Acid-catalyzed reaction behavior of 1-phenylselenocyclopropylmethanols

Article abstract of DOI:10.1246/cl.2008.946

The reaction of 1-phenylselenocyclopropylmethanols with TsOH in methanol proceeded smoothly to afford the homoallylic ethers, ring-enlargement products, and ring-opening products depending upon the kind of substituent on the cyclopropane ring or α-carbon.

Full text of DOI:10.1246/cl.2008.946

946
Chemistry Letters Vol.37, No.9 (2008)
Acid-catalyzed Reaction Behavior of 1-Phenylselenocyclopropylmethanols
Mitsunori Honda,Ã Toshiaki Nishizawa, Yuko Nishii, and Masahito Segi
Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University,
Kakuma-machi, Kanazawa 920-1192
(Received June 16, 2008; CL-080598; E-mail: honda@t.kanazawa-u.ac.jp)
The reaction of 1-phenylselenocyclopropylmethanols with
on starting cyclopropylmethanols and reaction conditions.
Especially, it’s notable that 4H-selenochromene derivative
was formed, since few reports about the preparation of that
compound have been published so far.11
TsOH in methanol proceeded smoothly to afford the homoallylic
ethers, ring-enlargement products, and ring-opening products
depending upon the kind of substituent on the cyclopropane ring
or ꢀ-carbon. On the other hand, in the case of the absence of
methanol as nucleophile, 4H-selenochromene derivatives were
obtained exclusively.
The phenylselenocyclopropylmethanols 1a–1f having
aliphatic groups on the cyclopropane ring were treated with
TsOH in methanol. The results are shown in Table 1. The
reaction was completed in 3 h under reflux and then a mixture
of the usual homoallylic rearrangement products 2 and ring-
enlargement products 312 were obtained in good yields (Entries
1–5). The homoallylic rearrangement products 2 were yielded
as a Z isomer regardless of the substituent on the cyclopropane
ring and ꢀ-carbon. The ring-enlargement products 3 were
obtained as a mixture of two types of regioisomeric cyclobutene
derivatives. In addition, the cyclobutanone derivatives 4 were
yielded in the reaction of cyclopropylmethanols having a phenyl
group on the ꢀ-carbon (Entries 1, 3, and 5). These ring-enlarge-
ment products 3 and 4 would be formed via cyclobutyl cation1
derived from cyclopropylmethyl cation.7 Exceptionally, the for-
mation of homoallyl derivatives was not observed at all in the
reaction using cyclopropylmethanols 1f as a starting material
(Entry 6). In this reaction the cyclobutanone derivative 4 was
yielded predominantly.
The treatment of cyclopropylmethanols 1g and 1h having
a phenyl group at the 2-position of the cyclopropane ring and
ꢀ-carbon was carried out under similar conditions as above.
The results are shown in Table 2. It is noteworthy that these re-
actions proceeded to afford 3-phenylselenohomoallylic products
2 exclusively, as a mixture of geometrical isomers with prefer-
ence for Z isomer, without the formation of ring expansion prod-
ucts, regardless of configuration of the cyclopropane ring in
starting material 1.
Cyclopropylmethyl cations are interesting species1,2 and
have been used extensively as useful intermediates in organic
synthesis.3 Especially, homoallylic rearrangement of cyclopro-
pylmethyl cations is known as the Julia olefin synthesis that
leads to the stereoselective formation of the E-homoallyl deriv-
atives.4–6 In this context, we have recently reported the homoal-
lylic rearrangement of a cyclopropylmethyl cation having a silyl
group at the 1-position of the cyclopropane ring (Scheme 1).7
The reaction proceeded to give the corresponding E-homoallyl
ethers, and then the protiodesilylation8 of resulting homoallyl
ethers proceeded with retention of configuration. 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 a Julia reaction using the correspond-
ing cyclopropylmethanols.4 However, it was difficult to trans-
form the silyl group into other functional groups, with the
exception of protiodesilylation.8
The above observation prompted us to attempt the introduc-
tion of a phenylselenyl instead of a silyl group to the 1-position
of the cyclopropane ring. Organic compounds containing seleni-
um atom are very useful material in organic synthesis.9 In partic-
ular, phenylselenyl groups are available for further versatile
transformation.9,10 In this paper, we describe the generation of
cyclopropylmethyl cations by the reaction of 1-phenylselenocy-
clopropylmethanols with acid-catalyst and the following rear-
rangement reaction behavior. In these reactions, ring-enlarge-
ment compounds, ring-opening products, and 4H-selenochro-
mene derivatives were yielded along with desired phenylseleno-
homoallylic compounds, depending upon the kind of substituent
Additionally, the reaction of cyclopropylmethanols 1i–1l
Table 1. Reaction of 1-phenylselenocyclopropylmethanols
with TsOH
R3
SePh R3
+
R3
R2
SePh
R
R1 R2
MeO
SePh
O
R
TsOH
R
+
R2
R2
MeOH
Reflux, 3 h
R
R3
R1
OH
R1
R1
1
2
3
4
R2
R1
Si
R2
R1
Si
TsOH
Ratio/%b
R
R
Entry Substratea R1
R2
H
R3
R
Yield/%c
MeOH
"Homoallylic
+
2
3
4
OH
Rearrangement"
1
2
3
4
5
6
1a
1b
1c
1d
1e
1f
Me
H
Me Ph
t-Bu 27 73
Me Me Ph 57 34
t-Bu 34 66
25 41 34
64
78
77
81
67
81
R1 Si
R1
—
9
TBAF
MeO
"Protio-
desilylation"
MeO
—
Si=silyl group
R2
E Selective
R2
-Olefin
R
R
H
n-Bu
H
Ph
t-Bu
33 27 40
14 86
Z
—
aMolar ratio; cyclopropylmethanol:TsOH = 1:1.2. bDetermined by
1H NMR analysis. cIsolated yield.
Scheme 1. Stereoselective construction of Z-homoallyl deriva-
tives from 1-silylcyclopropylmethanols.
Copyright Ó 2008 The Chemical Society of Japan

Chemistry Letters Vol.37, No.9 (2008)
947
Table 2. Reaction of 1-phenylselenocyclopropylmethanols
having phenyl group on cyclopropane ring and ꢀ-carbon
Table 4. Reaction of 1-phenylselenocyclopropylmethanols in
the absence of nucleophiles
SePh
Ph SePh
R2
R1
Ph
SePh
TsOH
tBu
Acid
Ph
Ph
Se
MeOH
Reflux, 3 h
MeO
tBu
Solvent
rt, 2h
OH
OH
Ph
1
2
1l
7
Entry
Substratea
R1
R2
Yield/%b
E/Zc
Entry
Acida
Solvent
Yield/%b
1
2
1g
1h
Ph
H
H
Ph
57
76
11/89
28/72
1
2
3
TsOH
TMSOTf
CH3CN
CH2Cl2
CH2Cl2
69
47
85
aMolar ratio; cyclopropylmethanol:TsOH = 1:1.2. bIsolated yield.
cDetermined by 1H NMR analysis.
.
BF3 OEt2
aMolar ratio; cyclopropylmethanol:acid = 1:1.2. bIsolated yield.
having a phenyl group at the 2-position of the cyclopropane ring
and an alkyl group on the ꢀ-carbon was carried out. The results
are shown in Table 3. In all cases two types of ketones, 5 derived
by formal migration of the phenylselenyl group competing with
the ring-opening and 6 derived by elimination of the phenylse-
lenyl group, were yielded in moderate yields as a mixture with
preference for 5, regardless of the bulkiness of the alkyl substitu-
ent on the ꢀ-carbon of starting alcohols.
methanol proceeded smoothly to afford the usual homoallylic
rearrangement products, ring-enlargement products and ring-
opening products depending upon the kind of substituents on
the cyclopropane ring or ꢀ-carbon. On the other hand, in the case
of the absence of nucleophile such as methanol, phenyl groups
on selenium acted as nucleophile, and selenochromene deriva-
tive was obtained in good yield. Further studies to extend the
scope of selenochromene derivatives synthesis are currently un-
der way and will be reported including reaction mechanisms in
due course.
As mentioned above, in the reaction of 1-phenylseleno-
cyclopropylmethanols with TsOH, the products having oxygen
functions 2, 4, 5, and 6 were obtained. The oxygen functions
would be introduced by the nucleophilic addition of methanol
used as solvent to cyclopropylmethyl cation or its ring-enlarged
cyclobutyl cation intermediate. Then, we have become
interested in the reaction behavior of cyclopropylmethyl cation
in the absence of nucleophile. So the reaction of compound 1l
with TsOH in acetonitrile was carried out. The reaction was
completed in 2 h at room temperature and gave the 4H-seleno-
chromene derivative 7 in good yield. The results are shown in
Table 4. In this reaction, the phenyl group on selenium would
act as nucleophile instead of methanol, and then a C–C bond
was formed between the carbons at the 2-position of the cyclo-
propane ring and o-position of the phenyl group. The same reac-
tions using Lewis acid in dichloromethane were examined. The
reaction with trimethylsilyl triflate as an acid afforded 7 in
moderate yield (Entry 2). In contrast, the treatment of 1l with
boron trifluoride diethyl etherate gave 7 in high yield (Entry 3).
In summary, generation and reaction behavior of cyclo-
propylmethyl cations derived from 1-phenylselenocyclopropyl-
methanols with acid-catalyst have been described. The
reaction of 1-phenylselenocyclopropylmethanols with TsOH in
References and Notes
1
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For recent reports about utilization of cyclopropylmethyl
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2
3
4
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¨
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Table 3. Ring-opening reaction of 2-phenyl-1-phenylseleno-
cyclopropylmethanols with TsOH
7
8
9
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SePh
PhSe
Ph
O
O
TsOH
Ph
R
+
R
R
Ph
MeOH
Reflux, 3 h
OH
1
5
6
Ratio/%b
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Entry
Substratea
R
Yield/%c
5
6
1
2
3
4
1i
1j
1k
1l
Me
Et
79
74
78
65
21
26
22
35
62
77
68
57
i-Pr
t-Bu
aMolar ratio; cyclopropylmethanol:TsOH = 1:1.2. bDetermined by
1H NMR analysis. cIsolated yield.
12 S. Halazy, A. Krief, Tetrahedron Lett. 1981, 22, 1829.
Published on the web (Advance View) August 2, 2008; doi:10.1246/cl.2008.946