Radical 3-exo-tet cyclization of 1,3-dihalopropanes with SmI2 to form cyclopropanes

Article abstract of DOI:10.1016/j.tet.2008.05.081

The preparation of 1,1-disubstituted and monosubstituted cyclopropanes from corresponding 2,2-disubstituted and 2-monosubstituted 1,3-dihalopropanes, respectively, with SmI₂ in THF was efficiently carried out. The reaction mechanism was propose

Full text of DOI:10.1016/j.tet.2008.05.081

Tetrahedron 64 (2008) 7247–7251
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Radical 3-exo-tet cyclization of 1,3-dihalopropanes with SmI2 to form
cyclopropanes
*
Tsuyoshi Ohkita, Yuhsuke Tsuchiya, Hideo Togo
Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The preparation of 1,1-disubstituted and monosubstituted cyclopropanes from corresponding 2,2-di-
substituted and 2-monosubstituted 1,3-dihalopropanes, respectively, with SmI2 in THF was efficiently
carried out. The reaction mechanism was proposed to proceed in a radical 3-exo-tet manner based on
Baldwin’s rule.
Received 17 March 2008
Received in revised form 16 May 2008
Accepted 16 May 2008
Available online 21 May 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Radical
3-exo-tet
Samariun diiodide
Cyclopropane
1,3-Dihalopropane
1. Introduction
because of ring strain8 and carbon-centered radicals are generally
nucleophilic and therefore require electron-deficient olefinic
The cyclopropane ring is highly strained; nevertheless, a wide
variety of naturally occurring cyclopropane derivatives bearing
potent biological activities are known.1 Seaweed pheromones,
hormosirene and dictyopterene, are examples of hydrocarbons
containing cyclopropane and olefinic groups.1b Therefore, synthetic
study of the cyclopropane ring is still very important. Formation of
cyclopropanes with olefinic groups has been accomplished
with free carbene derived from haloform under basic conditions,2
diazo-olefins with Rh, Cu, or Co catalyst,3 Ti(IV)-mediated cyclo-
propanation,4 the Simmons–Smith reactions,5 and others.6 These
cyclopropanation reactions proceed efficiently, particularly those
that employ diazo-olefins with Rh or Cu catalyst and the Simmons–
Smith reaction. However, in general, electron-rich olefins are re-
quired, because these reactions proceed in an electrophilic manner.
On the other hand, the preparation of cyclopropanes via a radical
pathway is interesting and challenging. Examples of the radical
formation of cyclopropanes include radical 3-exo-trig cyclization
(favored), radical 3-exo-tet cyclization (favored), and radical 3-exo-
dig cyclization (disfavored), based on Baldwin’s rule,7 although
studies are limited. Among them, a few reports on radical 3-exo-trig
cyclization are available. In this cyclization, generally, cyclo-
propylmethyl radicals formed are thermodynamically disfavored
groups.9 Thus, for the typical radical reaction system, methyl 5-
bromo-4,4-dimethoxy-2-pentenoate was treated with Bu3SnH and
AIBN in refluxing benzene. However, the expected cyclopropane
derivative was not formed10 because ring-opening reaction of the
formed cyclopropylmethyl radical occurred rapidly. On the other
hand, electrochemical reductive cyclization of ethyl-5-meth-
anesulfonyloxy-4,4-dimethyl-2-pentenoate was efficiently carried
out to form corresponding cyclopropane.11 Photolysis of 2-
substituted butyrophenones gave corresponding cyclopropyl
phenyl ketones through a Norrish II type pathway.12 As examples of
metal-induced radical 3-exo-trig cyclization, the formation of
11
transfer (SET) reduction of 9
bearing a -bromo- -unsaturated ketone group, with chromous
acetate was reported,13 and treatment of
-iodo- and -bromo-a,b-
b-hydroxy-5,9-cyclopregnane-3,20-dione by single electron
a
-bromo-11 -hydroxyprogesterone
b
d
a,b
d
d
unsaturated esters with SmI2 in the presence of tert-butyl alcohol in
THF gave corresponding cyclopropanes.14 The same treatment of
g,g-disubstituted d-oxo-a,b-unsaturated esters with SmI2 in the
presence of tert-butyl alcohol in THF provided corresponding
cyclopropanols via ketyl radicals.15 Among these cyclopropanation
methods, the SmI2-mediated radical 3-exo-trig cyclization to
cyclopropanes is the most effective and practical. To the best of our
knowledge, studies of radical 3-exo-tet cyclization of 1,3-dihalo-
propanes are extremely limited. 1,3-Dihalopropanes, mainly
1,3-diiodopropane derivatives, can be reductively cyclized to cy-
clopropanes by metal reduction, such as Na,16a–c halogen–metal
* Corresponding author.
E-mail address: togo@faculty.chiba-u.jp (H. Togo).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.05.081

7248
T. Ohkita et al. / Tetrahedron 64 (2008) 7247–7251
exchange, such as t-BuLi,17 and metal hydride reduction, such as
LiAlH4,16b,c and it is proposed that some of these reactions proceed
through a radical pathway. Treatment of 1,3-diiodopropane with
benzoyl peroxide at 110 ꢀC gave cyclopropane in quite good yield.18
Treatment of 2,2-disubstituted 1,3-diiodopropane with Bu3SnH in
refluxing benzene gave corresponding cyclopropane in good
yield.16c As a related reaction, the formation of substituted cyclo-
propanes from the reaction of 2-substituted 1,3-diiodopropanes
with (C6F13CH2CH2)3SnH or Ph3SnH and AIBN under highly diluted
conditions through homolytic cyclization of intermediate 3-iodo-
propyl radicals in a radical 3-exo-tet manner was reported, and
Table 2
Preparation of cyclopropanes from 1,3-dibromopropanes with SmI2
R
R
Br
Br
R
SmI2 (5.5 eq.)
THF, 70 °C, 3 h
R
Entry
Yielda (%)
5 (90)c
87
R
R
R
Br
Br
1b
2
radical cyclization proceeded in the range of 5ꢁ105 sꢂ119
.
3
80
CH3
CH3O
Cl
These results suggest that radical 3-exo-tet cyclization may
proceed efficiently according to Baldwin’s rule where 3-exo-tet
cyclization is favored.7 Recently, we reported the simple and effi-
cient preparation of disubstituted and monosubstituted cyclopro-
panes from corresponding 1,3-dihalopropanes with zinc powder in
refluxing ethanol.20 However, the reactivity of 1,3-dichloro-
propanes was extremely poor and the reaction mechanism remains
unknown. Here, as part of our study of environmentally benign
organic synthesis using radical reactions,21 we would like to report
an efficient and simple SmI2-mediated radical 3-exo-tet cyclization
of 2,2-disubstituted and 2-monosubstituted 1,3-dihalopropanes to
provide the corresponding cyclopropanes in THF, instead of typical,
but toxic radical reagent Bu3SnH.
4
82
5
80 (4)c
6
7
82
9
Br
Br
52 (4)c
90
Cl
R
8
9
a
Isolated yield.
Reaction was carried out at rt.
Yield of recovered starting material.
b
c
2. Results and discussion
Then, 2,2-disubstituted and 2-monosubstituted 1,3-dibromo-
When 2,2-dibenzyl-1,3-diiodopropane was treated with SmI2
(2.5 equiv), an excellent SET reagent,22 in THF at room temperature,
the deep blue color faded away after 2 h to provide 1,1-dibenzylcy-
clopropane in 99% yield, as shown inTable 1 (entry 1). Based on these
results, 2,2-di(arylmethyl)-1,3-diiodopropanes bearing p-methyl,
p-methoxy, and p-chloro groups were successfully cyclized to give
corresponding 1,1-di(arylmethyl)cyclopropanes in good yields (en-
tries 2–4). 2-Monoarylmethyl-1,3-diiodopropane could be also
converted into corresponding cyclopropane in good yield under the
same conditions (entry 7). However, the reactivity of 2,2-dialkyl
substituted 1,3-diiodopropane was decreased (entry 5). Thus, the
reaction was carried out under THF refluxing conditions (3 h) to give
corresponding cyclopropane in good yield (entry 6).
propanes were treated with SmI2 (5.5 equiv) in THF at room tem-
perature. However, the reaction did not proceed despite use of
excess SmI2, as shown in Table 2 (entry 1), and the starting material
was recovered. Therefore, the reaction was carried out under THF
refluxing conditions for 3 h to provide corresponding 1,1-di-
substituted and monosubstituted cyclopropanes in good yields, as
shown in Table 2 (entries 2–8).
The reactivity of 2,2-disubstituted and 2-monosubstituted 1,3-
dichloropropanes was decreased. Thus, corresponding cyclopro-
panes were obtained in moderate yields (50–70%), together with
the starting material, even if the reactions were carried out in THF
under refluxing temperature for 48 h, as shown in Table 3.
From these results, the cyclization of 2,2-disubstituted and
2-monosubstituted 1,3-dihalopropanes to corresponding cyclo-
propanes with SmI2 is useful and practical, especially for 2,2-
Table 1
Preparation of cyclopropanes from 1,3-diiodopropanes with SmI2
R
R
I
R
R
SmI2 (2.5 eq.)
THF, r.t. 3 h
I
Table 3
Entry
Yielda (%)
R
Preparation of cyclopropanes from 1,3-dichrolopropanes with SmI2
R
R
Cl
Cl
R
R
R
R
I
I
SmI2 (5.5 eq.)
THF, 70 °C, 48 h
1
99
2
93
CH3
CH3O
Cl
Entry
Yielda (%)
69 (19)b
49 (34)b
23 (59)b
71
R
3
98
R
R
Cl
Cl
1
2
3
4
4
98
CH3
CH3O
Cl
5
57 (23)b
84
9
6c
9
I
I
7
70 (25)b
Cl
Cl
Cl
60 (15)b
R
5
Cl
R
a
Isolated yield.
b
c
a
Yield of recovered starting material.
Reaction was carried out at 70 ꢀC for 3 h with SmI2 (5.5 equiv).
Isolated yield.
b
Yield of recovered starting material.

T. Ohkita et al. / Tetrahedron 64 (2008) 7247–7251
7249
Table 4
results, we propose that the present cyclization reaction of 2,2-di-
substituted and 2-monosubstituted 1,3-dihalopropane with SmI2
proceeds in a radical 3-exo-tet manner, as shown in Scheme 1. Thus,
SET from SmI2 to 1,3-dihalopropane occurs to form corresponding
Evidence of radical 3-exo-tet reaction mechanism with SmI2
Ph
Ph
Ph
Ph
I
SmI2 (2.5 eq.)
THF (5 ml), additive (0.1 ml)
r.t. 3 h
R
anion radical (a), followed by a-cleavage to provide 3-halopropyl
radical (b). Then, radical 3-exo-tet cyclization of 3-halopropyl radical
(b) occurs to form the corresponding cyclopropane.
Entry
1
R
Additive
H2O
Yielda (%)
27 (71)b
R
R
X
X
R
R
I
I
SmI2
2
3
4
5
D2O
19 (63)b
X = I, Br, Cl
None
D2O
13 (73)b (14)c
2 (52)b (23)c
7 (21)b (65)d
CH3
CH3
S
S
e-
None
Se
Se
6e
None
28 (59)d
•
radical
3-exo-tet
R
X
a
Isolated yield.
Yield of recovered starting material.
Yield of reductive product A.
Yield of reductive product B.
Reaction was carried out at 70 ꢀC.
R
b
c
X
X
(a)
d
e
SmI2
X•
SmXI2
A:
B:
Ph
CH3
S
X
Ph
Ph
CH3
Se
CH3
Ph
e-
•
:
R
R
R
R
disubstituted and 2-monosubstituted 1,3-diiodopropanes and
1,3-dibromopropanes.
X
X
(b)
To clarify the reaction mechanism, the following experiments
were carried out. When 2,2-dibenzyl-1,3-diiodopropane was treated
with SmI2 (2.5 equiv) in THF containing H2O (0.1 ml) at room
temperature, 1,1-dibenzylcyclopropane was obtained in 27% yield,
together with the staring material in 71% yield. Here, 2,2-dibenzyl-1-
iodopropane and 2,2-dibenzylpropane, which could be formed by
reacting of corresponding carbanions with H2O, were not observed at
all, as shown in Table 4 (entry 1), although the reactivity was mark-
edly decreased. Similarly, when 2,2-dibenzyl-1,3-diiodopropane was
treated with SmI2 (2.5 equiv) in THF containing D2O (0.1 ml) at room
temperature, 1,1-dibenzylcyclopropane was obtained in 19% yield,
together with the starting material in 63% yield. Here again, 2,2-
dibenzyl-1-iodopropane-3d and 2,2-dibenzylpropane-1d,3d were
not formed at all (entry2). These results suggest that the carbanion
species, i.e., anion 3-exo-tet cyclization does not occur to form cy-
clopropanes. Today, it is well known that aryl chalcogenides (ArS and
ArSe groups) are a good radical leaving group having high radi-
cophilicity, similar to iodine and bromine atoms, especially for aryl
selenide.21c Thus, 2,2-dibenzyl-3-(40-methylphenylthio)-1-iodopro-
pane and 2,2-dibenzyl-3-phenylseleno-1-iodopropane were treated
with SmI2 (2.5 equiv) in THF at room temperature and warming
conditions, respectively, to give 1,1-dibenzylcyclopropane, the start-
ing material, and 2,2-dibenzylpropyl 40-methylphenyl sulfide and
2,2-dibenzylpropyl phenyl selenide, respectively, as shown inTable 4
(entries 3, 5, and 6), although the reactivity was lower than that of
2,2-dibenzyl-1,3-diiodopropane. However, 1,1-dibenzylcyclopro-
pane was formed even at room temperature, and the yield was in-
creased in THF under warming conditions (entry 6). It is well known
that the radicophilicity of the phenylseleno group is higher than that
of the phenylthio group.21c When the reaction of 2,2-dibenzyl-3-(40-
methylphenylthio)-1-iodopropane with SmI2 (2.5 equiv) was carried
out in THF containing D2O (0.1 ml), again 2,2-dibenzyl-3d-propyl 40-
methylphenyl sulfide was not formed at all (entry 4). Based on these
Scheme 1.
As an another mechanism, formation of propan-1,3-biradical
intermediate via simultaneous double-SET from 2 equiv of SmI2,
followed by its intramolecular radical coupling pathway can be also
proposed. However, in view of high reactivity of carbon-centered
radicals9 and rapid radical 3-exo-tet cyclization rate,19 we believe
the present cyclization of 2,2-disubstituted and 2-monosubstituted
1,3-dihalopropanes to corresponding cyclopropanes proceeds via
radical 3-exo-tet manner.
3. Conclusions
SmI2-mediated cyclopropanation of 2,2-disubstituted and
2-monosubstituted 1,3-dihalopropanes in THF was successfully
carried out in high yields, especially for 2,2-disubstituted and 2-
monosubstituted 1,3-diiodopropanes and 1,3-dibromopropanes.
The cyclization mechanism was proposed to proceed in a radical
3-exo-tet manner based on Baldwin’s rule. The present cyclization
with SmI2 is another simple, practical, and environmentally benign
method for the preparation of 1,1-disubstituted and mono-
substituted cyclopropanes from corresponding 2,2-disubstituted
and 2-monosubstituted 1,3-dihalopropanes.
4. Experimental section
4.1. General
1H NMR and 13C NMR spectra were obtained with JEOL-JNM-
GSX-400, JEOL-JNM-LA-400, and JEOL-JNM-LA-500 spectrometers.
Chemical shifts are expressed in parts per million downfield from
d units. Mass spectra were recorded on JEOL-HX-110 and
JEOL-JMS-ATII15 spectrometers. IR spectra were measured with
a JASCO FT/IR-200 spectrometer. Melting points were determined
TMS in

7250
T. Ohkita et al. / Tetrahedron 64 (2008) 7247–7251
with a Yamato Melting Point Apparatus Model MP-21. Silica gel 60
(Kanto Kagaku Co.) was used for column chromatography, and
Wakogel B-5F was used for preparative TLC. Sm powder was
obtained from commercially available ingot (Aldrich).
4.3.1. 1,1-Dibenzylcyclopropane
Oil; IR (neat) 3030, 2920, 1500, 1460, 1020, 760, 700 cmꢂ1 1H
;
NMR (400 MHz, CDCl3)
d
¼7.31–7.25 (4H, m), 7.24–7.16 (6H, m), 2.56
(4H, s), 0.52 (4H, s); 13C NMR (100 MHz, CDCl3)
d¼140.1 (q), 129.5
(t), 128.0 (t), 126.0 (t), 41.5 (s), 20.8 (q), 10.7 (s); MS (FAB): m/z 222;
HRMS (EI) found: 222.1422 m/z, calcd for C17H18: Mþ¼222.1409.
4.2. General procedure for preparation of 2,2-disubstituted
1,3-dihalopropanes
4.3.2. 1,1-Bis(p-methylbenzyl)cyclopropane
Oil; IR (neat) 3000, 2920, 1520, 1020, 810 cmꢂ1 1H NMR
;
NaH (60% purity, 3 mmol) was added to a solution of dimethyl
malonate (1 mmol) in DMF (15 ml) at 0 ꢀC. Then, benzylic bromide
or alkyl bromide (3 mmol) was added and the obtained mixture
was stirred at 70 ꢀC for 1 h under argon atmosphere. The reaction
mixture was quenched by the addition of water (5 ml) and was
extracted with ether (20 mlꢁ5). Ether extract was dried over
Na2SO4 and filtered. After removal of the solvent, the residue was
(400 MHz, CDCl3)
d
¼7.08 (8H, d, J¼1.7 Hz), 2.51 (4H, s), 2.33 (6H, s),
0.48 (4H, s); 13C NMR (100 MHz, CDCl3)
d¼137.0 (q), 135.3 (q), 129.4
(t), 128.7 (t), 41.1 (s), 21.0 (p), 20.9 (q), 10.6 (s); MS (FAB): m/z 250;
HRMS (EI) found: 250.1734 m/z, calcd for C19H22: Mþ¼250.1722.
4.3.3. 1,1-Bis(p-methoxybenzyl)cyclopropane
Oil; IR (neat) 2910, 2840, 1610, 1510, 1250, 1180, 1040, 820 cmꢂ1
;
purified by column chromatography on silica gel to provide
disubstituted dimethyl malonate (85–90% yields).
a,a-
1H NMR (400 MHz, CDCl3)
d
¼7.09 (4H, d, J¼8.7 Hz), 6.83 (4H, d,
J¼8.7 Hz), 3.80 (6H, s), 2.49 (4H, s), 0.47 (4H, s); 13C NMR (100 MHz,
LiAlH4 (1.3 mmol) was added to a solution of a,a-disubstituted
CDCl3)
d
¼157.8 (q), 132.2 (q), 130.3 (t), 113.5 (t), 55.2 (p), 40.6 (s),
dimethyl malonate (1 mmol) in THF (10 ml) at 0 ꢀC. After stirring
for 1.5 h under THF refluxing conditions, the reaction mixture was
quenched by the addition of water (5 ml) at 0 ꢀC, and was extracted
with ether (20 mlꢁ3). Ether extract was dried over Na2SO4 and
filtered. After removal of the solvent, the residue was purified by
column chromatography on silica gel to provide 2,2-disubstituted
1,3-propanediol (91–96% yields).
21.1 (q), 10.5 (s); MS (FAB): m/z 283; HRMS (FAB) found: 282.1620
m/z, calcd for C19H22O2: MþH¼282.1620.
4.3.4. 1,1-Bis(p-chlorobenzyl)cyclopropane
Oil; IR (neat) 2920, 1490, 1400, 1070, 1010, 800 cmꢂ1 1H NMR
;
(400 MHz, CDCl3)
d
¼7.24 (4H, d, J¼8.4 Hz), 7.07 (4H, d, J¼8.4 Hz),
2.48 (4H, s), 0.53 (4H, s); 13C NMR (100 MHz, CDCl3)
d¼138.2
To a solution of 2,2-disubstituted 1,3-propanediol (1 mmol) in
THF (15 ml) were added I2 (3 mmol), triphenylphosphine (3 mmol),
and imidazole (4 mmol) under argon atmosphere. The obtained
mixture was stirred for 24 h under refluxing conditions. Then, the
reaction mixture was quenched by the addition of satd aq Na2SO3
(3–5 ml) and was extracted with ether (20 mlꢁ3). Ether extract was
dried over Na2SO4 and filtered. After removal of the solvent, the
residue was purified by column chromatography on silica gel to
give 2,2-disubstituted 1,3-diiodopropane (92–96% yields).
To a solution of 2,2-disubstituted 1,3-propanediol (1 mmol) in
THF (15 ml) were added CBr4 (2.5 mmol) and triphenylphosphine
(3 mmol) under argon atmosphere. The obtained mixture was
stirred for 24 h under refluxing conditions. Then, the reaction
mixture was quenched by the addition of water (5 ml) and was
extracted with ether (20 mlꢁ3). Ether extract was dried over
Na2SO4 and filtered. After removal of the solvent, the residue was
purified by column chromatography on silica gel to give 2,2-di-
substituted 1,3-dibromopropane (86–95% yields).
(q), 131.8 (q), 130.6 (t), 128.2 (t), 40.8 (s), 20.6 (q), 10.8 (s); MS (FAB):
m/z 290; HRMS (FAB) found: 290.0627 m/z, calcd for:
MþH¼290.0629.
4.3.5. 1,1-Didodecylcyclopropane
Oil; IR (neat) cmꢂ1
;
1H NMR (400 MHz, CDCl3)
d¼3.19 (4H, s),
1.43–1.10 (44H, m), 0.88 (6H, t, J¼6.9 Hz); 13C NMR (100 MHz,
CDCl3)
d
¼36.0 (s), 31.9 (s), 29.9 (s), 29.6 (s), 29.4 (s), 26.6 (s), 22.7 (s),
19.2 (q), 14.1 (p), 11.9 (s); MS (FAB): m/z 378; HRMS (EI) found:
378.4230 m/z, calcd for: Mþ¼378.4226.
4.3.6. p-Chlorobenzylcyclopropane
Oil; IR (neat) 3080, 3000, 1490, 1070, 1010, 820 cmꢂ1 1H NMR
;
(400 MHz, CDCl3)
d
¼7.24 (2H, d), 7.18 (2H, d), 2.51 (2H, d), 0.53 (1H,
m), 0.19 (4H, d); 13C NMR (100 MHz, CDCl3)
d
¼140.5 (q), 132.6 (q),
129.6 (t),128.3 (t), 39.6 (s), 11.7 (t), 4.6 (s); MS (FAB): m/z 210; HRMS
(EI) found: 166.0551 m/z, calcd for C10H11Cl: Mþ¼166.0549.
To a solution of 2,2-disubstituted 1,3-propanediol (1 mmol) in
CCl4 (15 ml) was added triphenylphosphine (3 mmol) under argon
atmosphere. The obtained mixture was stirred for 24 h under
refluxing conditions. Then, the reaction mixture was quenched by
the addition of water (5 ml) and was extracted with ether (20 mlꢁ3).
Ether extract was dried over Na2SO4 and filtered. After removal of the
solvent, theresiduewaspurifiedbycolumnchromatographyonsilica
gel to give 2,2-disubstituted 1,3-dichloropropane (85–90% yields).
4.3.7. Dodecylcyclopropane
Oil; IR (neat) 2920, 2850, 1460, 1020, 820, 720 cmꢂ1 1H NMR
;
(400 MHz, CDCl3)
d
¼1.45–1.20 (20H, m), 1.19 (2H, dt, J¼7.3, 7.0 Hz),
0.89 (3H, t, J¼6.9 Hz), 0.72–0.60 (1H, m), 0.39 (2H, ddd, J¼8.1, 5.5,
4.1 Hz), ꢂ0.01 (2H, dt, J¼5.5, 4.1 Hz); 13C NMR (100 MHz, CDCl3)
d¼34.8 (s), 31.9 (s), 29.67 (s), 29.64 (s), 29.5 (s), 29.3 (s), 22.7 (s),14.1
(p), 10.9 (t), 4.3 (s); MS (EI): m/z 210; HRMS (EI) found: 210.2361
m/z, calcd for C15H30: Mþ¼210.2348.
4.3. General procedure for SmI2-mediated cyclopropanation
of 1,3-diiodopropanes
4.3.8. 2,2-Dibenzy-3-iodopropyl 40-methylphenyl sulfide
Oil; IR (neat) cmꢂ1; 1H NMR (400 MHz, CDCl3)
d
¼7.52–7.40 (4H,
m), 7.30–7.18 (8H, m), 7,09–7.05 (2H, m), 3.11 (2H, s), 2.94 (4H, s),
2.80 (2H, s), 2.31 (3H, s); 13C NMR (100 MHz, CDCl3)
All reactions were carried out under argon atmosphere. THF was
dried and freshly distilled over sodium/benzophenone system. 1,3-
Diiodopropane(1 mmol)wasaddedtoasolutionofSmI2 (2.5mml)in
THF (5 ml), which was prepared from the reaction of Sm (2.5 mmol)
with 1,2-diiodoethane (2.5 mmol) in THF. After 3 h at room tem-
perature, the reaction mixture was quenched by the additions of H2O
(0.1 ml), and was extracted with ether (20 mlꢁ3). The ether extract
was dried over Na2SO4 and filtered. After removal of the solvent, the
residue was purified by preparative TLC or column chromatography
on silica gel to provide 1,1-dibenzylcyclopropane in 99% yield.
d¼34.8 (s), 31.9
(s), 29.67 (s), 29.64 (s), 29.5 (s), 29.3 (s), 22.7 (s), 14.1 (p), 10.9 (t), 4.3
(s); MS (EI): m/z 472; HRMS (EI) found: 472.0730 m/z, calcd for:
Mþ¼472.0722.
Acknowledgements
Financial support from a Grant-in-Aid for Scientific Research on
Priority Area (18045008) by the Ministry of Education, Science,
Sports, and Culture is gratefully acknowledged.

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