Acid-catalyzed reaction behavior of 1-silylcyclopropylmethanols

Article abstract of DOI:10.1016/j.tetlet.2006.06.002

Treatment of 1-silylcyclopropylmethanols with TsOH in methanol gives different homoallyl ethers depending upon the configuration of substituents on cyclopropane ring and the kinds of substituents on carbinyl carbon. Especially, the reaction of cyclopropyl

Full text of DOI:10.1016/j.tetlet.2006.06.002

Tetrahedron Letters 47 (2006) 5751–5754
Acid-catalyzed reaction behavior of
1-silylcyclopropylmethanols
Mitsunori Honda,* Takahito Mita, Toshiaki Nishizawa, Toru Sano,
Masahito Segi and Tadashi Nakajima
Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa,
Ishikawa 920-1192, Japan
Received 9 May 2006; revised 30 May 2006; accepted 1 June 2006
Available online 21 June 2006
Abstract—Treatment of 1-silylcyclopropylmethanols with TsOH in methanol gives different homoallyl ethers depending upon the
configuration of substituents on cyclopropane ring and the kinds of substituents on carbinyl carbon. Especially, the reaction of
cyclopropylmethanols having no substituents on the same side with silyl group on cyclopropane ring proceeds to give the corre-
sponding E-homoallyl ethers with high stereoselectivity. The following protiodesilylation of resulting homoallyl ethers proceeds with
retention of configuration.
Ó 2006 Elsevier Ltd. All rights reserved.
Cyclopropylcarbinyl cations are interesting species1 and
have been used extensively as useful intermediates in
organic synthesis.2 Especially, homoallylic rearrange-
ment of cyclopropylcarbinyl cation is known as the Julia
olefin synthesis that leads to stereoselective formation of
the E-homoallyl derivatives (Scheme 1).3–5 In contrast,
we have recently reported that the homoallylic rear-
rangement of cyclopropylsilylcarbinyl cation having a
n-, s-alkyl group on carbinyl carbon led to stereoselec-
tive formation of E-silyl-substituted homoallyl deriva-
tives6 and the following protiodesilylation proceeded
with retention of configuration (Scheme 2).5a In conse-
quence, we presented that a bulky silyl group acted as
a directing group for the stereoselectivity on this olefin
synthesis and the geometry of the alkene moiety of
protiodesilylated products was the opposite to that of
Julia reaction using the corresponding cyclopropylmeth-
anols. However, the reaction of cyclopropylsilylcarbinyl
cation having a bulky alkyl group such as a t-butyl
Scheme 2. Stereoselective construction of Z-homoallyl derivatives
from cyclopropylsilylmethanols.
group on carbinyl carbon gave the undesired Z-isomer
exclusively. The above observation led to us to attempt
the homoallylic rearrangement of cyclopropylcarbinyl
cation having a silyl group at the 1-position of cyclopro-
pane ring,7 which may afford E-silyl-substituted homo-
allyl derivatives effectively. In this letter, we describe
the generation of cyclopropylcarbinyl cations by the
reaction of 1-silylcyclopropylmethanols with acid-cata-
lyst and then following the rearrangement reaction
behavior. Furthermore, the protiodesilylation8 of the
resulting silyl-substituted homoallylic compounds for
stereoselective formation of Z-homoallyl derivatives is
reported.
Scheme 1. Julia olefin synthesis.
Keywords: Cyclopropylmethanol; Homoallylic rearrangement; Tri-
methylsilyl group; Protiodesilylation.
*
The preparation of 1-silylcyclopropylmethanols 1–8 was
Corresponding author. Tel.: +81 76 234 4789; fax: +81 76 234
4800; e-mail: honda@t.kanazawa-u.ac.jp
accomplished as follows (Scheme 3). The treatment of
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.06.002

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M. Honda et al. / Tetrahedron Letters 47 (2006) 5751–5754
binyl carbon provided 1,2-anti-3Z-homoallyl ether
derivative 15 having the t-butyl group at allylic position.
In the reaction of bicyclic compound 8, cis isomer
reacted to give the corresponding anti-E-isomer 16 as
with the reaction of 6 (Scheme 7). On the other hand,
the reaction of trans-8 proceeded to afford Z-homoallyl
ether 17 (Scheme 8).
These results suggest that the stereochemistry of homo-
allylic rearrangement of the silylcyclopropylmethanols is
dependent on the configuration of substituents on the
three-membered ring. Thus, the following mechanism
for the reaction was proposed (Schemes 9 and 10). For
the reaction of cyclopropylmethanols having a substitu-
ent (Ph or Me) located on the opposite site of silyl group
on cyclopropane ring, the acid protonates at the oxygen
atom of starting alcohols and bisected cation spe-
cies3a,5,12 A and B are formed (Scheme 9). The formation
of bisected cation A seems to be favored compared to B
by the less strain between R group and R1 group on the
three-membered ring. Thus, Z-silylalkenes 9–13 are
formed selectively. Since the attack of methanol to cat-
ion intermediate A proceeds in an SN20 manner, no epi-
merization is observed at all. On the other hand, in the
case of the reaction using 2,3-cis-dimethylcyclopropyl-
methanols, bisected cation C is formed exclusively
(Scheme 10). As a result, the reaction leads to 1,2-syn-
3E-silylalkene 14 with high stereoselectivity. In contrast,
to avoid the formation of steric hindered trisubstituted
alkene, the cation C would be transformed to a more
stable cation species D via bicyclobutonium ions1a,13 in
the reaction of 2,3-cis-dimethylcyclopropylmethanols
having a t-butyl group on the carbinyl carbon. Conse-
Scheme 3. Preparation of 1-trimethylsilylcyclopropylmethanols.
dibromocyclopropanes with n-butyllithium followed by
reaction with chlorotrimethylsilane gave the corre-
sponding trimethylsilylcyclopropane derivatives in high
yields.9 The resulting cyclopropane derivatives were
treated with n-butyllithium and the subsequent reaction
with aldehyde gave the desired cyclopropylmethanols
1–8. Incidentally, the bicyclic compound 8 was yielded
as a mixture of cis and trans isomers. Therefore, this
mixture was separated by column chromatography on
silica-gel, and then each isomer was used as a starting
material.
The silylcyclopropylmethanols 1–3 having a phenyl
group that is located on the opposite site of silyl group
on cyclopropane ring were treated with TsOH in meth-
anol. The homoallylic rearrangement proceeded to give
the Z-isomer of silyl-substituted homoallyl ethers 9–11
in moderate to high yields, with high stereoselectivity
independent of the kind of the substituent on carbinyl
carbon (Scheme 4).10,11 In this reaction, the cleavage
of C1–C2 bond of the cyclopropane ring was observed
exclusively. Similarly, the reaction of 2,3-trans-dimethyl-
cyclopropylmethanols 4 and 5 was smoothly proceeded
to afford the corresponding 1,2-anti-3Z-homoallyl ethers
12 and 13 (Scheme 5). It should be noted that the epi-
merization was not observed in this rearrangement
reaction.
More noteworthy, the same reaction of 2,3-cis isomer 6
having a phenyl group on the carbinyl carbon afforded
the 1,2-syn-3E-isomer 14 selectively (Scheme 6). How-
ever, the reaction of 7 having a t-butyl group on the car-
Scheme 6. Homoallylic rearrangement of 1-silyl substituted 2,3-cis-
dimethylcyclopropylmethanols.
Scheme 7. Homoallylic rearrangement of 7-silyl substituted cis-bi-
cyclo[4.1.0]hept-7-ylmethanol 8.
Scheme 4. Homoallylic rearrangement of 2-phenyl-1-silylcyclo-
propylmethanols.
Scheme 5. Homoallylic rearrangement of 1-silyl substituted 2,3-trans-
dimethylcyclopropylmethanols.
Scheme 8. Homoallylic rearrangement of 7-silyl substituted trans-
bicyclo[4.1.0]hept-7-ylmethanol 8.

M. Honda et al. / Tetrahedron Letters 47 (2006) 5751–5754
5753
Scheme 9. Mechanism of the homoallylic rearrangements of silylcyclopropylmethanols 1–5.
Scheme 10. Mechanism of the homoallylic rearrangements of 2,3-cis-dimethylcyclopropylmethanols.
quently, 1,2-anti-3Z-silylalkene 15 was yielded with high
stereoselectivity. The reaction of bicyclic compounds 8
would proceed similarly as mentioned above.
The protiodesilylation of vinylsilane proceeds with
complete retention of the configuration.8 Thus, protio-
desilylation of resulting E-silyl-substituted homoallyl
derivative 14 was examined and the result is shown in
Scheme 11. Treatment of 14 with tetrabutylammonium
fluoride (TBAF) in hexamethylphosphoric triamide
gave the corresponding Z-protiodesilylated compound
18. Thus, it was found that the geometry of the alkene
moiety of protiodesilylated products is the opposite
to that of Julia reaction using the corresponding
cyclopropylmethanols.
Scheme 12. Conversion of 6 into tetrahydrofuran derivative 21.
as with the reaction in methanol mentioned above.
Treatment of the resulting alcohol 19 with TBAF fol-
lowed by intramolecular bromo etherification with
NBS gave the corresponding tetrahydrofuran derivative
21.14 The vicinal coupling constant observed between
Stereochemical assignment of homoallyl derivatives was
performed as follows (Scheme 12). The reaction of silyl-
cyclopropylmethanol 6 with TsOH in water/THF pro-
ceeded to give the corresponding homoallyl alcohol 19
1
the protons on C-4 and C-5 in the H NMR spectrum
and the NOE experiments clearly indicated the trans
arrangement of two methyl groups, which is correlated
to 1,2-syn-configuration in homoallyl alcohol 19. Thus,
the stereoconfiguration of other products was predicted
by comparing with the chemical shifts and coupling
constants.
In conclusion, acid-catalyzed homoallylic rearrange-
ment of 1-silylcyclopropylmethanols has been described.
Scheme 11. Protiodesilylation of homoallyl ether 14.

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M. Honda et al. / Tetrahedron Letters 47 (2006) 5751–5754
6. For reports about synthesis and reaction of silyl-substi-
tuted homoallyl alcohol, see: (a) Semeyn, C.; Blaauw, R.
H.; Hiemstra, H.; Speckamp, W. N. J. Org. Chem. 1997,
62, 3426–3427; (b) Dobbs, A. P.; Martinovic, S. Tetra-
hedron Lett. 2002, 43, 7055–7057; (c) Miura, K.; Hosomi,
A. Synlett 2003, 143–155.
7. (a) For reviews on the cyclopropane chemistry, see: Small
Ring Compounds in Organic Synthesis I–V; de Meijere, A.,
Ed.; Topics in Current Chemistry; Springer: Berlin,
Heidelberg; 1986, 1987, 1988, 1990, 1996; Vols. 133, 135,
144, 155, 178; (b) Wong, H. N. C.; Hon, M.-Y.; Tse, C.-
W.; Yip, Y.-C.; Tanko, J.; Hudlicky, T. Chem. Rev. 1989,
89, 165–198; (c) de Meijere, A.; Wessjohann, L. Synlett
1990, 20–32.
1-Silylcyclopropylmethanols reacted with TsOH in
methanol to afford different homoallyl ethers depending
upon the configuration of substituents on cyclopropane
ring and the kinds of substituents on carbinyl carbon.
Especially, the reaction of cyclopropylmethanols having
no substituents on the same side with silyl group on
cyclopropane ring proceeded to give the corresponding
E-homoallyl ethers. The protiodesilylation of resulting
homoallyl ethers proceeded with retention of configura-
tion, thus it was found that the geometry of the alkene
moiety of protiodesilylated products is the opposite to
that of Julia reaction using the corresponding cyclopro-
pylmethanols. Further studies are aimed at expanding
the scope of these reactions, and introduction of other
functional group instead of silyl group and the following
the homoallylic rearrangement reaction is now in pro-
gress in our laboratory. The results will be reported in
due course.
8. Oda, H.; Sato, M.; Morisawa, Y.; Oshima, K.; Nozaki, H.
Tetrahedron Lett. 1983, 24, 2877–2880.
9. Kitatani, K.; Hiyama, T.; Nozaki, H. J. Am. Chem. Soc.
1975, 97, 949–951.
10. Typical procedure for the homoallylic rearrangement of 1-
silylcyclopropylmethanol with TsOH:1-silylcyclopropyl-
methanol solution (2 mmol in 10 ml of methanol) was
placed in a round-bottomed flask under argon, followed
by the addition of TsOH (2.4 mmol) at 0 °C. The mixture
was stirred for 2 h. The reaction was quenched with a
sodium hydrogen carbonate aqueous solution. The prod-
uct was extracted with pentane, washed with brine, dried
with anhydrous Na2SO4, concentrated under reduced
pressure, and separated with silica gel chromatography
using a mixture of hexane and dichloromethane as the
eluent, affording the corresponding homoallyl ethers.
Selected spectral properties of compound 14 are as
follows. IR (neat): 3060, 3025, 2950, 2940, 1615, 1455,
Acknowledgments
This work was partially supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Sci-
ence, Sports and Culture, Japan.
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