Reaction of 1,4-bis(trimethylsilyl)-2-butene with aromatic aldehydes catalyzed by TiCl4: an approach to (1-vinylallyl)benzene type derivatives

Article abstract of DOI:10.1016/j.tetlet.2006.03.179

1,4-bis(Trimethylsilyl)-2-butene 1 can react with alkyl and aromatic aldehydes in the presence of titanium tetrachloride to give α-(trimethylsilyl)methyl homoallylic alcohols and (1-vinylallyl)benzene type compounds in poor to good yield according to the

Full text of DOI:10.1016/j.tetlet.2006.03.179

Tetrahedron Letters 47 (2006) 3857–3860
Reaction of 1,4-bis(trimethylsilyl)-2-butene with aromatic
aldehydes catalyzed by TiCl4: an approach to
(1-vinylallyl)benzene type derivatives
Qianqian Ding, Anne-Sophie Chapelon, Cyril Ollivier* and Maurice Santelli*
ˆ
`
Universite´ Paul Ce´zanne, Faculte´ des Sciences et Techniques de Saint-Je´rome, Laboratoire de Synthese Organique, associe au
´
CNRS UMR 6180, Avenue Normandie-Niemen, 13397 Marseille Cedex 20, France
Received 20 February 2006; revised 27 March 2006; accepted 29 March 2006
Available online 27 April 2006
Dedicated to Professor Jean-Franc¸ois Normant on the occasion of his 70th birthday
Abstract—1,4-bis(Trimethylsilyl)-2-butene 1 can react with alkyl and aromatic aldehydes in the presence of titanium tetrachloride to
give a-(trimethylsilyl)methyl homoallylic alcohols and (1-vinylallyl)benzene type compounds in poor to good yield according to the
related position of each substituents present on the aromatic ring. In the last case, the reaction involves a SE02 type electrophilic sub-
stitution of 1,4-bis(trimethylsilyl)-2-butene by aromatic aldehydes activated by TiCl4, followed by a 1,2-migration of a vinyl group.
ꢀ 2006 Elsevier Ltd. All rights reserved.
During these last few decades, organosilicon chemistry
remained omnipresent in organic synthesis.1 Many areas
have witnessed a growth in the preparation of new
silicon-containing compounds and their successful use
in modern synthetic transformations. Indeed, they
usually served as key intermediates in the elaboration
of complex molecules.2 Among them, allylsilanes have
attracted considerable attention as versatile reagents
for carbon–carbon bond formation.3 In 1955, Calas first
showed that protolysis of allylsilanes by acetic acid
occurred with an allylic shift.4 Twenty years later,
Sakurai and Hosomi explored the condensation of
allyltrimethylsilane with aldehydes in the presence of
Lewis acid, to generate the corresponding homoallylic
alcohols.5 The reaction involves a SE02 mechanism where
the regioselective attack of the activated aldehyde at the
carbon–carbon double bond resulted in the intermediate
formation of a carbenium ion type A (Scheme 2), which
is stabilized by the carbon–silicon bond in b-position
through hyperconjugation.3,6 Soon after, Calas and
react with propanal and AlCl3 to furnish the a-(trimeth-
ylsilyl)methyl homoallylic alcohol in 40% yield.8
Recently, we performed the same experiment on pival-
dehyde in dichloromethane at ꢀ78 ꢁC using TiCl4 as
Lewis acid. Compound 2 was liberated in high yield
(94%), whereas condensation with benzaldehyde
resulted in the formation of another compound identi-
fied as (1-vinylallyl)benzene 3 (75%) (Scheme 1).9–11
A plausible mechanism for this reaction is depicted in
Scheme 2 and suggests that the formation of (1-vinyl-
allyl)-benzene 3 first comes from a SE02 type electrophilic
substitution of 1,4-bis(trimethylsilyl)-2-butene 1 by benz-
aldehyde activated by titanium tetrachloride. The alkoxy
titanium formed evolves into an ion pair including a
benzylic carbenium ion B which undergoes a 1,2-vinyl
shift and generates the rearranged carbenium ion C
stabilized by the neighboring carbon–silicon bond.
b-Elimination of the second trimethylsilyl group liberates
the dienic adduct 3. Formation of the rearranged product
is highly dependent upon the relative stability of both
carbocation intermediates B and C. For success, the
transient b-silylated carbocation C has to be more
stable than its benzyl counterpart B. Indeed, ab initio
computational studies at the B3LYP/6-311 G(d,p) level
show an energy difference between both carbenium ion
`
Dunogues confirmed the previous results and also
showed that 1,4-bis(trimethylsilyl)-2-butene 17 could
*
Corresponding authors. Tel.: +33 4 91 28 80 03; fax: +33 4 91 28 38
65 (C.O.); tel.: +33 91 28 88 25 (M.S.); e-mail addresses:
cyril.ollivier@univ.u-3mrs.fr; m.santelli@univ.u-3mrs.fr
4
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.03.179

3858
Q. Ding et al. / Tetrahedron Letters 47 (2006) 3857–3860
OH
R = t-Bu
O
SiMe3
(2) 94%
1) TiCl4 (1.25 eq.)/CH2Cl2
R
H
—80 °C, 3-4 h
2) H2O
Ph
Me3Si
R = Ph
SiMe3
(1) 34/66
(3) 75 %
Scheme 1.
TiCl4
O
OTiCl3
OTiCl3
SiMe3
Ph
H
Ph
Ph
SiMe3
SiMe3
Me3Si
SiMe3
A
Ph
(3)
Ph
SiMe3
SiMe3
B
C
E = —835.552019 Hartrees
E = — 835.553807 Hartrees
Scheme 2.
intermediates B and C of 1.12 kcal/mol in favor of the
formation of C, as suggested above.
Reasons for such a variation of reactivity between the
three tolualdehydes may be explained by considering
first the influence of the methyl substituent on the
formation and stabilization of the intermediate B.
Indeed, carbenium ions formed adjacent to the aromatic
ring are stabilized by hyperconjugation/resonance or
Baker–Nathan effect13 and this much better with ortho-
and para-substituted precursors than the corresponding
meta-isomer. By consequence, the presence of the
electrodonating methyl substituent at the para-position
can also limit the subsequent 1,2-migration process. By
opposition, the presence of the methyl substituent at
the ortho-position results in a steric hindrance, which
should partially prevent a charge stabilization favoring
at the same time the formation of the b-silylated carbo-
cation type C.
The proposed mechanism is in accordance with precedent
studies reported in 1981 by Fleming and co-workers12
showing that c-silylated tertiary alcohols could rearrange
in the presence of protic acid through a similar sequence.
However, no allusion to vinyl migration or to similar
experiments with c-silylated secondary alcohols was
mentioned.
In order to extend the scope of this transformation, we
were interested in studying the reactivity of methyl-substi-
tuted benzaldehydes. As shown in Table 1, the outcome of
the condensation of 1,4-bis(trimethylsilyl)-2-butene 1
with tolualdehydes proved to be quite dependent on the
relative position of the substituents on the aromatic ring.
By far, the best result was obtained with ortho-tolualde-
hyde under the previously described conditions. The
meta-oriented substrate provides the adduct 5 in a moder-
ate yield whereas reaction with its para-isomer appears to
be less favored. Although 1 was completely consumed in
each case, a small amount of starting aldehyde still
remained present together with more or less side products.
In an effort to optimize the procedure, the reaction
mixture was warmed up to room temperature. Unfortu-
nately, no significant improvement was observed.
Encouraged by these results, we tested the condensation
procedure on 2- and 4-methoxybenzaldehydes. Table 2
shows that, when the reaction is conducted at ꢀ80 ꢁC,
2-methoxybenzaldehyde can be converted into
1-methoxy-2-(1-vinylallyl)-benzene 8 in only 21% yield
together with the intermediate alcohol 9 (63%), whereas
4-methoxybenzaldehyde leads to the adduct 7 as results
of two successives SE02 reactions. This example mainly
shows the effect of electrodonating substituents on the
stabilization of the benzylic carbenium ions through

Q. Ding et al. / Tetrahedron Letters 47 (2006) 3857–3860
3859
Table 1.
Table 3.
Entry
Aldehyde
Conditions
Product
Yield (%)
96
Entry Aldehyde
Conditions
Product
Yield (%)
1
3.5 h, ꢀ80 ꢁC
3.5 h, ꢀ80 ꢁC
79
1
CHO
CHO
CHO
(4)
(5)
(10)
CHO
2
3
4.5 h, ꢀ80 ꢁC
64
CHO
CHO
2
3.5 h, ꢀ80 ꢁC
62
CHO
(11)
3.5 h, ꢀ80 ꢁC
40
41
CHO
CHO
ꢀ80 ꢁC!rt, 4 h
3
3.5 h, ꢀ80 ꢁC
7
24
(6)
ꢀ80 ꢁC!rt, 3 h
mesomeric resonance. As discussed before, an ‘ortho
effect’ is proposed to explain the interesting difference of
reactivity with both 2- and 4-methoxybenzaldehydes.
(12)
given that after allylation of each aldehyde function,
the influence of substituent electronic effects on the
1,2-vinyl shift is almost similar.
Finally, to illustrate the synthetic potential of this
methodology, we undertook experiments with aromatic
dialdehydes. As can be seen in Table 3, treatment of
phthaldialdehyde and isophthalaldehyde with 2.2 equiv
of 1,4-bis(trimethylsilyl)-2-butene and 2.5 equiv of
titanium tetrachloride at ꢀ80 ꢁC gave the desired 1,2-
and 1,3-bis-(1-vinylallyl)-benzene adducts 10 and 11 in
good to moderate yield, respectively. We next examined
the behavior of terephthalaldehyde. After optimization,
only a 24% yield of compound 12 was isolated when the
reaction was carried out at room temperature. At the
light of these results, we can draw a parallel between
the reactivity of tolualdehydes and phthalaldehydes
In summary, aromatic aldehydes placed in the presence
of 1,4-bis(trimethylsilyl)-2-butene and TiCl4 evolve to
(1-vinylallyl)benzene type compounds via a SE02 type
electrophilic substitution/1,2-vinyl shift reaction
sequence in poor to good yield, according to the substi-
tution on the aromatic ring. Influence of the electronic
nature of these substituents on the outcome of the reac-
tion process is still under study. Then, these compounds,
rarely encountered in the literature, represent interesting
precursors of highly functionalized 1,3-dienic systems.
Table 2.
Entry
Aldehyde
Conditions
Product
Yield (%)
35
OMe
OMe
1
4 h, ꢀ80 ꢁC
Me3Si
SiMe3
CHO
(7)
OMe
2
3 h, ꢀ80 ꢁC (ꢀ80 ꢁC!rt, 4 h)
21 (40)
OMe
CHO
(8)
(9)
OMe
OH
63 1/6 dr
Me3Si

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Q. Ding et al. / Tetrahedron Letters 47 (2006) 3857–3860
7. Weyenberg, D. R.; Toporcer, L. H.; Nelson, L. E. J. Org.
Chem. 1968, 33, 1975.
Acknowledgements
`
8. Deleris, G.; Dunogues, J.; Calas, R. Tetrahedron Lett.
1976, 16, 2449.
We are grateful to the Centre National de la Recherche
`
Scientifique (CNRS) and the Ministere de l’Education
9. For different transformations using 1,4-bis(trimethylsilyl)-
Nationale for the financial support. A.-S.C. thanks the
`
2-butene 1 as reagent, see: (a) Calas, R.; Dunogues, J.;
´
ˆ
‘Region Provence-Alpes-Cote d’Azur’ and the CNRS
Pillot, J. P.; Biran, C.; Pisciotti, F.; Arreguy, B. J. Org.
Chem. 1975, 40, 149; (b) Abed, D. E.; Santelli-Rouvier, C.;
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Roux, M.; Santelli, M.; Parrain, J.-L. Org. Lett. 2000, 2,
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for a grant.
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Soc. Chim. Fr. 1971, 3057; (b) Hirashita, T.; Hayashi, Y.;
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in dry CH2Cl2 (30 ml) was added dropwise a solution of
benzaldehyde (2.0 ml, 20 mmol) in dry CH2Cl2 (5 ml)
under argon at ꢀ60 ꢁC. After 5 min stirring, the mixture
was cooled to ꢀ90 ꢁC and a solution of 1,4-bis(trimeth-
ylsilyl)-2-butene 1 in dry CH2Cl2 (5 ml) was slowly added,
and the resulting solution was stirred for 3.5 h at ꢀ80 ꢁC.
The reaction was monitored by TLC analysis. The mixture
was quenched with a saturated NH4Cl solution (50 ml)
and was stirred for 1 h at rt. The aqueous layer was
extracted with CH2Cl2 (3 · 25 ml). The combined organic
layers were washed with a saturated NaHCO3 solution
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17.2 Hz, 2H), 4.06 (br t, J 6.8 Hz, 1H). dC (75 MHz,
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