Anodic Phenol-Coupling Reaction
FULL PAPER
ane/ethyl acetate 98:2, then 95:5) yielded 2 as colourless solid (7.82g,
32.3 mmol, 85%). M.p. 1358C (cyclohexane, value in ref. [17]: m.p. 134–
1358C); H NMR (300 MHz, CDCl3): d=2.27 (s, 12H; CH3), 5.04 (s, 2H;
6.61 (d, 4J
A
G
4-H); elemental analysis calcd (%) for C22H30O4 (358.47): C 73.71, H
8.44; found: C 73.64, H 8.44.
1
OH), 6.85 (s, 2H; 4-H), 6.98 ppm (s, 2H; 6-H); elemental analysis calcd
(%) for C16H18O2 (242.13): C 79.31, H 7.49; found: C 79.21, H 7.35.
5,5’-Dimethoxy-2,2’-biphenol (10): Sodium[tetrakis(4-methoxyphenoxy)-
G
borate] (10a) (2.11 g, 4.0 mmol), acetonitrile (25 mL), 3.1 F, subjected to
column chromatography (cyclohexane/ethyl acetate 75:25, then 70:30)
yielded 10 (0.93 g, 3.8 mmol, 48%); m.p. 1258C (cyclohexane, value in
ref. [20]: m.p. 125–1268C); 1H NMR (400 MHz, CDCl3): d=3.75 (s, 6H;
OCH3), 6.52(brs, 2H; OH), 6.78–6.82(m, 4H; 4-H, 6-H); 6.87 ppm (d,
Sodium[(3,3’,5,5’-tetramethyl-2,2’-biphenoxy)bis(2’’,4’’-dimethylphenoxy)-
borate] (6): The solution of sodium[tetrakis(2,4-dimethylphenoxy)borate]
A
(5) (0.49 g, 0.9 mmol) and 3,3’,5,5’-tetramethyl-2,2’-biphenol (2) (0.23 g,
0.9 mmol) in THF (5 mL) was stirred for 2h at RT. The reaction mixture
was concentrated to half the volume and stored for 12h at 4 8C. The crys-
talline precipitate was isolated by filtration and subsequent washing with
diethyl ether (2mL). Drying in high vacuum yielded 6 as colourless solid
(0.32g, 0.6 mmol, 69%). 1H NMR (300 MHz, [D8]THF): d=2.01 (s, 6H;
CH3), 2.07 (s, 6H; CH3), 2.10 (s, 6H; CH3), 2.26 (s, 6H; CH3), 6.56 (dd,
3J
(246.26): C 68.28, H 5.73; found: C 67.99, H 5.69.
5,5’-Dihydroxy-[6,6’]bi(benzo[1,3]dioxolyl) (11): Sodium
[1.3]dioxol-5-yloxy)borate] (11a) (1.63 g, 2.8 mmol), acetonitrile (25 mL),
A
A
N
G
N
AHCTREUNG
5.2F, subjected to column chromatography (cyclohexane/ethyl acetate
80:20, then 75:25) yielded 11 (0.51 g, 1.9 mmol, 34%); m.p. 2018C (cyclo-
hexane, value in ref. [6]: m.p. 201–2028C); 1H NMR (300 MHz,
[D6]DMSO): d=5.91 (s, 4H; 2-H), 6.50 (s, 2H; 4-H), 6.67 (s, 2H; 7-H),
8.87 ppm (brs, 2H; OH); elemental analysis calcd (%) for C14H10O6
(274.23): C 61.32, H 3.68; found: C 61.35, H 3.47.
3J
C
G
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7.21 ppm (d, J
d=17.59 (CH3), 17.83 (CH3), 20.77 (CH3), 20.96 (CH3), 119.44, 126.39,
126.93, 127.58, 127.78, 129.07, 130.30, 130.68, 130.73, 132.24, 153.72,
155.46 ppm; 11B NMR (64 MHz, [D8]THF): d=5.44 ppm; HRMS: calcd
for C32H34BO4 [MÀNa]À: 493.2556; found: 493.2547.
3,3’-Di-tert-butyl-5,5’6,6’-tetramethyl-2,2’-biphenol
[tetrakis(2-tert-butyl-4,5-dimethylphenoxy)borate]
(12):
(12a)
Sodium-
(1.01 g,
A
Sodium[bis(3,3’,5,5’-tetramethyl-2,2’-biphenoxy)borate] (7): The warm
E
1.4 mmol), acetonitrile (25 mL), 6.2 F, subjected to column chromatogra-
phy (cyclohexane/ethyl acetate 98:2) yielded 12 (0.29 g, 0.8 mmol, 30%);
m.p. 1638C (cyclohexane, value in ref. [21]: m.p. 161–1628C); 1H NMR
suspension (508C) of boric acid (0.77 g, 12.4 mmol) in methanol (25 mL)
was combined with the warm solution (508C) of 3,3’,5,5’-tetramethyl-2,2’-
biphenol (2) (6.00 g, 24.8 mmol) in methanol (25 mL) and the reaction
mixture was heated for 10 min under reflux conditions. The resulting sol-
ution was chilled to 08C and sodium methanolate (2.3 mL of a 5.4m solu-
tion in methanol, 12.4 mmol) was added dropwise, followed by immedi-
ate formation of a precipitate. The desired product was filtered off and
subsequently washed with cold methanol (10 mL). The filtrate was con-
centrated under reduced pressure and a second crop was isolated as de-
scribed above. Drying in high vacuum provided 7 as colourless solid
(4.92g, 9.6 mmol, 77%). Single crystals of 7 for X-ray analysis were ob-
tained along with the second crop from methanol. 1H NMR (400 MHz,
CD3CN): d=2.00 (s, 12H; CH3), 2.29 (s, 12H; CH3), 6.91 (s, 4H; 4-H),
6.97 ppm (s, 4H; 6-H); 13C NMR (75 MHz, CD3CN): d=17.53 (CH3),
20.96 (CH3), 128.51, 129.64, 130.13, 130.74, 131.72, 153.16 ppm; 11B NMR
(64 MHz, CD3CN): d=7.99 ppm; HRMS: calcd for C32H32BO4 491.2399
[MÀNa]À; found: 491.2288.
(400 MHz, CDCl3): d=1.40 (s, 18H; C(CH3)3), 1.82(s, 6H; CH ), 2.26 (s,
A
3
6H; CH3), 4.80 (s, 2H; OH), 7.13 ppm (s, 2H; 4-H); elemental analysis
calcd (%) for C24H34O2 (354.53): C 81.31, H 9.67; found: C 81.36, H 9.56.
5,5’-Dimethyl-2,2’-biphenol (13): Sodium[tetrakis(4-methylphenoxy)bo-
N
rate] (13a) (2.23 g, 4.8 mmol), acetonitrile (25 mL), 2.3 F, subjected to
column chromatography (cyclohexane/ethyl acetate 90:10, then 85:15)
yielded 13 (0.60 g, 2.8 mmol, 30%); m.p. 1558C (cyclohexane, value in
ref. [22]: m.p. 154–1558C); 1H NMR (300 MHz, CDCl3): d=2.31 (s, 6H;
CH3), 6.01 (brs, 2H; OH), 6.87–6.90 (m, 2H; 3-H), 7.06–7.08 ppm (m,
4H; 4-H, 6-H); elemental analysis calcd (%) for C14H14O2 (214.26): C
78.48, H 6.59; found: C 78.21, H 6.40.
5,5’-Di-tert-butyl-2,2’-biphenol (14): Sodium
A
AHCTREUNG
ed to column chromatography (cyclohexane/ethyl acetate 90:10) yielded
14 (0.40 g, 1.3 mmol, 20%); m.p. 1968C (cyclohexane, value in ref. [23]:
m.p. 207–2088C); 1H NMR (300 MHz, CDCl3): d=1.32(s, 18H; CH 3),
General procedure for the anodic oxidation of sodium
A
6.96 (d, 3J
N
ACHTREUNG
A
N
ACHTREUNG
was dissolved in acetonitrile and transferred into a nondivided, standard
electrolysis cell[16] equipped with two platinum sheets as anode and cath-
ode, respectively. At 408C a galvanostatic electrolysis with a current den-
sity of 12.5 mAcmÀ2 was performed. During electrolysis, the polarity was
reversed every 60 s to avoid electrode coating. Completion of the reac-
tion was indicated by a sudden increase in the terminal voltage, at which
point the electrolysis was stopped. Citric acid (ca. 0.30 g, 1.6 mmol) was
added and the reaction mixture was diluted with hot water (100 mL) fol-
lowed by stirring for 5 min and extraction with tert-butyl methyl ether
(TBME, 330 mL). The combined organic layers were washed with
brine (50 mL), dried (MgSO4) and concentrated in vacuo. Purification by
column chromatography yielded the corresponding biphenol as colourless
solid.
ACHTREUNG
2H; 4-H).
X-ray crystal-structure analysis for 7: formula C36H48BNaO8, M=642.54,
light-yellow crystal 0.600.300.10 mm3, a=20.647(1) b=8.087(1) c=
21.940(1) , b=103.44(1)8, V=3563.0(5) 3, 1calc =1.198 gcmÀ3
, m=
0.093 mmÀ1, empirical absorption correction (0.946ꢀTꢀ0.991), Z=4,
monoclinic, space group C2/c (No. 15), l=0.71073 , T=198 K, w and f
À1
scans, 14017 reflections collected (Æh, Æk, Æl), [(sinq)/l]=0.66
,
4222 independent (Rint =0.048) and 2456 observed reflections [Iꢁ2s(I)],
221 refined parameters, R=0.060, wR2 =0.172, max. residual electron
density 0.46 (À0.34) eÀ3, hydrogen atoms calculated and refined as
riding atoms.
Data sets were collected by using a Nonius KappaCCD diffractometer
equipped with a rotating anode generator. Programs used: data collection
COLLECT (Nonius B.V., 1998), data reduction Denzo-SMN[24], absorp-
tion correction Denzo[25], structure solution SHELXS-97[26], structure re-
finement SHELXL-97[27], graphics DIAMOND 3.0d (Crystal Impact,
Bonn, Germany).
3,3’,5,5’,6,6’-Hexamethyl-2,2’-biphenol (8): Sodium
A
ACHTREUNG
subjected to column chromatography (cyclohexane/ethyl acetate 98:2,
then 95:5) yielded 8 (1.83 g, 6.8 mmol, 66%); m.p. 1698C (cyclohexane,
value in ref. [18]: m.p. 136–1388C); 1H NMR (300 MHz, CDCl3): d=1.86
(s, 6H; CH3), 2.25 (s, 12H; CH3), 4.56 (s, 2H, OH), 7.02ppm (s, 2H; 4-
H); elemental analysis calcd (%) for C18H22O2 (270.37): C 79.96, H 8.20;
found: C 79.94, H 8.16.
CCDC 298666 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
3,3’-Di-tert-butyl-5,5’-dimethoxy-2,2’-biphenol (9): Sodium[tetrakis(2-tert-
A
butyl-4-methoxyphenoxy)-borate] (9a) (0.97 g, 1.3 mmol), acetonitrile
(14 mL), 6.4 F, subjected to column chromatography (cyclohexane/ethyl
acetate 98:2, then 95:5) yielded 9 (0.54 g, 1.5 mmol, 58%); m.p. 2268C
(cyclohexane, value in ref. [19]: m.p. 228–2298C); 1H NMR (400 MHz,
CDCl3): d=1.42(s, 18H; CH 3), 3.76 (s, 6H; OCH3); 5.00 (s, 2H; OH),
Acknowledgements
Financial support by BASF AG and the International Graduate College
“Template-Directed Chemical Synthesis” (DFG) is highly appreciated.
Chem. Eur. J. 2006, 12, 7482– 7488
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7487