro-
moundecyl trityl ether, 14, and 10-undecenyl trityl ether,
15, with diorganometals 2b and 2g. The results, summarized
in Scheme 6, show that dianion 2g is able to cause both
debromination and detritylation of ether 14, as well as
direct detritylation of ether 15, to yield 10-undecen-1-ol,
16. On the other hand, the less reactive dianion 2b selectively
debrominates ether 14 without affecting the trityl car-
bon-oxygen bond. In keeping with this result, 2b was found
unreactive toward trityl ether 15.22
Electrochemistry. For the electrochemical experiments, an
EG&G-PARC 173/179 potentiostat-digital coulometer, an
EG&G-PARC 175 universal programmer, and a Nicolet 3091
12-bit resolution digital oscilloscope were used. The electroche-
mical experiments were conducted under an Ar atmosphere, in
an all-glass cell that was thermostated at 25 °C. The experiments
were carried out inside a double-wall copper Faraday cage.
The cage and all instruments were connected to a common
ground. To minimize the ohmic drop between the working
and the reference electrodes, the feedback correction was
employed.
The electrochemical experiments were performed by using
homemade microdisk (1 mm diameter) glassy carbon (Tokai
GC-20) electrodes that were prepared as previously reported.27
The electrodes were stored in ethanol and, before experiments,
were polished with a 0.25 μm diamond paste (Struers) and
ultrasonically rinsed with ethanol for 5 min. The electrodes were
electrochemically activated in the background solution by
means of several voltammetric cycles at 0.5 V s-1 between the
anodic and cathodic solvent/electrolyte discharges, until the
quality features described in ref 28 were obtained. The reference
electrode was a homemade Ag/AgI. Its potential was always
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´
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3. Summary
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In this paper we report that a simple competitive reaction
can be employed to determine the relative reducing
capabilities of differently substituted 1,2-diaryl-1,2-diso-
diumethanes 2. The reliability of the proposed methodol-
ogy is nicely consistent with the electrochemical
determination of the reduction potentials of the corre-
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semiquantitative comparison of the chemical and electro-
chemical results, we propose that the formal potentials for
radical-anion formation could be used to estimate the
reducing power of vic-diorganometals. The outcome of
reactions carried out with selected acceptors provides
further support to our findings, thereby highlighting a
potential interest of 1,2-diaryl-1,2-disodiumethanes as tun-
able synthetic equivalents of an activated form of Na metal
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