The synthesis of dihexylphenylsulfonium tetrafluoroborate 13a
can be selectively achieved by heating, without copper salts, 9a and
8
for a prolonged period at high temperature (180 uC, 18 h,
Scheme 4, entry e). Its formation can be rationalized by a
competing nucleophilic attack of the unreacted sulfide 9a on either
the sulfonium salt 10a or any other electrophilic species possessing
an hexyl substituent. We have found that heating equimolar
amounts of hexyldiphenylsulfonium tetrafluoroborate 10a and
hexyl phenyl sulfide, for 1 hour at 110 uC in toluene, provides
diphenyl sulfide and dihexylphenylsulfonium tetrafluoroborate 13a
Scheme 7 Synthesis of hexyl selenol from hexyldiphenylsulfonium
tetrafluoroborate.
In conclusion, we have disclosed the transformation of hexyl
thiol to hexyl selenocyanate, hexyl selenol, dihexyl diselenide and a
series of hexyl selenides. Hexyldiphenylsulfonium tetrafluoroborate
is the key intermediate in these transformations and diphenyl
sulfide proved to be an extremely valuable leaving group.
Generalization of this reaction is on the way.
(10% yield each).§
Finally, the synthesis of a series of organoselenium compounds
has been efficiently achieved from hexyldiphenylsulfonium tetra-
fluoroborate 10a by selective substitution of the diphenyl sulfide
moiety by various nucleophilic selenium reagents (Scheme 5).
a
Alain Krief,* Willy Dumont and Michael Robert
a
ab
a
Laboratoire de Chimie Organique de Synth e` se, Facult e´ s Universitaires
N.-D. de la Paix, 61 rue de Bruxelles, Namur B-5000, Belgium.
E-mail: alain.krief@fundp.ac.be; Fax: +32(0)81724536;
Tel: +32(0)81724539
b
Fonds pour la Formation a` la Recherche dans l’Industrie et
l’Agriculture, 5 rue d’Egmont, Bruxelles B-1000, Belgium
Notes and references
Scheme 5 Substitution of hexyldiphenylsulfonium tetrafluoroborate
{
Such selectivity should not be expected in the case of trialkylsulfonium
salts bearing different alkyl groups on sulfur.
Diphenyl iodonium tetrafluoroborate was prepared from diphenyl
with selenium nucleophiles.
{
iodonium chloride and silver (II) oxide followed by treatment with an
aqueous solution of tetrafluoroboric acid (215 uC, 0.2 h, 60% yield).
Diphenyl iodonium chloride was synthesized from benzene on sequential
reaction with (i) potassium iodate in acetic anhydride, (ii) sulfuric acid in
acetic acid and (iii) hydrolysis using an aqueous solution of ammonium
chloride (90% yield).
Thus hexyldiphenylsulfonium tetrafluoroborate 10a reacts at
room temperature with sodium methyl-, benzyl-, phenyl- or
nitrophenylselenolates to produce the corresponding selenides in
very good yield whether the reaction is carried out in ethanol or
DMF (20 uC, 1 h, 70–80% yield, Scheme 5)."
§
Hexyldiphenylsulfonium tetrafluoroborate 10a remains unchanged on
heating at 110 uC for 24 h.
Nucleophilic substitutions of alkyldiarylsulfonium salts are rare. See
The sulfonium salt 10a also reacts with the reagents generated
"
from selenium and either sodium borohydride (2 equiv., 6 equiv.
7
8
reference 4. Related reactions involving trialkylsulfonium salts will be
disclosed soon.
EtOH, in DMF) or sodium hydride (1.1 equiv. in DMF) to
produce selectively dihexyl selenide 14 (76%, Scheme 6, entry a) or
dihexyl diselenide 15 (78%, Scheme 6, entry b) respectively.
1
D. L. J. Clive, Tetrahedron, 1978, 34, 1049; M. Clarembeau and A. Krief,
Tetrahedron Lett., 1984, 25, 3625; D. J. Procter, J. Chem. Soc., Perkin
Trans 1, 1999, 641; D. J. Procter, J. Chem. Soc., Perkin Trans 1, 2000,
8
35.
L. Field, T. E. Parsons and R. R. Crenshaw, J. Am. Chem. Soc., 1964, 29,
18.
F. Krollpfeiffer and W. Hahn, Chem. Ber., 1953, 86, 1049; V. Franzen,
H. J. Schmidt and C. Mertz, Chem. Ber., 1961, 94, 2942; T. W. Milligan
and B. C. Minor, J. Org. Chem., 1963, 28, 235; H. J. Schmidt and
C. Mertz, Chem. Ber., 1961, 94, 2942; B. Badet and M. Julia, Tetrahedron
Lett., 1979, 1101; V. K. Aggarwal, A. Thompson and R. V. H. Jones,
Tetrahedron Lett., 1994, 35, 8659; K. Miyatake, K. Yamamoto, K. Endo
and E. Tsuchida, J. Org. Chem., 1998, 63, 7522.
2
3
9
Scheme 6 Synthesis of dihexyl selenide and of dihexyl diselenide from
hexyldiphenylsulfonium tetrafluoroborate.
4
5
6
B. Badet, L. Jacob and M. Julia, Tetrahedron, 1981, 37, 887; B. Badet,
M. Julia and C. Lefebvre, Bull. Soc. Chim. Fr., 1984, 431.
T. Migita, T. Shimizu, Y. Asami, J. Shiobara, Y. Kato and M. Kosugi,
Bull. Chem. Soc. Jpn., 1980, 53, 1385.
J. W. Knapczyk and W. E. McEwen, J. Am. Chem. Soc., 1969, 91, 149;
J. V. Crivello and J. H. W. Lam, J. Org. Chem., 1978, 43, 3055.
A. Krief, M. Trabelsi, W. Dumont and M. Derock, Synlett, 2003, 1751.
A. Krief and M. Derock, Tetrahedron Lett., 2002, 43, 3083.
Hexyldiphenylsulfonium tetrafluoroborate 10a reacts also with
potassium selenocyanate in DMF, as well as in ethanol in which
the reaction proved to be faster.
Hexyl selenocyanate 16 has been, in turn, efficiently reduced to
the corresponding sodium hexylselenolate on reaction with sodium
9
7
8
4
borohydride (1.25 equiv. NaBH , ethanol, 20 uC, 0.25 h) to give
hexyl selenol 3a after acid hydrolysis (Scheme 7).
9 A. Krief, C. Delmotte and W. Dumont, Tetrahedron, 1997, 53, 12147.
2
168 | Chem. Commun., 2005, 2167–2168
This journal is ß The Royal Society of Chemistry 2005