Electroreductive generation of recyclable organic reductant from N,N′-dioctyl-4,4′-bipyridinium and Pd-catalyzed reductive coupling of aryl halides

Article abstract of DOI:10.1055/s-2008-1087386

Electroreduction of N,N′-dioctyl-4,4′-bipyridinium bis(triflimide) [C₈V²⁺][Tf₂N^-] ₂ in THF gave a dark blue solution of the corresponding quinoid C₈V⁰, which worked as an efficient organic reductant for Pd-catalyzed reductive coupling of aryl bromides to give the corresponding biphenyl derivatives in good yields. After usual workup, [C₈V ²⁺][Tf₂N^-]₂ was recovered and reused for generation of the organic reductant C₈V⁰. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1087386

LETTER
85
Electroreductive Generation of Recyclable Organic Reductant from
N,N¢-Dioctyl-4,4¢-bipyridinium and Pd-Catalyzed Reductive Coupling of
Aryl Halides
E
M
lectroreductive Gene
a
n
cyclable
O
rg
a
anic Reduc
b
tant u Kuroboshi, Ryoto Kobayashi, Takayuki Nakagawa, Hideo Tanaka*
Department of Applied Chemistry, Okayama University, Tsushima-naka 3-1-1, Okayama 700-8530, Japan
Fax +81(86)2518079; E-mail: tanaka95@cc.okayama-u.ac.jp
Received 11 September 2008
Abstract: Electroreduction of N,N¢-dioctyl-4,4¢-bipyridinium bis(tri-
2
+
–
+ e–
THF
flimide) [C V ][Tf N ] in THF gave a dark blue solution of the
8
2
2
0
Oct
N
N
Oct
Oct
N
N Oct
corresponding quinoid C V , which worked as an efficient organic
8
⋅
2Tf2N–
reductant for Pd-catalyzed reductive coupling of aryl bromides to
give the corresponding biphenyl derivatives in good yields. After
C8V2+][Tf2N ]2
–
C8V0
[
2
+
–
usual workup, [C V ][Tf N ] was recovered and reused for gener-
8
2
2
0
ation of the organic reductant C V .
8
Key words: coupling, electron transfer, halides, reductions, palla-
dium
Pd cat.
Hal
+
C8V0
+ C8V2+
THF
60 °C
R
R
R
1
2
0
Scheme 1 Electrochemical generation of C V and reductive cou-
Formation of carbon–carbon bonds using transition-metal
catalysts is a fundamental reaction in organic synthesis.
Combinations of organic reductants and transition-metal
catalysts have been used to promote several reductive
8
0
pling of aryl halides with a combination of Pd catalyst and C V
8
tion of nitroalkene to aldehyde,9 and reductive
debromination of vic-dibromoalkane to alkene. C V
and/or C V also reduced C–C double and triple bonds in
the presence of Pd/C catalyst and C=O double bond in a
combination with enzymes. As C V is soluble in wa-
ter, and C V and C V are soluble in organic solvents, it
was usually used in aqueous organic solvents, in which re-
action with water, such as protonation of the intermedi-
ates, would be a serious side reaction. The bipyridinium
derivatives would be, therefore, used more widely if they
can be used in a nonaqueous aprotic polar organic sol-
vents. The bipyridinium derivatives having various func-
tional groups and counteranions can be easily prepared
1
carbon–carbon bond-formation reactions. Electron trans-
10
•+
1
fer from the organic reductants, which dissolve in usual
organic solvents, to the transition-metal catalysts and/or
organometallic intermediates occurs smoothly. Further-
more, redox potential of the organic reductants is tunable
by appropriate structural modification. Recently, we re-
0
1
11
12
2+
1
+
0
1
1
ported that N,N,N¢,N¢-tetrakis(dimethylamino)ethylene
2
(
TDAE) worked as an organic reductant in cross-cou-
3
pling reactions between aldehydes, alkenyl halides, and
allyl halides with NiBr /CrCl catalysts and in reductive
coupling of aryl halides with Pd catalyst. From the view
point of green-sustainable chemistry, the organic reduc-
tant should be used repeatedly. However, TDAE is hardly
4
2
3
5
13
from commercially available 4,4¢-bipyridyl. In this
2
+
recovered since its oxidized form, TDAE , is moisture-
sensitive and is decomposed during the workup process.
Furthermore, TDAE is air-sensitive, and chemical modi-
fication of TDAE is difficult to achieve. Therefore, we
sought recyclable organic reductant, which can be gener-
ated from their ‘stable’ precursors (oxidized form) by
electroreduction in situ.
study, we found that (1) N,N¢-dioctyl-4,4¢-bipyridinium
2+
–
bis(triflimide) [C V ][Tf N ] was soluble in several or-
8
2
2
2+
0
ganic solvents, (2) electroreduction of [C V ] gave C V
in THF, which worked as an organic reductant to promote
Pd-catalyzed reductive coupling of aryl halides
8
8
(
Scheme 1).
2+
–
N,N¢-Dioctyl-4,4¢-bipyridinium bis(triflimide) [C V ][Tf N ]
was prepared as follows (Scheme 2). Alkylation of
2
+
8
2
2
N,N¢-Dimethyl-4,4¢-bipyridinium (C V ) is an organic
1
2
+
reductant precursor. C V is stable under air and easily
handled; C V is easily reduced with several reductants
such as dithionite to generate radical cation C V and
1
4
1
[
[
,4¢-bipyridyl with octyl bromide (OctBr) in DMF at
2
+
1
05 °C gave N,N¢-dioctyl-4,4¢-bipyridinium dibromide
•
+
1
2+
–
C V ][Br ] in 84% yield. Anion exchange of
0
8 2
quinoid C V , which promoted reduction of a-diketone to
2+
–
+
–
1
C V ][Br ] with Li Tf N in dichloromethane and
water at room temperature for 30 minutes gave
C V ][Tf N ] , which was obtained from the organic
6
8
2
2
a-hydroxyketone, reductive dehalogenation of a-haloke-
7
8
tone, reductive desulfonylation of a-nitrosulfone, reduc-
2+
–
[
8 2 2
14
layer.
2
+
–
SYNLETT 2009, No. 1, pp 0085–0088
Advanced online publication: 12.12.2008
DOI: 10.1055/s-2008-1087386; Art ID: U09608ST
x
x.
x
x.
2
0
0
8
The product [C V ][Tf N ] is soluble in THF, DME,
1
8
2
2
,4-dioxane, DMF, NMP, MeCN, acetone, EtOAc,
CH Cl , MeOH, and EtOH, insoluble in hexane, cyclo-
2
2
©
Georg Thieme Verlag Stuttgart · New York

8
6
M. Kuroboshi et al.
LETTER
0
Oct-Br
Table 1 C V /Pd-Promoted Reductive Coupling of p-Bromoben-
8
(
2.4 equiv)
zonitrile (1a) to 4,4¢-Dicyanobiphenyl (2a)
N
N
Oct
N
N
Oct⋅2Br–
DMF
05 °C, 12 h
+
–
Bu4N Tf2N , THF
1
–
[
C8V2+][Br ]2 (84%)
C8V2+][Tf2N ]2
–
C8V0
[
undivided cell
r.t., 30 mA, 2 F/mol
+
–
Li [Tf2N ] (2.4 equiv)
Oct
N
N
Oct⋅2Tf2N–
H2O–CH2Cl2
r.t., 30 min
–
[
C8V2+][Tf2N ]2 (98%)
PdCl2(PhCN)2
(5 mol%)
2
+
–
Scheme 2 Preparation of [C V ][Tf N ]
2
8
2
Br
CN
NC
CN
THF, Ar
0 °C, time
6
hexane, and water, and makes a liquid–liquid two-phase
mixture with Et O, CHCl , benzene, and toluene. Two re-
1
a (0.5 mmol)
2a
2
3
•
+
Entry Anode
Cathode Solvent Time Yield of Yield of
versible redox waves appeared at E = –0.44 V {[C V ]/
1
/2
8
(h)
2a (%)a 1a (%)a
2
+
0
•+
[
C V ]} and –0.89 V {C V /[C V ]} vs. Ag/AgCl in a
cyclic voltammogram of [C V ][Tf N ] .
8
8
8
2
+
–
–d
8
2
2
1
2
3
4
5
6
7
8
9
0
1
2
Mg
Al
Pt
Pt
Pt
Pt
GC
Pb
Al
Pt
Pt
Pt
Pt
Pt
THF
2
96
85
8
2
+
–
Electroreduction of [C V ][Tf N ] in THF gave a dark
4b
8
2
2
THF
6
0
blue solution of C V , which worked as an organic reduc-
8
Zn
THF
24b
2b
6
65
97
24
34
44
tant in Pd-catalyzed reductive coupling of aryl bromide
(
Table 1). A typical procedure is as follows (entry 1). An
Pb
THF
–
Mg rod anode (f 6 mm) and a Pt-plate cathode (1 × 1.5
2
cm ) were immersed in a THF (3 mL) solution of
Mg
Mg
Mg
Mg
Mg
Mg
Mg
Mg
THF
75
60
49
98
93
95
96
–
2
+
–
+
–
[
C V ][Tf N ] (1.0 mmol) containing Bu N Tf N (2.0
8 2 2 4 2
THF
6
mmol) as a supporting electrolyte in an undivided cell.
The solution was electrolyzed under constant current con-
ditions (30 mA) at room temperature. After 2 F/mol-
THF
6
dioxane
DME
DMF
NMP
MeCN
5
–d
2
+
–
[
C V ][Tf N ] of electricity was passed (107 min), a
8 2 2
0
dark blue solution (C V –THF) was obtained. The solu-
–d
8
8
tion was added to a mixture of 4-bromobenzonitrile (1a,
1
1
1
48
48
–c
–d
0
.5 mmol) and a catalytic amount of PdCl (PhCN) (0.025
2 2
mmol) in THF (1 mL). The resulting mixture was stirred
at 60 °C for two hours. After the usual workup, 4,4¢-di-
cyanobiphenyl (2a) was obtained in 96% yield.
–d
–d
a
b
c
d
Isolated yield.
Among the anode materials examined thus far, Mg and Al
Reaction was quenched when the blue color of the mixture vanished.
A tarry mixture was formed during electrolysis.
Not detected.
gave 2a in good yields, whereas Zn and Pb gave poor re-
0
sults (entries 1–4). Though C V was readily re-oxidized
8
2
+
to [C V ] on the anode, the electroreduction of
[
8
+
2
–
C V ][Tf N ] proceeded smoothly in an undivided cell
8 2 2
since oxidation and dissolution of Mg and Al predomi- ing phosphine ligands, such as PdCl (PPh ) and
2
3 2
nantly occurred during the electrolysis at the anode. As Pd(PPh ) , gave 2a in 19–22% yield and 60–65% of 1a
3
4
the cathode materials, Pt gave the best results (entry 1, was recovered (entries 5, 6). The coupling reaction did not
6%), and glassy carbon, Pb, and Al cathodes were less proceed at all in the absence of Pd catalyst (entry 7).
9
effective to afford 2a in 75–49% yields (entries 5–7). The
coupling reaction proceeded smoothly in THF; similar re-
actions in dioxane, DME, DMF, and NMP required longer
reaction time (5–48 h) to give 2a in 95–98% yield (entries
The reductive coupling reactions of several aryl halides
were carried out in a manner similar to that described
above (Table 3). The coupling proceeded smoothly with
aryl bromides having electron-withdrawing substituents
such as cyano, keto, ester, and chlorine (entries 1–6).
Electronic effects of electron-donating groups were im-
portant: p-bromoanisole (1g) gave the coupling product
8
–11). In MeCN, a tarry mixture was formed during the
2
+
–
electroreduction of [C V ][Tf N ] and no appreciable
amount of 2a was obtained (entry 12).
8
2
2
0
The organic reductant C V in THF could be prepared by 2g in low yield (entry 7), whereas m-isomer 1h afforded
8
1
5
electrolysis in a divided cell. The reductive coupling of 2h in 73% yield (entry 8). In the case of substrates having
a, however, required much longer reaction time to com- easily reducible substituents such as nitro (1i) and formyl
plete (30 h, 91%). The Mg ion would work as a Lewis (1j) groups, the corresponding coupling products 2i and 2j
acid and coordinate to bromide to help labilize 1a, in- were obtained in moderate yields by using a divided cell
1
2
+
1
6
creasing the reaction rate.
(entries 10 and 12), whereas complex mixtures including
the coupling products and/or partially reduced products
were obtained in an undivided cell (entries 9 and 11), in-
dicating that reduction of the nitro and formyl groups
17
Several Pd catalysts were also examined (Table 2). The
catalysts PdCl (PhCN) , PdCl , Pd(OAc) , and Pd (dba)
3
gave 2a in good yield (entries 1–4), whereas catalysts hav-
2
2
2
2
2
Synlett 2009, No. 1, 85–88 © Thieme Stuttgart · New York

LETTER
Electroreductive Generation of Recyclable Organic Reductant
87
0
Table 2 Effects of Pd Catalysts
Table 3 Pd/[C V ]-Promoted Reductive Coupling of ArX
8
Entry
Pd catalyst
Time (h)
Yield (%)a
Entry
R
Time (h) Yield of 2 (%)a
2
a
1a
–
1
2
3
4
5
6
7
8
4-NCC H Br (1a)
2
42
4
96 (0)
6
3
1
2
3
4
5
6
PdCl (PhCN)
2
0.5
4
96
90
96
99
22
19
–
2
2
4-EtC(O)C H Br (1b)
91 (0)
6
3
PdCl2
–
4-MeOC(O)C H Br (1c)
71 (28)
84 (0)
6
3
Pd(OAc)2
–
4-ClC H Br (1d)
18
20
41
6
3
Pd (dba)
8
–
2
3
3-NCC H Br (1e)
71 (14)
82 (0)
6
3
PdCl (PPh )
48
48
48
65
60
87
2
3 2
3-MeOC(O)C H Br (1f)
6 3
Pd(PPh3)
4
4-MeOC H Br (1g)
4.5
18 (61)
73 (21)
6
3
7
–b
3-MeOC H Br (1h)
18
6
3
a
Isolated yield.
The reaction was performed without Pd catalyst.
c.m.b
57 (0)
9
0
4-HC(O)C H Br (1i)
4
6
b
6
3
c
1
1
1
4-O NC H Br (1j)
2
7
c.m.b
55(5)
2
6
3
Pd(II)
c
d
C8V0
12
13
C8V2+
4-EtOC(O)C H Cl (1k)
28
40
16
31
0 (94)
0 (83)
[
]
6
3
Ar-Ar
Ar-Br
1
Pd(0)
2
1
4
5
4-NCC H Cl (1l)
6 3
e
1
4-NCC H I (1m)
64 (27)
6
3
Ar-Pd(II)-Ar
Ar-Pd(II)-Br
f
(
C)
(A)
16
4-MeOC
6
H
3
I (1n)
14 (68)
C8V0
a
Isolated yield. Recoveries of the starting material 1 are listed in pa-
rentheses.
[
Ar-Pd(0)]–
B)
b
Complex mixture; both coupling and reduction of aldehyde or nitro
(
Ar-Br
C8V2+
groups occurred.
c
V0.
1
A divided cell was used for preparation of C
8
d
PdCl was used as a Pd catalyst. 4-Amino-4¢-nitrobiphenyl (15%)
2
0
Scheme 3 A plausible reaction mechanism of C V -mediated
reductive coupling of aryl halides
8
was also obtained.
e
Compound 2a.
Compound 2g.
f
would be accelerated with Mg2+ ion. The reductive cou-
pling of aryl chlorides 1k and 1l did not proceed at all and
most of the starting materials were recovered (entries 13
0
generate C V gradually, which would work as a real re-
8
ductant.19
and 14), whereas aryl iodides 1m and 1n gave the corre- Recovery and reuse of the bipyridinium compound were
sponding coupling compounds 2a and 2g in rather low successfully performed. After usual extraction with
yields (entries 15 and 16).
EtOAc, the organic layer was concentrated under reduced
pressure. The residue was washed with toluene. The tolu-
ene washings were combined and purified to give the de-
sired product 2a. The residue (after washing with toluene)
A plausible mechanism is shown in Scheme 3. The Pd(II)
catalysts would be reduced with C V to give Pd(0) spe-
cies. Oxidative addition of ArBr 1 to the Pd(0) species
0
8
2+
–
was dried in vacuo to give [C V ][Tf N ] , confirmed by
8
2
2
would give an ArPd(II)X A, which would be reduced with
1
0
–
IR and H NMR spectra. The residue was used for the sec-
C V to give [ArPd(0)] B species. The second oxidative
8
ond run of the reductive coupling to give 2a in 76% yield.
addition of 1 to the complex B would give ArPd(II)Ar C,
which would afford ArAr 2 and Pd(0) species via reduc- The electroreductive coupling using a catalytic amount of
2
+
–
20
tive elimination.
[C V ][Tf N ] did not proceed: by using 0.025 mmol
8 2 2
2
+
–
2
+
of [C V ][Tf N ] , benzonitrile was obtained in 31%
8 2 2
yield, and the coupling product 2a was not detected. Di-
rect reduction of 1a with Mg was the main pathway.
Bipyridinium [C V ] was reduced to give radical cation
8
•
+
0
[
C V ] (one-electron reduction) and quinoid C V (two-
8
8
electron reduction). The coupling product 2a was ob-
tained in good yield (87%) from 1a using 1 mol equivalent In conclusion, we prepared N,N¢-dioctyl-4,4¢-bipyridini-
0
•+ 18
2+
–
of C V , whereas 2 mol equivalents of [C V ] gave a um bis(triflimide) [C V ][Tf N ] . Electroreduction of
8
8
8
2
2
2
+
–
0
mixture of 2a (59%) and 1a (32%). These observations in- [C V ][Tf N ] in THF gave an organic reductant, C V ,
dicate that [C V ] is less efficient for this Pd-catalyzed which promoted Pd-catalyzed reductive coupling of aryl
coupling than C V . Disproportionation of C V would halides to give the corresponding biaryls. [C V ][Tf N ]
2
8
2
2
8
•
+
8
0
•+
2+
–
8
8
8
2
Synlett 2009, No. 1, 85–88 © Thieme Stuttgart · New York

8
8
M. Kuroboshi et al.
LETTER
could be recovered and reused to generate the organic re-
ductant.
(13) (a) Bird, C. L.; Kuhn, A. T. Chem. Soc. Rev. 1981, 10, 49.
(
b) Hünig, S.; Berneth, H. Top. Curr. Chem. 1980, 92, 1;
Chem. Abstr. 1980, 93, 237989n. (c) Kamogawa, H.; Sato,
S. Bull. Chem. Soc. Jpn. 1991, 64, 321. (d) Kingh, R. P.;
Shreeve, J. M. Inorg. Chem. 2003, 42, 7416. (e) Kijima,
M.; Sakawaki, A.; Sato, T. Bull. Chem. Soc. Jpn. 1994, 67,
Acknowledgment
This research was partially supported by the Ministry of Education,
Science, Sports and Culture, Grant-in-Aid for Scientific Research
2323. (f) Depature, L.; Surpateanu, G. Heterocycles 2002,
5
7, 2239.
(
C), 19550108, 2007-2009, and Electric Technology Research
2+
–
1
(
14) Purity of [C V ][Tf N ] was confirmed by H NMR,
8 2 2
Foundation of Chugoku.
13
1
C NMR, IR, and elemental analysis. H NMR (200 MHz,
CD Cl ): d = 0.8–1.0 (m, 6 H), 1.20–1.50 (m, 20 H), 1.90–
2
2
2
4
.20 (m, 4 H), 4.64 (t, J = 7.6 Hz, 4 H), 8.46 (d, J = 6.9 Hz,
References and Notes
13
H), 8.93 (d, J = 6.9 Hz, 4 H). C NMR (50 MHz, CD Cl ):
2
2
d = 13.41, 22.16, 25.59, 28.41, 28.48, 31.01, 31.21, 62.57,
(
1) (a) Formic acid: Mukhopadhyay, S.; Yaghmur, A.; Baidossi,
1
3
1
3
19.28 (q, J = 319.1 Hz), 127.03, 144.96, 149.50. IR (KBr):
M.; Kundu, B.; Sasson, Y. Org. Process Res. Dev. 2003, 7,
136, 3104, 3074, 2952, 2929, 2861, 1644, 1347, 1203,
641. (b) Hydroquinone: Hennings, D. D.; Iwama, T.; Rawal,
–
1
133, 1058 cm . Anal. Calcd for C H F N O S : C,
V. H. Org. Lett. 1999, 1, 1205. (c) Ascorbic acid: Ram,
R. N.; Singh, V. Tetrahedron Lett. 2006, 47, 7625.
2) (a) Burkholder, C.; Dolbier, R. W. Jr.; Médebielle, M.
Tetrahedron Lett. 1997, 38, 821. (b) Pawelke, G. J.
Fluorine Chem. 1991, 52, 229. (c) Takeuchi, N.; Aït-
Mohand, S.; Médebielle, M.; Dolbier, R. W. Jr. Tetrahedron
Lett. 2002, 43, 4317. (d) Médebielle, M.; Kato, K.; Dolbier,
R. W. Jr. Tetrahedron Lett. 2003, 44, 7871.
3) Kuroboshi, M.; Tanaka, M.; Kishimoto, S.; Goto, K.;
Mochizuki, M.; Tanaka, H. Tetrahedron Lett. 2000, 41, 81.
4) Kuroboshi, M.; Tanaka, M.; Goto, K.; Mochizuki, M.;
Tanaka, H. Synlett 1999, 1930.
30 42 12
4
8 4
8.21; H, 4.49; N, 5.94. Found: C, 38.28; H, 4.57; N, 5.93.
2
+
–
[
C V ][Tf N ] was dried in vacuo at 100 °C overnight and
(
8 2 2
used without further purification.
(
15) In a cathodic compartment of a divided cell was placed a
2
+
–
THF (3 mL) solution of [C V ][Tf N ] (1 mmol),
8
2
2
+
–
2
[
Bu N ][Tf N ] (2 mmol), and a Pt (1 × 1.5 cm ) cathode. In
an anodic compartment was placed a THF (3 mL) solution of
Bu N ][Tf N ] (2 mmol) and a Mg anode. A constant
4
2
+
–
[
(
(
(
4 2
current (25 mA) was applied at r.t. until 2 F/mol
2
+
–
[
C V ][Tf N ] of electricity was passed. The resulting dark
8 2 2
blue solution in cathodic cell was added to a mixture of 1a
0.5 mmol) and a catalytic amount of PdCl (PhCN) (0.025
(
5) (a) Kuroboshi, M.; Waki, Y.; Tanaka, H. Synlett 2002, 637.
2
2
mmol) by means of cannulation. The whole mixture was
stirred for 30 h at 60 °C. Usual workup and purification by
(
2
b) Kuroboshi, M.; Waki, Y.; Tanaka, H. J. Org. Chem.
003, 68, 3938. (c) Kuroboshi, M.; Takeda, T.; Motoki, R.;
column chromatography (SiO ) gave 2a (0.227 mmol, 91%).
Tanaka, H. Chem. Lett. 2005, 34, 530.
2
(
(
16) Iyer, S.; Kulkarni, G. M.; Ramesh, C. Tetrahedron 2004, 60,
(
(
(
(
6) Endo, T.; Saotome, Y.; Okawara, M. Tetrahedron Lett.
2
163.
17) In the case of Pd/TDAE-promoted reductive coupling of aryl
bromides, PdCl , PdCl (PhCN) , Pd(OAc) , and Pd (dba)
1985, 26, 4525.
7) Park, K. K.; Lee, C. W.; Oh, S.-Y. J. Chem. Soc., Perkin
Trans. 1 1990, 2356.
8) Park, K. K.; Lee, C. W.; Choi, S. Y. J. Chem. Soc., Perkin
Trans. 1 1992, 601.
2
2
2
2
2
3
gave the coupling products, whereas Pd(PPh ) and
3 4
PdCl (PPh ) did not promote the coupling, and the starting
2
3 2
aryl bromides were recovered quantitatively.
9) Tomioka, H.; Ueda, K.; Ohi, H.; Izawa, Y. Chem. Lett. 1986,
2
+
–
(
18) A THF solution of [C V ][Tf N ] (1 mmol) and
1359.
8 2 2
+
–
[
Bu N ][Tf N ] (2 mmol) was electrolyzed under constant
4 2
(
(
10) Maidan, R.; Goren, Z.; Becker, J. Y.; Willner, I. J. Am.
Chem. Soc. 1984, 106, 6217.
11) (a) Shosenji, H.; Nakano, Y.; Yamada, K. Chem. Lett. 1988,
current conditions (30 mA) at r.t. until 1 F/mol
2
+
–
[
C V ][Tf N ] of electricity was passed. The solution was
8 2 2
used for the reductive coupling of 1a (0.5 mmol) in the
presence of PdCl (PhCN) (0.025 mmol) to give 2a and 1a
1033. (b) Mandler, D.; Willner, I. J. Phys. Chem. 1987, 91,
3600. (c) Coche, L.; Moutet, J.-C. J. Am. Chem. Soc. 1987,
109, 6887. (d) Kashiwagi, Y.; Shibayama, N.; Anzai, J.;
2
2
in 59% and 32% yield, respectively.
(
(
19) Hammarstroem, L.; Almgren, M.; Norrby, T. J. Phys. Chem.
Osa, T. Electrochemistry 2000, 68, 42; Chem. Abstr. 2000,
32, 70660h.
1992, 96, 5017.
1
20) In an undivided cell were placed a mixture of 1a (0.5 mmol),
(
12) Yuan, R.; Watanabe, S.; Kuwabata, S.; Yoneyama, H.
2
+
–
+
–
[
C V ][Tf N ] (0.025 mmol), [Bu N ][Tf N ] (2.0 mmol),
8 2 2 4 2
J. Org. Chem. 1997, 62, 2494.
a catalytic amount of PdCl (PhCN) (0.025 mmol), and THF
2
2
(
3 mL). A Mg anode and a Pt cathode were immersed in the
solution, and a constant current (5 mA) was supplied at 60
C until 2 F/mol-1a of electricity was passed.
°
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