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a brown oil. H NMR (400 MHz, CDCl3) δ 8.53 (s, 1H), 8.37 (s, 13C NMR (101 MHz, CDCl3) δ 190.6, 166.6 (d, J = 2V5ie5wHArzt)ic,le1O3n3lin.0e
1H), 8.24 (d, J = 8.9 Hz, 1H), 8.16 (d, J = 8.0 Hz, 1H), 7.63 (ddd, J (d, J = 3.0 Hz), 132.3 (d, J = 10 Hz), 116.4 (DdO, IJ: =102.1303H9z/C).6RA05536B
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= 7.9, 4.9, 1.8 Hz, 1H), 7.50 – 7.41 (m, 1H), 7.19 – 7.04 (m, 1H), 3,4‐Dimethoxybenzaldehyde14 white solid, H NMR (400 MHz,
2.21 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 156.1, 153.4, 149.4, CDCl3) δ 9.84 (s, 1H), 7.45 (d, J = 9.6 Hz, 1H), 7.40 (s, 1H), 6.97
148.8, 137.2, 136.6, 133.2, 123.2, 120.6, 120.4, 18.1.
2,2‐Bipyridinyl‐5‐carboxylic acid
(d, J = 8.2 Hz, 1H), 3.96 (s, 3H), 3,93 (s, 3H); 13C NMR (101 MHz,
Potassium CDCl3) δ 190.9, 154.5, 149.7, 130.2, 126.9, 110.4, 108.9, 56.2,
(3).11
permanganate (12.3 g, 78 mmol) was added in 7 portions at 1 56.1
h intervals to a solution of 2 (3.4 g, 20 mmol) in water (200 mL). 1‐Naphthaldehyde9 light yellow liquid, 1H NMR (400 MHz,
The mixture was heated at 70 °C for 3 h and then at 90 °C for 4 CDCl3) δ 10.30 (s, 1H), 9.16 (d, J = 8.6 Hz, 1H), 7.99 (d, J = 8.2 Hz,
h more. The brown mixture was then filtered while hot 1H), 7.88 (d, J = 7.0 Hz, 1H), 7.82 (d, J = 8.2 Hz, 1H), 7.65 – 7.55
through celite and washed with hot water (2 x 25 mL). The (m, 1H), 7.51 (m, 2H); 13C NMR (101 MHz, CDCl3) δ 193.6, 136.7,
filtrate was concentrated to approximately 10 mL under 135.3, 133.8, 131.4, 130.6, 129.1, 128.5, 127.0, 124.9.
reduced pressure, and then 1 M HCl was added slowly until a
pH of 4 was obtained. The residue was then filtered and dried
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Results and discussion
to obtain pure 3 (1.2 g, 30%) as a white solid. H NMR (400
MHz, DMSO) δ 9.19 (s, 1H), 8.76 (d, J = 4.3 Hz, 1H), 8.42‐8.54
(m, 3H), 8.01 (t, J = 7.1 Hz, 1H), 7.52‐7.55 (m, 1H); 13C NMR
(101 MHz, DMSO) δ 166.6, 158.8, 154.7, 150.6, 150.0, 138.7,
137.9, 127.0, 125.4, 121.7, 120.7.
The first step toward the preparation of bifunctional ligand
holding a bipyridine unit and TEMPO is to synthesize bipyridine
derivatives bearing a side arm containing a functional group,
which will be used to connect TEMPO (Scheme 1S). 2,2'‐
Bipyridinyl‐5‐carboxylic acid was prepared according to the
literature procedure. 11 The bifunctional ligand was prepared
following the procedure by using 2,2'‐bipyridinyl‐5‐carboxylic
acid and 4‐amino‐TEMPO. The obtained solid labeled as Bpy‐
TEMPO was characterized by HRMS and by EPR (see
Supporting Information). An EPR spectrum of Bpy‐TEMPO was
recorded at room temperature. The characteristic triplet (g =
2.008) arising from the hyperfine structure coupling of the
single electron shows the existence of the nitroxyl radical.
Then, we evaluate the activity of the catalyst in the
oxidation of alcohols. 1‐Octanol was used as a test substrate to
optimize the reaction conditions. The results are summarized
in Table 1. Several frequently used Cu salts were examined
(Table 1, entries 1‐10). Among the screened Cu salts, cuprous
salts show much better catalytic activity than cupric salts
(Table 1, entries 1‐7). The use of CuI afforded the desired
aldehyde in high yield in the presence of NMI as the additive
and CH3CN as the solvent for 12 h (Table 1, entry 3). To our
great surprise, excellent yield could also be obtained in
reducing reaction time (Table 1, entry 8). Cu(OTf) used as Cu
salt only 40% of yield was achieved, whereas [Cu(CH3CN)4]OTf
was used giving in 88% of yield (Table 1, entries 9 and 10). A
series of frequently used additives were examined (Table 1,
entries 11‐13). When DBU was used as the additive, trace
product was obtained (Table 1, entry 11). The use of DMAP
and DABCO afforded 89% and 14% yields, respectively (Table 1,
entries 12 and 13). When the additive was not used, the
product was obtained in only 8% of yield (Table 1, entry 14).
The reaction can also be conducted under open air, albeit with
slightly low yield (Table 1, entry 15). Finally, we demonstrated
the practical applicability of the present catalytic system. The
oxidation of 1‐octanol was performed on a 5 mmol scale (20
times scale) and afforded products in 95% yield, albeit with a
somewhat longer reaction time.
Bpy‐TEMPO (4).12 To a solution of 2,2‐Bipyridinyl‐5‐carboxylic
acid (232 mg, 1.16 mmol), EDCI (268 mg, 1.4 mmol, 1.2 equiv)
and HOBt (214 mg, 1.4 mmol, 1.2 equiv) in DMF (8 mL) was
added 4‐aminoTEMPO (240 mg, 1.4 mmol, 1.2 equiv.). The
mixture was stirred at room temperature for 30 h, poured into
water and extracted with AcOEt. The organic layer was washed
with brine and dried over Na2SO4. Filtration, concentration in
vacuo, and purification by silica gel flash column
chromatography (AcOEt / Petroleum ether /EtN3= 2/1/1) gave
287 mg (70%) of a light brown solid. HRMS (ESI) for C20H26N4O2
[M+H]+, calcd: 354.2011, found: 354.2064.
Tetradecanal13 white solid, 1H NMR (400 MHz, CDCl3) δ 9.76 (t,
J = 1.8 Hz, 1H), 2.41 (td, J = 7.4, 1.8 Hz, 2H), 1.66 – 1.56 (m, 2H),
1.27 (d, J = 16.5 Hz, 20H), 0.88 (t, J = 6.8 Hz, 3H); 13C NMR (101
MHz, CDCl3) δ 202.9, 43.9, 31.9, 29.7, 29.7, 29.6, 29.6, 29.4,
29.4, 29.2, 22.7, 22.1, 14.1.
Cinnamaldehyde14 light yellow liquid, 1H NMR (400 MHz, CDCl3)
δ 9.61 (d, J = 7.7 Hz, 1H), 7.46– 7.48 (m, 2H), 7.40 – 7.29 (m,
4H), 6.66 – 6.53 (m, 1H); 13C NMR (101 MHz, CDCl3) δ 193.7,
152.8, 133.9, 131.3, 129.1, 128.6, 128.5.
Phenylpropiolaldehyde14 yellow liquid, 1H NMR (400 MHz,
CDCl3) δ 9.36 (s, 1H), 7.53 (dd, J = 5.2, 3.3 Hz, 2H), 7.42 (ddd, J
= 6.7, 4.5, 1.3 Hz, 1H), 7.34 (t, J = 7.5 Hz, 2H); 13C NMR (101
MHz, CDCl3) δ 176.9, 133.4, 131.4, 128.8, 119.5, 95.2, 88.5.
Benzaldehyde15 colourless oil liquid, 1H NMR (400 MHz, CDCl3)
δ 9.88 (s, 1H), 7.75 (d, J = 8.1 Hz, 2H), 7.49 (dd, J = 11.9, 4.1 Hz,
1H), 7.39 (t, J = 7.5 Hz, 2H); 13C NMR (101 MHz, CDCl3) δ 191.6,
135.3, 133.4, 128.6, 127.9.
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4‐Methylbenzaldehyde15 colourless liquid, H NMR (400 MHz,
CDCl3) δ 9.96 (s, 1H), 7.77 (d, J = 8.0 Hz, 2H), 7.33 (d, J = 7.8 Hz,
2H), 2.44 (s, 3H); 13C NMR (101 MHz, CDCl3) δ 192.1, 145.6,
134.2, 129.9, 129.8, 21.9.
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4‐Nitrobenzaldehyde16 light yellow acicular crystal, H NMR
(400 MHz, CDCl3) δ 10.16 (s, 1H), 8.40 (d, J = 8.6 Hz, 2H), 8.08
(d, J = 8.7 Hz, 2H); 13C NMR (101 MHz, CDCl3) δ 190.4, 151.2,
140.1, 130.6, 124.4.
Next, we applied the optimum reaction conditions to
examine the substrate scope. The results are summarized in
Table 2. As we know, the oxidation of unactivated primary
aliphatic alcohols to the aldehydes is a challenging issue in the
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4‐Fluorobenzaldehyde16 colourless liquid, H NMR (400 MHz,
CDCl3) δ 9.89 (s, 1H), 7.89 – 7.78 (m, 2H), 7.13 (t, J = 8.3 Hz, 2H);
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