Table 3 Reactivity of 1a–c with SnCl4 and SbCl3
tributadienyl chlorostannanes, we examined the reactivity of 1a
with a substoichiometric amount (0.5 eq.) of tin tetrachloride
(entry 2). In this case, butadienyltrichlorotin 2a was obtained
along with the starting silane 1a (1+1 mixture), implying that
these compounds do not react with each other. To explain this
non-reactivity and the selectivity in favour of 2a (vs bis(butadie-
nyl)dichlorostannane), we think that the butadienyl ligand of 2a
largely decreases the electrophilic character of the tin atom.
The reaction at 20° C of SbCl3 with silane 1a in CDCl3 gave
dienyldichlorostibine 3a§ in 87% yield as a mixture with
butadiene and trimethylsilyl chloride (entry 3).8 Equally, SbCl5
reacts at low temperature (260 °C) with 1a and yields
butadienyltetrachlorostibine 4a¶ and quantitatively trimethylsi-
lyl chloride (entry 4). The dienylstibine 4a exhibited a low
stability at room temperature and decomposed after a few
hours.
In contrast, reaction of 1a with excess of stibine pentachlor-
ide (3 eq.) at 220° C did not afford 4a but a mixture of
trichlorobutene derivatives was quantitatively obtained
(Scheme 2). To explain the trichlorinated products, we postulate
that the reaction would proceed via the formation of 4a which,
in the presence of SbCl5, would undergo a chlorine–antimony
exchange followed by 1,2 or 1,4 electrophilic chlorination of the
diene moiety.9
a
Entry Allenylsilanes 1
1
MCln
SnCl4
Dienylstannanes 2 Yield (%)
96
2
3
4
5
6
B
B
B
SbCl3
SnCl4
SbCl3
SnCl4
SbCl3
87
83
75
85b
78b
a Transmellation reactions with tin tetrachloride and antimony trichloride
were respectively conducted at 20 °C and 240 °C in CH2Cl2. b A 1+1
mixture of E and Z isomers was obtained.
Notes and references
‡ Filtration of the suspension led to a very small amount by weight of
precipitate insoluble in either CDCl3 or CD2Cl2 . 1H and 13C NMR analyses
carried out in DMSO-d6 did not permit the precise structure of the product
to be obtained.
Scheme 2
No reaction was observed between compound 1a and SiCl4,
GeCl4 or AsCl3 even at 80 °C (entries 7–9). With titanium
tetrachloride (entry 5) or boron trifluoride (entry 6) which are
strong Lewis acids, we were not able to establish the formation
of butadienyl derivatives. For example, with 1 equivalent of
BF3·Et2O, approximately 12% conversion of 1a into butadiene
was observed while a large excess of Lewis acid (more than 10
equivalents) was necessary to observe complete conversion into
butadiene and trimethylsilyl fluoride as observed by 1H NMR.
This partial protolysis of 1a already observed during the Lewis
acid promoted reaction of allylsilanes is difficult to explain,
nevertheless we think that a minor amount of HCl could be
present in TiCl4 and acts in this partial protolysis reaction.
In order to evaluate the scope of the reaction, we then tested
other b-allenylsilanes (Scheme 3). Reaction of tin tetrachloride
or stibine trichloride with a range of b-allenyl trimethylsilanes
proceeded with regiocontrol to give substituted butadienyl
chlorostannanes or stibines respectively with fair yields (Table
3).
§ 1H NMR (400 MHz, CDCl3) d (ppm): 5.38 (d, J = 10.5 Hz, 1H4); 5.55 (d,
J = 17.6 Hz, 1H5); 6.20 (s, 1 H1); 6.46 (s, H2); 7.06 (dd, J = 10.5, 17.6 Hz,
1H3). 13C NMR (100 MHz, CDCl3) d (ppm): 118.8 (Ca); 129.6 (Cd); 137.6
(Cb); 160.0 (Cc).
¶
1H NMR (300 MHz, CDCl3) d (ppm): 5.54 (d, J = 10.7 Hz, 1H4); 5.66
(d, J = 16.9 Hz, 1H5); 6.19 (bs, 1H1); 6.21 (bs, 1H2); 6.75 (dd, J = 10.7,
16.9 Hz, 1H3). 13C NMR (75 MHz, CDCl3) d (ppm): 122.3 (Ca); 127.2 (Cd);
132.7 (Cb); 158.9 (Cc).
1 R. Calas, J. Dunogues, G. Deleris and F. Pisciotti, J. Organomet. Chem.,
1974, 69, C15–17.
2 M. Santelli and J.-M. Pons, Lewis Acids and Selectivity in Organic
Synthesis, CRC Press, Boca Raton, 1996.
3 S. E. Denmark, T. Wilson and T. M. Willson, J. Am. Chem. Soc., 1988,
110, 984; S. E. Denmark, E. J. Weber, T. Wilson and T. M. Willson,
Tetrahedron, 1989, 45, 1053; S. E. Denmark and N. G. Almstead,
Tetrahedron, 1992, 48, 5565; S. E. Denmark and N. G. Almstead, J. Am.
Chem. Soc., 1993, 115, 3133.
4 L. C. Dias, P. R. R. Meira and E. Ferreira, Org. Lett., 1999, 1, 1335.
5 M. Lahrech, S. Hacini, J.-L. Parrain and M. Santelli, Tetrahedron Lett.,
1997, 38, 3395.
6 J.-C. Guillemin and L. Lassalle, Organometallics, 1994, 13, 1525; J.-C.
Guillemin, L. Lassalle, P. Dréan, G. Wlodarczak and J. Demaison, J. Am.
Chem. Soc., 1994, 116, 8930; L. Lassalle, S. Legoupy and J.-C.
Guillemin, Organometallics, 1996, 15, 3466; T. Janati, J.-C. Guillemin
and M. Soufiaoui, J. Organomet. Chem., 1995, 486, 57; L. Lassale, T.
Janati and J.-C. Guillemin, J. Chem. Soc., Chem. Commun., 1995, 699; S.
Le Serre and J.-C. Guillemin, Organometallics, 1997, 16, 5844; S. Le
Serre, J.-C. Guillemin, T. Karpati, L. Soos, L. Nyulászi and T.
Veszprémi, J. Org. Chem., 1998, 63, 59; J.-C. Guillemin and K. Malagu,
Organometallics, 1999, 18, 5259.
In conclusion, we have shown that the reaction of Lewis
acidic halides such as tin tetrachloride or stibine trichloride with
b-allenylsilanes leads only to the corresponding butadienyl
derivatives, via a transposition reaction. This approach allows
the synthesis of new butadienyl tin or antimony derivatives.
Other Lewis acid halide derivatives such as GeCl4, SiCl4, BF3
or TiCl4 were found non reactive.
7 I. Fleming and M. Taddei, Synthesis, 1985, 899; S. P. Bew and J. B.
Sweeney, Synthesis, 1994, 698.
8 For the synthesis of vinyldichlorostibine see: S. Legoupy, L. Lassalle, J.-
C. Guillemin, V. Metail, A. Senio and G. Pfister-Guillouzo, Inorg.
Chem., 1995, 34, 1466.
9 SbCl5 was recently used in the chlorination reaction of aromatics, see: R.
Rathore, A. S. Kumar, S. V. Lindeman and J. K. Kochi, J. Org. Chem.,
1998, 63, 5847 and references therein.
Scheme 3
CHEM. COMMUN., 2002, 644–645
645