Deoxygenative dimerization of benzylic and allylic alcohols, and their ethers and esters using lanthanum metal and chlorotrimethylsilane in the presence of a catalytic amount of iodine and copper(I) iodide

Article abstract of DOI:10.1246/bcsj.76.635

Benzylic and allylic alcohols were deoxygenatively dimerized by a treatment with lanthanum metal and chlorotri-methylsilane in the presence of a catalytic amount of iodine, giving the corresponding coupling products, alkanes, in moderate-to-good yields. This dimerization reaction was dramatically accelerated by the addition of a catalytic amount of copper(I) iodide. Similarly, ethers and esters were deoxygenatively dimerized by La/Me₃SiCl/^cat.I₂/^cat.CuI system in the presence of a catalytic amount of H₂O.

Full text of DOI:10.1246/bcsj.76.635

c. Jpn.
© 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 635–641 (2003)
635
e Chemical
ciety of Ja-
n
e Chemical
ciety of Ja-
n
Deoxygenative Dimerization of Benzylic and Allylic Alcohols, and Their
Ethers and Esters Using Lanthanum Metal and Chlorotrimethylsilane in
the Presence of a Catalytic Amount of Iodine and Copper(Ⅰ) Iodide
La Metal-Mediated Deoxygenative Dimerization
T. Nishino et al.
03
5
Toshiki Nishino, Yutaka Nishiyama,* and Noboru Sonoda*
1
Department of Applied Chemistry, Faculty of Engineering, Kansai University, Suita, Osaka 564-8680
(Received October 4, 2002)
SJA8
09-2673
294
Benzylic and allylic alcohols were deoxygenatively dimerized by a treatment with lanthanum metal and chlorotri-
methylsilane in the presence of a catalytic amount of iodine, giving the corresponding coupling products, alkanes, in
moderate-to-good yields. This dimerization reaction was dramatically accelerated by the addition of a catalytic amount
of copper(Ⅰ) iodide. Similarly, ethers and esters were deoxygenatively dimerized by La/Me3SiCl/cat.I2/cat.CuI system in
the presence of a catalytic amount of H2O.
02
02
0.1
The development of new synthetic reactions using lantha-
noid metal salts and organolanthanoid compounds has been
steadily increasing in organic chemistry.1 In contrast to many
reports available concerning the reduction of organic com-
pounds with low-valent lanthanoid compounds, such as samar-
ium diiodide,2 there are limited examples concerning the direct
use of lanthanoid metals as the reducing reagent.3 We recently
succeeded in the direct use of lanthanum metal on the reduc-
tion of carbonyl compounds, imines, and alkyl and aryl ha-
lides.4 We found that benzylic and allylic alcohols were deox-
ygenatively dimerized by a treatment with lanthanum metal
and chlorotrimethylsilane in the presence of a catalytic amount
of iodine. Furthermore, it was clarified that the reaction was
Scheme 1.
dramatically accelerated by the addition of a catalytic amount
ichiometric amount of halogenation reagent for the synthesis
of alkyl halides. Many alcohols can be purchased from com-
mercial sources, and easily synthesized from various organic
compounds, and alkyl halides are generally synthesized by the
substitution reaction of alcohols and their derivatives.7 Conse-
quently, the development of a deoxygenative dimerization
method of alcohols has attracted much attention; however,
there are few reports on the transformation. To the best of our
knowledge, low-valent titanium8 and niobium9 compounds
prepared by the reduction of metal halides are limited reagents
for the deoxygenative dimerization of alcohols. During the
course of the study on the direct use of zerovalent lanthanum
metal in organic synthesis, we found that some alcohols easily
underwent deoxygenative dimerization to give the correspond-
ing hydrocarbons (Table 1).
of copper(Ⅰ) iodide. We also found that this reaction system
was applicable to the deoxygenative dimerization of ethers and
esters. Significant features of these reactions are as follows: (i)
the formation of alkyl iodide as an intermediate with a catalyt-
ic amount of iodine, (ii) the generation of active zerovalent
copper as a catalyst of a coupling reaction, and (iii) lanthanum
playing a double role: as a generator of iodination reagent, io-
dotrimethylsilane, and as a reducing reagent of alkyl iodide
and/or copper(Ⅰ) iodide. This paper discloses the full results of
the deoxygenative dimerization of alcohols, ethers, and esters
with lanthanum metal and chlorotrimethylsilane in the pres-
ence of a catalytic amount of iodine and copper(Ⅰ) iodide in de-
tail (Scheme 1).5
Results and Discussion
When benzhydrol (1a) was treated with lanthanum metal
and chlorotrimethylsilane (2 equiv) in the presence of a cata-
lytic amount of iodine in THF as a solvent at 25 °C for 8 h,
1,1,2,2-tetraphenylethane (2a), the deoxygenative dimerized
product of 1a, was obtained along with diphenylmethane (en-
try 4). The reaction did not take place in the absence of iodine
or chlorotrimethylsilane (entries 1–3). The use of acetonitrile
as a solvent led to an increase in the conversion of 1a and the
Deoxygenative Dimerization of Alcohols. The reductive
coupling of alkyl halides to the corresponding alkanes is a use-
ful method for constructing carbon-carbon bonds. Although
reductive coupling can be accomplished with various re-
agents,6 there are some disadvantages for the utilization of
alkyl halides as a starting material: (i) an instability of tertiary
iodides, (ii) a lachrymatory property of some halides, such as
benzylic bromide, and (iii) the requirement of an excess or sto-

636 Bull. Chem. Soc. Jpn., 76, No. 3 (2003)
La Metal-Mediated Deoxygenative Dimerization
Table 1. Deoxygenative Dimerization of Benzhydrol with
Lanthanum Metala)
Table 2. Effect of Metal Halides on the Deoxygenative
Dimerization of 1aa)
Metal
Temp.
Yield/(%)b)
Entry
Halide
—
CuI
CuBr
CuCl
CuBr2
AgI
(°C)
82
25
25
25
25
25
25
25
25
25
82
82
82
2a
3a
35
13
8
1
2c)
3
4
5
6
7
8
9
10
11
12
13
54
87
88
91
96
85
91
84
99
87
68
58
59
7
4
I2
mmol
—
0.2
—
0.2
0.2
0.2
0.2
0.2
0.2
Me3SiCl
mmol
—
—
2.0
2.0
2.0
2.0
2.0
Time
Yield/(%)b)
Entry
Add. Solv.
h
8
8
8
8
8
1
2a
0
3a
0
14
4
1
2
3
4
—
—
—
—
—
—
THF
THF
THF
THF
CH3CN
CH3CN
NiI2
0
0
PbI2
CoI2
FeI2
ZnI2
TiI4
15
1
5
0
2
6
27
33
35
13
0
5
51
54
87
0
13
24
18
6c)
7
CuId) CH3CN 10 min
MnI2
8e)
9f)
2.0
2.0
CuId) CH3CN
CuId) CH3CN 10 min
8
a) Reaction conditions: 1a (1.0 mmol), La (1.0 mmol),
Me3SiCl (2.0 mmol), I2 (0.2 mmol), metal halide
(0.2 mmol), and CH3CN (3.0 mL) for 1 h. b) GC yields.
c) 10 min.
3
4
a) Reaction conditions: 1a (1.0 mmol), La (1.0 mmol), and
solvent (3.0 mL). b) GC yield. c) 82 °C. d) CuI (0.2 mmol)
was added. e) La was not used. f) Mg was used instead of
La.
yield of 2a (entry 5). For the reaction at higher temperature
(82 °C), the reaction was promoted, however, the selectivity of
2a was not affected by the reaction temperature (entry 6). It is
interesting to note that the deoxygenative dimerization reaction
was dramatically accelerated by the addition of a catalytic
amount of metal halides. When 1a was treated with lanthanum
metal in the presence of chlorotrimethylsilane (2 equiv), a cat-
alytic amount of iodine (0.2 equiv), and copper(Ⅰ) iodide
(0.2 equiv) in acetonitrile at 25 °C, 1a was completely con-
sumed within 10 min, and 2a was obtained in 87% yield (entry
7). When magnesium metal was used as a reducing reagent in-
stead of lanthanum metal, 2a and 3a were hardly produced
(entry 9). The effect of various metal halides on the reaction of
1a was examined; the results are given in Table 2. The other
copper halides, and silver, nickel, lead, cobalt, and iron iodides
showed catalytic activity for the reaction of 1a; however, in the
case of zinc, titanium, and manganese iodides, no improve-
ment of the selectivity and yield was observed.
A preparative method of iodotrimethylsilane by a halogen
exchange reaction of chlorotrimethylsilane with magnesium
iodide (MgI2) has been developed by Krüerke.10 It was already
known that the treatment of alcohols with iodotrimethylsilane,
which was generated in situ by a reaction of chlorotrimethylsi-
lane with sodium iodide in acetonitrile, gave the corresponding
alkyl iodides in good yields.11,12 We have recently shown that
alkyl iodides were reductively coupled by lanthanum metal,
giving the corresponding alkanes.4c Based on the results de-
scribed above, a possible reaction pathway involving the for-
mation of alkyl iodide is suggested, as shown in Scheme 2.
The first step involves the generation of iodotrimethylsilane by
a halogen-exchange reaction of chlorotrimethylsilane with lan-
thanum iodide, which is generated in situ by the reaction of
lanthanum metal with iodine. Iodotrimethylsilane reacts with
alcohol, forming the corresponding alkyl iodide. In the ab-
sence of copper(Ⅰ) iodide, in situ generated alkyl iodide is re-
Scheme 2. A possible reaction path.
ductively coupled by lanthanum metal, giving the correspond-
ing symmetrical alkane, and subsequently lanthanum iodide
species (LaIn) is regenerated. Thus, the reaction does not re-
quire an excess or stoichiometric amount of iodination reagent
despite the formation of alkyl iodide as an intermediate. In or-
der to confirm the possibility of an intermediacy of iodotrime-
thylsilane generated in situ by the reaction of lanthanum metal,
iodine, and chlorotrimethylsilane, iodotrimethylsilane or the
equivalent, mixture of sodium iodide and chlorotrimethylsi-
lane, was examined independently in the reaction of 1a. As
shown in Scheme 3, the treatment of 1a with lanthanum metal
and iodotrimethylsilane or sodium iodide/chlorotrimethylsi-
lane gave the dimerization product without using iodine (cf.
Table 1, entry 3).
It was found that the deoxygenative dimerization of alcohols

T. Nishino et al.
Bull. Chem. Soc. Jpn., 76, No. 3 (2003) 637
Scheme 3.
Scheme 4.
Scheme 5. A possible path of the reaction of alcohols in the
presence of a catalytic amount of Cul.
was markedly accelerated by the addition of a catalytic amount
of copper(Ⅰ) iodide. In order to obtain further information on
the role of copper(Ⅰ) iodide, the reaction of benzyl bromide (5)
with lanthanum metal was examined in the presence or ab-
sence of copper(Ⅰ) iodide. The treatment of 5 with lanthanum
metal in the presence of a catalytic amount of iodine and cop-
per(Ⅰ) iodide (0.2 equiv) in acetonitrile as a solvent at 25 °C for
5 h gave 1,2-diphenylethane (2d) in 74% yield; however, in the
absence of copper(Ⅰ) iodide, the reaction proceeded extremely
slow (11%) (Scheme 4). It had already been known that the
activated zerovalent metal generated in situ by the reduction of
metal halide with reducing reagent shows a higher reducing
ability than that of a commercially available zerovalent met-
al.13 Ebert et al. reported that benzylic and allylic halides were
reduced by activated copper generated by the reduction of cop-
per salt with lithium naphthalenide, giving the reductive cou-
pling products within a few minutes in good yields.14 In fact,
when copper(Ⅰ) iodide was treated with an equal molar amount
of lanthanum metal in acetonitrile as a solvent at 25 °C for
15 min, lanthanum metal was gradually dissolved, giving a
dark-brown suspension. Subsequently, the addition of benzyl
bromide (5) to the solution produced 1,2-diphenylethane (2d)
within 1 h in 70% yield.15 These results suggest that the acti-
vated zerovalent copper plays an important role in the reduc-
tive dimerization of in situ generated alkyl iodide. Therefore,
the deoxygenative dimerization of alcohol appears to occur
through the reaction pathway via the reduction of alkyl iodide
with activated copper generated by the reduction of copper(Ⅰ)
iodide with lanthanum metal (Scheme 5). For the other metal
iodides bearing a large oxidation-reduction potential, it is pro-
posed that metal halides were reduced by lanthanum species to
produce the corresponding activated zerovalent metal, which
acts as a reducing agent in the reactions (Table 2, entries 6–
10).16
Table 3. Deoxygenative Dimerization of Various Alcohols
with La Metala)
Yield/%b)
Entry
1
1
R1
R2 R3
2
3
13
6
4
1b
C6H5
CH3 CH3 54
29
29
36
6
2c) 1b
3
1c
C6H5
CH3
H
72d) 11
4c) 1c
54
42
67
59
34
0
11
15
5
10
18
0
7
5
6
7
8
9
1d
1e
1f
1g
1h
C6H5
H
H
H
H
H
H
H
H
H
H
H
H
H
—
—
—
—
—
p-CH3O-C6H4
p-CH3-C6H4
p-Cl-C6H4
p-CN-C6H4
C6H5CHwCH
10 1i
(71)e) n.q.f) n.q.f)
75g) n.q.f) n.q.f)
11 1j —CHwCH—(CH2)3—
12 1k
13 1l
14 1m
C11H23
C10H21
C11H23
CH3 CH3 trace (46) (23)h)
CH3
H
H
H
trace trace trace
trace trace trace
a) Reaction conditions: alcohol (1.0 mmol), La (1.0 mmol),
Me3SiCl (2.0 mmol), I2 (0.2 mmol), CuI (0.2 mmol), and
CH3CN (3.0 mL) at 82 °C for 1 h. b) GC yield. The number
on parenthesis indicated isolated yield. c) CoI2 was used
1
instead of CuI. d) Dl: meso = 50:50. Determined by H
NMR.
e) 1,6-Diphenyl-1,5-hexadiene:1,4-diphenyl-1,5-
hexadiene:3,4-diphenyl-1,5-hexadiene = 32:49:19. f) Not
1
quantified. g) Dl:meso = 50:50. Determined by H NMR.
h) 2-Methyl-2-tridecene:2-methyl-1-tridecene = 88:12.
In order to develop applications of this reaction, various al-
cohols were treated with lanthanum metal and chlorotrimethyl-
silane in the presence of a catalytic amount of iodine and cop-
per(Ⅰ) iodide in acetonitrile solvent as the solvent (Table 3).
The reaction of α-methylbenzyl alcohol (1c) efficiently pro-

638 Bull. Chem. Soc. Jpn., 76, No. 3 (2003)
La Metal-Mediated Deoxygenative Dimerization
Table 4. Deoxygenative Dimerization of Ethers and Esters
with La Metala)
ceeded, giving 2,3-diphenylbutane (2c) in 72% yield (entry 3).
Similarly, benzyl alcohol (1d) was deoxygenatively dimerized
under the same reaction conditions as that of 1a to give 1,2-
diphenylethane (2d) in 42% yield (entry 5). Methoxy, methyl,
and chloro substituted benzyl alcohols gave the corresponding
1,2-diarylethanes in moderate yields; however, the deoxygen-
ative dimerization of 4-cyanobenzyl alcohol did not proceed
(entries 6–9). In the case of tertiary alcohol (1b), the yield of
the deoxygenative dimerization product (2b) was slightly de-
creased due to an increase in the yield of 2-phenylpropene (4b)
as a byproduct (entry 1). The use of cobalt(Ⅱ) iodide instead of
copper(Ⅰ) iodide led to a decrease in the yield of the coupling
product, despite the good result for the coupling of 1a (entries
2 and 4). This method can be applied to allylic alcohols to
form 1,5-dienes. The reaction of 2-cyclohexene-1-ol (1j) with
lanthanum metal afforded 3,3ꢀ-bicyclohexenyl (2j) in 75%
yield (entry 11). Similar treatment of cinnamyl alcohol (1i)
produced a mixture of three isomers of 1,5-hexadienes in 71%
yield (entry 10). In contrast to benzylic and allylic alcohols,
the reaction of tertiary aliphatic alcohols, 2-methyl-2-tridec-
anol, resulted in the formation of a deoxygenation product
and dehydration products in preference to a dimerization prod-
uct (entry 12). In the case of primary and secondary aliphatic
alcohols, the expected dimerization reactions did not occur,
and trimethylsilyl ethers were obtained in almost quantitative
yields (entries 13 and 14). The explanation is that the reaction
of aliphatic silyl ether with hydrogen iodide is slower than that
of benzylic and allylic silyl ether.17 As a result, the iodination
and following coupling reaction are probably suppressed due
to the consumption of hydrogen iodide by the competing reac-
tion, which is a reaction of hydrogen iodide with lanthanum
metal.18
Entry
1c)
Substrate
Product
Yield(%)b)
62
6j
6j
2j
2
3
2j
81d)
65
6a
6c
2a
4
5
2c
2j
54e)
57d)
7j
6
7
7a
7c
2a
2c
85
44e)
a) Reaction conditions: substrate (1.0 mmol), La
(1.0 mmol), Me3SiCl (2.0 mmol), I2 (0.2 mmol), CuI
(0.2 mmol), H2O (2.0 mmol), and CH3CN (3.0 mL) at
82 °C for 1 h. b) GC yield. c) H2O was not added. d) Dl:
1
meso = 50:50. Determined by H NMR. e) Dl: meso =
Deoxygenative Dimerization of Ethers and Esters.
In
50:50. Determined by GC.
the deoxygenative dimerization of alcohols with the La/
Me3SiCl/cat.I2/cat.CuI system, the reaction pathway was suggest-
ed to involve the conversion of alcohols into the corresponding
alkyl iodides. Since it was already disclosed that ethers and es-
ters were efficiently converted to alkyl iodides by a treatment
with iodotrimethylsilane or hydrogen iodide,19 it is expected
that the deoxygenative dimerization of ethers and esters may
take place by treatment with La/Me3SiCl/cat.I2/cat.CuI. The
deoxygenative dimerization of 3-heptyloxycyclohexen (6j)
gave 3,3ꢀ-bicyclohexenyl (2j), but the yield of 2j was lower
than that of cyclohexenol (1j) (Table 4, entry 1). The yield of
2j was improved by the addition of a catalytic amount of H2O
to the reaction mixture (entry 2). Various ethers and esters
were also deoxygenatively dimerized by a treatment with lan-
thanum metal and chlorotrimethylsilane in the presence of a
catalytic amount of iodine, copper(Ⅰ) iodide, and H2O (Table
4). It has been already shown that the reaction of iodotrimeth-
ylsilane or sodium iodide/chlorotrimethylsilane with H2O is an
efficient in situ generation method of hydrogen iodide.20 Then,
it was suggested that the generation of alkyl iodide from ethers
or esters was accelerated by hydrogen iodide, which was gen-
erated by the reaction of Me3SiI with H2O. In the case of the
deoxygenative dimerization of 6j, heptyloxytrimethylsilane
was obtained as a byproduct. From these results, the following
reaction pathway is suggested for the reaction of ethers. At
first, hydrogen iodide is generated by the reaction of iodotri-
Scheme 6.
methylsilane with H2O, and then the reaction of ether with hy-
drogen iodide takes place to yield alkyl iodide. The iodide is
reductively dimerized by zerovalent copper to afford the cou-
pling product and alcohol. The generated alcohol reacts with
iodotrimethylsilane, giving the corresponding silyl ether and
regenerating hydrogen iodide. Hence, the reaction was effi-
ciently accelerated even when a catalytic amount of H2O was
added (Scheme 6).

T. Nishino et al.
Bull. Chem. Soc. Jpn., 76, No. 3 (2003) 639
CDCl3) δ 4.76 (s, 2H), 6.97–7.21 (m, 20H); 13C NMR (99.5 MHz,
CDCl3) δ 56.3, 125.8, 128.1, 128.5, 143.4; IR (KBr) 3079, 3022,
Conclusions
2890, 1595, 1490, 1447, 1070, 1028, 744, 684 cm−1
.
In summary, we found that alcohols were deoxygenatively
dimerized by the treatment of lanthanum metal and chlorotri-
methylsilane in the presence of a catalytic amount of iodine.
The reaction was dramatically accelerated by the addition of a
catalytic amount of copper(Ⅰ) iodide. Similarly, ethers and es-
ters were deoxygenatively dimerized by using the La/Me3SiCl/
cat.I2/cat.CuI system in the presence of a small amount of water,
giving the corresponding dimerization products. The key fea-
tures of this approach were firstly the formation of alkyl iodide
as an intermediate with a catalytic amount of iodine, and sec-
ondary the generation of active zerovalent copper as a coupling
reagent. These features were linked to each other by lantha-
num, which played a doubly important role as a generator of
an iodination reagent and a reducing reagent of copper(Ⅰ) io-
dide, to constitute the catalytic cycle.
Diphenylmethane (3a). 1H NMR (400 MHz, CDCl3) δ 3.97
(s, 2H), 7.16–7.29 (m, 10H); 13C NMR (99.5 MHz, CDCl3) δ 41.9,
126.0, 128.4, 128.9, 141.0; IR (neat) 3061, 3026, 2907, 1599,
1493, 1451, 1076, 1029, 735, 689 cm−1
.
General Procedure of the Deoxygenative Coupling of Alco-
hols (1) Using Lanthanum Metal in the Presence of Copper(Ⅰ)
Iodide. After lanthanum powder (139 mg, 1.0 mmol), iodine
(51 mg, 0.2 mmol), and copper(Ⅰ) iodide (36 mg, 0.2 mmol) were
placed in a three-necked flask, CH3CN (3 mL) and alcohol
(1.0 mmol) were added. Then, chlorotrimethylsilane (217 mg,
2.0 mmol) was added, and the mixture was stirred at 82 °C for 1 h
under a nitrogen atmosphere. After the reaction, aq HCl was add-
ed to the reaction mixture and extracted with benzene. The organ-
ic layer was dried over MgSO4. The resulting mixture was filtered
and the filtrate was concentrated. Purification of the residue by
HPLC afforded the corresponding deoxygenative dimerization,
deoxygenation, and dehydration products. Products were charac-
terized by comparing their spectral data (1H- and 13C NMR and
IR) with those of authentic samples. The GC yields were deter-
mined by the internal-standard method.
Experimental
Instruments. 1H and 13C NMR spectra were recorded on a
JEOL JNM-GSX-400 (400 and 99.5 MHz) spectrometer using
CDCl3 as a solvent with tetramethylsilane as the internal standard.
FT-IR spectra were obtained on a Perkin Elmer Model PARA-
GON 1000 spectrophotometer. Mass spectra were measured on a
Shimadzu Model QP-5050A instrument. Gas chromatography
(GC) was carried out on a Shimadzu GC-14A instrument
equipped with a flame ionizing detector using a capillary column
(Hicap-CBP-1-S25-025, 0.25 mm × 25 m). HPLC separation
was performed on recycling preparative HPLC (Japan Analytical
Industry Co., Ltd. LC-908) equipped with JAIGEL-1H (20 mm ×
600 mm) and JAIGEL-2H (20 mm × 600 mm) columns and an RI
detector.
Reagents. Alcohols (1e, 1g, and 1h) were synthesized by re-
duction of the corresponding aldehydes with NaBH4. 2-Methyl-2-
tridecanol (1l) was synthesized by the reaction of ethyl dode-
canoate with MeMgI. Ethers (6) were prepared by the reaction of
the corresponding alcohols (1) with alkyl iodide in the presence of
sodium hydride. Esters (7) were prepared by the reaction of sodi-
um alkoxide with acetyl chloride. The other alcohols, iodine, met-
al halides, and chlorotrimethylsilane were commercially available
high-grade products, and were used without purification. Lantha-
num metal was a commercially available high-grade product, and
was used after powderization. The other reagents and solvents
were purified by the usual methods before use.
2,3-Dimethyl-2,3-diphenylbutane (2b):22
1H NMR (400
MHz, CDCl3) δ 1.31 (s, 12H), 7.05–7.18 (m, 10H); 13C NMR
(99.5 MHz, CDCl3) δ 25.2, 43.6, 125.3, 126.5, 128.5, 146.7; IR
(KBr) 3025, 2967, 2890, 1601, 1483, 1450, 1370, 1159, 1079,
1027, 758, 698 cm−1
.
2,3-Diphenylbutane (2c) (Mixture of meso and dl Isomers):23
1H NMR (400 MHz, CDCl3) δ 0.99–1.04 (m, 3H), 1.25–1.30 (m,
3H), 2.70–2.82 (m, 1H), 2.91–3.03 (m, 1H), 6.99–7.32 (m, 10H);
13C NMR (99.5 MHz, CDCl3) δ 18.0, 21.0, 46.5, 47.2 125.6,
125.9, 127.5, 127.6, 128.1, 145.7, 146.3; IR (CHCl3) 3060, 3025,
2987, 2925, 1601, 1483, 1450, 1370, 1159, 1079, 1027, 758,
699 cm−1
.
1,2-Diphenylethane (2d): 1H NMR (400 MHz, CDCl3) δ
2.91 (s, 4H), 7.16–7.29 (m, 10H); 13C NMR (99.5 MHz, CDCl3) δ
38.1, 126.0, 128.5, 128.6, 141.9; IR (neat) 3062, 2927, 2925,
2858, 1601, 1494, 1453, 1218, 1067, 1029, 755, 698 cm−1
.
1,2-Bis(4-methoxybenzene)ethane (2e):24
1H NMR (400
MHz, CDCl3) δ 2.81 (s, 4H), 3.76 (s, 6H), 6.79–7.07 (m, 8H); 13
NMR (99.5 MHz, CDCl3) δ 37.2, 55.2, 113.6, 129.2, 133.8, 157.6;
IR (KBr) 2963, 2914, 2849, 1609, 1509, 1242, 1029, 831, 721
C
cm−1
.
1,2-Bis(4-methylbenzene)ethane (2f):25
1H NMR (400
MHz, CDCl3) δ 2.30 (s, 6H), 2.84 (s, 4H), 7.06 (s, 8H); 13C NMR
(99.5 MHz, CDCl3) δ 21.0, 37.6, 128.1, 128.8, 135.1, 138.7; IR
Deoxygenative Coupling of Benzhydrol (1a) with Lantha-
num Metal. Lanthanum powder (139 mg, 1.0 mmol) and iodine
(51 mg, 0.2 mmol) were placed in a round-bottomed flask.
CH3CN (3 mL) and benzhydrol (184 mg , 1.0 mmol) were added
to the flask. Then, chlorotrimethylsilane (217 mg, 2.0 mmol) was
added, and the mixture was stirred at 25 °C for 8 h under a nitro-
gen atmosphere. The color of the solution gradually changed to
gray. After the reaction, aq HCl was added to the reaction mixture
and extracted with benzene. The organic layer was dried over
MgSO4. The resulting mixture was filtered and the filtrate was
concentrated. Purification of the residue by HPLC afforded the
1,1,2,2-tetraphenylethane (2a) and diphenylmethane (3a). The
products were characterized by comparing their spectral data (1H-
and 13C NMR and IR) with those of authentic samples. The GC
yields were determined by the internal standard method.
(KBr) 3001, 2915, 2854, 1512, 1452, 1142, 1098, 1042, 811 cm−1
.
1,2-Bis(4-chlorobenzene)ethane (2g):25
1H NMR (400
MHz, CDCl3) δ 2.84 (s, 4H), 7.02–7.23 (m, 8H); 13C NMR (99.5
MHz, CDCl3) δ 37.0, 128.3, 129.7, 131.6, 139.5; IR (KBr) 2924,
2859, 1488, 1087, 1013, 823, 791 cm−1
.
Mixture of 1,6-Diphenyl-1,5-hexadiene (2i–a), 1,4-Diphenyl-
1,5-hexadiene (2i–b), and 3,4-Diphenyl-1,5-hexadiene (2i–c):26
1H NMR (400 MHz, CDCl3) δ 2.34–2.41 (m, 1.3H, allylic CH2 of
2i–a), 2.57–2.69 (m, 1.0H, allylic CH2 of 2i–b), 3.37–3.45 (m,
0.5H, benzylic CH of 2i–b), 3.57–3.55 (m, 0.4H, benzylic CH of
2i–c), 4.78–6.44 (m, 5H), 7.01–7.34 (m, 10H); 13C NMR
(99.5 MHz, CDCl3) δ 32.9, 39.0, 49.9, 55.4, 114.5, 115.6, 125.8,
125.9, 126.2, 126.2, 126.8, 127.5, 127.9, 128.0, 128.2, 128.3,
128.3, 128.4, 129.8, 130.2, 131.2, 137.5, 137.5, 139.9, 141.3,
1,1,2,2-Tetraphenylethane (2a).21 1H NMR (400 MHz,

640 Bull. Chem. Soc. Jpn., 76, No. 3 (2003)
La Metal-Mediated Deoxygenative Dimerization
142.3, 143.5; IR (neat) 3080, 3059, 3025, 2921, 2841, 1599, 1493,
29, (1992). d) S. Kobayashi, Synlett, 1994, 689. e) Y. Kamochi
and T. Kubo, J. Syn. Org. Chem. Jpn., 52, 285 (1994). f) T.
Imamoto, “Lanthanides in Organic Synthesis,” Academic Press
(1994). g) F. Matsuda, J. Syn. Org. Chem. Jpn., 53, 987 (1995).
h) G. A. Molander and C. R. Harris, Chem. Rev., 96, 307 (1996).
i) Y. Ito, Y. Fujiwara, and T. Yamamoto, “Kikan Kagaku Sousetu;
Organic Synthesis by Means of Lanthanoids No. 37,” Gakkai
Press Center, Tokyo (1998). j) S. Kobayashi, “Lanthanide: Chem-
istry and Use in Organic Synthesis,” Springer-Verlag, Berlin,
Herdelberg (1999). k) P. G. Steel, J. Chem. Soc., Perkin Trans. 1,
2001, 2727, and references cited therein.
1449, 964, 911, 743, 699 cm−1
.
3,3ꢀ-Bicyclohexenyl (2j) (mixture of meso and dl Isomers):27
1H NMR (400 MHz, CDCl3) δ 1.31–2.13 (m, 14H), 5.53–5.73 (m,
4H); 13C NMR (99.5 MHz, CDCl3) δ 22.2, 22.3, 25.4, 25.9, 26.0,
40.1, 127.4, 127.7, 128.0, 128.1, 130.1, 130.2, 130.3, 130.4,
130.4, 130.5, 130.6; IR (neat) 3016, 2926, 2857, 2835, 1446,
1141, 898, 722 cm−1
.
Deoxygenative Coupling of 1a Using Lanthanum Metal and
Iodotrimethylsilane. Lanthanum powder (139 mg, 1.0 mmol)
was placed in a round-bottomed flask. CH3CN (3 mL) and 1a
(184 mg, 1.0 mmol) were added to the flask. Then, iodotrimethyl-
silane (400 mg, 2.0 mmol) was added, and the mixture was stirred
at 25 °C for 8 h under a nitrogen atmosphere. After the reaction, a
similar work-up to that of the deoxygenative coupling of alcohols
using lanthanum metal was carried out.
Deoxygenative Coupling of 1a Using Lanthanum Metal, So-
dium Iodide, and Chlorotrimethylsilane. Lanthanum powder
(139 mg, 1.0 mmol) and sodium iodide (300 mg, 2.0 mmol) were
placed in a round-bottomed flask. CH3CN (3 mL) and 1a
(184 mg, 1.0 mmol) were added to the flask. Then, chlorotrimeth-
ylsilane (217 mg, 2.0 mmol) was added, and the mixture was
stirred at 25 °C for 8 h under a nitrogen atmosphere. After the re-
action, a similar work-up to that of the deoxygenative coupling of
alcohols using lanthanum metal was carried out. The GC yields
were determined by the internal-standard method.
Reductive Coupling of Benzyl Bromide (5) with Lanthanum
Metal. Lanthanum powder (139 mg, 1.0 mmol) and iodine
(51 mg, 0.2 mmol) were placed in a round-bottomed flask.
CH3CN (3 mL) and 5 (171 mg, 1.0 mmol) were added to the flask.
The mixture was then stirred at 25 °C for 5 h under a nitrogen at-
mosphere. After the reaction, a similar work-up to that of the
deoxygenative coupling of alcohols using lanthanum metal was
carried out. The GC yields were determined by the internal-stan-
dard method.
2
P. Girard, J. L. Namy, and H. B. Kagan, J. Am. Chem. Soc.,
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Reductive Coupling of 5 with Lanthanum Metal in the Pres-
5
T. Nishino, Y. Nishiyama, and N. Sonoda, Tetrahedron
ence of Copper(Ⅰ) Iodide.
After lanthanum powder
(139
Lett., 43, 3689 (2002).
mg, 1.0 mmol), iodine (51 mg, 0.2 mmol), and copper(Ⅰ) iodide
(36 mg, 0.2 mmol) were placed in a round-bottomed flask,
CH3CN (3 mL) and 5 (171 mg, 1.0 mmol) were added. The mix-
ture was then stirred at 25 °C for 5 h under a nitrogen atmosphere.
After the reaction, a similar work-up to that of the deoxygenative
coupling of alcohols using lanthanum metal was carried out. The
GC yields were determined by the internal-standard method.
General Procedure of the Deoxygenative Coupling of
Ethers (6) or Esters (7). After lanthanum powder (139 mg,
1.0 mmol), iodine (51 mg, 0.2 mmol), and copper(Ⅰ) iodide
(36 mg, 0.2 mmol) were placed in a three-necked flask, CH3CN
(3 mL), ether or ester (1.0 mmol) and H2O (4 mg, 0.2 mmol) were
added. Then, chlorotrimethylsilane (217 mg, 2.0 mmol) was add-
ed, and the mixture was stirred at 82 °C for 1 h under a nitrogen
atmosphere. The color of the solution gradually changed to gray.
After the reaction, a similar work-up to that of the deoxygenative
coupling of alcohols using lanthanum metal was carried out. The
GC yields were determined by the internal-standard method.
6
R. C. Larock, “Comprehensive Organic Transformations:
A guide to functional group preparations,” VCH Publishers, New
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7
a) R. Bohlmann, “Comprehensive Organic Synthesis,” ed
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8
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References
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1
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18 In the case of primary and secondary aliphatic alcohols,
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