Photoinduced reduction and carbonylation of organic chlorides with samarium diiodide

Full text of DOI:10.1021/ja963117p

J. Am. Chem. Soc. 1997, 119, 2745-2746
2745
Photoinduced Reduction and Carbonylation of
Organic Chlorides with Samarium Diiodide
Akiya Ogawa,* Yukihito Sumino, Taizoh Nanke,
Syoji Ohya, Noboru Sonoda,* and Toshikazu Hirao
Department of Applied Chemistry, Faculty of Engineering
Osaka UniVersity, Suita, Osaka 565, Japan
ReceiVed September 5, 1996
Herein we report that the irradiation with visible light
enhances the reducing ability of samarium diiodide. While
samarium diiodide1 is well-known to reduce organic bromides
and iodides to the corresponding hydrocarbons efficiently,2 the
reduction of organic chlorides with SmI2 alone is difficult. In
fact, the reduction of organic chlorides with SmI2 requires excess
amounts of HMPA.3 In marked contrast to this, irradiation of
the reaction mixture through Pyrex with a tungsten lamp enables
the efficient reduction of organic chlorides with SmI2 even in
the absence of HMPA (eq 1).4,5
Figure 1. UV-vis spectrum of SmI2 in THF (5.0 × 10-4 mol/L).
a
Table 1. Photoinduced Reduction of Organic Chlorides with SmI2
Figure 1 shows the UV-vis spectrum of SmI2 in THF. To
specify the wavelength effecting the higher reducing power of
SmI2, we examined the photoinduced reduction of 1-chloro-
dodecane with SmI2 by varying the wavelengths of light (Table
1). While the reduction did not take place for irradiation with
near UV light (300-420 nm) (entry 1) or the light of wavelength
greater than 700 nm (entry 4), irradiation with the light of
wavelength between 560 and 800 nm led to the successful
reduction of 1-chlorododecane (entry 3). These results clearly
indicate that SmI2 was activated by irradiating with the light of
wavelength between 560 and 700 nm.6
The procedure can be employed with a variety of organic
chlorides such as secondary and tertiary alkyl chlorides and
aromatic chlorides, as represented in entries 5-11 of Table 1.
When the photoinduced reduction of o-chlorophenyl allyl ether
(1) with SmI2 was conducted in the presence of diethyl ketone,
a cyclic ether (2) was produced in 72% yield (eq 2). The
formation of 2 can be accounted for by the following processes,7-9
i.e., 5-exo cyclization of the aryl radical 3, followed by reduction
a RCl (0.15 mmol), SmI2 (0.33 mmol), THF (1.5 mL), 40 °C, 3-9
h, hν; tungsten lamp (500 W), Pyrex.
(1) For reviews concerning SmI2, see: (a) Kagan, H. B.; Namy, J. L.
Tetrahedron 1986, 42, 6573. (b) Kagan, H. B. New J. Chem. 1990, 14,
453. (c) Molander, G. A. In ComprehensiVe Organic Synthesis; Trost, B.
M., Ed.; Pergamon Press: Oxford, 1991; Vol. 1, Chapter 1.9, p 251. (d)
Soderquist, J. A. Aldrichimica Acta 1991, 24, 15. (e) Molander, G. A.
Chem. ReV. 1992, 92, 29. (f) Molander, G. A. Org. React. 1994, 46, 211.
(g) Imamoto, T. Lanthanides in Organic Synthesis; Academic Press:
London, 1994; pp 21-62. (h) Molander, G. A.; Harris, C. R. Chem. ReV.
1996, 96, 307.
with SmI2 and the subsequent addition of alkylsamarium species
4 to diethyl ketone. Similarly, the photoinitiated reduction of
chloroalkanes with SmI2 may proceed Via the formation of alkyl
radicals and alkylsamarium species.
Recently, a series of synthetic reactions have been developed
on the basis of the carbonylation of carbon radicals with carbon
monoxide.10 It may be expected that, in the photoinduced
(2) Girard, P.; Namy, J. L.; Kagan, H. B. J. Am. Chem. Soc. 1980, 102,
2693.
(3) (a) Inanaga, J.; Ishikawa, M.; Yamaguchi, M. Chem. Lett. 1987, 1485.
(b) Inanaga, J. ReV. Heteroat. Chem. 1990, 3, 75.
(4) Recently, we have developed that the Sm/SmI2 mixed reagent exhibits
higher reducing abilities in the reduction of alkyl bromides and iodides,
compared with those SmI2 or Sm metal used independently. However, the
Sm/SmI2 reagent was not effective for the reduction of alkyl chlorides. (a)
Ogawa, A.; Takami, N.; Sekiguchi, M.; Ryu, I.; Kambe, N.; Sonoda, N. J.
Am. Chem. Soc. 1992, 114, 8729. (b) Ogawa, A.; Nanke, T.; Takami, N.;
Sumino, Y.; Ryu, I.; Sonoda, N. Chem. Lett. 1994, 379.
(8) (a) Curran, D. P.; Fevig, T. L.; Totleben, M. J. Synlett 1990, 773.
(b) Totleben, M. J.; Curran, D. P.; Wipf, P. J. Org. Chem. 1992, 57, 1740.
(c) Curran, D. P.; Totleben, M. J. J. Am. Chem. Soc. 1992, 114, 6050. (d)
Curran, D. P.; Fevig, T. L.; Jasperse, C. P.; Totleben, M. J. Synlett 1992,
943.
(9) Inanaga, J.; Ujikawa, O.; Yamaguchi, M. Tetrahedron Lett. 1991,
32, 1737.
(10) (a) Ryu, I.; Kusano, K.; Ogawa, A.; Kambe, N.; Sonoda, N. J. Am.
Chem. Soc. 1990, 112, 1295. (b) Ryu, I.; Yamazaki, H.; Kusano, K.; Ogawa,
A.; Sonoda, N. J. Am. Chem. Soc. 1991, 113, 8558. (c) Ryu, I.; Yamazaki,
H.; Ogawa, A.; Kambe, N.; Sonoda, N. J. Am. Chem. Soc. 1993, 115, 1187.
(d) Tsunoi, S.; Ryu, I.; Fukushima, H.; Tanaka, M.; Komatsu, M.; Sonoda,
(5) Imamoto, T.; Tawarayama, Y.; Kusumoto, T.; Yokoyama, M. J.
Synth. Org. Chem. Jpn. 1984, 42, 143.
(6) The absorbance of SmI2 (λmax ) 565 and 617 nm) is identified as a
4f6 f 4f55d1 transition: (a) Evans, D. F.; Fazakerley, G. V.; Phillips, R. F.
J. Chem. Soc. A 1971, 1931. (b) Namy, J. L.; Girard, P.; Kagan, H. B. N.
J. Chim. 1981, 5, 479. (c) Okaue, Y.; Isobe, T. Inorg. Chem. Acta 1988,
144, 143. A possible reduction pathway might involve a single-electron
transfer from photoexcited SmI2 species to organic chlorides.
(7) (a) Molander, G. A.; Harring, L. S. J. Org. Chem. 1990, 55, 6171.
(b) Molander, G. A.; Kenny, C. J. Org. Chem. 1991, 56, 1439.
S0002-7863(96)03117-4 CCC: $14.00 © 1997 American Chemical Society

2746 J. Am. Chem. Soc., Vol. 119, No. 11, 1997
Communications to the Editor
Table 2. Photoinduced Carbonylation of Alkyl Chlorides with CO
and SmI2
cyclohexanecarbonyl chloride with SmI2 (8 equiv) at 38 °C for
0.5 h upon irradiation with visible light afforded cyclohexyl
cyclohexylmethyl ketone (5d) in 64% yield. Furthermore, the
photoinduced carbonylation of 9-decenyl chloride with SmI2
and CO under controlled conditions gave rise to 49% of R-ketol
(6b). It was also known that the controlled reaction of acyl
a
chlorides with SmI2 afforded R-ketols.14e Therefore, these
results suggest that the photoinduced carbonylation with SmI2
included the formation of acylsamarium species (as a key
intermediate), which may dimerize to give asymmetrical ketones.
As to the carbonylation step, the following two mechanistic
pathways can be proposed: The first postulates the reaction of
alkyl radical with CO to give acyl radical, which undergoes
further reduction with excess SmI2 to acylsamarium species.
The second includes the reaction of alkylsamarium with CO.15
However, the second mechanistic pathway can be ruled out
easily by the fact that the photoinduced reaction of an alkyl-
samarium (n-C12H25SmI2) with CO (50 atm) at 40 °C did not
afford the desired carbonylated product at all. In order to clarify
the formation of acyl radicals in this carbonylation, several
attempts to capture acyl radicals with olefins were performed,
but no trace of addition products could be detected.17 In
addition, in the carbonylation of 4-heptenyl chloride (entry 3
in Table 2), any product derived from 5-exo cyclization of the
acyl radical was not detected. Moreover, the present carbony-
lation could proceed even under the atmospheric pressure of
CO,18 while the radical carbonylation usually requires higher
pressures of CO.10 However, these observations can be
explained if the electron transfer from SmI2 to acyl radicals is
extremely fast.19 We are currently examining the application
of this photoinduced new reduction system with SmI2 to
different classes of substrates, as well as clarifying the precise
mechanism of this carbonylation.
a RCl (0.5 mmol), CO (50 atm), SmI2 (4 mmol), THF (20 mL), 50
°C, 9 h, hν > 400 nm (xenon lamp 500 W, filter).
reduction of alkyl chlorides with SmI2, the copresence of carbon
monoxide leads to a novel carbonylation involving alkyl radicals
(or alkylsamarium species) as key intermediates. Thus, we
examined the photoinitiated reaction of alkyl chlorides with SmI2
in the presence of carbon monoxide.11,12 When the reaction of
1-chlorododecane with SmI2 was carried out under the pressure
of carbon monoxide (50 atm) upon irradiation with a xenon
lamp through a filter (hν > 400 nm),13 carbonylation of
1-chlorododecane took place successfully, giving 89% of
dodecyl tridecyl ketone (5, R ) n-C12H25), which incorporated
two dodecyl and two carbon monoxide units (eq 3 and entry 1
in Table 2). On the other hand, no carbonylation took place in
the dark.
Table 2 represents the results of the photoinduced carbon-
ylation of alkyl chlorides with CO and SmI2. The carbonylation
of alkyl chlorides bearing an olefinic unit proceeded successfully
to give the corresponding asymmetrical ketones in good yields
(entries 2 and 3). Similarly, secondary alkyl chlorides such as
cyclohexyl chloride underwent photoinduced carbonylation to
provide the products consisting of two alkyl and two carbon
monoxide units (entry 4). With tertiary alkyl chlorides like
1-adamantyl chloride and aryl chlorides like â-naphthyl chloride,
however, no carbonylation took place at all (only reduction to
the corresponding hydrocarbons occurred).
Acknowledgment. This research was supported in part by a Grant-
in-Aid for Scientific Research on Priority Areas “New Development
of Rare Earth Complexes” no.08220243 from the Ministry of Education,
Science, and Culture, Japan. We thank Dr. Ilhyong Ryu for helpful
suggestion and advice concerning the carbonylation reactions.
1
Supporting Information Available: Experimental details and H
NMR spectra (8 pages). See any current masthead page for ordering
and Internet access instructions.
Recently, Kagan et al. reported that the reaction of acyl
chlorides with SmI2 generated acylsamarium species, which
underwent dimerization to give asymmetrical ketones in the
presence of excess amounts of SmI2.14 In fact, the reaction of
JA963117P
(15) The third hypothesis suggests that the alkyl radical reacts with
samarium carbonyl species16 to give acylsamarium species directly. Thus,
we attempted to detect samarium carbonyl species with IR spectrometer:
After the reaction of SmI2 with CO (50 atm) upon visible light irradiation
(in the absence of substrates), CO was purged and immediately IR spectra
of the resulting solution was measured. However, no absorbance assigned
to samarium carbonyl species was detected.
(16) For a carbonyl complex of samarium, see: Kolobova, N. E.;
Suleimanov, G. Z.; Kazimirchuk, E. I.; Khandozhko, V. N.; Mekhdiev, R.
Yu.; Lokshin, B. V.; Ezernitskaya, M. G.; Beletskaya, I. P. IzV. Akad. Nauk
SSSR, Ser. Khim. 1985, 2833.
(17) The tin radical-mediated carbonylation of alkyl iodides with CO in
the copresence of excess styrene proceeds Via the capture of acyl radicals
with styrene: Ryu, I.; Kusano, K.; Yamazaki, H.; Sonoda, N. J. Org. Chem.
1991, 56, 5003.
(18) The photoinduced reaction of 1-dodecyl chloride (0.5 mmol) with
SmI2 (4 mmol) and CO (1 atm) in THF (20 mL) at 50 °C for 6 h provided
39% of dodecyl tridecyl ketone and 52% of n-dodecane.
N. Synlett 1995, 1249. (e) Ryu, I.; Muraoka, H.; Kambe, N.; Komatsu,
M.; Sonoda, N. J. Org. Chem. 1996, 61, 6396. (f) Ryu, I.; Sonoda, N.;
Curran, D. P. Chem. ReV. 1996, 96, 177. (g) Ryu, I.; Sonoda, N. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1050 and references cited therein.
(11) For the reactions of divalent organosamarium complexes with CO,
see: (a) Evans, W. J.; Grate, J. W.; Hughes, L. A.; Zhang, H.; Atwood, J.
L. J. Am. Chem. Soc. 1985, 107, 3728. (b) Evans, W. J.; Grate, J. W.;
Hughes, L. A.; Drummond, D. K.; Zhang, H.; Atwood, J. L. J. Am. Chem.
Soc. 1986, 108, 1722. (c) Evans, W. J. Polyhedron 1987, 6, 803. (d) Evans,
W. J.; Drummond, D. K. J. Am. Chem. Soc. 1988, 110, 2772. (e) Evans,
W. J.; Drummond, D. K.; Chamberlain, L. R.; Doedens, R. J.; Bott, S. G.;
Zhang, H.; Atwood, J. L. J. Am. Chem. Soc. 1988, 110, 4983.
(12) Collin, J.; Kagan, H. B. Tetrahedron Lett. 1988, 29, 6097.
(13) The photoinduced carbonylation was conducted by using a stainless
steel autoclave bearing glass windows. For the detailed experimental
procedure, see the Supporting Information.
(14) (a) Girard, P.; Couffignal, R.; Kagan, H. B. Tetrahedron Lett. 1981,
22, 3959. (b) Souppe, J.; Namy, J. L.; Kagan, H. B. Tetrahedron Lett.
1984, 25, 2869. (c) Sasaki, M.; Collin, J.; Kagan, H. B. Tetrahedron Lett.
1988, 29, 6105. (d) Collin, J.; Dallemer, F.; Namy, J. L.; Kagan, H. B.
Tetrahedron Lett. 1989, 30, 7407. (e) Collin, J.; Namy, J. L.; Dallemer,
F.; Kagan, H. B. J. Org. Chem. 1991, 56, 3118. (f) Namy, J. L.; Colomb,
M.; Kagan, H. B. Tetrahedron Lett. 1994, 35, 1723.
(19) The rate constants for the reaction of primary alkyl radicals with
SmI2 in THF/HMPA are reported to be 5 × 105 to 7 × 106 M-1 s-1
(Hasegawa, E.; Curran, D. P. Tetrahedron Lett. 1993, 34, 1717). While
the rate constant for the decarbonylation of PhCH2CO• is known to be 1.08
× 107 s-1 (41 °C), the reaction of phenylacetyl chloride with SmI2 did not
give any decarbonylated product.14b This suggests that the reduction of
acyl radicals by SmI2 is much faster than that of primary alkyl radicals.