A novel photoinduced reduction system of low-valent samarium species: Reduction of organic halides and chalcogenides, and its application to carbonylation with carbon monoxide

Article abstract of DOI:10.1016/j.tet.2003.08.070

Visible light irradiation is found to enhance the reducing ability of samarium diiodide (SmI₂) dramatically. Organic halides (RCl, RBr, RI) and chalcogenides (RSPh, RSePh, RTePh) are smoothly reduced to the corresponding hydrocarbons by using this SmI₂-hv system. The photoactivation can be also applied to ytterbium diiodide (YbI₂) successfully. When the reduction of alkyl chlorides (RCl) by using the SmI ₂-hv system is conducted under the pressure of carbon monoxide, unsymmetric ketones (RC(O)CH₂R) are obtained as carbonylating products. A mechanistic pathway may involve the formation of acylsamarium species (RC(O)SmI₂), which undergo dimerization, followed by reduction with SmI₂, leading to the unsymmetric ketones.

Full text of DOI:10.1016/j.tet.2003.08.070

Tetrahedron 59 (2003) 10499–10508
A novel photoinduced reduction system of low-valent samarium
species: reduction of organic halides and chalcogenides, and its
application to carbonylation with carbon monoxide
a
Yukihito Sumino, Nami Harato, Yuri Tomisaka and Akiya Ogawa
b
b
b,*
a
Bulk Chemicals Process R & D Department Manufacturing Technology R & D Laboratories, Shionogi & Co., Ltd., 1-3, Kuise,
Terajima 2-chome, Amagasaki, Hyogo 660-0813, Japan
Department of Chemistry, Faculty of Science, Nara Women’s University, Kitauoyanishi-machi, Nara 630-8506, Japan
b
Received 7 May 2003; accepted 22 August 2003
Abstract—Visible light irradiation is found to enhance the reducing ability of samarium diiodide (SmI
RBr, RI) and chalcogenides (RSPh, RSePh, RTePh) are smoothly reduced to the corresponding hydrocarbons by using this SmI
The photoactivation can be also applied to ytterbium diiodide (YbI ) successfully. When the reduction of alkyl chlorides (RCl) by using the
2
) dramatically. Organic halides (RCl,
2
–hv system.
2
SmI –hv system is conducted under the pressure of carbon monoxide, unsymmetric ketones (RC(O)CH R) are obtained as carbonylating
2
2
products. A mechanistic pathway may involve the formation of acylsamarium species (RC(O)SmI
2
), which undergo dimerization, followed
2
by reduction with SmI , leading to the unsymmetric ketones.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
The mechanism of electron transfer by SmI2 can be
1
explained by inner-sphere and/or outer-sphere processes.
4
Samarium diiodide (SmI ) is widely employed as a useful
2
reducing agent in organic synthesis, because of its
suitable solubility in organic solvent such as THF and
appropriate reducing ability. SmI itself acts as a useful
2
single-electron-transfer reagent for various synthetic reac-
tions, for example, C–C bond formation reactions such as
The reduction of haloalkanes takes place through the outer-
sphere process, whereas the reduction of carbonyl com-
pounds proceeds via the inner-sphere process. In the
presence of HMPA, the outer-sphere process is accelerated
because of the bulkiness of HMPA. On the other hand,
lithium halides are reported to accelerate effectively the
1
,2
3
,4
5
14
Barbier reaction,
6
Reformatsky-type reaction, pinacol
7
inner-sphere electron transfer process.
coupling, ketyl radical-olefin coupling, and medium-size
b,8
5
15
ring formation.
mild conditions, SmI is also available for the synthesis of
Since these reactions proceed under
Besides HMPA, it is known that the use of alcohol,
1
6
7a,17,18
19
amine, acid or base,
and water as cosolvents
increases the reducing ability of SmI . Moreover, the
2
9
10
natural products like taxol analogues, nonadolides, and
1
2
20
1
b-lactams. As can be seen from these synthetic reactions,
SmI itself can reduce several functional groups, such as
addition of metal reagents like Sm metal, other lanthanoid
2
1
7a,12,22
23,24
metals, FeCl , Fe(acac) , Fe(DBM) ,
NiI2,
Pd deriva-
tives, Zn–Hg, and Mischmetal are also employed with
2
3
3
3
2
5
26
4a,27
aldehydes, ketones, alkyl bromides or iodides, a,b-unsatu-
1
CrCl3, Co derivatives, Cu derivatives,
2
28
29
30
rated carbonyl compounds, and epoxides. However, the
reduction with SmI alone often requires long period of
SmI . Some electrochemical data are reported for these
2
2
1
4,31
heating and stirring. Thus, some additives are utilized to
enhance the reducing ability of SmI . In particular, HMPA
SmI -additive systems,
which indicate the relative
reducing abilities of these SmI -based reduction systems.
2
2
2
(
reagent. Indeed, the reducing ability of SmI is dramati-
hexamethylphosphoramide) is the most effective activating
1
3
Although these SmI -based reduction systems involve
2
2
cally increased in the presence of HMPA, compared with
the SmI single system (SmI /THF).
electron-transfer process from the ground-state of low-
valent samarium species, we have recently developed a
novel photoinduced reduction system with SmI . In
2
2
2
this photoinduced system of SmI (SmI –hv), alkyl
2
2
7
b,32–34
35
chlorides, selenides, and tosylates are reduced to
the corresponding alkanes effectively through the powerful
Keywords: samarium; photoinduced reduction; carbon monoxide;
carbonylation; dechlorination; deselenation.
*
Corresponding author. Tel./fax: þ81-742-20-3979;
electron-transfer process from an excited state of SmI . In
2
addition, the photoinduced carbonylation takes place when
e-mail: a.ogawa@cc.nara-wu.ac.jp
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2003.08.070

10500
Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
the visible light-irradiated reduction of chloroalkanes with
SmI is conducted under the pressure of carbon monoxide.
2
In addition to SmI , the corresponding ytterbium reagent
2
3
6
(YbI2) is also activated by photoirradiation. Herein we
wish to report full details of the photoinduced reduction and
reductive carbonylation with SmI and some mechanistic
2
insight into this carbonylation.
2. Results and discussion
2.1. Photoinduced reduction system of samarium
diiodide
2
4
Figure 1. UV–vis. spectrum of SmI
2
in THF (5.0£10 mol/L).
A THF solution of SmI , which appears deep blue color,
2
exhibits its absorption maximum in the visible region
¼565 and 617 nm), which can be assigned as a
Table 1. Photoinduced reduction of 1-chlorododecane
(
4
l
max
6
5
1
37
f !4f 5d transition (Fig. 1).
Thus, the irradiation with the light of wavelength in these
regions is expected to generate the excited Sm species,
which might show different reactivities from the Sm species
in the ground state. While the reduction of 1-chlorodo-
Entry
Wavelength (nm)
Yield (%)
1
2
3
4
5
6
.300
300–420
.500
560–800
.700
Dark
88
Trace
91
66
Trace
0
decane with SmI alone at 408C does not proceed at all, the
2
irradiation through Pyrex with a tungsten lamp
hv.300 nm) enables the efficient reduction of 1-chlorodo-
(
decane with SmI2 (Table 1, entry 1). To specify the
Reaction conditions: n-C12
(1.5 mL), 408C, 4 h. Irradiation with tungsten lamp (500 W).
H
25I (0.15 mmol), SmI
2
(0.33 mmol), THF
wavelength effecting the higher reducing power of SmI , we
2
examined the photoinduced reduction of 1-chlorododecane
3
2
with SmI by varying the wavelengths of light (Table 1).
2
Table 2. Photoinduced reduction of organic chlorides, tosylates, and chalcogenides with SmI
2
Entry
1
Substrate (R-X)
Yield of R-H (%)
88
Entry
8
Substrate (R-X)
Yield of R-H (%)
99
2
3
86
92
9
83
84
10
4
5
89
99
11
12
24
79 (n-C11H )
84
6
77
13
68
7
59
14
38
Reaction conditions (entries 1–4): RCl (0.15 mmol), SmI
entries 5–14): substrate (0.25 mmol), SmI (2 mmol), THF (10 mL), 678C (entries 5, 8 and 14: 408C), 8–16 h (entry 5, 1 h; entry 6, 10 h; entry 7, 30 h).
Irradiation with a tungsten lamp (500 W) through Pyrex (entry 8, hv.400 nm; entry 14, hv.500 nm).
2
(0.33 mmol), THF (1.5 mL), 408C, 3–9 h. Irradiation with a tungsten lamp (500 W) through Pyrex.
(
2

Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
10501
The reduction does not take place upon irradiation with near
UV light (300–420 nm) (entry 2) or the light of wavelength
greater than 700 nm (entry 5), whereas the irradiation with
the light of wavelength greater than 500 nm successfully
induces the desired reduction of n-C H Cl (entry 3).
The observed rate constant for the SmI –hv system is
2
similar as that for the SmI -single system (SmI –THF).
2
2
This result requires some comments: the excited SmI has a
2
much more powerful reducing ability, but its concentration
in this reaction system is very low. Although the excited
SmI can reduce alkyl chloride to generate alkyl radical, the
1
2 25
Irradiation with the light of wavelength between 560 and
00 nm is also effective for this reduction (entry 4). These
results clearly indicate that the light of wavelength between
60 and 700 nm is essential for the activation of SmI2.
2
8
reduction of alkyl radical to alkylsamarium diiodide takes
place mainly by the SmI in the ground state, which is
present in situ in high concentration.
2
5
Table 2 represents the results of the photoinduced reduction
of group 16 and 17 heteroatom compounds with SmI2.
Secondary alkyl, tertiary alkyl, and aryl chlorides are
reduced to the corresponding hydrocarbons efficiently
2.2. Photoinduced reduction system of ytterbium
3
diiodide
6
Although ytterbium diiodide (YbI ) can be prepared easily
2
(
entries 1, 2, and 4). Although the reduction of dodecyl
tosylates with SmI is known to take place in the dark at
from ytterbium metal and 1,2-diiodoethane in THF similarly
to SmI , the practical use of YbI in organic synthesis has
been limited, because of its lower reducing ability and lower
2
2
2
6
78C for 10 h, the same reduction under photoirradiation
conditions proceeds very smoothly even at 408C for 1 h
entry 5). By using the SmI –hv system, diacetone-D-
solubility in common organic solvents. YbI exhibits its
2
(
absorption maximum in near-UV regions (Fig. 2), i.e.
¼307, 342, and 390 nm, which can be identified as a
2
glucosyl tosylate undergoes detosylation chemoselectively
entry 6). Next, we examined the reduction of organo-
chalcogen compounds, i.e. organic sulfides, selenides, and
l
max
1
4
13
1
37
(
4f !4f 5d transition.
3
5
tellurides, which cannot be reduced by SmI alone. By
2
employing the SmI –hv systems, C–S, C–Se, and C–Te
2
bond cleavage proceeds, as shown in Table 2 (entries 7–14).
In particular, seleno groups can be removed reductively
from a variety of organic selenides effectively (entries
3
8
–13). The C(sp )–Se bonds of primary and secondary
alkyl selenides undergo reductive cleavage smoothly with
2
SmI –hv, whereas the cleavage of C(sp )–Se bond does not
2
take place at all (entry 11). b-Alkoxyl selenides that can be
obtained easily by the oxyselenation of olefins, are also
converted into the corresponding ethers in high yield by
2
5
Figure 2. UV–vis. spectrum of YbI
2
in THF (40£10 mol/L).
using this SmI –hv system (entry 10). Compared with
2
selenides, the reduction of sulfides proceeds slowly and
requires higher temperature (678C, 30 h), probably due to
the higher bond energy of C–S bond (entry 7). In the case of
dodecyl phenyl telluride, the cleavage of C–Te bonds
Thus, the irradiation with near-UV light leads to the
pronounced enhancement of the reducing ability of YbI2,
as shown in Eq. (2).
3
2
occurs at both C(sp )–Te and C(sp )–Te centers (entry 14).
ð2Þ
Similar conditions can be employed with alkyl iodides and
tosylates (entries 1 and 4 in Table 3), but the reduction of
dodecyl chloride and dodecyl phenyl selenide gives rise to
poor yields of dodecane (entries 3 and 5). The reduction of
undecyl a-naphthyl telluride resulted in the formation of
both undecane and naphthalene (entry 6). Unambiguously,
these results indicate that, upon irradiation with the light of
ð1Þ
In the SmI –HMPA system, the first bimolecular rate
2
wavelength over 300 nm, YbI exhibits a similar reducing
2
power as that of samarium diiodide itself in THF.
constants for the reduction of primary alkyl radicals to
the corresponding alkylsamarium diiodide is estimated,
by using 5-hexenyl radical clock system, to be
Similarly, we examined the
SmI -mediated Barbier reaction of 5-hexenyl chloride
6
21 21 38
0
.5–7.0£10 M
s
.
ð3Þ
2
(0.1 M) with diethyl ketone upon irradiation with visible
light (Eq. (1)). Based on the ratio of the cyclic and acyclic
To enhance the synthetic utility of YbI –hv, we further
2
Barbier adducts (1/2¼29/71) and the rate constant for
examined the catalytic use of YbI in the reduction of
2
5
21
39
the cyclization of 5-hexenyl radical (4.9£10 s at 408C),
organic bromides. Since the reduction potential of YbI
3
(Yb /Yb ) is estimated to be 21.15 eV, co-reductants
2
þ
bearing a moderate reducing power seem to be suitable for
2þ
the bimolecular rate constant for the photoinduced reduction
of primary alkyl radicals with SmI is roughly estimated to
2
5
21 21
40
be 10 M
s
(at 408C).
this purpose. Thus, the YbI -catalyzed reduction of dodecyl
2

1
0502
Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
Table 4. Photoinduced carbonylation of alkyl chlorides with CO and SmI
a
2
Table 3. Photoinduced reduction with YbI
2
Entry
Chloride
Product
Yield
%)
(
Entry
X
Yield (%)
1
2
89
63
hv
Dark
1
2
3
4
5
6
I
Br
Cl
73
99
27
73
25
40
4
Trace
No reaction
Trace
No reaction
7
OTs
SePh
Te-a-naphthyl
3
4
61
68
b
c
a
Substrate (0.5 mmol), YbI
n-C11H23TeC10H -a is employed.
2
(4.0 mmol), THF (20 mL), 608C, 8 h.
b
c
7
Both undecane and naphthalene are formed in 40 and 20% yields,
respectively.
5
6
7
35
8
bromide is conducted by using excess amounts of
3
þ
0
aluminium metal (Al /Al ¼21.66 eV) as a co-reductant.
The catalytic reaction proceeds successfully, giving
dodecane in 88% yield (Eq. (3)). In the absence of a
catalytic amount of YbI2 (or in the dark), the present
reduction does not occur at all.
0
RCl (0.5 mmol), CO (50 atm), SmI2 (4 mmol), THF (20 mL), 508C, 9 h,
hv.400 nm (Xenon lamp 500 W, filter).
2
chlorides with CO and SmI2
.3. Photoinduced reductive carbonylation of alkyl
3
2
the case of 10-chloro-1-decanol (entry 7). In these cases,
reduction to the corresponding hydrocarbons takes place in
preference to the carbonylation. If the carbonylation
proceeds via the formation of acyl radical, ether or alcohol
compounds might accelerate a second electron transfer, i.e.
the reduction of alkyl radical to alkylsamarium species
might occur rapidly, in preference to the reaction of alkyl
radical with carbon monoxide. Also, in the cases of tertiary
alkyl chlorides like 1-adamantyl chloride and aryl chlorides
like b-naphthyl chloride, no carbonylation takes place at all
The present photoinduced reduction of alkyl chlorides
RCl) with SmI proceeds through single-electron transfer
processes, and involves the formation of alkyl radical and
(
2
alkylsamarium species (R· and RSmI ) as key intermediates.
2
Recently, alkylsamarium species are reported to react with
4
1
isocyanides forming imidoylsamarium species. Further-
more, carbon monoxide, bearing an isoelectronic structure
with isocyanide, is known to react with alkyl radicals under
high pressure conditions, generating acyl radical species.
Thus, we examined the photoirradiated reaction of alkyl
(only reduction to the corresponding hydrocarbons occurs).
chlorides with SmI under the pressure of carbon monoxide.
2
The present photoinduced carbonylation may involve the
formation of an acylsamarium species as a key intermediate.
Kagan et al. previously reported that the reduction of acyl
chlorides by excess amounts of SmI provided the same
2
unsymmetrical ketones through the dimerization of acyl-
42
samarium species and the following further reduction.
The reaction is conducted by employing a stainless steel
autoclave bearing glass windows, through which the
photoirradiation is performed. When the reaction of
1
-chlorododecane with SmI is carried out under 50 atm
2
of CO upon irradiation with xenon lamp through a filter
hv.400 nm), the desired carbonylation takes place
successfully, providing 89% of dodecyl tridecyl ketone
(
As to the carbonylation step, several mechanistic pathways
can be proposed, as depicted in Scheme 1. The first
hypothesis is that alkyl halide is reduced to an alkyl-
samarium species, which reacts with carbon monoxide to
afford an acylsamarium species (path A). Thus, the reaction
of an alkylsamarium iodide with pressurized CO was
investigated. After 1-chlorododecane was treated with
(
3, R¼n-C H ), which incorporates two dodecyl and two
1
2 25
carbon monoxide units (Eq. (4)). In the dark, the same
reductive carbonylation does not take place at all.
ð4Þ
SmI –hv at room temperature, carbon monoxide was
2
Table 4 represents the results of the photoinduced
carbonylation of alkyl chlorides with CO and SmI . The
introduced into this solution upon photoirradiation. How-
ever, the desired carbonyl compound was not obtained at all,
and instead dodecane was formed as a simple reduced
product. This result may suggest that acylsamarium iodide
(RC(O)SmI ) is not formed by the reaction of an
2
alkylsamarium iodide (RSmI ) with CO. However, another
2
2
carbonylation of alkyl chlorides bearing an olefinic unit
proceeds successfully to give the corresponding asym-
metrical ketones in good yields (entries 2 and 3). Similarly,
secondary alkyl chlorides such as cyclohexyl chloride
undergo photoinduced carbonylation to provide the corre-
sponding carbonylated product (entry 4). In contrast, the
yields are decreased in the case of ether compounds (entries
possibility is that RSmI is unstable at room temperature
2
and decomposes before the reaction with CO. Therefore,
further detailed experiments at lower temperature are
required.
5
and 6), and the carbonylation does not take place at all in

Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
10503
Scheme 1. Possible pathways for the carbonylation.
The second hypothesis is that the alkyl radical might
directly react with carbon monoxide to afford an acyl radical
species, and then the acyl radical undergoes single-electron
reduction to provide an acylsamarium species (path B). Ryu
and Sonoda reported that acyl radicals are formed when
alkyl halides are treated with AIBN and tin hydride under
(418C) (Eq. (6)), the reaction of phenylacetyl chloride with
SmI does not afford any decarbonylated product. These
facts suggest that the reduction of acyl radicals by SmI is
2
45
2
much faster than the reduction of usual alkyl radicals.
4
3
ð6Þ
the pressure of carbon monoxide. To elucidate whether
this carbonylation involves acyl radical intermediates, we
examined the present carbonylation in the presence of
excess amounts of alkenes. If an acyl radical is formed, this
radical might be trapped by alkenes like styrene, providing
However, a third possibility cannot be excluded: samarium
carbonyl species might be involved (path C). A samar-
4
6,47
4
4
ium(0) carbonyl complex was reported previously.
the corresponding three-component coupling product.
However this type of reaction does not occur (Eq. (5)).
Intriguingly, the reactivity of SmI2 in the presence of
carbon monoxide is decreased, compared with the reactivity
of SmI in the absence of carbon monoxide. For instance,
2
ð5Þ
the photoinduced reduction of 1-chloroadamantane with
SmI2 proceeded smoothly in the absence of carbon
monoxide to afford adamantane in 88% yield. Under the
pressure of carbon monoxide, however, both carbonylation
and reduction of chloroadamantane are extremely inhibited:
adamantane is obtained only in 6% yield (Eq. (7)).
Furthermore, intramolecular trapping of the acyl radical was
attempted by using cis-4-heptenyl chloride. However, no
cyclic compound was detected at all and only asymmetric
ketone was obtained in 66% yield (Scheme 2).
ð7Þ
One possibility is that the acyl radical formed in this
reaction may be reduced to an acylsamarium species very
rapidly. In fact, while the rate constant for the decarbonyla-
tion of benzylcarbonyl radical is known to be 1.08£10 s
A similar phenomenon is also observed with the SmI2–
HMPA system. 1-Chlorododecane is reduced with SmI2
efficiently in the presence of HMPA, whereas the same
7
21
reduction using the SmI –HMPA system does not take
2
Scheme 2. Photoinduced carbonylation of 4-heptenyl chloride.

10504
Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
place at all in the presence of carbon monoxide (Eq. (8)).
These results clearly indicate that carbon monoxide affects
the reactivity of SmI . Since samarium ions have a high
oxophilicity, carbon monoxide might coordinate to the
samarium species. This might contribute to the decrease in
the reducing ability of SmI2.
unsymmetrical ketones in good yields. This carbonylation
proceeds via the formation of an acylsamarium species.
The synthetic applications of this carbonylation and the
elucidation of the precise mechanism for the carbonylation
step are now under investigation.
2
4. Experimental
ð8Þ
4.1. General comments
1
Since the reduction of haloalkane is reported to proceed via
the outer-sphere process, carbon monoxide retards this
process. Similarly, the inner-sphere process might be also
reduced. This is strongly supported by the fact that
unsymmetrical ketones formed by this carbonylation are
not reduced to alcohols or pinacols during the reaction.
H NMR spectra were recorded on JEOL JNM-GSX-270
(270 MHz) and JEOL JNM-AL400 (400 MHz) spectro-
meters using CDCl as the solvent with Me Si as the
3 4
1
3
internal standard. C NMR spectra were taken on JEOL
JNM-GSX-270 (68 MHz) and JEOL JNM-AL400
(100 MHz) spectrometers using CDCl
1
as the solvent.
Chemical shifts in C NMR were measured relative to
3
3
A THF solution of SmI in the presence of carbon monoxide
2
CDCl
3
and converted to dMe Si value by using dCDCl3¼76.9
4
is irradiated with visible light, followed by the addition of
alkyl chloride after CO release. This reaction affords the
unsymmetrical ketone in 23% yield (Eq. (9)). This result
suggests the possibility that a samarium carbonyl species
generated in situ may act as a carbonylating agent. Thus, we
attempted to detect the samarium carbonyl species with an
IR spectrometer. After the reaction of SmI2 with CO
ppm. IR spectra were determined on a Perkin Elmer Model
1600 spectrometer. Melting points were determined on a
Yanagimoto micro melting point apparatus. Mass spectra
were obtained on a JEOL JMS-DX303 in the analytical
section of Osaka University (Faculty of Engineering).
Elemental analyses were also performed there.
(
50 atm) upon irradiation with visible-light in the absence of
Unless otherwise noted, materials were obtained from
commercial suppliers and purified by distillation or
recrystallization. Tosylates (Table 2, entries 5 and 6) were
prepared from the corresponding alcohols by the reaction
with tosyl chloride in the presence of DMAP (4-(N,N-di-
substrates, CO is purged and immediately the IR spectra of
the resulting solution is measured. However, no absorbance
assigned to a samarium carbonyl species is detected. Even if
a samarium carbonyl species is formed, it could exist for
only a very short time in the absence of CO.
4
8
methylamino)pyridine). Alkyl phenyl chalcogenides
Table 2, entries 7–9, and 12–14) were obtained by the
(
reaction of phenyllithium (1.8 M in THF, commercially
available) with elemental sulfur, selenium, and tellurium
(08C–rt, 1 h), followed by alkylation with the corresponding
alkyl halides (rt (or 2158C for entries 12–13), overnight).
4
9
ð9Þ
Vinylic selenide (Table 2, entry 11) was synthesized by the
addition of benzeneselenol to phenylacetylene under neutral
5
0
conditions. b-Hydroxy selenide (Table 2, entry 10) was
prepared by the oxyselenation of cyclohexene using
phenylselenenyl bromide and 1-decanol. Samarium powder
in oil (99.9%) was purchased from High Purity Chemicals,
and was used after washing with dry pentane, followed by
drying for 4 h under reduced pressure. 1,2-Diiodoethane
was purified by washing of its ether solution with sat.
sodium thiosulfate, followed by drying under reduced
pressure.
3
. Conclusion
A novel photoinduced reduction system with SmI has been
2
developed. Irradiation with visible-light dramatically
enhances the reducing ability of SmI . By using this
SmI –hv system, alkyl chlorides, bromides, sulfides,
2
selenides, tellurides, and tosylates can be reduced effi-
ciently, while the same reduction does not proceed (or
requires prolonged reaction time and higher temperature) by
4.2. Representative procedure for the photoinduced
reduction of organic chlorides and chalcogenides with
SmI2
2
Representative procedure for the photoinduced reaction of
organic chlorides with SmI is as follows: In a 10 mL two-
use of SmI alone. These findings can be also applied to
2
2
ytterbium diiodide (YbI ) in THF. In this case, upon
2
necked flask (Pyrex) was placed under argon atmosphere
samarium powder (0.33 mmol), 1,2-diiodoethane
(0.33 mmol), and freshly distilled (sodium/benzophenone
ketyl) THF (1.5 mL). The mixture was stirred at ambient
temperature for 1 h, resulting in the formation of a dark blue
irradiation with near-UV light, YbI2 exhibits a similar
reducing power to that of SmI itself in THF. In these
2
reductions, alkyl radicals and alkylsamarium diiodides
might be involved. Thus, when the photoinduced reduction
of alkyl chlorides is conducted under the pressure of
solution of SmI . After the addition of organic chloride
2
carbon monoxide, a novel SmI -induced carbonylation
2
of alkyl chlorides has occurred to afford the corresponding
(0.15 mmol) to the solution, the flask was set in a water bath
maintained at 408C and irradiated for 3–9 h using a tungsten

Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
10505
lamp (500 W) with stirring. The reduction of aliphatic
primary or secondary alkyl chlorides requires ca. 3 h, while
THF (20 mL), and 1,2-diiodoethane (4.0 mmol). Heating of
the mixture at 678C for 1 h with magnetic stirring provided
6
–9 h is essential for the aliphatic tertiary alkyl chlorides
and aryl chlorides (e.g. Table 2, entry 1: 3 h; entries 2 and 4:
h). After the reaction was complete, the resulting mixture
ytterbium diiodide (YbI ) in THF.
2
6
After the addition of substrate (dodecyl iodide, bromide,
chloride, tosylate, sulfide, selenide, and telluride)
(0.5 mmol) to the YbI -THF, the flask was set in a water
was diluted with diethyl ether, washed with sat. NaHCO3,
and dried over MgSO . Concentration and distillation
provided the corresponding hydrocarbons.
4
2
bath maintained at 608C and irradiated for 8 h by a tungsten
lamp (500 W) with stirring. After the reaction was
complete, the resulting mixture was diluted with diethyl
ether, washed with sat. NaHCO , and dried over MgSO .
The photoinduced reductions of organic chalcogenides with
SmI were usually conducted by using excess amounts of
SmI , in order to complete the reaction in a shorter time:
2
2
3
4
5
1
a
Concentration and distillation provided dodecane.
mixture of chalcogen compound (0.25 mmol) and SmI2
2 mmol) in THF (10 mL) was irradiated with a tungsten
lamp through Pyrex at 408C (Table 2, entries 5, 8, and 14) or
78C (entries 6, 7, and 9–13). As can be seen from the
(
4.5. YbI -catalyzed reduction of dodecyl bromide with
2
aluminum upon photoirradiation
6
results of the reduction of dodecyl chalcogenides at 408C,
the tosylate and the selenide underwent efficient reduction
within 1 h and 8 h, respectively. On the other hand, the
reduction of the sulfide required higher temperature and
prolonged reaction time (678C, 30 h). Reaction times (entry)
are exemplified as follows: 10 h (entries 6 and 10); 16 h
In a 20 mL two-necked flask equipped with a condenser
were placed under argon atmosphere ytterbium powder
(0.1 mmol), freshly distilled (sodium/benzophenone ketyl)
THF (10 mL), and 1,2-diiodoethane (0.1 mmol). Heating
of the mixture at 678C for 1 h with magnetic stirring
provided YbI . Dodecyl bromide (1 mmol) and aluminum
2
(
entry 9); 12 h (entry 11). After similar workups, the
(4.0 mmol) were added to the YbI –THF solution, and
2
purification of the reduced products were performed by
preparative TLC (silica gel) (entries 6, 10, 12 and 13). In the
cases of hydrocarbons as the product, GC analysis was
carried out (entries 5, 7–9, 11, and 14).
stirred at 678C for 40 h. After the reaction was complete,
the resulting mixture was diluted with diethyl ether,
washed with sat. NaHCO , and dried over MgSO .
Concentration and distillation provided the corresponding
dodecane.
3
4
To exclude the possibility that the reduction proceeds through
the photoinduced generation of carbon radical from the
corresponding selenides and tellurides which exhibit their
absorption in the near-UV region, the photoirradiation was
performed through filters (hv.400 or 500 nm). The fact that
the reaction proceeded smoothly suggests that the reduction
does not involve the direct generation of carbon radicals from
the selenides and tellurides as the major pathway.
4.6. Representative procedure for the photoinduced
carbonylation of organic chlorides with SmI and CO
2
Samarium diiodide was prepared, similarly as described
above (paragraph 4.2), from samarium powder (4 mmol),
1,2-diiodoethane (4 mmol), and THF (20 mL). The carbon-
ylation was conducted by using a 50 mL stainless steel
autoclave equipped with glass windows. In a Pyrex glass
tube (length 95 mm; i.d. 25 mm) with a magnetic stirring
bar were placed under argon atmosphere alkyl chloride
4.3. The photoinduced reduction of 5-hexenyl chloride
with SmI2
5
1
(0.5 mmol) and a solution of samarium diiodide (4 mmol)
5-Hexenyl chloride (0.5 mmol) was added to the THF
solution of SmI (1.1 mmol) and the mixture was stirred at
408C for 4 h. Then, 2-octanone (1.5 mmol) was added and
the resulting solution was stirred at 408C for 4 h. After the
in THF (20 mL) by syringe technique. The glass tube was
immediately inserted into the autoclave, and the apparatus
was flushed several times with carbon monoxide and
charged with carbon monoxide at 50 atm. The reaction
was conducted by irradiating with a xenon lamp (500 W)
through a filter (hv.400 nm) for 9 h upon heating at 508C.
After the reaction was complete, carbon monoxide was
purged in a well-ventilated hood. The resulting mixture was
poured into 1N hydrochloric acid (30 mL), and the products
were extracted with diethyl ether (30 mL£3). The combined
extracts were washed each two times with sat. NaCl and
then 5% NaS O , and dried over MgSO . After filtration and
2
reaction was complete, the resulting mixture was diluted
with diethyl ether, washed with sat. NaHCO , and dried
3
over MgSO . Concentration and distillation provided
4
alcohol (1) and (2) with the ratio of 29/71. As the rate
constant (k ) for cyclization of 5-hexenyl radicals is
c
21
5
4
.19£10 s (at 408C), the bimolecular rate constant for
the reduction of R· with SmI –hv is roughly estimated to be
2
5
21 21
1
0 M
s
(at 408C).
2
3
4
evaporation of the solvent, the products were isolated by
using column chromatography on silica gel or preparative
TLC on silica gel.
4.4. Representative procedure for the photoinduced
reduction with YbI2
Ytterbium powder in oil (99.9%) was purchased from High
Purity Chemicals, and was used after washing with dry
pentane, followed by drying 4 h under reduced pressure.
4.6.1. 13-Hexacosanone. [Reg. No. 120134-49-8]. White
1
solid; mp 59–618C; H NMR (270 MHz, CDCl ) d 0.88 (t,
3
J¼7.0 Hz, 6H), 1.26 (br s, 38H), 1.56 (br quint, J¼7.3 Hz,
1
3
4
H), 2.38 (t, J¼7.3 Hz, 4H); C NMR (100 MHz, CDCl ) d
3
In a 20 mL two-necked flask equipped with a condenser
were placed under argon atmosphere ytterbium powder
13.31, 21.86, 28.41, 23.08, 28.44, 28.51, 28.58, 28.64,
28.81, 30.97, 31.07, 41.94, 210.42; IR (KBr) 2921, 2851,
1705, 1464, 1164, 1068, 908, 733 cm2 ; MS (EI), m/z¼330
1
(
4.0 mmol), freshly distilled (sodium/benzophenone ketyl)

10506
Y. Sumino et al. / Tetrahedron 59 (2003) 10499–10508
þ
Exact mass (M ) calcd for 380.4018, found 380.4010.
þ
þ
(
M , 2), 211 (C H C(O) , 100), 197 (C H C(O) , 69).
1
CO provided the corresponding dodecane in more than 95%
yield.
3
27
12 25
þ
4
cous oil; H NMR (270 MHz, CDCl ) d 1.27 (br s, 18H),
.6.2. 1,21-Docosadiene-11-one. Pale yellow highly vis-
1
4.9. The photoinduced reductive carbonylation of
n-dodecyl chloride with SmI treated with pressurized
CO previously
3
2
1
.37 (m, 4H), 1.55 (m, 4H), 2.03 (br q, J¼7.6 Hz, 4H), 2.38
(
t, J¼7.3 Hz, 4H), 4.92 (d, J¼11.1 Hz, 2H), 5.01 (d, J¼
1
3
1
2
2
1
2
8.6 Hz, 2H), 5.80 (m, 2H); C NMR (68 MHz, CDCl ) d
3
In a 50 mL stainless steel autoclave equipped with glass
windows was placed a THF solution (20 mL) of SmI2
(4 mmol). Carbon monoxide was charged at 50 atm and the
photoirradiation through a filter (hv.400 nm) was con-
ducted at 408C for 12 h in the absence of the substrate. After
CO was purged in a well-ventilated hood, n-dodecyl
chloride (0.5 mmol) was added to the solution and the
resulting solution was stirred at 408C under argon
atmosphere upon photoirradiation. After 9 h, the resulting
3.88, 28.88, 28.91, 29.06, 29.10, 29.24, 29.25, 29.29,
9.35, 29.38, 29.40, 29.41, 33.77, 33.79, 42.80, 42.82,
14.10, 114.12, 139.19, 139.22, 211.74; IR (NaCl) 2921,
2
1
848, 1704, 1643, 1462, 991, 911, 725 cm . HRMS calcd
for C H O 320.3079, found 320.3082.
22 40
1
4
.6.3. 3,13-Hexadecadiene-8-one. Highly viscous oil; H
NMR (270 MHz, CDCl ) d 0.95 (t, J¼7.6 Hz, 6H), 1.31 (m,
3
2
5
2
1
3
1
H), 1.60 (m, 4H), 2.02 (m, 8H), 2.42 (t, J¼7.6 Hz, 4H),
mixture was diluted with Et O (50 mL), washed with
2
1
3
.28–5.42 (m, 4H); C NMR (68 MHz, CDCl ) d 14.28,
3
aqueous saturated NaHCO , and dried over MgSO . The
4
3
0.46, 23.44, 23.69, 26.41, 26.81, 29.30, 42.01, 42.65,
28.07, 128.57, 131.93, 132.51, 211.22; IR (NaCl)
004, 2962, 2934, 2872, 1712, 1460, 1406, 1371,
yields of 13-hexacosanone and dodecane (23% and 7%
respectively) were determined by GC analysis.
2
1
303, 1260, 1069, 796, 712 cm ; MS (EI), m/z¼167
þ þ
M 2CH CHvCHCH , 14), 139 (C H C(O) , 7), 125
3 2 8 15
(
(
Acknowledgements
þ
þ
þ
C H C(O) , 11), 111 (C H , 26), 97 (C H , 40). HRMS
8
7
13
15
7 13
calcd for C H O 236.2140, found 236.2146.
16 28
This work was supported in part by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science and Technology, Japan, and Nagase Science
and technology foundation.
4
.6.4. 1,2-Dicyclohexylethanone. [Reg. No. 6713-49-1].
1
H NMR (270 MHz, CDCl ) d 0.92 (br quint, J¼10.8 Hz,
3
2
H), 1.27 (m, 10H), 1.67 (m, 4H), 1.78 (br d, J¼7.3 Hz, 5H),
1
3
2
2
2
1
.30 (br d, J¼6.8 Hz, 3H); C NMR (68 MHz, CDCl ) d
3
5.68, 26.10, 26.78, 28.32, 48.41, 51.22, 214.05; IR (NaCl)
924, 2852, 1706, 1448 cm ; MS (EI), m/z¼208 (M , 26),
2
1
þ
25 (c-C H CH C(O) , 60), 111 (c-C H C(O) , 41), 97
References
þ
þ
6
11
þ
2
6 11
þ
(
c-C H CH , 100), 83 (c-C H , 100).
11
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n-Dodecyl chloride (0.5 mmol) and styrene (2 mmol) were
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2
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preseure of CO (50 atm) upon irradiation through a filter
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same photoirradiated treatment of SmI
2
in THF in the absence
gradually.
of substrates led to the decomposition of SmI
2