Photoaccelerated reductive coupling of acid chlorides with conjugate dienes and styrenes by use of neodymium metal in N,N-dimethylacetamide

Article abstract of DOI:10.1246/cl.2009.16

Upon photoirradiation, neodymium metal powder in N,N-dimethylacetamide (DMAC) exhibits excellent reducing ability for the reductive coupling of benzoyl chlorides with conjugate dienes and styrenes. Copyright

Full text of DOI:10.1246/cl.2009.16

16
Chemistry Letters Vol.38, No.1 (2009)
Photoaccelerated Reductive Coupling of Acid Chlorides with Conjugate Dienes and Styrenes
by Use of Neodymium Metal in N,N-Dimethylacetamide
Zhi-fang Li,1;2 Yuri Tomisaka,1 Akihiro Nomoto,1 Yongmin Zhang,ꢀ3 and Akiya Ogawaꢀ1
1Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University,
1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531
2Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education,
Hangzhou Normal University, Hangzhou 310012, P. R. China
3Department of Chemistry, Zhejiang University, Xi-xi Campus, Hangzhou 310028, P. R. China
(Received September 24, 2008; CL-080917; E-mail: ogawa@chem.osakafu-u.ac.jp)
Upon photoirradiation, neodymium metal powder in N,N-
Table 1. Reductive coupling of benzoyl chloride with a 1,3-
dienea
dimethylacetamide (DMAC) exhibits excellent reducing ability
for the reductive coupling of benzoyl chlorides with conjugate
dienes and styrenes.
O
CH3
CH3
CH3
O
CH3
CH3
Ln / hν
DMAC
Cl
+
CH3 O
Recently lanthanoid metal salts and organolanthanoid com-
pounds have been widely employed in organic synthesis. Among
them, divalent lanthanoid salts, especially samarium diiodide,
work as useful reducing agents in synthetic organic reactions.
Zero-valent lanthanoid metals also bear potential reducing abil-
ity. However, the use of zero-valent lanthanoid metals them-
selves directly in organic synthesis is still rare. The advantages
of the use of lanthanoid metals are the electron economies com-
pared with divalent lanthanoid species, because lanthanoid met-
als can afford three electrons from the zero-valent state to the
stable trivalent state. In addition, another advantage of the use
of lanthanoid metals is easy operation. However, the problems
of the use of lanthanoid metals are the heterogeneous nature
in organic solvents and lower reactivity. In order to increase the
reducing ability of lanthanoid metals, some additives are em-
ployed. For example, Nishiyama et al. found that iodoalkanes
could be reduced with lanthanum metal in the presence of a
catalytic amount of iodine.1 Samarium metal2a,2b and cerium
metal2c have been reported to promote pinacol coupling reac-
tions by using iodine as the activating reagent. The silylative
coupling reaction mediated by ytterbium/Me3SiBr in hexa-
methylphosphoramide has also been reported by Fujiwara et al.3
Talukdar and Fang described the coupling reaction of aromatic
aldehydes mediated by samarium in the presence of aqueous
hydrochloric acid.4
Recently, we have found that photoirradiation dramatically
enhances the reducing ability of some rare earth metals (e.g., Ce,
Nd, Sm, and Eu) toward the reductive deiodation of iodoal-
kanes.5 In this paper, we wish to report that neodymium metal
upon photoirradiation (Nd/hꢀ) acts as an electron-economical
reducing agent for the reductive coupling of aroyl chlorides with
conjugate dienes and styrenes with easy operation.6,7
When a mixture of benzoyl chloride (1 mmol) and 2,3-di-
methyl-1,3-butadiene (2 mmol) in DMAC (N,N-dimethylacet-
amide) (5 mL) was treated with lanthanoid metals powder
(0.5 mmol) such as samarium, cerium, neodymium, and europi-
um under photoirradiation conditions for 2 h,8 the cross coupling
product was obtained in good yield. It should be noted that when
the reaction was performed in the dark, the yield was low. When
the reaction was performed in THF, acetonitrile, or DME, no
reaction took place at all (Table 1).
Ln
Condition
Sovent
Time/h
Yield/%b
Sm
Sm
Sm
Sm
Sm
Ce
hꢀ
hꢀ
hꢀ
dark
hꢀ
dark
hꢀ
dark
hꢀ
dark
hꢀ
THF
CH3CN
DME
5
5
5
6
2
6
2
6
2
6
2
0
0
0
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
DMAC
58
94
20
83
42
95
55
78
Ce
Nd
Nd
Eu
Eu
aReaction conditions: Benzoyl chloride (1 mmol), 2,3-dimeth-
yl-1,3-butadiene (2 mmol), Ln (0.5 mmol), hꢀ (Xe lamp),
DMAC. Isolated yield based on benzoyl chloride used.
b
By using neodymium metal powder under photoirradiation,
4-toluoyl chloride and 4-chlorobenzoyl chloride can also react
with 1,3-diene smoothly to give the corresponding coupling
products in high yields (Scheme 1).
Under the same reaction conditions, the cross coupling of
benzoyl chloride with isoprene was also examined. The benzoyl
radical C selectively attacks the isoprene a position to give the
coupling product A9 in good yield. The product B formed
through b attack was not obtained at all (Scheme 2). This regio-
selectivity can be explained by the difference in stability be-
tween allylic radical intermediates D and E.
Next, we examined the reductive coupling by using a cyclic
diene. When the photoirradiated reaction of benzoyl chloride
(1 mmol) with 1,3-cyclohexadiene (1.1 mmol) was conducted
in the presence of neodymium metal powder (0.5 mmol), another
type of coupling product F was obtained in 65% yield
(Scheme 3). In this case, the allyl radical G formed in situ from
aroyl radical and 1,3-cyclohexadiene is a secondary radical, and
does not homocouple, most probably owing to steric factors. The
allyl radical G undergoes single electron transfer from low-
valent Nd species, generating allyl anion species H, which is
aroylated with aroyl chloride to give the coupling product F.
Furthermore, the present photoinduced coupling reaction of
aroyl chlorides with conjugated dienes using Nd metal powder
can be applied to reductive coupling with styrene derivatives
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.1 (2009)
17
R
R
O
O
O
CH3
CH3
80% (R =H)
74% (Me)
85% (Cl)
Ph
O
O
CH3
Nd / hν
Nd / hν
Cl
Cl
+
+
+
Cl
+
DMAC
CH3
CH3 O
O
DMAC
R
R
CH3
R
R
R = H, Me, Cl
Yield = 85-95%
Ph
Ph
O
O
Nd / hν
Scheme 1.
70%
DMAC
O
O
O
O
O
55%
(syn:anti
= 50:50)
Nd / hν
Nd / hν
Cl
Cl
DMAC
+
DMAC
O
A 86% (only E,E)
Nd / hν
Scheme 5.
This work is supported by Grant-in-Aid for Scientific Re-
search on Priority Areas (Area 444, No. 19020061) and Scientif-
ic Research (B, No. 19350095), from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. Z. F. Li ac-
knowledges the Japan Society for the Promotion of Science
(JSPS) for a postdoctoral fellowship.
dimerization
O
- Cl-
O
O
b
b
a
a
E
C
D
O
O
not formed
B
References and Notes
1
2
3
a) T. Nishino, T. Watanabe, M. Okada, Y. Nishiyama, N.
Sonada, J. Org. Chem. 2002, 67, 966. b) T. Nishino, M. Okada,
T. Kuroki, T. Watanabe, Y. Nishiyama, N. Sonada, J. Org.
Chem. 2002, 67, 8696.
a) R. Yanada, N. Negoro, M. Okaniwa, T. Ibuka, Tetrahedron
1999, 55, 13947. b) R. Yanada, T. Ibuka, J. Synth. Org. Chem.
Jpn. 2000, 58, 597. c) T. Imamoto, T. Kusumoto, Y. Hatanaka,
M. Yokoyama, Tetrahedron Lett. 1982, 23, 1353.
a) W. Jin, Y. Makioka, T. Kitamura, Y. Fujiwara, J. Org. Chem.
2001, 66, 514. b) Y. Taniguchi, T. Kuno, M. Nakahashi, K.
Takaki, Y. Fujiwara, Appl. Organomet. Chem. 1995, 9, 491.
S. Talukdar, J.-M. Fang, J. Org. Chem. 2001, 66, 330.
a) Y. Tomisaka, K. Tsuchii, A. Ogawa, J. Alloys Compd. 2006,
408–412, 427. Also, see: b) A. Ogawa, Y. Sumino, T. Nanke, S.
Ohya, N. Sonada, T. Hirao, J. Am. Chem. Soc. 1997, 119, 2745.
c) A. Ogawa, S. Ohya, T. Hirao, Chem. Lett. 1997, 275. d) Y.
Sumino, N. Harato, Y. Tomisaka, A. Ogawa, Tetrahedron
2003, 59, 10499.
a) Y. Liu, Y. Zhang, Tetrahedron Lett. 2004, 45, 1295. b) Y. Liu,
Y. Zhang, Tetrahedron 2003, 59, 8429. c) Y. Liu, X. Liu, Y.
Zhang, Tetrahedron Lett. 2003, 44, 1667.
For Mg/R3SiCl-induced reductive coupling of acyl halides or
acid anhydrides with electron-deficient olefins, see: a) T. Ohno,
H. Aramaki, H. Nakahiro, I. Nishiguchi, Tetrahedron 1996, 52,
1943. b) T. Ohno, M. Sakai, Y. Ishino, T. Shibata, H.
Maekawa, I. Nishiguchi, Org. Lett. 2001, 3, 3439. c) I.
Nishiguchi, Y. Yamamoto, M. Sakai, T. Ohno, Y. Ishino, H.
Maekawa, Synlett 2002, 759.
Scheme 2.
O
O
Nd / hν
DMAC
+
Nd / hν
Cl
65%
(only trans)
O
- Cl-
O
F
Cl
O
O
O
Nd / hν
4
5
G
H
Scheme 3.
O
Ph
O
Nd / hν
6
7
+
Cl
DMAC
O
80%
O
- Cl-
Nd / hν
Cl
O
O
O
Nd / hν
Scheme 4.
8
9
In the stoichiometric reaction, Ln metals were changed to
LnCl3, and the resulting solution was homogeneous.
Only E,E isomer was obtained, and no formation of Z isomers
(Scheme 4).10 In this case, the reductive coupling reaction pro-
ceeded similarly to the case of cyclic dienes, providing the cor-
responding coupling product derived from two molecules of
benzoyl groups and one molecule of styrene. Representative re-
sults of the reductive coupling of aroyl chlorides with styrenes
using a Nd/hꢀ system are shown in Scheme 5.
In summary, under photoirradiation, lanthanoid metals, such
as cerium, neodymium, samarium, and europium metals indicate
higher reducing abilities toward the reductive transformation of
acid chlorides. By using these novel photoinduced reduction sys-
tems of rare earth metals, benzoyl chloride reacts with dienes
and styrenes, giving the corresponding coupling products in
good yields.
were confirmed (see ref. 6): E,E isomer: ꢀmax(KBr)/cmꢁ1
:
3062, 2949, 1686, 1596, 1580, 1448. 1H NMR ꢁH(CDCl3):
8.01–7.96 (4H, m), 7.58–7.55 (2H, m), 7.48–7.44 (4H, m),
5.31 (2H, d, J ¼ 1:2 Hz), 3.64 (4H, s), 2.13–2.11 (4H, t,
J ¼ 3:2 Hz), 1.68 (6H, s). 13C NMR ꢁ(CDCl3): 182.4, 120.6,
116.6, 113.4, 112.7, 112.1, 112.0, 49.3, 33.0, 11.7. MS(EI)
m=z(%): 347 (Mþ þ 1, 0.72), 346 (Mþ, 1.56), 241 (0.68), 226
(2.17), 173 (5.11), 105 (100.00), 77 (50.93).
10 Benzoyl chloride (1 mmol), styrene (1.1 mmol), and Nd powder
(0.5 mmol) were usually employed for the reductive coupling
reaction with styrenes. Similar results were obtained when ben-
zoyl chloride (2 mmol), styrene (1.1 mmol), and Nd (0.8 mmol)
were used.
Published on the web (Advance View) November 29, 2008; doi:10.1246/cl.2009.16