Arene catalysed sodium reactions

Article abstract of DOI:10.1039/a907037k

2-Methyl-1-phenylpropan-1-ol and phenyltrimethylsilane were prepared in yields >85%, using naphthalene catalysed sodium reactions, whereby phenylsodium, prepared from the reaction of chlorobenzene, sodium powder and naphthalene (5%), was quenched with iso

Full text of DOI:10.1039/a907037k

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Arene catalysed sodium reactions
Tania R. van den Ancker*a and Margaret J. Hodgsonb
a Department of Biological and Physical Sciences, University of Southern Queensland,
Toowoomba, Queensland, 4350, Australia
b Faculty of Science and Technology, Griffith University, Nathan, Queensland, 4111, Australia
Received (in Cambridge, UK) 10th August 1999, Accepted 31st August 1999
Table 1 Yields of phenylsodium from the reaction of sodium powder
2-Methyl-1-phenylpropan-1-ol and phenyltrimethylsilane
were prepared in yields >85%, using naphthalene catalysed
sodium reactions, whereby phenylsodium, prepared from
the reaction of chlorobenzene, sodium powder and
naphthalene (5%), was quenched with isobutyraldehyde or
chlorotrimethylsilane respectively.
with catalytic amounts of naphthalene at Ϫ78 ЊC for 1 h, and the reac-
tion with an electrophile, Eϩ a
Arene (%)
Eϩ
Yield (%)b
Yield (%)c
10
5
2
1
5
H2O
H2O
H2O
98
99
90
90
95
95
90
90
The use of alkali metal arene radical anion complexes,
85d
85d
85
ϩ
ArHϪ M , as soluble sources of metal in the formation of
ؒ
H2O
organoalkali metal species from organic halides is well estab-
lished with early work focusing on the use of lithium naphtha-
lenide.1 Many radical anion derivatives of lithium have been
prepared in recent years. The 4,4Ј-di-tert-butylbiphenyl (DBB)
complex is particularly noteworthy, in that while it acts as a
source of lithium, removal of the DBB by-product is facilitated
by its low volatility.2 Other approaches to overcoming the
objection of having solutions of the target organolithium
species loaded with the arene by-product are the use of a
catalytic amount of arene,3 macromolecular supported lithium
naphthalenide complexes4 and polymer supported arene-
catalysed reactions.5 Each of these approaches prove quite
successful in the generation of lithium complexes from a range
of organic compounds including: halogenated compounds,
allylic and benzylic alcohols, or their silylated derivatives.3–7
Sodium arene radical anion complexes have received much
less attention than the lithium counterparts although they do
afford organosodium complexes in relatively high yields.8 As
with their lithium counterparts, the solutions of these reagents
are loaded with the arene by-product. We have developed a
method for the preparation of sodium reagents using polymer
supported sodium naphthalenide, generating high yields of the
desired sodium complexes, which are readily removed from
the recyclable polymer by-product by filtration.4,7 A draw back
of this method is that the polymer supported sodium com-
plex is quite unstable, resulting in reduced yields, limiting the
value of the polymer as a useful reagent for the generation of
sodium complexes. The work presented here follows from
the successes of the above processes in developing a technique
for the preparation of sodium complexes via arene-catalysed
reactions (Scheme 1).
PriCHO
ClSiMe3
5
85
a Average of three runs. b Yield of phenylsodium, established by
quenching an aliquot with 0.1 M HCl, back-titrating with 0.1 M
NaOH, average of three titrations. c Isolated yield of the quenched
product. d Due to the small scale of reaction, percentages lower than 5%
were difficult to perform accurately. Therefore the average of two runs is
given.
Prior to the investigation of the reaction of sodium metal
with catalytic amounts of arene, an investigation into the
optimum reaction conditions was carried out. The variables
considered were the type of arene (naphthalene, biphenyl and
4,4Ј-di-tert-butylbiphenyl), reaction temperatures (Ϫ78, Ϫ30
and 0 ЊC) and the reaction time (0.5, 1, 2 and 4 hours) for step
(ii) in Scheme 1. The results of the trial indicated the best con-
ditions were sodium with naphthalene at Ϫ78 ЊC for 1 hour.9
Following this, an investigation into the use of sodium metal
with varying percentages of arene was carried out.9 The sodium
metal is not completely consumed in these reactions; particle
size of the metal is indeed known to be a controlling factor in
the formation of organoalkali metal compounds.10 Hence the
use of sodium powder (<0.1 mm particle size) was investigated.
Sodium powder with catalytic amounts of naphthalene was
tested for the ability to form phenylsodium (Table 1).† Phenyl-
sodium was quenched with different electrophiles; H2O,
ClSiMe3 and PriCHO, affording the desired compounds, ben-
zene, phenyltrimethylsilane and 2-methyl-1-phenylpropan-1-ol
respectively, in high yields. Noteworthy is the absence of other
by-products often generated in these reactions. Early studies
on the reaction of sodium naphthalenide with phenylhalides,
resulted in the formation of biphenyl and terphenyls, derived
from the intermediate anion radical, as well as the expected
product, benzene.11 The use of the arene in only catalytic
quantities has eliminated the generation of these higher arenes.
The generation of the organosodium reagent and subsequent
formation of the quenched compounds can be followed by a
simple colour change. Initially the reaction mixture shows the
dark green colour of the sodium arene; after the addition of
the chlorobenzene the colour gradually changes to that of the
organosodium reagent, dark red. The quenching of the organo-
sodium reagent causes the disappearance of the colour of
the organosodium reagent and the formation of the final
products (usually affording a clear–pale yellow solution). Thus
it is not necessary to follow the reaction through spectroscopic
or chromatographic means.
Scheme 1 Reagents and conditions: (i) Ϫ78 ЊC, THF, 20 min, (ii)
Ϫ78 ЊC, 1 h, (iii) Eϩ = H2O, PriCHO or ClSiMe3, Ϫ78 to 25 ЊC, 3 h, (iv)
H2O.
We have thus developed a more practical method for generat-
ing organosodium complexes: the preparation of the sodium
J. Chem. Soc., Perkin Trans. 1, 1999, 2869–2870
This journal is © The Royal Society of Chemistry 1999
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1 For example, M. A. Beswick and D. S. Wright, Alkali Metals,
in Comprehensive Organometallic Chemistry II: Review of
the Literature 1982–1994, ed. E. W. Abel, F. G. A. Stone and
G. Wilkinson, Pergamon Press, Oxford, 1995, vol. 1, ch. 1, and
references therein.
2 P. K. Freeman and L. L. Hutchinson, Tetrahedron Lett., 1976, 22,
1849.
radical anion complex is avoided, the reaction is clean and easy
to follow through colour changes, and the work up is simplified,
with reduced quantities of arene by-products for removal.
We thank M. L. Williams for helpful discussions and Griffith
University for support of this project.
A
3 M. Yus and D. J. Ramon, J. Chem. Soc., Chem. Commun., 1991, 398.
4 T. R. van den Ancker, G. R. Hanson, F. C. Lee and C. L. Raston,
Chem. Commun., 1997, 125.
5 C. Gomez, S. Ruiz and M. Yus, Tetrahedron Lett., 1998, 39, 1397.
6 For example, M. Yus, Chem. Soc. Rev., 1996, 96, 155, and references
therein.
Notes and references
† In a typical experiment: to a cooled (Ϫ78 ЊC) green suspension of
sodium powder‡ (0.27 g, 11.7 mmol) and naphthalene (0.075 g, 0.58
mmol) in THF (60 ml) was slowly added a solution of chlorobenzene
(1.05 g, 9.36 mmol) in THF (40 ml) and the resulting deep red mixture
was stirred at Ϫ78 ЊC for 1 h. The excess of sodium powder was filtered,
at Ϫ78 ЊC, affording the deep red–purple organosodium reagent,
phenylsodium. The activity of the solution was determined by titration.
The remaining solution of phenylsodium was then quenched by
addition of the desired electrophile, H2O, ClSiMe3 or PriCHO. The
resulting solutions were subsequently hydrolysed, extracted into diethyl
ether and/or hexane, filtered, dried over anhydrous Na2SO4, and
the solvent was removed in vacuo affording benzene, phenyltrimethyl-
silane and 2-methyl-1-phenylpropan-1-ol respectively (85–90%, purity
checked by 1H NMR spectroscopy).
7 T. R. van den Ancker and C. L. Raston, J. Organomet. Chem., 1998,
550, 283.
8 For example, A. Mordini, Sodium and Potassium, in Comprehensive
Organometallic Chemistry II: A Review of the Literature 1982–1994,
ed. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon
Press, Oxford, 1995, vol. 2, ch. 2, and references therein; G. Boche,
D. R. Schneider and H. Wintermayr, J. Am. Chem. Soc., 1980,
102, 5697.
9 T. R. van den Ancker and M. J. Hodgson, unpublished results.
10 M. Schlosser, Angew. Chem., Int. Ed. Engl., 1964, 3, 287.
11 N. L. Holy, Chem. Rev., 1974, 74, 275.
‡ Sodium powder was obtained as a slurry in toluene (30 wt% <0.1 mm
particle size). It was filtered and dried in vacuo and stored under argon,
prior to use.
Communication 9/07037K
2870
J. Chem. Soc., Perkin Trans. 1, 1999, 2869–2870