Rapid and precise preparation of reactive benzeneselenolate solutions by reduction of diphenyl diselenide with hydrazine-sodium methanolate

Article abstract of DOI:10.1039/a903686e

Solutions of sodium benzeneselenolate sufficiently reactive to effect 'aromatic substitution and ester dealkylation are prepared in DMSO or NMP from diphenyl diselenide and hydrazine hydrate by titration with methanolic sodium methanolate.

Full text of DOI:10.1039/a903686e

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Rapid and precise preparation of reactive benzeneselenolate
solutions by reduction of diphenyl diselenide with hydrazine–
sodium methanolate
Lars Henriksen* and Nicolai Stuhr-Hansen
Department of Chemistry, University of Copenhagen, Universitetsparken 5,
DK-2100 Copenhagen, Denmark. E-mail: larsh@kiku.dk
Received (in Cambridge) 7th May 1999, Accepted 14th June 1999
Solutions of sodium benzeneselenolate sufficiently reactive
to effect aromatic substitution and ester dealkylation are
prepared in DMSO or NMP from diphenyl diselenide and
hydrazine hydrate by titration with methanolic sodium
methanolate.
observed after exposure of the reagent solution to 120 ЊC for 24
h. In contrast DMSO oxidizes the neutral benzeneselenol quan-
titatively into 2 within minutes at room temperature. In this way
an excess of reagent is efficiently quenched upon addition of the
equivalent amount of acid. On the other hand the reduction of
2
in DMSO cannot be used for reaction sequences which
The benzeneselenolate ion (1) is a powerful nucleophilic species
which, apart from its utilization in the construction of selenium
containing materials, has a wide range of applications as a tool
involve either the production of benzeneselenol or an acid
catalyzed reaction of 1 as a subsequent step. Solutions of
benzeneselenol can be generated when the titration procedure is
carried out in N-methylpyrrolidone (NMP) and the equivalent
amount of acid is subsequently added. 3-(Phenylseleno)-
propanenitrile (3) has been prepared from acrylonitrile and
methyl 3-(phenylseleno)propanoate (4) from methyl acrylate by
application of this modification (Scheme 2, i).
1
in organic synthesis. Since benzeneselenol is an obnoxious and
highly oxygen-sensitive substance the simple deprotonation
route to 1 is impractical and solutions of 1 are usually gener-
ated by in situ reduction of the stable and less volatile diphenyl
diselenide (2). Compound 2 is readily reduced and several
2
reagents have been used for this purpose. The reduction with
3
sodium tetrahydroborate is the most commonly used pro-
i
1
+ CH2=CH-Z
PhSeCH2CH2-Z
cedure. However, this preparation gives 1 as a boron complex
3
: Z = CN
4
with diminished nucleophilic reactivity. Reactive solutions of 1
4: Z = CO Me
2
4
have been prepared from 2 by reduction with alkali metals or
ii
5
PhCO2– + PhSeMe
alkali metal hydrides in an inert solvent.
1 + PhCO2Me
The reduction of 2 with a combination of hydrazine and
iii
sodium hydroxide has been accomplished using an excess of the
1
+ Ar-X
5-10
Ar-SePh
11-16
6
reagents. We have found that the reduction of 2 with hydrazine
hydrate proceeds almost instantaneously at room temperature
in DMSO (or similar solvents) upon addition of a concentrated
Scheme 2 Conditions: i, NMP, 1 equiv. of AcOH, 20 ЊC, 15 min;
ii, DMSO, 2 equiv. of 1, 95 ЊC, 3 h; iii, DMSO, N atmosphere, temper-
2
(
~5 M) solution of sodium methanolate in methanol to give a
homogeneous solution of 1 (Scheme 1a).
ature and reaction period: see Table 1.
The demethylation of methyl benzoate (Scheme 2, ii) was
2
PhSeSePh + N2H4 + 4 MeO–
4 PhSe + N2 + 4 MeOH
–
a)
b)
investigated in order to assess the nucleophilic reactivity of 1 in
4
2
1
the present solvent. Liotta et al. reported that this reaction is
completed in 3 h in refluxing THF–HMPA (5:1). With identical
reagent concentrations we observed the same reaction period
at 95 ЊC. As could be expected the reactivity of 1 is slightly
lowered by hydroxylic solvation in DMSO–methanol but not
more than can be compensated by the higher reaction temper-
atures accessible in this solvent.
PhSe–
N2H4 + O2
N2 + 2 H2O
Scheme 1
The reaction can be carried out as a colorimetric titration
with a sharp end-point (yellow to colorless) to produce a solu-
tion containing a precisely defined amount of 1 which is free of
excess base. Only the equivalent amount of hydrazine is needed
but we prefer a slight (10–20%) excess in order to ensure that
the methanolate ion is the limiting reagent. At the same time
the excess hydrazine protects the reagent against oxidation by
atmospheric oxygen through a catalytic cycle (Scheme 1b). The
solvent is purged by the nitrogen evolved in the reduction and
an inert atmosphere is needed only for prolonged reaction
periods.
The utilization of an elevated reaction temperature makes it
possible to extend the range of aryl halides which can undergo
uncatalyzed nucleophilic substitution with 1 (Scheme 2, iii). A
series of examples indicating the conditions for and the scope
of the reaction is presented in Table 1.
The conversions of halobenzonitriles, 7, and 8, into 13 and
14 , respectively, have previously been effected only with Ni-
9
10
catalysis or by electrochemical stimulation. An excess of
1 was applied in the preparation of 15 in order to suppress the
by-products from a competing unimolecular elimination of
isobutene from 9. The relative reaction rates of 7 and 8 as well
as the product distribution from 10 show that the order of
reactivity is ArBr > ArCl. This feature indicates that the
observed substitutions take place by a SRN1 type of mechan-
A prerequisite for the titration method is that the diselenide is
rigorously purified from adhered diphenyl triselenide. Otherwise
an orange–brown color persists in the reduced solution. The com-
bination of hydrazine and base reduces selenium to highly
7
11
colored polyselenide ions and an excess of selenium even at a
ism. The transformation of 10 appears to represent the limit
level of 0.2 mol% (below the limit for detection by conventional
analysis) prevents the observation of a defined end-point. We
prepared 2 in a satisfactory quality by purification via
of the uncatalyzed thermal substitution reaction. Little or no
product was observed from simple aryl halides or from aryl
halides with a meta-acceptor substituent.
In conclusion the reduction of 2 with hydrazine hydrate and
sodium methanolate in DMSO or NMP provides a rapid route
8
dihydroxy phenylselenonium toluene-p-sulfonate.
Compound 1 is not oxidized by DMSO. No trace of 2 is
J. Chem. Soc., Perkin Trans. 1, 1999, 1915–1916
1915

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Table 1 Nucleophilic aromatic substitution with 1 in DMSO–MeOH
e.g. at 60 ЊC, 1–2 kPa (membrane pump) or at ~90 ЊC in a
stream of nitrogen.
Substrate
Product
t/h
T/ЊC
Yield (%)
Conjugate addition of benzeneselenol
NO2
Br
NO2
SePh
To a solution of 1 (10 mmol) prepared in NMP was added a
mixture of acetic acid (10 mmol) and the appropriate acrylic
acid derivative (10 mmol). After 10 min the mixture was poured
into water and the product isolated by extraction (hexane–ethyl
acetate, 4:1), flash chromatography (silica gel 60) and bulb-to-
bulb distillation (10 Pa, air bath 200 ЊC). Yields: 3, 93%, purity
a
1
20
76
5
11
O2N
O2N
a
1
1
20
79
Br
CN
Cl
SePh
(
GC-MS), 98% ; 4, 84%, purity (GC-MS), 96%.
6
12
CN
(
Phenylseleno)arenes (11–17)
a
125
125
72
SePh
The haloarene (10 mmol) was added to a solution of 1 (10
mmol) and the mixture was stirred in a nitrogen atmosphere as
specified in Table 1. The reaction mixture was poured into water
and extracted with ether. The ether phase was filtered through
alumina (neutral, 6 g) and solid residues from evaporation were
recrystallized: 2-nitrophenyl phenyl selenide (11), mp 90 ЊC
7
13
NC
NC
a
2
0
68
Br
SePh
8
14
1
2
(
from ethanol) (lit., 91 ЊC); 4-nitrophenyl phenyl selenide (12),
12
CO2But
Br
CO2But
SePh
mp 60 ЊC (from ethanol) (lit., 54 ЊC); 2-(phenylseleno)-
a
10a
2
2
2
0
4
4
125
125
125
48
benzonitrile (13), mp 73 ЊC (from methanol) (lit.,
70 ЊC);
4-(phenylseleno)benzonitrile (14), mp 52 ЊC (from hexane)
9
15
13
(
lit., 52 ЊC). A 50% excess of 1 was applied in the preparation
of tert-butyl 2-(phenylseleno)benzoate (15). The product was
purified by column chromatography (silica gel 60, pentane).
Cl
b
54
ϩ
80
Cl
Br
Colorless oil [Found: C, 61.2%; H 5.5%; M ( Se) 334;
SePh
Br
80 77
1
6
C H O Se requires C, 61.2%; H 5.4%; M( Se), 334]; δ( Se)
17 18 2
(57.3 MHz; CDCl ; Me Se), 469 ppm.
3
2
1
0
b
6
SePh
1
7
Notes and references
1
2
3
4
R. Monahan, D. Brown, L. Waykole and D. Liotta, in Organo-
selenium Chemistry, ed. D. Liotta, John Wiley & Sons, New York,
a
b
Of isolated, pure compound. Inseparable product mixture, com-
position analyzed by GC-MS.
1
987, ch. 4.
D. L. Klayman, in Organic Selenium Compounds, eds. D. L.
Klayman and W. H. H. Günther, John Wiley & Sons, New York,
1
973, p. 71, 96.
(a) B. Sjögren and S. Herdevall, Acta Chem. Scand., 1958, 12, 1347;
b) K. B. Sharpless and R. F. Lauer, J. Am. Chem. Soc., 1973, 95,
697.
(a) D. Liotta, W. Markiewick and H. Santisteban, Tetrahedron Lett.,
to clean solutions of 1 containing a precisely defined amount of
a reagent with a sufficiently high nucleophilic reactivity for
most synthetic purposes.
(
2
1
977, 50, 4365; (b) D. Liotta, U. Sunay, H. Santisteban and
Experimental
W. Markiewick, J. Org. Chem., 1981, 46, 2605.
5
6
P. Dowd and P. Kennedy, Synth. Commun., 1981, 11, 935.
L. Syper and J. Mlochowski, Synthesis, 1984, 439.
Preparation of 1 M sodium benzeneselenolate solutions
DMSO (Lab-Scan), 25% sodium methanolate in methanol
7 H. Eggert, O. Nielsen and L. Henriksen, J. Am. Chem. Soc., 1986,
108, 1725.
8
(
Aldrich) and hydrazine hydrate (Fluka) were used directly.
L. Henriksen and N. Stuhr-Hansen, Synth. Commun., 1996, 26,
897.
NMP (Aldrich) was distilled from sodium methanolate prior to
use in order to remove an unknown impurity causing a red
coloring of the reagent solution. Diphenyl diselenide (2) was
purified by oxidation to dihydroxy phenylselenonium toluene-
p-sulfonate followed by reduction of the recrystallized salt
according to ref 8. To a stirred solution containing 2 (5 mmol)
and hydrazine hydrate (2.75 mmol) in DMSO or NMP (8 ml)
was added 25% methanolic sodium methanolate (approxi-
mately 2 g, the last 0.2 g added dropwise with intervals of 5 s
until the yellow color of 2 disappeared). A reagent with
increased reactivity can be obtained by removing the methanol,
1
9
H. J. Christau, B. Chabaud, R. Labaudiniere and H. Christol,
Organometallics, 1985, 4, 657.
1
0 (a) C. Degrand, J. Org. Chem., 1987, 52, 1421; (b) C. Degrand,
R. Prest and M. Nour, Phosphorus Sulfur, Relat. Elem., 1988, 38,
2
01.
11 A. B. Pierini and R. A. Rossi, J. Org. Chem., 1979, 44, 4667.
12 L. Engman and D. Stern, J. Org. Chem., 1994, 59, 5179.
13 C. J. Degrand, J. Chem. Soc., Chem. Commun., 1986, 1113.
Communication 9/03686E
1
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J. Chem. Soc., Perkin Trans. 1, 1999, 1915–1916