Dilithium tetrachlorocuprate(II) catalyzed oxidative homocoupling of functionalized grignard reagents

Article abstract of DOI:10.1055/s-0032-1316841

An efficient procedure is described for the oxidative homocoupling of functionalized Grignard reagents using a catalytic amount of dilithium tetrachlorocuprate(II) (CuLi₂Cl₄) in the presence of pure oxygen gas. This method is applied successfully to a variety of aryl, heteroaryl, alkyl, alkenyl and alkynyl halides, which are converted into the corresponding homocoupled products in good to excellent yields. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0032-1316841

518▌
PAPER
paper
Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling of
Functionalized Grignard Reagents
Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling
Si-Kai Hua,b Qiu-Peng Hu,b Jiangmeng Ren,*b Bu-Bing Zeng*a,b
a
Shanghai Key Laboratory of New Drug Design, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237,
P. R. of China
b
Shanghai Key Laboratory of Chemical Biology, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237,
P. R. of China
Fax +86(21)64253689; E-mail: renjm@ecust.edu.cn; E-mail: zengbb@ecust.edu.cn
Received: 24.09.2012; Accepted after revision: 16.12.2012
Michael additions, etc.3 Although homocouplings using
organocopper (RCu or R2LiCu) species as the reducing
and coupling reagents are known,4 the reactions suffered
from several limitations. The reaction conditions em-
Abstract: An efficient procedure is described for the oxidative ho-
mocoupling of functionalized Grignard reagents using a catalytic
amount of dilithium tetrachlorocuprate(II) (CuLi2Cl4) in the pres-
ence of pure oxygen gas. This method is applied successfully to a
variety of aryl, heteroaryl, alkyl, alkenyl and alkynyl halides, which ployed were usually harsh, with low to moderate yields of
are converted into the corresponding homocoupled products in
good to excellent yields.
products being obtained. The scope of the reactions was
also limited to aryl and terminal alkynes. A stoichiometric
Key words: homocoupling,
Grignard reagents, oxidant, metalation
dilithium
tetrachlorocuprate(II),
amount (or more) of the copper salt was needed and poor
functional group tolerance was apparent.4 Herein, we re-
port an efficient and practical method for the dilithium tet-
rachlorocuprate(II) catalyzed homocoupling of Grignard
Transition metal catalyzed homocoupling reactions of or- reagents containing different functional groups.
ganohalogen compounds to form carbon–carbon bonds
represent a powerful tool in modern organic chemistry.1
N
Br
MgBr
Br
2-iodopropane
CuLi2Cl4, N2
Instead of using the classical palladium- and nickel-based
catalysts, research has been devoted to developing meth-
ods that employ other metal reagents such as titanium(IV)
chloride (TiCl4),1a thallium(I) chloride (TlCl),1b oxovana-
dium(V) ethoxydichloride [VO(OEt)Cl2],1c,d iron(III)
chloride (FeCl3),1e–j cobalt(II) chloride (CoCl2),1g,k,l cop-
per(I) bromide (CuBr),1m manganese(II) chloride
(MnCl2)1f,n,o and zinc bromide (ZnBr2).1p In recent years,
this methodology has evolved into a general and efficient
strategy for the synthesis of natural products, pharmaceu-
ticals, dyes, agrochemicals, chiral ligands and catalysts,
conducting materials, functional polymers, etc.2
Br
+
Br
N
N
N
3%
31%
Scheme 1 Coupling reactions catalyzed by dilithium tetrachlorocu-
prate(II) (CuLi2Cl4)
The initial investigation was conducted using naphthalen-
1-ylmagnesium bromide (1a) as a model substrate and the
results are summarized in Table 1. When the reaction was
performed under a pure nitrogen atmosphere, 1,1′-binaph-
thalene (1b) was isolated in only 3% yield (Table 1, entry
1). However, it was surprising that 1,1′-binaphthalene
(1b) was obtained in 35% yield in the presence of 2-iodo-
propane under nitrogen (Table 1, entry 2). As reported
previously,1f,h,m the presence of an oxidant was crucial in
this type of reaction. It was therefore speculated that 2-io-
dopropane might play a role as an oxidant. Subsequently,
it was observed that 2-iodopropane had less effect when a
stronger oxidant was present in the reaction system (Table
1, entries 3–6). In the initial screening of the oxidant
(Table 1, entries 3, 5 and 7–9), it was found that pure ox-
ygen gas was an excellent oxidant, giving 1b in a high
88% yield (Table 1, entry 5).
During our initial studies on the dilithium tetrachlorocu-
prate(II) (CuLi2Cl4) catalyzed cross-coupling reaction be-
tween (5-bromopyridin-3-yl)magnesium bromide and 2-
iodopropane under a nitrogen atmosphere,3 we were sur-
prised to find that only a trace amount of the desired prod-
uct, 3-bromo-5-isopropylpyridine had formed, and that a
homocoupling by-product, 5,5′-dibromo-3,3′-bipyridine,
was obtained in 31% yield (Scheme 1). Based on the
above result, we envisaged that dilithium tetrachlorocu-
prate(II) could catalyze the homocoupling reaction of var-
ious Grignard reagents. To the best of our knowledge, the
dilithium tetrachlorocuprate(II) catalyst was always ap-
plied in cross-couplings, ring-opening of epoxides,
In 2008, Moglie and co-workers reported using copper(II)
chloride–lithium–4,4′-di-tert-butylbiphenyl (CuCl2–Li–
DTBB) to catalyze the homocoupling reactions of aryl,
heteroaryl, benzyl and alkenyl Grignard reagents.1q
Whilst the present work shows that dilithium tetrachloro-
SYNTHESIS 2013, 45, 0518–0526
Advanced online publication: 10.01.2013
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0032-1316841; Art ID: SS-2012-H0751-OP
© Georg Thieme Verlag Stuttgart · New York

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Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling
519
Table 1 Screening of the Reaction Conditionsa
cuprate(II) works just as well. To further explore whether
copper(II) chloride or lithium chloride (LiCl) played a key
role in this reaction, model reactions were again per-
formed using catalytic amounts of copper(II) chloride
and/or lithium chloride, in tetrahydrofuran at room tem-
perature, under an oxygen atmosphere for two hours. In
the absence of copper(II) chloride, only a trace amount of
the desired product was obtained (Table 1, entry 10). In
contrast, when lithium chloride was absent, the desired
product 1b was obtained in moderate yield, indicating that
the copper salt was important for this reaction to proceed
(Table 1, entry 11). However, it was apparent that the ad-
dition of lithium chloride improved the reaction yield. It
was speculated that not only did lithium chloride increase
the solubility of copper(II) chloride,5 it also promoted
smoothly the in situ transformation of the Grignard re-
agents into copper reagents during the catalytic cycle, due
to the high polarity of the lithium cation (Li+).6 Subse-
quently, dilithium tetrachlorocuprate(II) (5 mol%) in the
presence of oxygen was found to be the best catalyst for
this homocoupling reaction (Table 1, entry 5). The addi-
tion of a smaller quantity of dilithium tetrachlorocu-
prate(II) (2.5 mol%) resulted in a lower yield (Table 1,
entry 16), whereas the yield was not improved by adding
twice the amount of the catalyst (Table 1, entry 17). The
ability of copper(I) chloride (CuCl) to act as the catalyst
in this homocoupling was also investigated.4b The yield
reached a maximum of 20% when one equivalent of cop-
per(I) chloride (with or without lithium chloride), and
without oxygen was used. Even in the presence of oxygen,
the yield was only improved to 63% (Table 1, entries 18–
22). During the reaction, it was found that copper(I) chlo-
ride was poorly soluble in tetrahydrofuran.
MgBr
Cu salt
LiCl, THF
1a
1b
Entry
Conditions
N2
Yield (%)b
1
3c
2
2-iodopropane (1.2 equiv), N2
dry air
35c
65c
66c
88c
88c
84c
85c
56c
trace
60
3
4
2-iodopropane (1.2 equiv), dry air
O2
5
6
2-iodopropane (1.2 equiv), O2
ClCH2CH2Cl (1.2 equiv)
7
8
BrCH2CH2Br (1.2 equiv)
9
NaNO2 (1.2 equiv)
10
11
12
13
14
15
16
17
18
19
20
21
22
CuCl2 (0 mol%), LiCl (5 mol%), O2
CuCl2 (5 mol%), LiCl (0 mol%), O2
CuCl2 (5 mol%), LiCl (5 mol%), O2
CuCl2 (5 mol%), LiCl (20 mol%), O2
CuCl2 (2.5 mol%), LiCl (10 mol%), O2
CuCl2 (10 mol%), LiCl (10 mol%), O2
CuLi2Cl4 (2.5 mol%), O2
72
88
64
87
59
CuLi2Cl4 (10 mol%), O2
87
With these promising results, the substrate scope was next
investigated and the results are shown in Table 2. These
experiments indicated that a variety of Grignard reagents
could be quickly transformed into the corresponding
products under the optimized homocoupling conditions.
CuCl (1.0 equiv)
12
CuCl (1.0 equiv), LiCl (2.0 equiv)
CuCl (5 mol%), O2
20
43
Interestingly, aromatic bromides possessing electron-
donating methyl, methoxy and ethoxy groups (at ortho-,
meta- or para-positions) could be converted efficiently
into the corresponding biaryls 1b–8b (Table 2, entries 1–
8). Homocouplings of bromopyridine derivatives, which
are important ligands in coordination chemistry and in
some catalysts, also proceeded well (Table 2, entries 9–
14). It was noteworthy that the present reaction system
tolerated strongly electron-withdrawing groups (nitro, es-
ter, nitrile and chloride) to afford the desired products
15b–18b in moderate to excellent yields (Table 2, entries
15–18). The synthesis of biaryls containing four ortho-
substituents is often challenging,1l but proved straightfor-
ward using the present system (Table 2, entry 16). Alkyl
bromides underwent smooth transformations to give the
corresponding coupling products 19b–23b in reasonable
to good yields. Among these, it was noticeable that some
of the alkyl substrate was transformed into the corre-
sponding alcohol (Table 2, entries 19 and 20). (2-Bromo-
CuCl (5 mol%), LiCl (10 mol%), O2
CuCl (10 mol%), LiCl (20 mol%), O2
50
63
a Reaction conditions: 1a (5 mmol), THF, r.t., 2 h.
b Yield of isolated product after column chromatography.
c CuLi2Cl4 (5 mol%) was used.
ethyl)benzene gave 1,4-diphenylbutane (23b) in low
yield, which might be due to rapid β-H elimination occur-
ring as a side process.7 The oxidative homocoupling of al-
kenyl derivative 24a was also investigated (Table 2, entry
24), with the coupling reaction proceeding efficiently to
give diene product 24b with good stereoselectivity (E/E,
E/Z = 95:5). Moreover, the reaction was successfully ex-
tended to alkynyl Grignard reagents; the product diynes
25b and 26b were isolated in excellent yields (Table 2, en-
tries 25 and 26).
© Georg Thieme Verlag Stuttgart · New York
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S.-K. Hua et al.
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Table 2 Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling of Grignard Reagentsa
CuLi2Cl4 (5 mol%)
RMgX
R R
THF, dry O2
Entry
Substrate
Product
Yield (%)b
MgBr
1
2
88
1a
2a
1b
MgBr
OMe
OMe
OMe
79
2b
3b
MgBr
3
4
5
96
90
90
3a
4a
MgBr
4b
MeO
MgBr
MeO
OMe
5a
5b
MeO
MgBr
OMe
6
7
98
86
OMe
6a
6b
OEt
MgBr
EtO
EtO
7a
7b
8
9
87
80
MgBr
8a
8b
N
O
O
MgCl
O
O
O
O
N
N
9a
9b
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Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling
521
Table 2 Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling of Grignard Reagentsa (continued)
CuLi2Cl4 (5 mol%)
RMgX
R
R
THF, dry O2
Entry
Substrate
Product
Yield (%)b
MgCl
O
O
O
O
O
N
10
82
N
N
O
O
10b
10a
O
O
O
O
O
11
12
N
N
76
84
N
MgCl
11b
11a
N
N
N
MgCl
12a
12b
N
13
14
79
77
N
N
MgCl
13a
13b
14b
N
N
N
MgCl
14a
NO2
NO2
15
16
89c
MgCl
O2N
15a
15b
16b
COOMe
MgCl
COOMe
COOMe
79c
16a
NC
O
CN
O
O
O
O
O
17
18
78c
MgCl
CN
17a
17b
Cl
MgCl
82c
Cl
Cl
18a
18b
C10H21MgBr
19a
C20H42
19b
19
20
60d (36)e
62d (33)e
C12H25MgBr
20a
C24H50
20b
© Georg Thieme Verlag Stuttgart · New York
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Table 2 Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling of Grignard Reagentsa (continued)
CuLi2Cl4 (5 mol%)
RMgX
R
R
THF, dry O2
Entry
Substrate
Product
Yield (%)b
MgBr
21
89
21a
22a
23a
21b
MgBr
22
23
24
87
55
86
22b
MgBr
MgBr
23b
(E/Z >99:1)f
24a
(E/E, E/Z = 95:5)f 24b
OMe
MgBr
25
26
89
91
MeO
MeO
25a
25b
OTBS
MgBr
TBSO
TBSO
26a
26b
a Unless otherwise stated, all the reactions were performed using RMgX (3 mmol), CuLi2Cl4 (0.15 mmol) in THF at r.t. for 2 h under an O2
atmosphere.
b Yield of isolated product after column chromatography.
c The reaction was performed at –30 °C.
d CuLi2Cl4 (10 mol%) was used.
e Yield of the isolated corresponding alcohol.
f The stereoselectivity was determined by GC–MS.
This coupling procedure could also be extended to an in- pared in 42% yield from precursor 29 via the same
tramolecular variant, and further applied in total synthe- reaction sequence.
sis. To illustrate this potential, the developed reaction
Studies on the reaction mechanism of these oxidative cou-
system was applied in the synthesis of Amaryllidaceae al-
plings are few,4b especially for copper(II)-catalyzed ho-
kaloids (Scheme 2). 2,2′-Diiodo-N-methyl-4,5-methyl-
mocouplings. Based on the literature,4b a tentative
enedioxybenzanilide
(27)
was
treated
with
catalytic mechanism is proposed (Scheme 3). Copper(II)
can be rapidly reduced in situ into a copper(I) species (R–
CuI) by the Grignard reagent.5 Next, there are three possi-
ble catalytic cycles as copper, in any oxidative state (Cu0,
CuI or CuII), is catalytically active in homocoupling reac-
tions. The first is the copper(I)/copper(III) (CuI/CuIII) cat-
alytic cycle in which the copper(I) species (R–CuI) reacts
with the Grignard reagent in the presence of oxygen to
generate a copper(III) intermediate (R–CuIIIX–R), which
isopropylmagnesium chloride in tetrahydrofuran at –30
°C to give the corresponding di-Grignard reagent via io-
dine–magnesium exchange. Next, under the optimized
coupling conditions, intramolecular coupling afforded N-
methylcrinasiadine (28) in 45% overall yield, which was
comparable with those reported earlier.1f,h Similarly, com-
pound 30, a derivative of N-methylcrinasiadine, was pre-
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Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling
523
Commercially available reagents and solvents were used without
further purification unless otherwise stated. THF was distilled from
Na/benzophenone under argon prior to use. CuCl2 and LiCl were
used after drying under vacuum at room temperature. CuLi2Cl4 soln
was freshly prepared by reacting CuCl2 (0.15 mmol) and LiCl (0.3
mmol) in anhyd THF (5 mL). i-PrMgCl and PhMgCl were freshly
prepared by treatment of Mg turnings (3.5 mmol) with 2-chloropro-
pane (3.3 mmol) or chlorobenzene (3.3 mmol) in anhyd THF (3.3
mL). All the Grignard reagents listed in Table 2 were prepared ac-
cording to the general experimental procedures. Determination of
the purity of substrates and reaction monitoring was accomplished
by TLC using silica gel Polygram SILG/UV 254 plates. All the
yields refer to those of isolated products after column chromatogra-
phy on Yantai Jiangyou silica gel (300–400 mesh) using PE–EtOAc
as the eluent. Petroleum ether (PE) refers to the fraction boiling in
the 60–90 °C range. Melting points were recorded using a Jingke
I
O
O
O
1) i-PrMgCl, THF
N
N
2) CuLi2Cl4, THF
dry O2, –30 °C
Me
I
Me
O
O
O
27
28
isolated yield: 45%
I
O
MeO
1) i-PrMgCl, THF
N
N
2) CuLi2Cl4, THF
dry O2, –30 °C
Me
I
MeO
Me
MeO
O
OMe
29
30
isolated yield: 42%
Scheme 2 Preparation of N-methylcrinasiadine (28) and its derivative
1
WRS-1B digital melting point apparatus and are uncorrected. H
30
(400 MHz) and 13C (100 MHz) NMR spectra were recorded using a
Bruker Avance 400 MHz spectrometer. TMS was employed as the
internal standard. Mass spectra were determined by EI ionization on
a Micromass GCT CA055 spectrometer. HRMS (for novel com-
pounds) were recorded on the same instrument. The analytical data
of the known compounds were found to correspond with those re-
ported in the literature.
releases copper(I) by reductive elimination to give the ho-
mocoupled product (R–R). The second catalytic cycle (in-
volving Cu0/CuI/CuII species) can afford a copper(II)
intermediate (R–CuII–R) via single transmetalation of the
copper(I) species (R–CuI) in the presence of oxygen. This
could then give the homocoupling product (R–R) by re-
ductive elimination; the resulting copper(0) can be oxi-
dized either to copper(I) or copper(II). The third process
proceeds by way of a copper(0)/copper(II) (Cu0/CuII) cat-
alytic cycle. Double transmetalation of the intermediate
copper(II) species with two molecules of the Grignard re-
agent affords the copper(II) intermediate (R–CuII–R); this
species can also release copper(0) by reductive elimina-
tion to afford the homocoupled product (R–R).
Grignard Reagents; General Procedures
Method A: Substrates 1a–8a and 19a–24a
A dry, N2-flushed 100 mL three-necked, round-bottom flask,
equipped with a magnetic stir bar, a reflux condenser and a 50 mL
pressure-equalizing dropping funnel, was charged with Mg turnings
(31 mmol) in anhyd THF (20 mL) at r.t. The dropping funnel was
charged with a soln of the appropriate bromide precursor (30 mmol)
in anhyd THF (10 mL). The bromide (ca. 1 mL of the soln) was add-
ed to the flask, and the contents were stirred until the Grignard re-
action commenced. When the initial vigorous reaction had
subsided, the remainder of the bromide was added at a rate such that
the mixture refluxed gently. Generally the addition was completed
within 20 min, and almost all of the Mg dissolved. The mixture was
heated at reflux temperature for a further 1 h and then cooled to r.t.
Method B: Substrates 9a–14a6a,8
A dry, N2-flushed 50 mL round-bottom flask, equipped with a mag-
netic stir bar, was charged with the appropriate pyridyl bromide (3
mmol) in anhyd THF (3 mL) at r.t. A soln of i-PrMgCl in anhyd
THF (3.3 mL, 3.3 mmol, 1.0 M) was added via a syringe. The re-
sulting mixture was stirred at r.t. for ca. 30 min until the Br–Mg ex-
change was complete (monitored by TLC).
Method C: Substrates 15a8b
A dry, N2-flushed 50 mL round-bottom flask, equipped with a mag-
netic stir bar, was charged with 1-iodo-2-nitrobenzene (3 mmol) in
anhyd THF (3 mL). The mixture was cooled to –30 °C, and a soln
of PhMgCl in anhyd THF (3.3 mL, 3.3 mmol, 1.0 M) was added via
a syringe. The resulting mixture was stirred at –30 °C for ca. 30 min
until the I–Mg exchange was complete (monitored by TLC).
Scheme 3 A proposed mechanism for the homocoupling reaction
Method D: Substrates 16a–18a6a,8
A dry, N2-flushed 50 mL round-bottom flask, equipped with a mag-
netic stir bar, was charged with the appropriate aryl iodide (3 mmol)
in anhyd THF (3 mL). The mixture was cooled to –30 °C, and a soln
of i-PrMgCl in anhyd THF (3.3 mL, 3.3 mmol, 1.0 M) was added
via a syringe. The resulting mixture was stirred at –30 °C for ca. 30
min until the I–Mg exchange was complete (monitored by TLC).
In summary, an efficient and practical reaction system has
been developed for the oxidative homocoupling of
organomagnesium compounds, under mild conditions,
using commercially available dilithium tetrachlorocu-
prate(II) as the catalyst and oxygen as the oxidant. The re-
actions were applicable to various aryl, heteroaryl, alkyl,
alkenyl and alkynyl Grignard reagents possessing differ-
ent functional groups. We are currently working toward
exploiting this methodology in the total synthesis of natu-
ral products.
Method E: Substrates 25a and 26a9
A dry, N2-flushed 50 mL three-necked round-bottom flask,
equipped with a magnetic stir bar and a reflux condenser, was
charged with Mg turnings (3.1 mmol) in anhyd THF (3 mL) at r.t.
Bromoethane (3 mmol) was added to the flask via a syringe at a rate
such that the mixture refluxed gently. The mixture was stirred for a
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 518–526

524
S.-K. Hua et al.
PAPER
further 1 h at r.t. to afford EtMgBr. Next, the terminal alkyne (3
mmol) was added via a syringe and the resulting mixture was heated
at reflux temperature for 2 h and then cooled to r.t.
13C NMR (100 MHz, CDCl3): δ = 55.7, 111.1, 120.4, 127.8, 128.6,
131.5, 157.1.
MS (EI): m/z (%) = 214 (100) [M]+.
Oxidative Homocoupling; General Procedure10
4,4′-Diethoxy-1,1′-biphenyl (7b)12
A dry, N2-flushed 50 mL round-bottom flask, equipped with a mag-
netic stir bar, was charged with the appropriate freshly prepared
Grignard reagent (3 mmol) in anhyd THF (3 mL) at the specified
temperature (see Table 2). A soln of CuLi2Cl4 in anhyd THF (5 mL,
0.15 mmol, 0.03 M) was added in one portion using a syringe. Si-
multaneously, dry O2 was bubbled into the mixture via a cannula.
After stirring for 2 h, the flow of O2 was stopped and the mixture
was quenched with sat. aq NH4Cl soln (5 mL). The solvent was re-
moved and the aq layer extracted with EtOAc (3 × 20 mL). The
combined organic phase was washed with brine (20 mL), dried over
anhyd Na2SO4 and concentrated under vacuum. The residue was pu-
rified by flash chromatography on silica gel to provide the product.
Yield: 86%; white solid; mp 174.2–175.1 °C.
1H NMR (400 MHz, CDCl3): δ = 1.46 (t, J = 7.2 Hz, 6 H), 4.09 (q,
J = 7.2 Hz, 4 H), 6.96 (d, J = 8.8 Hz, 4 H), 7.49 (d, J = 8.8 Hz, 4 H).
13C NMR (100 MHz, CDCl3): δ = 14.9, 63.5, 114.7, 127.7, 133.4,
158.0.
MS (EI): m/z (%) = 242 (100) [M]+.
1,1′,2,2′-Tetrahydro-5,5′-biacenaphthylene (8b)13
Yield: 87%; yellow solid; mp 169.3–170.1 °C.
1H NMR (400 MHz, CDCl3): δ = 3.53 (s, 8 H), 7.32–7.38 (m, 6 H),
7.44 (d, J = 7.2 Hz, 2 H), 7.54 (d, J = 6.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 30.2, 30.6, 119.1, 119.3, 121.6,
1,1′-Binaphthalene (1b)1h
Yield: 88% (on 3 mmol scale), 86% (on 30 mmol scale); white sol-
id; mp 157.2–157.7 °C.
1H NMR (400 MHz, CDCl3): δ = 7.28–7.35 (m, 2 H), 7.44–7.46 (m,
2 H), 7.50–7.56 (m, 4 H), 7.62–7.66 (m, 2 H), 7.98–8.01 (m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 125.4, 125.8, 126.0, 126.6, 127.8,
127.9, 128.2, 132.9, 133.6, 138.5.
127.7, 129.6, 131.0, 133.5, 139.4, 145.6, 146.0.
MS (EI): m/z (%) = 306 (100) [M]+.
5,5′-Di(1,3-dioxolan-2-yl)-3,3′-bipyridine (9b)14
Yield: 80%; white solid; mp 99.4–100.1 °C.
1H NMR (400 MHz, CDCl3): δ = 4.08–4.19 (m, 8 H), 5.94 (s, 2 H),
MS (EI): m/z (%) = 254 (76) [M]+, 253 (100).
8.02 (s, 2 H), 8.76 (s, 2 H), 8.87 (s, 2 H).
13C NMR (100 MHz, CDCl3): δ = 65.5, 101.7, 132.7, 133.0, 134.0,
148.0, 148.8.
HRMS (EI): m/z [M]+ calcd for C16H16N2O4: 300.1110; found
300.1113.
2,2′-Dimethoxy-1,1′-binaphthalene (2b)11
Yield: 79%; white solid; mp 196.6–197.2 °C.
1H NMR (400 MHz, CDCl3): δ = 3.80 (s, 6 H), 7.17 (d, J = 8.4 Hz,
2 H), 7.26 (t, J = 7.2 Hz, 2 H), 7.36 (t, J = 7.2 Hz, 2 H), 7.50 (d,
J = 5.6 Hz, 2 H), 7.92 (d, J = 8.0 Hz, 2 H), 8.02 (d, J = 8.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 56.9, 114.3, 119.7, 123.6, 125.3,
126.3, 128.0, 129.3, 129.4, 134.1, 155.0.
MS (EI): m/z (%) = 314 (100) [M]+.
6,6′-Di(1,3-dioxolan-2-yl)-3,3′-bipyridine (10b)
Yield: 82%; white solid; mp 173.7–174.7 °C.
1H NMR (400 MHz, CDCl3): δ = 4.12–4.24 (m, 8 H), 5.95 (s, 2 H),
7.67 (d, J = 8.0 Hz, 2 H), 7.95 (dd, J = 8.0, 2.0 Hz, 2 H), 8.86 (d,
J = 2.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 65.7, 103.4, 120.9, 133.5, 135.3,
147.8, 156.9.
HRMS (EI): m/z [M]+ calcd for C16H16N2O4: 300.1110; found
300.1111.
1,1′-Biphenyl (3b)1h
Yield: 96%; white solid; mp 69.6–70.3 °C.
1H NMR (400 MHz, CDCl3): δ = 7.35–7.39 (m, 2 H), 7.45–7.49 (m,
4 H), 7.60–7.63 (m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 127.2, 127.3, 128.5, 141.3.
MS (EI): m/z (%) = 154 (100) [M]+.
5,5′-Di(1,3-dioxolan-2-yl)-2,2′-bipyridine (11b)
Yield: 76%; white solid; mp 123.8–124.1 °C.
1H NMR (400 MHz, CDCl3): δ = 4.06–4.20 (m, 8 H), 5.95 (s, 2 H),
7.94 (dd, J = 8.4, 6.4 Hz, 2 H), 8.46 (d, J = 8.4 Hz, 2 H), 8.78 (d,
J = 0.8 Hz, 2 H).
4,4′-Dimethyl-1,1′-biphenyl (4b)1h
Yield: 90%; white solid; mp 119.6 °C.
1H NMR (400 MHz, CDCl3): δ = 2.46 (s, 6 H), 7.20 (d, J = 8.0 Hz,
4 H), 7.55 (d, J = 8.0 Hz, 4 H).
13C NMR (100 MHz, CDCl3): δ = 65.4, 101.9, 121.0, 133.9, 135.3,
147.7, 156.3.
13C NMR (100 MHz, CDCl3): δ = 21.1, 126.8, 129.4, 136.7, 138.3.
MS (EI): m/z (%) = 182 (100) [M]+.
HRMS (EI): m/z [M]+ calcd for C16H16N2O4: 300.1110; found
300.1117.
3,3′-Dimethoxy-1,1′-biphenyl (5b)1h
Yield: 90%; white solid; mp 33.3–34.6 °C.
1H NMR (400 MHz, CDCl3): δ = 3.90 (s, 6 H), 6.95 (d, J = 8.0 Hz,
2 H), 7.17 (s, 2 H), 7.22 (d, J = 7.6 Hz, 2 H), 7.39 (t, J = 8.0 Hz, 2
3,3′-Dimethyl-2,2′-bipyridine (12b)15
Yield: 84%; colorless liquid.
1H NMR (400 MHz, CDCl3): δ = 2.15 (s, 6 H), 7.23 (dd, J = 7.6, 2.8
Hz, 2 H), 7.61 (d, J = 8.0 Hz, 2 H), 8.50 (d, J = 4.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 18.5, 122.9, 131.6, 138.3, 146.6,
H).
13C NMR (100 MHz, CDCl3): δ = 55.3, 112.8, 113.0, 119.7, 129.8,
142.7, 159.9.
MS (EI): m/z (%) = 214 (100) [M]+.
157.6.
MS (EI): m/z (%) = 184 (30) [M]+, 169 (100).
4,4′-Dimethyl-2,2′-bipyridine (13b)16
2,2′-Dimethoxy-1,1′-biphenyl (6b)1h
Yield: 79%; white solid; mp 171.9–172.4 °C.
Yield: 98%; white solid; mp 154.7–154.8 °C.
1H NMR (400 MHz, CDCl3): δ = 2.45 (s, 6 H), 7.15 (d, J = 4.4 Hz,
2 H), 8.24 (s, 2 H), 8.55 (d, J = 4.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 21.2, 122.0, 124.7, 148.2, 148.9,
1H NMR (400 MHz, CDCl3): δ = 3.80 (s, 6 H), 7.00–7.06 (m, 4 H),
7.28 (t, J = 4.0 Hz, 2 H), 7.36 (t, J = 7.2 Hz, 2 H).
156.0.
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Dilithium Tetrachlorocuprate(II) Catalyzed Oxidative Homocoupling
525
MS (EI): m/z (%) = 184 (100) [M]+.
1H NMR (400 MHz, CDCl3): δ = 2.96 (s, 4 H), 7.22–7.25 (m, 6 H),
7.30–7.34 (m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 38.0, 125.9, 128.4, 128.5, 141.8.
MS (EI): m/z (%) = 182 (16) [M]+, 91 (100).
5,5′-Dimethyl-2,2′-bipyridine (14b)17
Yield: 77%; white solid; mp 113.7–114.1 °C.
1H NMR (400 MHz, CDCl3): δ = 2.41 (s, 6 H), 7.64 (d, J = 8.0 Hz,
2 H), 8.28 (d, J = 8.0 Hz, 2 H), 8.51 (s, 2 H).
13C NMR (100 MHz, CDCl3): δ = 18.3, 120.4, 133.1, 137.6, 149.4,
4,4′-Dimethylbibenzyl (22b)1n
Yield: 87%; white solid; mp 79.1–80.3 °C.
153.6.
1H NMR (400 MHz, CDCl3): δ = 2.35 (s, 6 H), 2.89 (s, 4 H), 7.12
(s, 8 H).
MS (EI): m/z (%) = 184 (100) [M]+.
13C NMR (100 MHz, CDCl3): δ = 21.1, 37.7, 128.3, 129.0, 135.3,
138.9.
MS (EI): m/z (%) = 210 (100) [M]+.
2,2′-Dinitro-1,1′-biphenyl (15b)1h
Yield: 89%; beige solid; mp 123.0–123.4 °C.
1H NMR (400 MHz, CDCl3): δ = 7.32 (d, J = 7.6 Hz, 2 H), 7.61 (t,
J = 7.6 Hz, 2 H), 7.70 (t, J = 7.6 Hz, 2 H), 8.23 (d, J = 8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): δ = 124.8, 129.2, 131.0, 133.5, 134.2,
1,4-Diphenylbutane (23b)19
Yield: 55%; white solid; mp 53.1–53.3 °C.
147.2.
1H NMR (400 MHz, CDCl3): δ = 1.69–1.73 (m, 4 H), 2.68 (t,
J = 6.8 Hz, 4 H), 7.20–7.23 (m, 6 H), 7.29–7.33 (m, 4 H).
MS (EI): m/z (%) = 198 (100) [M – NO2]+.
13C NMR (100 MHz, CDCl3): δ = 31.1, 35.8, 125.7, 128.3, 128.4,
142.6.
MS (EI): m/z (%) = 210 (67) [M]+, 91 (100).
Dimethyl 6,6′-Dimethyl-[1,1′-biphenyl]-2,2′-dicarboxylate
(16b)18
Yield: 79%; yellow solid; mp 41.6 °C.
1H NMR (400 MHz, CDCl3): δ = 1.94 (s, 6 H), 3.60 (s, 6 H), 7.35
(t, J = 7.6 Hz, 2 H), 7.46 (d, J = 7.6 Hz, 2 H), 7.88 (d, J = 7.6 Hz, 2
H).
13C NMR (100 MHz, CDCl3): δ = 20.1, 51.8, 127.0, 127.7, 129.3,
133.6, 136.6, 141.2, 167.5.
MS (EI): m/z (%) = 298 (8) [M]+, 235 (100).
(1E,3E)-1,4-Diphenylbuta-1,3-diene (24b)1f
Yield: 86%; white solid; mp 149.8–150.5 °C.
1H NMR (400 MHz, CDCl3): δ = 6.67–6.74 (m, 2 H), 6.95–7.03 (m,
2 H), 7.24–7.28 (m, 2 H), 7.34–7.38 (m, 4 H), 7.46–7.48 (m, 4 H).
13C NMR (100 MHz, CDCl3): δ = 126.4, 127.6, 128.7, 129.3, 132.8,
137.4.
MS (EI): m/z (%) = 206 (100) [M]+.
2,2′-Dicyano-4,5,4′,5′-bis(methylenedioxy)biphenyl (17b)
Yield: 78%; white solid; mp 124.3–125.2 °C.
1,4-Bis(4-methoxyphenyl)buta-1,3-diyne (25b)22
Yield: 89%; white solid; mp 139.7–139.9 °C.
1H NMR (400 MHz, CDCl3): δ = 3.85 (s, 6 H), 6.88 (d, J = 9.2 Hz,
4 H), 7.49 (d, J = 8.8 Hz, 4 H).
13C NMR (100 MHz, CDCl3): δ = 55.3, 73.0, 81.2, 114.0, 114.1,
1H NMR (400 MHz, DMSO-d6): δ = 6.05 (s, 4 H), 6.55 (s, 2 H),
7.11 (s, 2 H).
13C NMR (100 MHz, DMSO-d6): δ = 89.6, 98.2, 102.7, 110.3,
117.8, 140.7, 152.9, 158.4.
HRMS (EI): m/z [M]+ calcd for C16H8N2O4: 292.0484; found
292.0479.
134.0, 160.3.
MS (EI): m/z (%) = 262 (100) [M]+.
4,4′-Dichloro-1,1′-biphenyl (18b)1l
Yield: 82%; white solid; mp 139.9–140.2 °C.
1H NMR (400 MHz, CDCl3): δ = 7.43 (dt, J = 8.4, 2.4 Hz, 4 H),
7.50 (dt, J = 8.8, 2.4 Hz, 4 H).
13C NMR (100 MHz, CDCl3): δ = 128.2, 129.1, 133.8, 138.4.
MS (EI): m/z (%) = 222 (100) [M]+.
1,8-Bis[(tert-butyldimethylsilyl)oxy]-octa-3,5-diyne (26b)23
Yield: 91%; colorless oil.
1H NMR (400 MHz, CDCl3): δ = 0.11 (s, 12 H), 0.95 (s, 18 H), 2.53
(t, J = 6.4 Hz, 4 H), 3.74 (t, J = 6.4 Hz, 4 H).
13C NMR (100 MHz, CDCl3): δ = –4.5, 16.5, 24.3, 26.1, 61.0, 85.2,
103.8.
Eicosane (19b)19
Yield: 60%; white solid; mp 35.5–36.1 °C.
MS (EI): m/z (%) = 366 (1) [M]+, 127 (100).
Intramolecular Oxidative Homocoupling; General Procedure
A dry, N2-flushed 50 mL round-bottom flask, equipped with a mag-
netic stir bar, was charged with the appropriate diiodide (27 or 29)
(1 mmol) in anhyd THF (5 mL). The mixture was cooled to –30 °C
and a soln of i-PrMgCl in anhyd THF (1.1 mL, 2.2 mmol, 2.0 M)
was added dropwise. After stirring at –30 °C for 30 min, the I–Mg
exchange was complete (monitored by TLC). Next, a soln of
CuLi2Cl4 in anhyd THF (4 mL, 0.12 mmol, 0.03 M) was added in
one portion using a syringe. Simultaneously, dry O2 was bubbled
into the reaction mixture via a cannula. After stirring for 2 h, the
flow of O2 was stopped and the mixture was quenched with sat. aq
NH4Cl soln (5 mL). The solvent was evaporated in vacuo and the aq
layer extracted with EtOAc (3 × 20 mL). The combined organic
phase was washed with brine (20 mL), dried over anhyd Na2SO4
and concentrated under vacuum. The residue was purified by flash
chromatography on silica gel to afford the desired product.
1H NMR (400 MHz, CDCl3): δ = 0.90 (t, J = 6.8 Hz, 6 H), 1.22–
1.35 (m, 36 H).
13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 29.4, 29.7, 31.9.
MS (EI): m/z (%) = 282 (13) [M]+, 57 (100).
Tetracosane (20b)20
Yield: 62% (on 3 mmol scale), 58% (on 30 mmol scale); white sol-
id; mp 49.0–49.4 °C.
1H NMR (400 MHz, CDCl3): δ = 0.90 (t, J = 6.8 Hz, 6 H), 1.25–
1.32 (m, 44 H).
13C NMR (100 MHz, CDCl3): δ = 14.1, 22.7, 29.4, 29.7, 31.9.
MS (EI): m/z (%) = 338 (3) [M]+, 57 (100).
Bibenzyl (21b)21
Yield: 89%; white solid; mp 50.0–52.0 °C.
N-Methylcrinasiadine (28)3
Yield: 45%; white solid; mp 247.8–248.6 °C.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 518–526

526
S.-K. Hua et al.
PAPER
F.; Stang, P. J., Eds.; Wiley-VCH: Weinheim, 1998.
1H NMR (400 MHz, CDCl3): δ = 3.86 (s, 3 H), 6.13 (s, 2 H), 7.27
(t, J = 7.2 Hz, 1 H), 7.38 (d, J = 8.0 Hz, 1 H), 7.51 (t, J = 7.2 Hz, 1
H), 7.61 (s, 1 H), 7.92 (s, 1 H), 8.08 (d, J = 8.0 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 29.9, 100.4, 101.9, 106.9, 115.1,
119.3, 122.4, 122.8, 128.8, 130.5, 137.4, 148.4, 152.2.
(c) Beller, M.; Zapf, A.; Magerlein, W. Chem. Eng. Technol.
2001, 24, 575. (d) Handbook of Combinatorial Chemistry:
Drugs, Catalysts, Materials; Nicolaou, K. C.; Hanko, R.;
Hartwig, W., Eds.; Wiley-VCH: Weinheim, 2002.
(3) For an excellent overview of the use of dilithium
tetrachlorocuprate(II) in organic synthesis, see: Thompson,
A. S.; Kim, J. T.; Gevorgyan, V. e-EROS, Encyclopedia of
Reagents for Organic Synthesis; John Wiley & Sons: New
York, 2004, doi: 10.1002/047084289X.rd268.pub2.
(4) (a) Iyoda, M. Adv. Synth. Catal. 2009, 351, 984. (b) Kochi,
J. K. J. Organomet. Chem. 2002, 653, 11. (c) Kauffmann, T.
Angew. Chem., Int. Ed. Engl. 1974, 13, 291. (d) Miyake, Y.;
Wu, M.; Rahman, M. J.; Kuwatani, Y.; Iyoda, M. J. Org.
Chem. 2006, 71, 6110. (e) Dubbaka, S. R.; Kienle, M.;
Mayr, H.; Knochel, P. Angew. Chem. Int. Ed. 2007, 46,
9093.
MS (EI): m/z (%) = 253 (100) [M]+.
8,9-Dimethoxy-5-methylphenanthridin-6(5H)-one (30)24
Yield: 42%; white solid; mp 221.7–222.5 °C.
1H NMR (400 MHz, CDCl3): δ = 3.81 (s, 3 H), 4.04 (s, 3 H), 4.09
(s, 3 H), 7.29–7.33 (m, 1 H), 7.40 (d, J = 8.0 Hz, 1 H), 7.52 (t,
J = 7.2 Hz, 1 H), 7.56 (s, 1 H), 7.91 (s, 1 H), 8.13 (d, J = 7.6 Hz, 1
H).
13C NMR (100 MHz, CDCl3): δ = 29.9, 56.1, 56.2, 102.5, 109.0,
115.1, 119.1, 119.6, 122.2, 122.6, 128.2, 128.6, 137.5, 149.7, 153.2,
161.1.
MS (EI): m/z (%) = 269 (100) [M]+.
(5) (a) Bäckvall, J.-E.; Sellén, M. J. Chem. Soc., Chem.
Commun. 1987, 827. (b) Kochi, J. K. Organometallic
Mechanisms and Catalysis; Academic Press: New York,
1978, 381.
(6) (a) Krasovskiy, A.; Knochel, P. Angew. Chem. Int. Ed. 2004,
43, 3333. (b) Hatano, M.; Ito, O.; Suzuki, S.; Ishihara, K.
J. Org. Chem. 2010, 75, 5008.
Acknowledgment
We are grateful for financial support from the national ‘863’ Project
of China (2006AA609Z447 and 2007AA02Z301), the 111 Project
(B07023), Shanghai Foundation of Science and Technology
(09JC1404200), and The Fundamental Research Funds for the Cen-
tral Universities (WY1113007).
(7) Frisch, A. C.; Beller, M. Angew. Chem. Int. Ed. 2005, 44,
674.
(8) (a) Varchi, G.; Ricci, A.; Cahiez, G.; Knochel, P.
Tetrahedron 2000, 56, 2727. (b) Sapountzis, I.; Knochel, P.
Angew. Chem. Int. Ed. 2002, 41, 1610. (c) Knochel, P.;
Dohle, W.; Gommermann, N.; Kneisel, F. F.; Kopp, F.;
Korn, T.; Sapountzis, I.; Vu, V. A. Angew. Chem. Int. Ed.
2003, 42, 4302.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnuIomprifgtooatrinSugpIoi
nnfomartit
(9) (a) Pradilla, R. F.; Lwoff, N.; Águila, M. Á.; Tortosa, M.;
Viso, A. J. Org. Chem. 2008, 73, 8929. (b) Miranda, L. D.;
Zard, S. Z. Org. Lett. 2002, 4, 1135.
(10) All of the homocoupling reactions were conducted on 3
mmol scale. The present system was also scaled 10-fold for
compounds 1b and 20b; these reactions proceeded
efficiently and no problems were encountered.
(11) Periasamy, M.; Nagaraju, M.; Kishorebabu, N. Synthesis
2007, 3821.
(12) Nishimura, N.; Yoza, K.; Kobayashi, K. J. Am. Chem. Soc.
2010, 132, 777.
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Synthesis 2013, 45, 518–526
© Georg Thieme Verlag Stuttgart · New York