Dalton Transactions
Communication
the beginning and the reaction was carried out at room tem-
perature for 4 hours (Table 3, entries 1–4, column 4). In order to
increase the yield, the supposedly more reactive p-fluoro-sub-
stituted dithioacetal 3g was employed. An important improve-
ment in the yields was observed in all cases (entries 1–4,
column 5). The formation of pinacol coupling products under
these conditions was not detected. Most intriguingly, these
“all-in-one” reactions work at room temperature, whereas in
the sequential procedure, heating for 90 min at 50 °C was
required to obtain good yields with 3a. In contrast, the use of
dithioacetals 3d or 3f was not successful under these “all-
in-one” conditions. Further studies on the understanding of
this promising process are underway.
Scheme 4 Reactivity differences between 1 and 2.
In conclusion, a new titanocene(II) equivalent without
additional organic ligands has been obtained from the
reduction of Cp2TiCl2 with dysprosium. This system has been
successfully employed in a phosphite-free Takeda carbonyl ole-
fination procedure and has shown good potential in an unpre-
cedented “all-in-one” procedure. The structural elucidation of
the new bimetallic titanocene(II) and its further applications
are currently under investigation.
We thank Prof. J. Szymoniak for helpful discussions and
Ms. S. Dufourd for carrying out preliminary experiments. G. B.
acknowledges the Region Champagne-Ardenne for a PhD scho-
larship. We appreciate the financial support from the CNRS
and the Université de Reims.
even more striking. Though with 1 the olefination of ester 4a
at room temperature gave a 57% yield of alkene 5i, the reaction
with 2 did not yield any 5i, even after heating at reflux for
1 hour. To solve this problem, dithioacetal 3f derived from p-
fluorothiophenol was prepared. This clearly led to an improved
reactivity towards 2 as the alkene 5i could now be obtained in
31% yield (Scheme 4). The reason for this difference in reactiv-
ity between 1 and 2 may be found in the coordination of the
stabilising ligands. For 1, it can be assumed that the second
triethylphosphite molecule is rather labile,3d hence readily pro-
viding a coordination site on titanium. In contrast, for 2, the
Lewis basic chloride anions of DyCl3 should bind strongly to
the Lewis acidic titanium centre. This may possibly lead to the
formation of more complex structures involving several titano-
cene and DyCl3 moieties, hence more reactive dithioacetals are
necessary in this case. To date no crystals of 2 suitable for
X-ray diffraction analysis could be obtained and further
studies to elucidate the nature of 2 are in progress.
Notes and references
1 J. J. Eisch, A. A. Adeosun and J. M. Birmingham,
Eur. J. Inorg. Chem., 2007, 39; and references therein.
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3 (a) U. Rosenthal, V. V. Burlakov, P. Arndt, W. Baumann and
A. Spannenberg, Organometallics, 2003, 22, 884; (b) F. Sato,
H. Urabe and S. Okamoto, Chem. Rev., 2000, 100, 2835;
(c) F. A. Hicks, N. M. Kablaoui and S. L. Buchwald, J. Am.
Chem. Soc., 1996, 118, 9450; (d) L. B. Kool, M. D. Rausch,
H. G. Alt, M. Herberhold, U. Thewalt and B. Wolf, Angew.
Chem., Int. Ed. Engl., 1985, 24, 394.
Lanthanides are known to have a relatively good functional
group tolerance, as confirmed by the above competition experi-
ment (Table 2, entry 10). It was therefore investigated whether a
simplified “all-in-one” procedure could be realized with 2 and 3a.
Indeed, promising results were obtained with several carbo-
nyl compounds when all the starting materials were present at
Table 3 A simplified “all-in-one” procedure
4 Reviews: (a) T. Takeda, Chem. Rec., 2007, 7, 24;
(b) R. C. Hartley, J. Li, C. A. Main and G. J. McKiernan, Tetra-
hedron, 2007, 63, 4825. Original publications: (c) T. Takeda,
A. Mori, T. Fujii and A. Tsubouchi, Tetrahedron, 2014, 70,
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2007, 13, 4074; (f) Y. Horikawa, M. Watanabe, T. Fujiwara
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Carbonyl
Yield (%)
with 3a
Yield (%)
with 3g
Entry
compound
Alkene
5 C. Macleod, R. C. Hartley and D. W. Hamprecht, Org. Lett.,
2002, 4, 75.
6 (a) G. Bousrez, F. Jaroschik, A. Martinez, D. Harakat,
E. Nicolas, X. F. Le Goff and J. Szymoniak, Dalton Trans.,
1
2
3
4
4a
4b
4c
4e
5a
33
12
35
32
65
35
45
57
5ba
5ca
5e
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