In situ generated tris(p-bromophenyl)amine radical cation promoted electron transfer reaction of cyclopropyl silyl ethers

Article abstract of DOI:10.1016/j.tet.2009.09.108

Tris(p-bromophenyl)aminium hexachloroantimonate and perchlorate were utilized to promote the oxidative ring-opening reaction of cyclopropyl silyl ethers giving ring-expanded ketones. Exploration of salt quantity effect on the reaction allowed us to hypoth

Full text of DOI:10.1016/j.tet.2009.09.108

Tetrahedron 65 (2009) 10876–10881
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
In situ generated tris(p-bromophenyl)amine radical cation promoted electron
transfer reaction of cyclopropyl silyl ethers
*
Eietsu Hasegawa , Koji Kakinuma, Tomoyo Yanaki, Shota Komata
Department of Chemistry, Faculty of Science, Niigata University, Ikarashi-2 8050, Niigata 950-2181, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 July 2009
Received in revised form
Tris(p-bromophenyl)aminium hexachloroantimonate and perchlorate were utilized to promote the ox-
idative ring-opening reaction of cyclopropyl silyl ethers giving ring-expanded ketones. Exploration of salt
quantity effect on the reaction allowed us to hypothesize that amine radical cation is regenerated
through the oxidation of neutral amine by hexachloroantimonate anion. Based on this hypothesis, amine
radical cation was initially generated by the treatment of parent amine with either antimony penta-
chloride or the mixture of silver perchlorate and molecular iodine, and subsequently reacted with same
substrates. The in situ generated amine radical cation was found to promote the reaction, and the ex-
pected products were obtained in better yields than via use of the corresponding salt reagents.
Ó 2009 Elsevier Ltd. All rights reserved.
10 September 2009
Accepted 28 September 2009
Available online 1 October 2009
ꢀ
þ
1
. Introduction
mechanism involving regeneration of (p-BrC
SbCl anion. Then, we report the results of the experiments in
which (p-BrC
(p-BrC N with SbCl
6
H
4
)
3
N
promoted by
6
ꢀ
þ
Radical ions that are generated by single electron transfer (SET)
processes of neutral organic molecules possess various chemical
reactivities.1 For example, radical cations undergo fragmentation,
radical addition, dimerization, disproportionation, and reaction
with nucleophiles. In addition to these chemical reactions, radical
cations can abstract an electron from other molecules to return to
their neutral forms, and therefore they are expected to act as SET
oxidants. Among radical cations to behave in this manner are tri-
arylamine radical cations, and they in fact promote various oxida-
6
H
4
)
3
N
is initially generated by the treatment of
or the mixture of AgClO and I , and
subsequently used for the reaction with same substrates. Com-
pounds investigated are shown in Chart 1.
6
H
4
)
3
5
4
2
,2
Me SiO
O
O
O
3
Me
R
R
Y
R
R
3
n
n
tive transformations of organic compounds. In many cases, the
appropriate amine radical cation salts are generally prepared be-
n
n
1
2
3
4
fore conducting reactions, and tris(p-bromophenyl)aminium hexa-
a (n = 1, R = Me) , b (n = 1, R = (CH ) CH=CH ),
2
2
2
chloroantimonate, (p-BrC
H
6 4
)
3
NSbCl
6
, has been most frequently
c (n = 1, R = (CH
2
)
3
CH=CH
2
), d (n = 2, R = Me), Y = Cl, OH
used for this purpose. Recently, we also used this radical cation salt
to promote oxidative ring-opening reaction of cyclopropyl silyl
ethers to give ring-expanded ketones. In addition, in situ generated
Chart 1.
4
radical cations are often used to promote SET reactions of other
2. Results and discussion
2.1. Reactions with aminium salt reagents, (p-BrC
Our preliminary investigation revealed that (p-BrC
1
f,5
molecules under the electrochemical
as well as photochemical
conditions.1
b,c,g,4a
We became interested in determining whether
NX
NSbCl
6 4 3
H )
ꢀ
þ
, could be generated in situ
the amine radical cation, (p-BrC
6
H
4
)
3
N
by certain chemical oxidants and subsequently used to promote the
6
H
4
)
3
6
6
transformation of cyclopropyl silyl ethers.
promoted the regioselective ring-opening of cyclopropyl silyl
In this paper, we first describe the reactions of cyclopropyl silyl
ethers 1 to give ring-expanded chloro adducts 3-Cl, that were fi-
ethers with (p-BrC
perchlorate, (p-BrC
6
H
4
)
H
3
NSbCl
NClO
6
and tris(p-bromophenyl)aminium
and hypothesize reaction
nally converted to the ring-expanded enones 2 by treatment with
4
6
4
)
3
4
,
a
NaOAc. In the reaction with the corresponding ClO
4
salt, 2 is di-
rectly produced from 1 without base treatment because of weak
nucleophilicity of ClO anion. The results of these salts promoted
4
*
Corresponding author. Tel./fax: þ81 25 262 6159.
2 2
reactions of 1 performed in CH Cl , MeCN and benzotrifluoride
(BTF) are summarized in Table 1.
E-mail address: ehase@chem.sc.niigata-u.ac.jp (E. Hasegawa).
0
040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.09.108

E. Hasegawa et al. / Tetrahedron 65 (2009) 10876–10881
10877
Table 1
6 4 3
p-BrC H )
NX promoted ring-opening reaction of 1a and subsequent treatment with NaOAcb
(
(
p-BrC H ) NSbCl
6
NaOAc
MeOH
6
4 3
O
O
O
Me
3
SiO
solvent
Me
R
R
OH
R
+
+
R
n
(p-BrC H ) NClO
n
n
n
6
4 3
4
1
2
3-OH
4
solvent
Entry
1
X
Solvent
Salt (equiv vs 1)
Yields (%)
2
3-OHc
4
1d
2
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
1b
1b
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
SbCl
CH
CH
CH
MeCN
MeCN
BTF
BTF
BTF
BTF
CH
CH
CH
CH
BTF
BTF
CH
CH
CH
Cl
Cl
Cl
2.0
1.0
0.5
2.0
0.5
2.0
1.0
0.5
0.1
2.0
1.0
0.7
0.5
1.0
0.5
2.0
1.0
0.5
79
74
66
43
63
67
89
67
24
78
66
75
61
74
63
18
48
0
0
2
0
5
0
0
Trace
8
8
Trace
4
Trace
Trace
2
2
4
10
6
10
1
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
2
2
2
2
2
2
3
4
d
5
6
7
d
d
8
9
Trace
19
0
0
0
0
0
0
0
10
11
12
13
14
15
16
17
18
Cl
2 2
Cl
2 2
Cl
2 2
Cl
2 2
d
4
0
ClO
ClO
ClO
4
2
Cl
2
Cl
2
Cl
2
4
4
2
2
0
0
26
36
e
e
24
a
b
c
1
(0.40 mmol), solvent (8 mL), N
2
, room temperature, 30 min.
ꢂ
NaOAc (5.1–6.0 equiv vs 1), MeOH (8.0 mL), 85 C, 2–3 h.
Isolated before base treatment.
Reported in Ref. 4b.
d
e
Average of two experiments.
In Table 1, we see that 2 was a major product and its yield varied
depending on the conditions employed in the reactions with SbCl
salt (entries 1–15). Hydroxy adduct 3-OH as well as external bond
cleavage product 4 were also obtained although the yields are
unpredictable yields of 2b. While the formation of 4b was negli-
gible in the reactions with 2.0 equiv of the salt (entry 16), it became
significant using less than 2.0 equiv of the salt (entries 17 and 18).
On the basis of these results, the following working hypotheses
6
relatively low. Notably, as the quantity of SbCl
formation of 4 became sizeable. Decreasing the salt quantity to
.1 equiv vs 1a led to the formation of a small amount of depro-
tected cyclopropanol (8%), not shown in entry 9. We were rather
surprised to find that the yields of 2 did not significantly drop even
when 0.5 equiv of the salt was used because the transformation of
6
salt decreased, the
can be made. First, SbCl
(p-BrC N to regenerate its radical cation, which is consistent
with the fact that SbCl can accept two electrons to become
NSbCl should act as three electron
5 6
originated from SbCl anion oxidizes
6 4 3
H )
0
5
1
i,12
SbCl
3
.
If so, (p-BrC
6
4
H )
3
6
transfer reagent. Thus, about 0.7 equiv of this salt could be a stoi-
chiometric amount to convert 1 to 3-Cl (see entry 12 in Table 1).
Second, 4 is not produced from SET reaction of 1 with the salt re-
agents. In other words, the precursor of 4 would not be the corre-
1
5
to 3 in principle requires two electron transfers from 1 (entries 3,
, 8, 13, 15).4
a,b,7
While the effect of solvent polarity on the reaction
13
is not obvious, it should be noted that BTF could be an alternative
solvent for CH Cl in these reactions because BTF was proposed as
an environmentally benign solvent and potential substitute to
sponding primary alkyl radical (will be discussed below).
A plausible reaction mechanism for 1 and (p-BrC
proposed in Scheme 1. SET between 1 and the aminium salt gives the
2
2
6 4 3 6
H ) NSbCl is
4
b,8–10
ꢀþ
ꢁ
14,15
CH
2
Cl
2
as well as benzene.
In comparison, use of the ClO
4
salt
ion pair of the radical cation of 1 (1 ) and SbCl
6
anion (SbCl
6
).
ꢀþ
ꢁ
was somewhat complicated; the yield of 2b was quite low using
Subsequently, desilylation of 1 is assisted by Cl , that is, derived
11
ꢁ
2
.0 equiv of the salt (entry 16). Decreasing the quantity of the salt
from SbCl
6
, to produce cyclopropoxy radical 5 and SbCl
5
. Regiose-
to 1.0 equiv (entry 17) and 0.5 equiv (entry 18) increased the for-
mation of 2b to a different extent. It is difficult to rationalize the
lective internal-bond cleavage of cyclopropane ring of 5 occurs to
produce tertiary alkyl radical 6. Efficient SET between 6 and
Me SiO
O
O
O
3
Ar NSbCl6
Me SiCl
3
3
R
R
R
1
SbCl
6
n
n
n
Ar N
SbCl
5
3
1
5
8
Ar = p-BrC H
6
4
Me
O
O
O
Ar N
3
Cl
Cl
R
R
R
9
not observed
n
-Cl
n
6
n
Ar N
3
3
7
Scheme 1.

10878
E. Hasegawa et al. / Tetrahedron 65 (2009) 10876–10881
ꢀ
þ
(
p-BrC
generated one by SbCl
. Nucleophiliccaptureof7by Cl givestheadduct3-Cl, whilehydroxy
adduct 3-OH is formed by the reaction between 6 and H O, most
6
H
4
)
3
N
, which comes form either starting SbCl
6
salt or in situ
We first needed to learn how SbCl
with 1 in the absence of (p-BrC N. When 1b was treated with
SbCl (1.1 equiv) in CH Cl , the reaction became complicated, and
3b-Cl could not be obtained. In the presence of (p-BrC
5 4 2
and AgClO /I interacted
5
is expected to give stable tertiary carbocation
6 4 3
H )
ꢁ
7
5
2
2
18
2
6
19
H
4
)
3
N, the
expected reaction pathways are shown in Scheme 3. Then, we
performed the reaction in which catalytic quantity of (p-BrC
(0.1 equiv) was used, and found that the reaction was also com-
plicated, which is probably due to the presence of an excess of SbCl
(see above). Therefore, we decided to use enough (p-BrC N to
fully consume SbCl . Under these conditions, the generation of
was confirmed by the evolution of characteristic
ꢁ
16
probably moisture, under the low concentration of Cl . Because of
the possibility of external bond cleavage of 5 to give primary alkyl
radical 8,4 we initially expected the formation of diagnostic spi-
rocyclization product 9, which is formed through a fast 5-exo radical
cyclization of 8b, in the reaction of 1b. However, 9 has been never
observed, and therefore we concluded that sequential processes from
6 4 3
H ) N
,7
5
6 4 3
H )
5
ꢀþ
6 4 3
H ) N
5
to 7 via 6 could take place faster than the process from 5 to 8.
(p-BrC
deep blue color (method A).
17
2
(
.2. Reaction with in situ generated amine radical cation,
ꢀ
6 4 3
p-BrC H ) N
D
+
1/2SbCl6 + 1/2SbCl
Ar N
3
1
1
/2Cl
3
Our results and the preceding discussion prompted us to in-
vestigate whether methods based on the salt preparations could
Ar = p-BrC H4
6
ꢀ
þ
also generate (p-BrC
method B in Scheme 2), and the resulting radical cation could
6
H
4
)
3
N
in situ (respective method A and
1
SbCl5
Scheme 3.
Ar N
3
1
7
promote the transformation of 1–2.
We also examined the reaction of 1b with AgClO
method B) in CH Cl
24%) and small amount of 2b (4%).
As described above, neither SbCl
of AgClO and I promoted the desired regioselective ring-opening
4
and I
2
(
method A)
(
(
2
2
and found the formation of iodo adduct 10b
2
0
2
(p-BrC H ) N + 3SbCl
2(p-BrC H ) NSbCl + SbCl3
6 4 3 6
6
4 3
5
5
nor the mixed reagent system
4
2
(
method B)
reaction of 1. Therefore, we applied both methods A and B to pro-
mote this transformation and the results are summarized in Table 2.
2
(p-BrC H ) N + 2AgClO + I2
2(p-BrC H ) NClO + 2AgI
6 4 3 4
6
4 3
4
6
Depending upon the conditions under which SbCl salt reagent
1
i,17
Scheme 2.
is prepared (Scheme 2),
1.5 equiv of (p-BrC
H
4
)
3
N is enough to
6
Table 2
ꢀ
þ
promoted ring-opening reaction of 1a and subsequent treatment with NaOAcb
(method A)
p-BrC H ) N / SbCl
In situ generated (p-BrC H ) N
6 4 3
(
NaOAc
MeOH
6
4 3
5
O
O
O
Me SiO
3
I
Me
R
solvent
R
+
+
R
R
n
n
n
n
10
(
p-BrC H ) N / AgClO / I2
6 4 3 4
1
2
4
for method B
solvent
(
method B)
Entry
1
1
Method
Solvent
Yields (%)
2
4
10
2 for saltc
1a
1b
1b
1b
1b
1c
1d
1a
1b
1b
1b
1b
1b
1c
1d
A
A
A
A
A
A
A
B
B
B
B
B
B
B
B
CH
CH
CH
Cl
2 2
Cl
2 2
Cl
2 2
80
58
77
57
78
65
72
76
0
0
0
0
0
0
0
0
0
5
3
5
4
0
0
d
d
d
d
d
d
d
10
Trace
5
4
4
66–79
61–78
d
2
3
4
5
6
7
8
9
MeCN
BTF
BTF
52g
63–74
h
47
68
d
h
BTF
CH
CH
2
Cl
Cl
2
f
f
f
2
2
74
18–48
d
g
g
g
g
10
11
12
13
14
15
MeCN
BTF
BTF
35
56
74
45
47
47
e
e
e
d
d
BTF
1
17
0
d
CH
CH
2
Cl
Cl
2
d
2
2
d
a
1
2 6 4 3 5 6 4 3 4
(0.40 mmol), solvent (8 mL), N , room temperature, 30 min; method A: (p-BrC H ) N (2.5 equiv), SbCl (1.1 equiv); method B: (p-BrC H ) N (2.5 equiv), AgClO
(
2.2 equiv), I
2
(1.1 equiv); Before addition of 1, reagent mixture is stirred for 15–20 min (see Experimental).
b
ꢂ
NaOAc (5.1–6.0 equiv vs 1), MeOH (8.0 mL), 85 C, 2–3 h.
Yields of 2 for salt reagent promoted reactions.
c
d
e
f
(
6 4 3
p-BrC H ) N (1.5 equiv).
Stirring of reagent mixture: 1 h, 2 h, 15 h for entries 11–13, respectively.
Average of three experiments (see Experimental).
Reported in Ref. 4a.
g
h
Reported in Ref. 4b.

E. Hasegawa et al. / Tetrahedron 65 (2009) 10876–10881
10879
react with 1.1 equiv of SbCl
5
, and a modest yield of 2b was obtained
4. Experimental section22
4.1. Reaction with (p-BrC
in CH
2
Cl
2
(entry 2). However, it is not sufficient to consume SbCl
5
ꢁ
generated in situ from SbCl
to use 2.5 equiv of (p-BrC
6
(Scheme 1), and therefore we decided
N, which significantly increased the
6
H
4
)
3
NX
6
H
4
)
3
yield of 2b (entry 3) and similarly produced 2a (entry 1). Method A
was also applied to other substrates 1c and 1d (entries 6 and 7).
Generally, the yields of 2 using method A are better than those
Both (p-BrC
from (p-BrC
Br , according to the literature procedures. (p-BrC
90% yield: mp 141.2–141.8 C (decomp.) (lit.
6
H
4
)
3
NSbCl
6
and (p-BrC
6
H
4
)
3
NClO
4
were prepared
6
4 3 3
H ) N, that was obtained by bromination of Ph N with
17
2
6
H
4
)
3
NSbCl
6
,
ꢂ
17
ꢂ
obtained in SbCl
also effective affording 2a in 76% yield (entry 8), and the yield of 2b
was improved compared to that for ClO salt promoted reaction
entry 9). This method was also applied to 1c and 1d to give 2c and
6
salt promoted reactions. Method B in CH
2
Cl
2
was
141–142 C,
ꢂ
decomp.). (p-BrC H ) NClO , 55% yield: mp 119.4 C (decomp.)
6 4 3 4
17
ꢂ
4
(lit. 129 C).
The procedure for (p-BrC
(
6
H
4
)
3
NSbCl
was previously reported. Reactions of 1 with SbCl
various conditions described in this paper were similarly per-
formed. Procedure of the reaction with (p-BrC NClO was es-
sentially same as that with SbCl salt except for not performing base
treatment of the crude reaction products. Details follow.
6
promoted reactions in BTF
4
b
2
d in modest yields (entries 14 and 15). Both methods proved ef-
6
salt under
fective in MeCN and BTF (entries 4–7 for method A, entries 10–13
for method B). In the case of method B, because of the lower sol-
ubility of the reagents in BTF, the mixture was necessarily stirred
for longer times before addition of 1b (entries 11–13).
6
H
4
)
3
4
6
Comparison of the two methods reveals that method A provides
more consistent results than method B on the basis of the yield of 2
although some results of latter method is compatible with those of
former. Also, it should be noted that small though not insignificant
amounts of byproducts such as 4 and 10 were obtained occasionally
using method B. In principle, the nature of the counter anion should
ꢀ
6 4 3
4.2. Reaction with in situ generated (p-BrC H ) N
D
ꢀ
þ
4.2.1. Reaction of 1b with (p-BrC
sented by entry 3 in Table 2. To (p-BrC
and SbCl (0.056 mL, 0.44 mmol) in CH
(114.7 mg, 0.40 mmol) in CH Cl (1 mL) under N
mixture was stirred for 30 min and followed by addition of satd
aqueous NaHCO . Then, filtration was performed, and the filtrate
was extracted with Et O. The extract was treated with water, satd
aqueous NaHCO , satd aqueous NaCl, and dried over anhydrous
MgSO . The residue obtained after concentration was subjected to
column chromatography (CH Cl /n-C
6
H
4
)
3
N
generated by SbCl
N (482.1 mg,1.00 mmol)
Cl (7 mL) was added 1b
. The resulting
5
, repre-
6
4 3
H )
5
2
2
influences the stability of a radical cation in its salt form. In fact, it is
2
2
2
ꢁ
known that SbCl
6
stabilizes the counter radical cations more sig-
nificantly than other anions, with the latter anions triarylamine
3
1
i
radical cations readily react with water. Thus, avoiding contami-
nation by water is more strictly required when using method B, and
this situation should be also considered in salt reagent promoted
reactions (see Table 1).
2
3
4
2
2
6
H
14¼1/1) to give the mixture
Also, we applied these methods to the oxidative ring-opening
reaction of bicyclic keto cyclopropanol 11, and the expected ben-
of 2a and 3a-Cl together with tris(p-bromophenyl)amine. Sub-
sequently, the product mixture was refluxed with NaOAc
21
zotropolone 12 was obtained although not optimized (Scheme 4).
(2.40 mmol) for 3 h in MeOH (8 mL). Then, extractionwith Et
performed, and the extract was treated with water, satd aqueous
NaHCO , satd aqueous NaCl, and dried over anhydrous MgSO . The
residue obtained after concentration was subjected to preparative
TLC (CH Cl /n-C
2
O was
When 11 was subjected to method A using BTF as the solvent, in-
complete reaction occurred giving a low yield of 12 (29% based on
3
4
5
3% conversion of 11) after treatment with NaOAc. On the other
hand, method B in CH Cl completely consumed 11 and produced
12 in moderate yield (37%).
2
2
2
2
6
H
14¼1/1) giving 2b (65.7 mg, 0.31 mmol, 77%).
Reactions of 1b under other conditions and reactions of other 1
and 12 were similarly performed. The average recovery of (p-
6 4 3
BrC H ) N was 80%.
(
method A)
BTF
NaOAc
MeOH
O
ꢀþ
generated by AgClO
O
4.2.2. Reaction of 1b with (p-BrC
H
4
)
N
and
OH
Me
6
3
4
OH
Me
I
2
, represented by entry 9 in Table 2. To a mixture of (p-BrC
6
H
4
)
3
N
(482.6 mg, 1.00 mmol), AgClO
4
(182.4 mg, 0.88 mmol) and I
2
ꢂ
(111.7 mg, 0.44 mmol) cooled at ꢁ30 C was added CH
2 2
Cl (7 mL)
(
method B)
CH Cl2
1
1
12
under N
by addition of 1b (114.7 mg, 0.40 mmol) in CH
resulting mixture was stirred for 30 min and followed by addition
of water. Then, extraction with Et O was performed. The extract
was treated with water, satd aqueous Na , satd aqueous
NaHCO , satd aqueous NaCl, and dried over anhydrous MgSO . The
residue obtained after concentration was subjected to column
chromatography (CH Cl /n-C
2
. Then, it was warmed to room temperature and followed
2
2
2
Cl (1 mL). The
Scheme 4.
2
2 2 3
S O
3
. Conclusion
As demonstrated above, we have developed a new means of
accessing the well-known tris(p-bromophenyl)amine radical cation
catalyst. Compared to the ordinary salt reagent based method, both
methods A and B are practical and effective and even more conve-
nient because isolation of the radical cation salts is not required. This
3
4
2
2
6
H
14¼1/1) to remove tris(p-bromo-
phenyl)amine from crude 2b. Subsequently, crude 2b was purified
by preparative TLC using same solvent system to give 2b (70.5 mg,
0.33 mmol, 83%). Other two trials of same experiment gave 2b in
84% and 55% yields.
would be advantageous particularly when counteranions that do not
Reactions of 1b under other conditions and reactions of other 1
and 12 were similarly performed. The average recovery of (p-
ꢁ
stabilize the radical cations are associated, unlike SbCl
6
. Also notably,
although not quantitative, we found that most of the amine could be
recovered and reused (see Experimental). We are investigating fur-
ther applications of method A and B to other SET reactions. In prin-
ciple, these in situ generation methods should be applicable to other
oxidizable compounds, and therefore it must promises to be par-
ticularly interesting to examine compounds whose radical cations
could not be easily isolated but behave as SET oxidants. Investigation
related to this issue is also in progress in our group.
6 4 3
BrC H ) N was 97%.
Substrates (1a, 1b,4a 1c, 1d, 1121) and products (2a, 2b,4a
4
a
4a
4a
4a
2c,4b 2d, 3a-Cl, 3a-OH, 4a, 10a, 12 ) are known com-
pounds. Spectral data of 4b, 10b, 10c are presented below. Depro-
tected alcohols of 1a and 1b obtained in the reactions were
4a
4a
7b
4a
7b
21
1
identified by direct comparison of their H NMR charts to those of
the precursor alcohols of 1a and 1b. The spectral data of depro-
tected alcohols of 1a and 1b are also reported.

1
0880
E. Hasegawa et al. / Tetrahedron 65 (2009) 10876–10881
Patai, S., Ed.; John Wiley & Sons: New York, NY, 1997; pp 1281–1354; (c)
4
.2.2.1. 4b. Pale yellow oil; IR (Neat) 2924, 1678, 1220 cmꢁ1; 1H
NMR (270 MHz, CDCl 1.20 (s, 3H), 1.56–1.82 (m, 2H), 1.89–2.14
m, 4H), 2.91–3.06 (m, 2H), 4.90–5.04 (m, 2H), 5.72–5.87 (m, 1H),
.20–7.32 (m, 2H), 7.42–7.48 (m, 1H), 8.02–8.06 (m, 1H); 13C NMR
68 MHz, CDCl 22.2, 25.4, 28.4, 33.7, 35.6, 44.5, 114.4, 126.5,
27.9, 128.5, 131.5, 132.8, 138.5, 143.0, 202.0; LRMS (EI) m/z (relative
Schmittel, M.; Ghorai, M. K. In Electron Transfer in Chemistry; Balzani, V., Ed.;
Wiley-VCH: Weinheim, 2001; Vol. 2, pp 5–54; (d) Hasegawa, E. J. Photoscience
3
) d
(
7
(
1
2003, 10, 61–69; (e) Roth, H. D. In Reactive Intermediate Chemistry; Moss, R. A.,
Platz, M. S., Jones, M., Jr., Eds.; John Wiley & Sons: Hoboken, 2004; Chapter 6,
pp 205–272; (f) Cossy, J.; Belloti, D. Tetrahedron 2006, 62, 6459–6470; (g)
Griesbeck, A. G.; Hoffmann, N.; Warzecha, K. D. Acc. Chem. Res. 2007, 40, 128–
3
) d
1
40; (h) Floreancig, P. E. Synlett 2007, 191–203; (i) Waske, P. A.; Tzvetkov, N. T.;
Mattay, J. Synlett 2007, 669–685; (j) Hoffmann, N. Chem. Rev. 2008, 108, 1052–
103; (k) Hoffmann, N. J. Photochem. Photobio C 2008, 9, 43–60.
þ
intensity) 214 (M , 5), 160 (100); HRMS (EI) calcd for C15
14.1358, found 214.1362.
18
H O
1
2
3
. (a) Bauld, N. L.; Bellville, D. J.; Harirchian, B.; Lorentz, K. T.; Pabon, R. A.;
Reynolds, D. W.; Wirth, D. D.; Chiou, H. S.; Marsh, B. K. Acc. Chem. Res. 1987,
20, 371–378; (b) Bauld, N. L. In Advances in Electron Transfer Chemistry;
Mariano, P. S., Ed.; JAI: Greenwich, 1992; Vol. 2, pp 1–66; (c) Barton, D. H. R.;
Haynes, R. K.; Leclerc, G.; Magnus, P. D.; Menzies, I. D. J. Chem. Soc., Perkin
Trans. 1 1975, 2055–2065; (d) Bellville, D. J.; Wirth, D. D.; Bauld, N. L. J. Am.
Chem. Soc. 1981, 103, 718–720; (e) Bauld, N. L.; Pabon, R. J. Am. Chem. Soc.
4.2.2.2. 10b. Pale yellow oil; IR (Neat) 2904, 1658, 1594,
ꢁ
1 1
1
214 cm ; H NMR (270 MHz, CDCl ) d 1.71–2.22 (m, 6H), 2.92–3.05
3
(
2
m, 2H), 3.44 (d, J¼10.3 Hz,1H), 3.59 (d, J¼10.3 Hz,1H), 4.91–5.04 (m,
H), 5.68–5.80 (m, 1H), 7.20–7.34 (m, 2H), 7.45–7.51 (m, 1H), 8.02–
.05 (m, 1H); 13C NMR (68 MHz, CDCl
14.8, 25.0, 27.9, 33.0, 33.8,
7.5, 115.0, 126.8, 128.0, 128.7, 131.1, 133.5, 137.5, 142.8, 197.3; LRMS
1983, 105, 633–634; (f) Hasegawa, E.; Mukai, T. Bull. Chem. Soc. Jpn. 1985, 58,
8
4
3
) d
3391–3392; (g) Lopez, L.; Calo, V.; Stasi., F. Synthesis 1987, 947–948; (h) Heyer,
J.; Dapperheld, S.; Steckhan., E. Chem. Ber. 1988, 121, 1617–1623; (i) Hasegawa,
E.; Mukai, T.; Yanagi, K. J. Org. Chem. 1989, 54, 2053–2058; (j) Kamata, M.;
Murayama, K.; Miyashi, T. Tetrahedron Lett. 1989, 30, 4129–4132; (k) Kamata,
M.; Murayama, K.; Suzuki, T.; Miyashi, T. J. Chem. Soc., Chem. Commun. 1990,
þ
(
EI) m/z (relative intensity) 340 (M , 3), 213 (100); HRMS (EI) calcd
for C15 17IO 340.0324, found 340.0321.
H
8
27–829; (l) Kamata, M.; Yokoyama, Y.; Karasawa, N.; Kato, M.; Hasegawa, E.
4
.2.2.3. 10c. Brown oil; IR (Neat) 2900, 1636, 1594, 1212 cmꢁ1;
H NMR (270 MHz, CDCl 1.23–1.78 (m, 4H), 1.98–2.06 (m, 2H),
.12–2.22 (m, 2H), 2.91–3.04 (m, 2H), 3.44 (d, J¼10.0 Hz, 1H), 3.59
d, J¼10.3 Hz, 1H), 4.91–5.01 (m, 2H), 5.67–5.80 (m, 1H), 7.22–7.34
Tetrahedron Lett. 1996, 37, 3483–3486; (m) Bauld, N. L.; Yang, J. Tetrahedron
Lett. 1999, 40, 8519–8522; (n) Ciminale, F.; Lopez, L.; Farinola, G. M. Tetrahe-
dron Lett. 1999, 40, 7267–7270; (o) Gao, D.; Bauld, N. L. J. Org. Chem. 2000, 65,
1
3
) d
2
(
(
6
276–6277; (p) Gao, D.; Bauld, N. L. Tetrahedron Lett. 2000, 41, 5997–6000;
q) Bauld, N. L.; Roh, Y. Tetrahedron Lett. 2001, 42, 1437–1439; (r) Ciminale, F.;
Lopez, L.; Farinola, G. M.; Sportelli, S.; Nacci, A. Eur. J. Org. Chem. 2002, 3850–
854; (s) Meyer, S.; Koch, R.; Metzger, J. O. Angew. Chem., Int. Ed. 2003, 42,
700–4703; (t) Sperry, J. B.; Whitehead, C. R.; Ghiviriga, I.; Walczak, R. M.;
(
13
m, 2H), 7.45–7.51 (m, 1H), 8.02–8.05 (m, 1H); C NMR (68 MHz,
15.2, 22.9, 25.1, 33.0, 34.0, 34.1, 47.7, 114.9, 126.8, 128.0,
28.7, 131.2, 133.5, 138.0, 142.9, 197.6; LRMS (EI) m/z (relative in-
3
4
3
CDCl ) d
1
Wright, D. L. J. Org. Chem. 2004, 69, 3726–3734; (u) Gerken, J. B.; Wang, S. C.;
Preciado, A. B.; Park, Y. S.; Nishiguchi, G.; Tantillo, D. J.; Little, R. D. J. Org.
Chem. 2005, 70, 4598–4608; (v) Matsuo, Y.; Muramatsu, A.; Kamikawa, Y.;
Kato, T.; Nakamura, E. J. Am. Chem. Soc. 2006, 128, 9586–9587; (w) Iida, K.;
Yoshida, J. Macromolecules 2006, 39, 6420–6424.
þ
tensity) 354 (M , 1), 141 (100); HRMS (EI) calcd for C16
54.0481, found 354.0481.
H19IO
3
ꢂ
4.2.2.4. Deprotected alcohol of 1a. White solid; mp 82–85 C, IR
4. (a) Hasegawa, E.; Yamaguchi, N.; Muraoka, H.; Tsuchida, H. Org. Lett. 2007, 9,
811–2814; (b) Hasegawa, E.; Ogawa, Y.; Kakinuma, K.; Tsuchida, H.; Tosaka, E.;
ꢁ
1 1
2
(
KBr) 3212, 2916, 1448 cm
J¼5.7 Hz, 1H), 1.26 (d, J¼5.7 Hz, 1H), 1.41 (s, 3H), 1.53–1.65 (m, 1H),
.92–2.01 (m, 1H), 2.18 (br s, 1H), 2.43 (td, J¼6.4, 14.8 Hz, 1H), 2.59–
.67 (m, 1H), 7.03–7.15 (m, 2H), 7.22–7.28 (m, 1H), 7.70–7.73 (m, 1H);
;
H NMR (200 MHz, CDCl
3
)
d
0.87 (d,
Takizawa, S.; Muraoka, H.; Saikawa, T. Tetrahedron 2008, 64, 7724–7728. Related
oxidative ring-opening reactions of cyclopropanol derivatives; (c) DePuy, C. H.;
Van Laren, R. J. J. Org. Chem. 1974, 39, 3360–3365; (d) Ito, Y.; Fujii, S.; Saegusa, T.
J. Org. Chem. 1976, 41, 2073–2074; (e) Ryu, I.; Ando, M.; Ogawa, A.; Murai, S.;
Sonoda, N. J. Am. Chem. Soc. 1983, 105, 7192–7194; (f) Sheller, M. E.; Mathies, P.;
Petter, B.; Frei, B. Helv. Chim. Acta 1984, 67, 1748–1754; (g) Gassman, P. G.;
Burns, S. J. J. Org. Chem. 1988, 53, 5576–5578; (h) Paolobelli, A. B.; Gioacchini, F.;
Ruzziconi, R. Tetrahedron Lett. 1993, 34, 6333–6336; (i) Iwasawa, N.; Hayakawa,
S.; Funahashi, M.; Isobe, K.; Narasaka, K. Bull. Chem. Soc. Jpn. 1993, 66, 819–827;
1
2
13
C NMR (50 MHz, CDCl
3
) d 19.0, 22.0, 26.4, 26.6, 27.0, 58.4, 123.9,
1
25.3, 126.2, 128.0, 133.1, 140.7; LRMS (EI) m/z (relative intensity) 174
þ
(
M , 48), 118 (100); HRMS (EI) calcd for C12
H14O 174.1043, found
1
74.1045.
(j) Ryu, I.; Matsumoto, K.; Kameyama, Y.; Ando, M.; Kusumoto, N.; Ogawa, A.;
Kambe, N.; Murai, S.; Sonoda, N. J. Am. Chem. Soc. 1993, 115, 12330–12339; (k)
Booker-Milburn, K. I.; Thompson, D. F. J. Chem. Soc., Perkin Trans. 1 1995, 2315–
2321; (l) Kirihara, M.; Yokoyama, S.; Kakuda, H.; Momose, T. Tetrahedron 1998,
ꢂ
4
.2.2.5. Deprotected alcohol of 1b. White solid; mp 91–93 C; IR
ꢁ
1 1
(
KBr) 3236, 2912, 1436 cm ; H NMR (270 MHz, CDCl
J¼5.9 Hz, 1H), 1.27 (d, J¼5.9 Hz, 1H), 1.56–1.79 (m, 2H), 1.92–2.03
m, 2H), 2.20–2.44 (m, 3H), 2.47–2.71 (m, 1H), 4.95–5.10 (m, 2H),
.81–5.96 (m, 1H), 7.03–7.15 (m, 2H), 7.22–7.28 (m, 1H), 7.69–7.72
m, 1H); 13C NMR (68 MHz, CDCl
21.8, 23.4, 27.0, 30.4, 31.2, 32.4,
3
) d 0.88 (d,
54, 13943–13954; (m) Iwasawa, N.; Funahashi, M.; Hayakawa, S.; Ikeno, T.;
Narasaka, K. Bull. Chem. Soc. Jpn. 1999, 72, 85–97; (n) Highton, A.; Volpicelli, R.;
Simpkins, N. S. Tetrahedron Lett. 2004, 45, 6679–6683; (o) Rinderhagen, H.;
Mattay, J. Chem.dEur. J. 2004, 10, 851–874; (p) Waske, P. A.; Mattay, J. Tetra-
hedron 2005, 61, 10321–10330; (q) Rinderhagen, H.; Waske, P. A.; Mattay, J.
Tetrahedron 2006, 62, 6589–6593; (r) Chiba, S.; Cao, Z.; Bialy, S. A. A.; Narasaka,
K. Chem. Lett. 2006, 35, 18–19; (s) Jiao, J.; Nguyen, L. X.; Patterson, D. R.; Flowers,
R. A., II. Org. Lett. 2007, 9, 1323–1326; (t) Jida, M.; Guillot, R.; Ollivier, J. Tetra-
hedron Lett. 2008, 48, 8765–8767. Similar oxidative cyclopropane ring-opening
reactions of sulfides and amines were also reported: (u) Takemoto, Y.; Ohra, T.;
Koike, H.; Furuse, S.; Iwata, C.; Ohishi, H. J. Org. Chem. 1994, 59, 4727–4729; (v)
Lee, H. B.; Sung, M. J.; Blackstock, S. C.; Cha, J. K. J. Am. Chem. Soc. 2001, 123,
(
5
(
5
3
) d
8.7, 114.8, 123.8, 125.3, 126.2, 127.9, 132.9, 138.9, 140.8; LRMS (EI)
m/z (relative intensity) 214 (M , 10), 159 (100); HRMS (EI) calcd for
þ
15
C H18O 214.1358, found 214.1354.
Acknowledgements
1
1322–11324.
. (a) Park, Y. S.; Wang, S. C.; Tantillo, D. J.; Little, R. D. J. Org. Chem. 2007, 72, 4351–
357; (b) Park, Y. S.; Little, R. D. J. Org. Chem. 2008, 73, 6807–6815.
5
We thank Mr. Hiroyuki Tsuchida (Niigata University) for his
assistance with some experiments and useful discussion.
4
6. In situ generation method is general for radical anion reagents because they are
usually too reactive toward molecular oxygen to be isolated as salt forms. rep-
resentative references for radical anion reagents are as follows. Book Reagents for
Radical and Radical Ion Chemistry as a Volume of Handbook of Reagents for Organic
Synthesis; Crich, D., Ed.; John Wiley &b Sons: New York, NY, 2008; Review: Holy,
N. L. Chem. Rev. 1974, 74, 243–277; Article: Yang, A.; Butela, H.; Deng, K.; Dou-
bleday, M. D.; Cohen, T. Tetrahedron 2006, 62, 6526–6535; One novel example in
which amine radical cations generated by ferrocenium assisted the enolate oxi-
dationwas previously reported: Jahn, U.; Hartmann, P. J. Chem. Soc., PerkinTrans.1
2001, 2277–2282.
7. (a) Hasegawa, E.; Tsuchida, H.; Tamura, M. Chem. Lett. 2005, 34, 1688–1689; (b)
Tsuchida, H.; Tamura, M.; Hasegawa, E. J. Org. Chem. 2009, 74, 2467–2475.
8. (a) Ogawa, A.; Curran, D. P. J. Org. Chem. 1997, 62, 450–451; (b) Maul, J. J.;
Ostrowski, P. J.; Ublacker, G. A.; Linclau, B.; Curran, D. P. In Modern Solvents in
Organic Synthesis; Knochel, P., Ed.; Springer: Berlin, 1999; pp 79–105.
9. Hasegawa, E.; Hirose, H.; Sasaki, K.; Takizawa, S.; Seida, T.; Chiba, N. Hetero-
cycles 2009, 77, 1147–1161.
References and notes
1
. (a) Eberson, L. Electron Transfer Reactions in Organic Chemistry; Springer: Berlin,
987; (b) Photoinduced Electron Transfer; Fox, M. A., Chanon, M., Eds.; Elsevier:
Amsterdam, 1988; Parts A–D; (c) Kavarnos, G. J. Fundamental of Photoinduced
Electron Transfer; VCH: New York, NY, 1993; (d) Advances in Electron Transfer
Chemistry; Mariano, P. S., Ed.; JAI: Greenwich, 1991–1999; Vols. 1–6; (e) Electron
Transfer in Chemistry; Balzani, V., Ed.; Wiley-VCH: Weinheim, 2001; Vols. 1–5;
f) Organic Electrochemistry, 4th ed.; Lund, H., Hammerich, O., Eds.; Marcel
Dekker: New York, NY, 2001; (g) CRC Handbook of Organic Photochemistry and
Photobiology, 2nd ed.; Horspool, W. M., Lenci, F., Eds.; CRC: Boca Raton, 2004;
h) Tetrahedron Symposiumdin Print. The Chemistry of Radical Ions; Floreancig,
P. E., Ed.; 2006; Vol. 62; (i) Todres, Z. V. Ion-Radical Organic Chemistry Principles
and Applications, 2nd ed.; CRC: Boca Raton, 2009.
1
(
(
2
. (a) Schmittel, M.; Burghart, A. Angew. Chem., Int. Ed. 1997, 36, 2550–2589; (b)
Berger, D. J.; Tanko, J. M. In The Chemistry of Double-Bonded Functional Groups;
10. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice; Oxford
University Press: Oxford, 1998.

E. Hasegawa et al. / Tetrahedron 65 (2009) 10876–10881
10881
1
1. When the crude reaction mixture was treated with aqueous NaHCO
of 2b raised to 38%. It was also found that reaction of 1b in the presence of
CO resulted in increasing the yield of 2 (37%). The origin of these base effects
is not clear at this moment.
2. Representative examples of SbCl
Ledwith, A.; White, A. C.; Woods, H. J. J. Chem. Soc. B 1970, 227–231; (b) Kamata,
M.; Otogawa, H.; Hasegawa, E. Tetrahedron Lett. 1991, 32, 7421–7424; (c) Ci-
minale, F.; Lopez, L.; Farinora, G. M.; Sportelli, S. Tetrahedron Lett. 2001, 42,
3
, the yield
16. Reaction of 6 with molecular oxygen, although the reaction was carried out
under nitrogen atmosphere, would be another source of 3-OH. Related refer-
ence: Kirihara, M.; Kakuda, H.; Ichinose, M.; Ochiai, Y.; Takizawa, S.;
Mokuya, A.; Okubo, K.; Hatano, A.; Shiro, M. Tetrahedron 2005, 61, 4831–4839
At this moment, it is difficult to specify the responsible reaction process to
produce 3-OH.
K
2
3
1
5
promoted SET reactions: (a) Cowell, G. W.;
17. Bell, F. A.; Ledwith, A.; Sherrington, D. C. J. Chem. Soc. C 1969, 2719–2720.
18. This observation also suggests that in situ generated SbCl
the transformation of 1b to 3b-Cl in SbCl salt reagent promoted reaction (see
Scheme 1). Since SbCl can also lead to Lewis acid promoted reactions, the
observation might be related to the Lewis acidic role of SbCl
19. Although one may consider the competitive SET of 1 and (p-BrC
SET with (p-BrC
N4 should be more efficient than that with 1 based on their
oxidation potentials.
20. When 1b was reacted with AgClO
tatively to give the alcohol. Reaction of 1b with I
1a with I in THF giving 10a (91%) was also reported in our previous paper.
5
is not responsible for
5685–5687.
6
13. Although a reasonable explanation for the formation of 4 is currently un-
5
available, basic conditions are known to often lead to same ring-opening re-
gioselectivity of bicyclic cyclopropanol derivatives: Kulinkovich, O. G. Chem.
5
.
6 4 3 5
H ) N to SbCl ,
Rev. 2003, 103, 2597–2632. Notably, when 1b was treated with nBu
mixed solvent of MeCN and THF, 4b was obtained (75%).
4
NF in the
6 4 3
H )
1
1
4. Oxidation potentials (Eox1/2 V vs. SCE) of 1 were reported to be þ1.53, þ1.36, þ1.
4
in CH
2
Cl
2
, deprotection took place quanti-
gave 10b (25%). Reaction of
4
a
3
6, and þ1.80 for 1a, 1b, 1c, and 1d, respectively. Therefore, SET from 1 to
2
ꢀþ
7b
(p-BrC
H
6 4
)
3
N
is estimated to be endergonic on the basis of the oxidation
2
15
potential of the amine (þ1.05 V vs. SCE). This thermodynamic disadvantage
Relatively low yield of 10b might be due to the possibility of reaction of I
2
with
would be overcome by the irreversible post-SET process, such as nucleophile
olefin moiety of 1b.
ꢀ
þ 4a,b,7
.
assisted desilylation of 1
5. Mann, C. K.; Barnes, K. K. Electrochemical Reactions in Nonaqueous Systems;
Marcel Dekker: New York, NY, 1970.
21. Iwaya, K.; Tamura, M.; Nakamura, M.; Hasegawa, E. Tetrahedron Lett. 2003, 44,
9317–9320.
22. General procedure, see Ref. 4b.
1