New desulfurdimerization of dithioketals induced by a 2,2'-bipyridine ligated nickel(0) complex

Article abstract of DOI:10.1039/a805589k

Desulfurdimerization of various aromatic dithioketals is efficiently induced by a 2,2'-bipyridine ligated nickel(0) complex under mild conditions.

Full text of DOI:10.1039/a805589k

View Article Online / Journal Homepage / Table of Contents for this issue
50 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 50±51$
New Desulfurdimerization of Dithioketals Induced by
a 2,2'-Bipyridine Ligated Nickel(0) Complex$
Moushine Lourak, Sandrine Becker, Yves Fort* and Paul Caubere*
Synthese Organique et Reactivite, associe au CNRS, INCM FR 1742, Faculte des Sciences,
Universite Henri Poincare±Nancy 1, BP 239, 54506 Vandoeuvre les Nancy Cedex, France
Desulfurdimerization of various aromatic dithioketals is efficiently induced by a 2,2'-bipyridine ligated nickel(0) complex
under mild conditions.
Table 1 Desulfurdimerization of dithioketals induced by
The coupling reaction of carbonyl derivatives induced by
TiCl3, well known as the McMurry reaction, is a very useful
NiCRA-bpya
Isolated
yield
procedure for the formation of carbon±carbon double
bonds.1 In the last decade, a new method starting from
dithioketals appeared as an alternative to this reaction.
Indeed, Luh et al. have shown that W(CO)6 or Mo(CO)6
promoted the desulfurdimerization of various dithioketals.2
However, this ecient reaction needs an excess of metal
carbonyl (1.5 to 4 equiv.) and must be carried out in
chlorobenzene at re¯ux for long reaction times (24±48 h).
In spite of this, the method appeared of some interest in
the synthesis of bowl-like polycyclic aromatic hydrocarbons3
or crown ethers hinged with bi¯uoroenylidene.4
Reduction
(%)c
Run Substrate
1
Ni/S
1
t/h
(%)b
1
85
77
13
2
1
2
21
In continuing our long-term interest in the desulfurization
processes5 induced by nickel containing complex reducing
agents (NiCRA),6 we found that under mild conditions our
reagents also produced desulfurdimerization of dithioketals
(Scheme 1). We describe in this paper our ®rst results in this
area.
3
4
1
18
1
58
51
40
48
0.5
5
6
7
1
1
1
10d
12d
18
40e
45f
±
57
51
15
A
systematic study performed with the dithioketal of
benzophenone showed us that: (i) a 2,2'-bipyridine ligated
nickel containing complex reducing agent (NiCRA-bpy)7
was the best candidate to achieve desulfurdimerization of
dithioketals. A non-ligated or triphenylphosphine ligated
reagent did not cause the reaction. (ii) The use of a
stoichiometric amount of NaH with respect to nickel salt
led to the most ecient reagent for desulfurdimerization
while an excess of hydride favoured the classical desulfuri-
zation process. (iii) A Ni/substrate ratio of 2, i.e. Ni/S ˆ 1,
led to the best yield of double bonded product. (iv) The
reaction must be carried out in re¯uxing THF. Reactions
performed in 1,2-dimethoxyethane (DME) only led to de-
sulfurization without coupling. Under these conditions,
tetraphenylethylene can be obtained in 85% isolated yield
after 1 h of reaction (Run 1, Table 1).
From these results, we examined the reactivity of various
dithioketals (Table 1). It appears that under mild conditions
ethylenic compounds can be obtained in moderate to good
yields starting from aromatic dithioketals. Under the
conditions used, no reduction of ethylenic compounds was
observed. It is interesting that the yields of the reaction with
monoaryl derivatives were apparently lower than those with
diaryl compounds. Presumably, the aryl groups stabilize the
reactive intermediate which could be a radicaloid or a
carbenoid species. Indeed, the mechanism of desulfurizations
induced by NiCRA was previously described as proceeding
by a single electron transfer in its ®rst step.5 On the other
hand, it is worth noting that adamantan-2-one dithioketal
aReaction performed on 1 mmol scale of substrate in THF at
reflux. bYield determined of double bonded dimeric product after
isolation by flash chromatography. cYield determined by GC
analysis. dReaction performed in THF at 45 8C. eZ/E ˆ 25/75.
fZ/E ˆ 45/55.
(run 7) only led to reduction in low yield. Such behaviour
was previously observed in treatment with Mo(CO)6.2a This
result may also be interpreted as a lack of stabilization of
the reaction intermediate.
In conclusion, NiCRA-bpys are e€ective in inducing
desulfurdimerization of aromatic dithioketals in THF at
re¯ux. The method developed appeared of interest since
our reagents are easily handled and less toxic than metal
carbonyl derivatives.
Experimental
Tetrahydrofuran was distilled from
a benzophenone±sodium
adduct and stored over sodium wire. tert-Butyl alcohol (Aldrich)
was distilled from sodium. Nickel acetate (Fluka) was dried under
vacuum (20 mmHg) at 110 8C for 16 h. 2,2'-Bipyridine (Aldrich)
was recrystallized before use from hexane. Sodium hydride (65%
in mineral oil, Fluka) was used after three washings with the
reaction solvent under nitrogen. All reactions were performed under
nitrogen.
*To receive any correspondence (e-mail: Yves.fort@sor.u-nancy.fr).
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

View Article Online
J. CHEM. RESEARCH (S), 1999 51
General procedure.ÐA solution of ButOH (20 mmol) in 10 ml
of dry THF was added dropwise to a mixture of degreased NaH
(40 mmol), Ni(OAc)2 (10 mmol) and 2,2'-bipyridine (20 mmol) in
20 ml of dry THF at 63 8C. After 1 h, the black reagent formed
was ready for use. The solution of dithioketal (5 mmol) in 10 ml of
dry THF was then added dropwise over a period of 15 min. The
reaction was monitored by GC analyses (Alltech Econo-Cap EC-5
column, 30 m Â0.32 mm IDÂ 0.25 ꢀm) and GC±MS (CI, CH4)
analyses (HP1, 15 m Â0.32 mm ID Â0.25 m) using dodecane as
internal standard. After completion, 10 ml of water was added
dropwise at 25 8C. Products were then extracted by diethyl ether
and separated by ¯ash chromatography (Merck silica gel, 230±400
mesh). Their spectroscopic data are in accordance with those of
authentic samples.
2 (a) L. L. Yeung, Y. C. Yip and T.-Y. Luh, J. Chem. Soc., Chem.
Commun., 1987, 981; (b) L. L. Yeung, Y. C. Yip and T.-Y. Luh,
J. Org. Chem., 1990, 55, 1874.
3 K. Yamamoto and H. Matsubara, J. Synth. Org. Chem., 1995,
53, 318.
4 (a) C.-H. Kuo, M.-H. Tsau, D. T. C. Weng, G. H. Lee, S. M.
Peng and T.-Y. Luh, J. Org. Chem., 1995, 60, 7380; (b) D. K. P.
Ng and T.-Y. Luh, Tetrahedron Lett., 1988, 329, 5131.
5 (a) S. Becker, Y. Fort, R. Vanderesse and P. Caubere, J. Org.
Chem., 1989, 54, 4848; (b) S. Becker, Y. Fort and P. Caubere,
J. Org. Chem., 1990, 55, 6194.
6 In the present paper we have adopted the convention of:
(a) P. Caubere, Pure Appl. Chem., 1985, 57, 1875; (b) P. Caubere,
Rev. Heteroatom. Chem., 1991, 4, 79; (c) P. Gallezot, C. Leclercq,
Y. Fort and P. Caubere, J. Mol. Catal., 1994, 93, 79.
7 Ligated complexes of Ni0 (also noted NiCRA-L) have been
previously found to be ecient in the homo- and cross-coupling
reaction of aryl and heteroaryl halides or in the amination of
aromatic halides: (a) M. Lourak, R. Vanderesse, Y. Fort and
P. Caubere, J. Org. Chem., 1989, 54, 4840; (b) M. Lourak,
R. Vanderesse, Y. Fort and P. Caubere, J. Org. Chem., 1989, 54,
4844; (c) Y. Fort, S. Becker and P. Caubere, Tetrahedron, 1994,
50, 11893; (d) E. Brenner and Y. Fort, Tetrahedron Lett., 1998,
in press.
Received, 20th July 1998; Accepted, 2nd October 1998
Paper E/8/05589K
References
1 (a) Y.-H. Lai, Org. Prop. Proced. Int., 1980, 12, 361; (b) J. E.
McMurry, Acc. Chem. Res., 1983, 16, 405.