Isolation and characterization of a trinuclear cobalt complex containing trigonal-prismatic cobalt in secondary alcohol aerobic oxidation

Article abstract of DOI:10.1021/om500003d

An unusual trinuclear cobalt complex was successfully isolated and characterized in the Co(OAc)₂·4H₂O-catalyzed aerobic oxidation of pyridine-based secondary alcohols. In this complex, a cobalt ion (the one in the middle, labeled Co2) has a novel trigonal-prismatic structure coordinated with six oxygen atoms from the substrate. The molecular oxygen present in air plays a major role in enabling this transformation to be catalytic. This aerobic catalytic reaction is very selective to pyridine-based secondary alcohols over primary alcohols.

Full text of DOI:10.1021/om500003d

Article
pubs.acs.org/Organometallics
Isolation and Characterization of a Trinuclear Cobalt Complex
Containing Trigonal-Prismatic Cobalt in Secondary Alcohol Aerobic
Oxidation
I. Karthikeyan, S. K. Alamsetti, and G. Sekar*
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, Tamil Nadu, India
S
* Supporting Information
ABSTRACT: An unusual trinuclear cobalt complex was
successfully isolated and characterized in the Co(OAc)2·
4H2O-catalyzed aerobic oxidation of pyridine-based secondary
alcohols. In this complex, a cobalt ion (the one in the middle,
labeled Co2) has a novel trigonal-prismatic structure
coordinated with six oxygen atoms from the substrate. The
molecular oxygen present in air plays a major role in enabling
this transformation to be catalytic. This aerobic catalytic
reaction is very selective to pyridine-based secondary alcohols
over primary alcohols.
Scheme 1. Cobalt-Catalyzed Aerobic Oxidation of Alcohol 1
ryl(di)azinyl ketone derivatives have shown a wide range
of biological activities such as being antihistamines,
A
antimalarial and antiarrhythmic agents, β2-adrenergic agonists,
and anticancer therapeutics.1 Owing to their biological
importance and usefulness, various synthetic approaches have
been developed to prepare these ketone derivatives. In
particular, the oxidation of secondary alcohols2 and benzylic
oxidation of the methylene group of aryl(di)azinylmethanes
have proven to be versatile synthetic strategies.3 Despite their
merits, the aforementioned methods suffer from harsh reaction
conditions, less functional group tolerance, multistep prepara-
tion of starting materials, the need for ligands to the metal
catalysts, and moderately sustainable oxidizing agents. Also, it is
difficult to address the exact reaction pathway with appropriate
evidence. Hence, it is important to develop a new catalytic
method which will be more economical, environmentally
benign, and easily available and have high functional group
tolerance and high selectivity with proper understanding of the
reaction pathway.
Recently, we had used chiral cobalt catalysts for the synthesis
of enantiomerically enriched benzoins and α-hydroxy esters
through oxidative kinetic resolution.4 Further extending the
scope of cobalt catalysts, in this paper we report for the first
time a Co(OAc)2-catalyzed selective secondary pyridine based
alcohol oxidation reaction and the isolation and character-
ization of an unusual trinuclear cobalt complex, which is formed
in the course of this oxidation reaction.
external ligand, base, or additive. To increase the efficiency of
the reaction, the oxidation reaction was further screened with
different types of cobalt salts, solvents, ratios of catalyst, and
temperatures to optimize the reaction conditions for this
aerobic oxidation reaction. The results are summarized in Table
1.
Initially, various cobalt salts were screened. Cobalt acetate
turned out to be the best reagent, and it resulted in 99%
isolated yield of the product in 30 min (Table 1, entry 1).
These results indicate that the counteranion acetate plays a
prominent role in this oxidation. Next, various solvents were
tested for this oxidation reaction, and among them dioxane
proved to be the most efficient solvent for this oxidation
reaction (99% isolated yield in 3.5 h; Table 1, entry 9). Ketone
2 was obtained with other solvents also, but the reaction time
was longer. It is possible that the coordinating nature of the
substrate with cobalt acetate could be more favorable in
dioxane than that in the other solvents.
Then the reaction was carried out in an open air atmosphere;
it took 4 h to provide 98% isolated yield (Table 1, entry 14)
which clearly shows that molecular oxygen present in the air is
sufficient. Therefore, we decided to carry out the reaction
further in an open air atmosphere. Finally, upon cobalt catalyst
screening, it was found that 10 mol % of catalyst gave 99%
To begin with, we carried out the aerobic oxidation of (2-
pyridyl)phenylmethanol (1) as a model substrate using a
catalytic amount of cobalt acetate (5 mol %) in the presence of
oxygen in toluene at 70 °C. This aerobic oxidation reaction
yielded 99% of the corresponding ketone, phenyl(pyridin-2-
yl)methanone (2), in 30 min (Scheme 1). It is interesting to
note that this aerobic oxidation reaction took place without any
Received: January 5, 2014
Published: April 2, 2014
© 2014 American Chemical Society
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Table 1. Optimization of Cobalt-Catalyzed Aerobic Oxidation of Secondary Alcohol
a
entry
cobalt source
loading (mol %)
solvent
T (°C)
atmosphere
time (h)
yield (%)
1
Co(OAc)2·4H2O
Co(NO)3·7H2O
CoSO4·7H2O
5
5
toluene
toluene
toluene
toluene
toluene
toluene
benzene
THF
70
70
70
70
70
50
50
50
50
50
50
50
50
50
50
50
50
50
50
O2
O2
O2
O2
O2
O2
O2
O2
O2
O2
O2
O2
O2
air
air
air
air
air
air
0.5
48
48
48
48
4
99
84
2
3
5
4
CoO
5
14
5
CoCl2·6H2O
5
6
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
Co(OAc)2·4H2O
5
98
94
98
99
37
98
98
7
5
21
9
8
5
9
5
dioxane
CHCI3
DMF
3.5
48
23
8
10
11
12
13
14
15
16
17
18
19
5
5
5
CH3CN
MeOH
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
5
48
4
34
b
5
98
1
18
6.5
3.5
2.5
1
96
98
96
99
97
2.5
5
10
20
a
b
Isolated yield. Reaction carried out in an open air atmosphere.
isolated yield in just 2.5 h (entry 18). After having optimized
the reaction conditions, we tested the substrate scope for this
oxidation reaction. Several pyridine-based secondary alcohols
containing both electron-withdrawing and electron-donating
groups were successfully oxidized to the corresponding ketones
in quantitative yield, as summarized in Figure 1.
and yielded selectively the corresponding oxidized products
95% (2n) and 97% (2m), respectively (Scheme 2).
Scheme 2. High Functional Group Tolerance of Cobalt-
Catalyzed Aerobic Oxidation Reaction
Interestingly, even groups typically sensitive toward oxidation
such as aldehydic (1n) and benzylic alcoholic groups (1m)
were well tolerated under the optimized reaction conditions
Our cobalt acetate catalyzed aerobic oxidation reaction is
very selective to 2-pyridinyl-based secondary alcohols over
primary alcohols. When pyridine-based alcohols containing
both primary and secondary alcohol groups such as substrates 3
were made to react under the optimized reaction conditions, in
all of the reactions only the secondary alcohol groups were
selectively oxidized over the primary alcoholic group (Table 2).
In particular, when the diol 3b was oxidized with the Co(OAc)2
catalyst, it only yielded the selective secondary alcohol oxidized
product 4b with 88% isolated yield (entry 2). However, the
same diol 3b when treated with other typical oxidizing agents
such as PDC, PCC, and DMP and under Swern oxidation
conditions gave almost a 1:1 mixture of products without any
selectivity, and the results are summarized in Table 3. These
results clearly show that the cobalt acetate catalyzed aerobic
oxidation is very selective for secondary alcohols due to the
increased acidity of doubly activated benzylic protons.
Motivated by the excellent selectivity afforded in the Co-
catalyzed oxidation protocol, we then strived to find out how
Figure 1. Substrate scope of the aerobic oxidation reaction.
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secondary alcohol 1, which can act as a bidentate ligand (β-
imino alcohol) to putatively give a five-membered cyclic
complex with cobalt acetate whose formation is not possible in
the case of other secondary alcohols 5−7 (Figure 2).
Table 2. Selective Aerobic Oxidation of Secondary Alcohols
over Primary Alcohols by Cobalt Acetate
Figure 2. Substrates which failed to undergo oxidation.
Thus, the pyridine nitrogen atom of alcohol 1 may
coordinate with cobalt acetate and this coordination may
increase the acidity of the benzylic methine proton, whereas
this is not possible in the case of diphenylmethanol, (3-
pyridyl)phenylmethanol, and (4-pyridyl)phenylmethanol. In
addition, the nitrogen atom of 1 can act as a base as well. To
investigate the exact mechanistic pathway of this aerobic
oxidation reaction, particularly the complexation nature of the
substrate 1 with Co(OAc)2, we attempted to isolate the
reaction complex from cobalt acetate and pyridinyl alcohol 1.
When a 1:1 ratio of cobalt acetate and pyridinyl alcohol 1 was
stirred in dioxane at room temperature for 30 min followed by
the slow evaporation of the solvent, pink crystals (crystal A)
were obtained and a notable quantity of the oxidized product
ketone 2 was found in the mother liquor. The XRD analysis of
this crystal A revealed that the very unusual trinuclear cobalt
species 8a was complexed with six molecules of (2-pyridyl)-
phenylmethanol along with a cocrystal of cobalt acetate trimer
8b (Figure 3).
a
b
Isolated yield. The appropriate quantity of starting material was
recovered.
Table 3. Various Typical Oxidizing Agent Mediated Selective
Oxidations of Diol
a
entry
reagent
time
yield (%)
yield (%)
1
2
3
4
5
Co(OAc)2·4H2O
PCC
4 days
4 h
88
24
29
21
23
0
18
34
30
31
PDC
4 h
DMP
2 days
9 h
Swern oxidation
a
All the oxidizing reagents were used in a 2 equiv amount in
dichloromethane solvent (5 mL). Swern oxidation was carried out in
DMSO as solvent.
Figure 3. ORTEP diagram of the cobalt trinuclear complex in crystal
A. H atoms have been omitted for clarity. Relevant bond lengths (Å)
and angles (deg): Co1−Co2 2.6351(8), Co1−N1 1.921(7), Co1−N2
1.927(6), Co1−N3 1.930(4), Co1−O1 1.881(3), Co1−O2 1.883(3),
Co1−O3 1.871(3), Co3−O4 2.102(2), Co3−O5 2.167(3); N1−
Co1−N2 99.0(2), N1−Co1−N3 98.4(2), N1−Co1−O1 86.0(2),
N1−Co1−O2 171.2(2), N1−Co1−O3 87.4(2). CCDC No.: 781092.
the cobalt acetate alone is responsible for the catalytic oxidation
without any ligand, additives, or base. We started with the
diphenylmethanol substrate 5 and noticed that it failed to
undergo any oxidation reaction, even when an external ligand
such as 1,10-phenanthroline or tetramethylethylenediamine
(TMEDA) was used along with cobalt acetate.
Surprisingly, other pyridine-based secondary alcohols such as
(3-pyridyl)phenylmethanol (6) and 4-pyridylphenylmethanol
(7) also failed to provide any oxidized product. In order to
further understand the selectivity of this oxidation reaction, we
performed the reaction with a mixture of the substrates (2-
pyridyl)phenylmethanol (1) and 2-pyridinemethanol. As we
expected, only substrate 1 was oxidized to provide the
corresponding ketone 2 in 96% isolated yield in 4 h, whereas
2-pyridinemethanol was recovered in a quantitative amount.
These results clearly indicate that there can be a complex
formation between cobalt acetate and the 2-pyridinyl-based
In order to accurately study the properties of complex 8a, it
is necessary to avoid the formation of cocrystal 8b. We found
that the cobalt acetate trimer cocrystal formation could be
avoided if the required or an excess quantity of alcohol is
present in the medium, as in the case of aerobic oxidation
reaction. Thus, when 1:10 ratios of cobalt acetate and pyridinyl
alcohol 1 were used for complex formation under the same
conditions, black crystals (crystal B) were isolated and a
reasonable quantity of the oxidation product 2 was seen in the
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mother liquor. The solid-state X-ray structure of the Co
complex 8a′ is shown in Figure 4. As expected, the cobalt
Figure 4. ORTEP diagram of cobalt trinuclear complex 8a′ (crystal
B). H atoms and acetic acid molecule have been omitted for clarity.
Relevant bond lengths (Å) and angles (deg): Co1−Co2 2.6351(8),
Co1−N1 1.929(7), Co1−N2 1.920(6), Co1−N3 1.920(4), Co1−O1
1.885(3), Co1−O2 1.882(5), Co1−O3 1.879(4); N1−Co1−N2
98.9(2), N1−Co1−N3 97.8(2), N1−Co1−O1 85.2(2), N1−Co1−
O2 170.3(2), N1−Co1−O3 90.4(2). CCDC No.: 789671.
Figure 5. Powder XRD spectrum of recovered residue and cobalt
acetate tetrahydrate.
Fe, and Zn were used as catalysts for the oxidation reaction of
1, all of them led to either very poor conversion or no reaction
at all. The results are summarized in Table 4. Then, when the
Table 4. Various Metal Acetate Catalyzed Oxidations of
Secondary Alcohols
triacetate cocrystal 8b is absent in this case and only the
trinuclear cobalt complex, bereft of any contaminations (8a′), is
present: the space group of crystal 8a′ is C2/c with unit
dimensions a = 29.163(2) Å, b = 17.1312(12) Å, and c =
18.0064(13) Å and cell angles α = 90.00°, β = 122.096(2)°, and
γ = 90.00°.
a
entry
metal salt
time (h)
yield (%)
35
In complex 8a′, all three cobalt atoms are present in a linear
arrangement and both of the terminal cobalt atoms (Co1 and
Co3) have a distorted-octahedral geometry with a coordination
number of 6 with 3 oxygen and 3 nitrogen atoms from 3
molecules of alcohol 1. The geometry of the cobalt (Co2) atom
present in the middle corresponds to a trigonal-prismatic
structure with 6 oxygen bridgehead coordination from all 6
alcohols. Thus, the middle cobalt (Co2) represents an unusual
trigonal-prismatic coordination geometry with a coordination
sphere of 6 oxygen atoms.5 In general, these types of complexes
have been reported only with a dithiolate ligand.6 The trigonal-
prismatic structure belongs to the Oh point group, as shown in
Figure 4. It can also be seen that the oxygen atoms attached to
the middle Co are arranged at the corners of the trigonal prism
with Co−O distances of Co2−O1 2.901(4) Å, Co2−O2
2.082(3) Å, and Co2−O3 2.078(5) Å. The triangular faces are
almost perfect triangles with O−O distances of O1−O2 2.568
Å, O2−O3 2.541 Å, and O3−O1 2.568 Å and angles of 60.33,
60.37, and 59.29°. These values are also consistent with
previous report.5 Finally, the utilization of complex 8a′ as a
catalyst for the aerobic oxidation reaction of 1 gave ketone 2 in
93% yield in 4.5 h.
When the isolated complex 8a′ was subjected to the optimal
reaction conditions without alcohol 1, it produced ketone 2 as
the product in 43% isolated yield in 6 h and cobalt remains
were recovered from the reaction mixture. Powder XRD data of
the recovered cobalt remains were found to be is very close to
the powder XRD data of cobalt(II) acetate tetrahydrate (Figure
5). The recovered cobalt remains from the decomposition of
complex 8a′ were then used as a catalyst for the oxidation of
alcohol 1, and as expected, oxidation took place to yield ketone
2. However, the reaction was slightly slow (4.5 h) and the
isolated yield of ketone 2 was 87%. Finally, when instead of
cobalt acetate other acetates of metals such as Pd, Mn, Cd, Rh,
1
2
3
4
5
6
Fe(OAc)2
[Rh(OAc)2]2
Pd(OAc)2
Cd(OAc)2
Zn(OAc)2
Mn(OAc)2
48
48
48
48
48
48
34
23
a
Isolated yield.
oxidation reaction of 1 was carried out under a nitrogen
atmosphere, the reaction faced a serious setback and the yield
was drastically reduced to 10%. However, the same reaction
under a nitrogen atmosphere with 1 equiv of cobalt acetate gave
a 93% yield of ketone.7
This result clearly indicates that molecular oxygen8 present in
air is helping the cobalt catalyst to regenerate for the next
catalytic cycle to provide a quantitative yield of the product.
Other cobalt salts such as CoCl2 did not provide any oxidation
product even after 2 days at 70 °C, which clearly shows that in
cobalt acetate the acetate counteranion plays a prominent role
in the oxidation reaction. To investigate this scenario, 10 mol %
(1 equiv with respect to cobalt chloride) of sodium acetate was
used along with CoCl2 under the optimized conditions.9 As we
expected, the aerobic oxidation reaction went smoothly and
provided 88% isolated yield in 3 h, which indicates the
importance of acetate ion in the oxidation reaction.
In summary, we have developed an efficient and selective
method to oxidize pyridine-based secondary alcohols using
Co(OAc)2 as a catalyst. An interesting trinuclear cobalt
complex was isolated and characterized. In this structure, the
cobalt ion (Co2) located in the middle has an unusual trigonal-
prismatic structure and is surrounded by the six oxygen atoms.
The molecular oxygen present in air plays a major role in
ensuring that the oxidation reaction is a catalytic process.
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3H), 7.78 (td, J = 1.6 Hz, J = 7.6 Hz, 1H), 7.48 (t, J = 7.6 Hz, 1H),
7.32−7.42 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 193.9, 155.1,
148.5, 137.1, 136.3, 132.9, 131.0, 128.2, 126.2, 124.6; IR (neat) 3057,
2926, 1661, 1576, 1308, 932, 742, 693 cm−1; HRMS (m/z) [M + H]+
calcd for C12H10NO 184.0762, found 184.0768.
Finally, our Co(OAc)2-catalyzed aerobic oxidation of pyridine-
based alcohols is very selective to secondary alcohols over
primary alcohols, thus providing a useful synthetic platform in
complicated organic syntheses.
(4-Methoxyphenyl)(pyridin-2-yl)methanone (2b): white solid; mp
92−94 °C (lit.11 mp 95−97 °C); Rf = 0.42 (hexanes/ethyl acetate, 70/
30 v/v); 1H NMR (400 MHz, CDCl3) δ 8.71 (d, J = 4.4 Hz, 1H), 8.12
(d, J = 8.8 Hz, 2H), 7.99 (d, J = 7.6 Hz, 1H), 7.88 (td, J = 1.6 Hz, J =
7.6 Hz, 1H), 7.43−7.50 (m, 1H), 6.97 (d, J = 8.8 Hz, 2H), 3.88 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 192.4, 163.7, 155.9, 148.5,
137.1, 133.6, 129.2, 125.9, 124.6, 113.7, 55.6; IR (neat) 3053, 3001,
2348, 2251, 1648, 1598, 1258, 912, 741 cm−1; HRMS (m/z) [M +
Na]+ calcd for C13H11NO2Na 236.0687, found 236.0692.
EXPERIMENTAL SECTION
■
General Considerations. Reactions were performed in an oven-
dried reaction tube in an open air atmosphere. Extra pure analytical
grade 1,4-dioxane and cobalt acetate tetrahydrate were purchased from
Sisco Research Laboratories (India) PVT. Ltd. Solvents used for
extraction and purification were technical grade and were distilled
before use. Reactions were monitored by thin-layer chromatography
on precoated aluminum-packed plates (0.25 mm, Merck Kieselgel 60
with fluorescent indicator UV254) and visualized by fluorescence
quenching. Column chromatography was performed with silica gel
(particle size 100−120 mesh, RANKEM). The wavenumbers of
recorded IR signals are quoted in cm−1. 1H and 13C NMR spectra were
recorded in CDCl3 solvent on a 400 MHz spectrometer. Data are
expressed as chemical shifts in parts per million (ppm) relative to
residual chloroform and CDCl3 (1H δ 7.26 and 13C δ 77.16,
respectively; likewise for other solvents where applicable) and TMS as
(4-Fluorophenyl)(pyridin-2-yl)methanone (2c): white solid; mp
68−70 °C (lit.12 mp 68−69 °C); Rf = 0.71 (hexanes/ethyl acetate, 80/
1
20 v/v); H NMR (400 MHz, CDCl3) δ 8.70−8.74 (m, 1H), 8.13−
8.20 (m, 2H), 8.06(d, J = 8 Hz, 1H), 7.91 (td, J = 1.6 Hz J = 7.6 Hz,
1H), 7.47−7.53 (m, 1H), 7.12−7.20 (m, 2H); 13C NMR (100 MHz,
CDCl3) δ 192.1, 165.7 (d, J = 253.1 Hz), 154.9, 148.5, 137.3, 133.9 (d,
J = 9.3 Hz), 132.5, 126.4, 124.7, 115.4 (d, J = 21.6 Hz); IR (neat)
2362, 1655, 1590, 1306, 909, 736 cm−1; HRMS (m/z) [M + H]+ calcd
for C12H9NOF 202.0668, found 202.0663.
1
internal standard on the δ scale. H coupling constants J are given in
(4-Chlorophenyl)(pyridin-2-yl)methanone (2d): white solid; mp
Hz and are rounded to the nearest 0.1 Hz.
58−60 °C (lit.11 mp 60−61 °C); Rf = 0.75 (hexanes/ethyl acetate, 80/
Experimental Procedure for Cobalt Complex 8a′ (Crystals A
and B) Preparation. Crystal B. In a clean 50 mL round-bottom flask,
Co(OAc)2·4H2O (24.9 mg, 0.1 mmol) and (2-pyridyl)-
phenylmethanol (1; 185 mg, 1 mmol) were added to 30 mL of 1,4-
dioxane, and the mixture was stirred at room temperature for 30 min.
The resulting mixture was filtered through Whatman filter paper, and
the resulting homogeneous solution was allowed to slowly evaporate at
room temperature. After 4 days, black crystals of B (8a′) started to
form; these were suitable for single-crystal X-ray analysis. Yield: 86 mg
(twice recovered from mother liquor), 67%. Mp: 138 °C. IR (KBr):
3049, 3069, 3027, 1568, 1022, 768 cm−1. Anal. Calcd for
C76H72Co3N6O15: C, 61.29; H, 5.28; N, 5.79. Found: C, 62.03; H,
5.21; N, 5.63.
Crystal A. Pink crystals of A (8a,b) were prepared by the same
procedure as for crystal B; Co(OAc)2·4H2O (249 mg, 1 mmol) and
(2-pyridyl)phenylmethanol (1; 185 mg, 1 mmol) were added in a 1:1
ratio. Yield: 173 mg, 81%. Mp: 129 °C. IR (KBr): 3419, 3064, 2851,
1570, 1482, 1444, 1396, 1033, 767 cm−1. Anal. Calcd for
C88H110Co6N6O34: C, 49.17; H, 5.16; N, 3.91. Found: C, 48.69; H,
4.52; N, 3.87.
Experimental Procedure for Oxidation of Alcohol 1 using
Complex 8a′ and Recovery, Reusing the Complex 8a′ Residue.
In a reaction tube, complex 8a′ (128.2 mg, 0.1 mmol) in 5 mL of 1,4-
dioxane was stirred at 50 °C for 4.5 h. The reaction progress was
monitored by TLC. The reaction mixture was concentrated, the
resulting residue was washed with diethyl ether until product 2
disappeared from the reaction mixture, and the combined organic
layers were concentrated and filtered through a silica pad to provide
phenyl(2-pyridyl)methanone (2; yield 46.9 mg, 43%). Solvent was
removed from the recovered cobalt remains, and the leftover cobalt
compound was considered as cobalt(II) acetate (on the basis of a
powder XRD study) and further used as a catalyst (24.9 mg, 0.1
mmol) to oxidize the alcohol 1 (185 mg, 1 mmol) to yield phenyl(2-
pyridyl)methanone (2; 159 mg, yield 87%) in 4.5 h.
Typical Experimental Procedure for Aerobic Oxidation. In a
reaction tube, a mixture of cobalt(II) acetate tetrahydrate (24.9 mg, 0.1
mmol) and phenyl(2-pyridyl)methanol (1; 185 mg, 1 mmol) in 5 mL
of 1,4-dioxane was stirred at 50 °C in an open air atmosphere for 3.5 h.
The progress of the reaction was monitored by TLC. The reaction
mixture was concentrated, and the resulting residue was directly
purified by silica gel column chromatography (eluents: hexanes and
ethyl acetate) to give phenyl(2-pyridyl)methanone (2; 181 mg, 99%
yield).
1
20 v/v); H NMR (400 MHz, CDCl3) δ 8.72 (d, J = 3.6 Hz, 1H),
8.02−8.12 (m, 3H), 7.93 (d, J = 7.6 Hz, 1H), 7.49−7.55 (m, 1H), 7.46
(d, J = 8.4 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 192.5, 154.7,
148.6, 139.5, 137.4, 134.6, 132.6, 128.6, 126.6, 124.8; IR (neat) 3058,
2927, 2855, 1665, 1581, 1308, 922, 740 cm−1; HRMS (m/z) [M + H]+
calcd for C12H9NOCl 218.0373, found 218.0370.
(Pyridin-2-yl)(p-tolyl)methanone (2e): white solid; mp 43−45 °C
(lit.13 mp 43−44 °C); Rf = 0.71 (hexanes/ethyl acetate, 80/20 v/v);
1H NMR (400 MHz, CDCl3) δ 8.63 (d, J = 4.4 Hz, 1H), 7.85−7.99
(m, 3H), 7.75−7.84 (m, 1H), 7.34−7.44 (m, 1H), 7.20 (d, J = 8 Hz,
2H), 2.34 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 193.6, 155.5,
148.5, 143.9, 137.1, 133.7, 131.2, 129.0, 126.1, 124.1, 21.8; IR (neat)
3055, 2925, 2856, 2361, 2105, 1659, 1606, 1309, 929, 740 cm−1;
HRMS (m/z) [M + H]+ calcd for C13H12NO 198.0919, found
198.0924.
(2-Methoxyphenyl)(pyridin-2-yl)methanone (2f): white solid; mp
78−80 °C (lit.14 mp 77−79 °C); Rf = 0.50 (hexanes/ethyl acetate, 70/
30 v/v); 1H NMR (400 MHz, CDCl3) δ 8.52−8.57 (m, 1H), 7.88 (dd,
J = 0.8 Hz, J = 6.8 Hz, 1H), 7.75 (td, J = 1.6 Hz, J = 7.6 Hz, 1H), 7.44
(dd, J = 1.6 Hz, J = 7.6 Hz, 1H), 7.36 (m, 1H), 7.29−7.35 (m, 1H),
6.93−6.99 (m, 1H), 6.88 (d, J = 8.4 Hz, 1H), 3.55 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 196.2, 158.3, 155.5, 148.9, 136.8, 132.9, 130.4,
128.2, 126.2, 123.2, 120.6, 111.7, 55.7; IR (neat) 3060, 2928, 2845,
2360, 1669, 1590, 1242, 923, 745 cm−1; HRMS (m/z) [M + H]+ calcd
for C13H12NO2 214.0868, found 214.0867.
(Naphthalen-1-yl)(pyridin-2-yl)methanone (2g): yellow solid; mp
43−45 °C (lit.13 mp 43−45 °C); Rf = 0.48 (hexanes/ethyl acetate, 70/
1
30 v/v); H NMR (400 MHz, CDCl3) δ 8.69 (d, J = 4.4 Hz, 1H),
8.22−8.29 (m, 1H), 8.16 (d, J = 7.6 Hz, 1H), 8.03 (d, J = 8.4 Hz,
1H),7.87−7.96 (m, 2H), 7.72(dd, J = 0.8 Hz, J = 7.2 Hz, 1H), 7.44−
7.58 (m, 4H); 13C NMR (100 MHz, CDCl3) δ 196.7, 156.6, 149.3,
137.1, 134.8, 134.0, 132.3, 131.4, 130.0, 128.6, 127.6, 126.6, 126.4,
125.8, 124.7, 124.3; IR (neat) 3055, 2928, 2250, 1665, 1577, 1298,
914, 738 cm−1; HRMS (m/z) [M + H]+ calcd for C16H12NO
234.0919, found 234.0923.
(Pyridin-2-yl)(o-tolyl)methanone (2h):13 colorless oil; Rf = 0.41
1
(hexanes/ethyl acetate, 70/30 v/v); H NMR (400 MHz, CDCl3) δ
8.72 (d, J = 2.8 Hz, 1H), 8.11 (d, J = 7.6 Hz, 1H), 7.92 (t, J = 7.6 Hz,
1H), 7.39−7.54 (m, 3H), 7.24−7.36(m, 2H), 2.40 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 197.5, 155.1, 149.3, 138.0, 137.5, 137.2, 131.3,
131.1, 130.2, 126.6, 125.2, 124.3, 20.6; IR (neat) 3056, 2978, 2928,
2860, 1672, 1578, 1314, 1273, 927, 743 cm−1; HRMS (m/z) [M + H]+
calcd for C13H12NO 198.0919, found 198.0917.
Phenyl(pyridin-2-yl)methanone (2a): white solid; mp 42−43 °C
(lit.10 mp 42 °C); Rf = 0.48 (hexanes/ethyl acetate, 80/20 v/v); H
(4-tert-Butylphenyl)(pyridin-2-yl)methanone (2i): colorless oil; Rf
1
NMR (400 MHz, CDCl3) δ 8.61 (d, J = 4.4 Hz, 1H), 7.89−8.01 (m,
= 0.60 (hexanes/ethyl acetate, 70/30 v/v); 1H NMR (400 MHz,
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CDCl3) δ 8.72 (d, J = 4.8 Hz, 1H), 7.98−8.04 (m, 3H), 7.88 (td, J =
1.6 Hz, J = 7.6 Hz, 1H), 7.44−7.53(m, 3H), 1.34 (s, 9H); 13C NMR
(100 MHz, CDCl3) δ 193.7, 156.7, 155.5, 148.6, 137.1, 133.6, 131.1,
126.1, 125.3, 124.7, 35.2, 31.2; IR (neat) 3056, 2963, 2867, 1661,
1604, 1309, 1271, 758 cm−1; HRMS (m/z) [M + H]+ calcd for
C16H18NO 240.1388, found 240.1382.
1588, 1452, 1053, 913, 739 cm−1; HRMS (m/z) [M + H]+ calcd for
C13H14NO2 216.1025, found 216.1028.
(6-(Hydroxymethyl)pyridin-2-yl)phenylmethanone (4a): yellow
oil; Rf = 0.53 (hexanes/ethyl acetate, 50/50 v/v); 1H NMR (400
MHz, CDCl3) δ 8.02 (d, J = 7.6 Hz, 2H), 7.92 (q, J = 7.6 Hz, 2H),
7.60 (t, J = 7.6 Hz, 1H), 7.44−7.53 (m, 3H), 4.84 (s, 2H); 13C NMR
(100 MHz, CDCl3) δ 193.6, 158.4, 153.7, 138.0, 136.2, 133.2, 131.0,
128.3, 123.5, 123.2, 64.0; IR (neat) 3438, 3069, 2929, 2845, 1715,
1664, 913, 740 cm−1; HRMS (m/z) [M + H]+ calcd for C13H12NO2
214.0868, found 214.0872.
(Pyridin-2-yl)(m-tolyl)methanone (2j): yellow oil; Rf = 0.54
1
(hexanes/ethyl acetate, 70/30 v/v); H NMR (400 MHz, CDCl3) δ
8.69 (d, J = 4.0 Hz, 1H), 7.98 (d, J = 7.6 Hz, 1H), 7.76−7.90 (m, 2H),
7.29−7.50 (m, 3H), 2.39 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
194.3, 155.2, 148.6, 137.9, 137.0, 136.3, 133.8, 131.3, 128.3, 128.1,
126.1, 124.6, 21.4; IR (neat) 3055, 2921, 2859, 1662, 1577, 1309, 747,
711 cm−1; HRMS (m/z) [M + H]+ calcd for C13H12NO 198.0919,
found 198.0920.
(Pyridin-2-yl)(4-(trifluoromethyl)phenyl)methanone (2k): yellow
oil; Rf = 0.73 (hexanes/ethyl acetate, 70/30 v/v); 1H NMR (400 MHz,
CDCl3) δ 8.70 (d, J = 4.4 Hz, 1H), 8.17 (d, J = 8.0 Hz, 2H), 8.10 (d, J
= 8.0 Hz, 1H), 7.91 (td, J = 1.6 Hz, J = 7.8 Hz, 1H), 7.72 (d, J = 8.0
Hz, 2H), 7.47−7.53 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 192.9,
154.2, 148.8, 139.4, 137.4, 134.0 (q, J = 32.4 Hz), 131.3, 126.9, 125.2
(q, J = 3.6 Hz), 124.9, 122.5; IR (neat) 3062, 2926, 2853, 1671, 1581,
1316, 1121, 743 cm−1; HRMS (m/z) [M + H]+ calcd for C13H9NOF3
252.0636, found 252.0641.
(4-Fluorophenyl)(6-(hydroxymethyl)pyridin-2-yl)methanol (3b):
1
yellow oil; Rf = 0.28 (hexanes/ethyl acetate, 50/50 v/v); H NMR
(400 MHz, CDCl3) δ 7.49 (t, J = 7.6 Hz, 1H), 7.17−7.24 (m, 2H),
7.08 (d, J = 7.6 Hz, 1H), 6.95 (d, J = 7.6 Hz, 1H), 6.87 (t, J = 8.4 Hz,
2H), 5.63 (s, 1H), 4.60 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 162.4
(d, J = 244.6), 160.4, 158.5, 138.7, 137.8, 128.7 (d, J = 8.1 Hz), 119.8,
119.5, 115.4 (d, J = 21.4 Hz), 74.6, 64.5; IR (neat) 3355, 2869, 2828,
1599, 1508, 1223, 1057, 913, 742 cm−1; HRMS (m/z) [M + H]+ calcd
for C13H13NO2F 234.0930, found 234.0936.
(4-Fluorophenyl)(6-(hydroxymethyl)pyridin-2-yl)methanone
1
(4b): yellow oil; Rf = 0.43 (hexanes/ethyl acetate, 50/50 v/v); H
NMR (400 MHz, CDCl3) δ 8.07−8.15 (m, 2H), 7.88−7.98 (m, 2H),
7.47 (d, J = 7.6 Hz, 1H), 7.16 (t, J = 8.4 Hz, 2H), 4.84 (s, 2H), 3.52
(bs, 1H); 13C NMR (100 MHz, CDCl3) δ 192.0, 165.9 (d, J = 253.9
Hz), 158.2, 153.8, 138.0, 133.8 (d, J = 9.3 Hz), 132.6, 123.5, 123.2,
115.5 (d, J = 21.7 Hz), 64.1; IR (neat) 3429, 2923, 1662, 1591, 1230,
908, 727 cm−1; HRMS (m/z) [M + H]+ calcd for C13H11NO2F
232.0774, found 232.0770.
(6-(Hydroxymethyl)pyridin-2-yl)(4-(trifluoromethyl)phenyl)-
methanol (3c): yellow oil; Rf = 0.26 (hexanes/ethyl acetate, 50/50 v/
v); 1H NMR (400 MHz, CDCl3) δ 7.59 (t, J = 7.6 Hz, 1H), 7.52 (d, J
= 8 Hz, 2H), 7.46 (d, J = 8 Hz, 2H), 7.17 (d, J = 7.6 Hz, 1H), 7.06 (d,
J = 7.6 Hz, 1H), 5.78 (s, 1H), 5.50 (bs, 1H), 4.70 (s, 2H); 13C NMR
(100 MHz, CDCl3) δ 159.8, 158.6, 146.7, 138.0, 129.9 (q, J = 32.1
Hz), 127.2, 126.1, 125.5 (d, J = 3.7 Hz), 122.8, 119.9 (d, J = 8.7 Hz),
74.8, 64.5; IR (neat) 3361, 2935, 2866, 1587, 1325, 1122, 1065, 913,
740 cm−1; HRMS (m/z) [M + H]+ calcd for C14H13NO2F3 284.0898,
found 284.0900.
(3,5-Dimethylphenyl)(pyridin-2-yl)methanone (2l): pale yellow
oil; Rf = 0.42 (hexanes/ethyl acetate, 80/20 v/v); 1H NMR (400
MHz, CDCl3) δ 8.71 (dt, J = 4.8 Hz, J = 0.8 Hz, 1H), 7.98 (dd, J = 8.0
Hz, J = 0.8 Hz, 1H), 7.84−7.91 (m, 1H), 7.61 (s, 2H), 7.43−7.49 (m,
1H), 7.21 (d, J = 0.4 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 194.6,
155.5, 148.7, 137.8, 137.0, 136.5, 134.8, 128.7, 126.1, 124.6, 21.3; IR
(neat) 3055, 2921, 2859, 1662, 1577, 1309, 747 cm−1; HRMS (m/z)
[M + Na]+ calcd for C14H13NONa 234.0895, found 234.0905.
4-(Hydroxy(pyridin-2-yl)methyl)benzaldehyde (1m): colorless oil;
1
Rf = 0.20 (hexanes/ethyl acetate, 70/30 v/v); H NMR (400 MHz,
CDCl3) δ 9.86 (s, 1H), 8.43 (s, 1H), 7.73 (d, J = 8 Hz, 2H), 7.55 (t, J
= 7.6 Hz, 1H), 7.48 (d, J = 8 Hz, 2H), 7.07−7.17 (m, 2H), 5.75 (s,
1H), 4.99 (bs, 1H); 13C NMR (100 MHz, CDCl3) δ 192.0, 160.1,
149.9, 148.1, 137.3, 135.8, 130.0, 127.5, 122.9, 121.3, 74.7; IR (neat)
3435, 2834, 2738, 2252, 1698, 1601, 1431, 1207, 1054, 910, 734 cm−1;
HRMS (m/z) [M + H]+ calcd for C13H12NO2 214.0868, found
214.0874.
4-Picolinoylbenzaldehyde (2m): white solid; mp 52−53 °C; Rf =
0.50 (hexanes/ethyl acetate, 70/30 v/v); 1H NMR (400 MHz, CDCl3)
δ 10.12 (s, 1H), 8.73 (d, J = 3.2 Hz, 1H), 8.21 (d, J = 8 Hz, 2H), 8.13
(d, J = 7.6 Hz, 1H), 7.89−8.06 (m, 3H), 7.49−7.60 (m, 1H); 13C
NMR (100 MHz, CDCl3) δ 193.1, 191.1, 154.2, 148.8, 141.3, 138.7,
137.4, 131.5, 129.3, 126.9, 124.8; IR (neat) 2927, 2849, 2749, 1704,
1657, 1574, 1305 cm−1; HRMS (m/z) [M + H]+ calcd for C13H10NO2
212.0712, found 212.0716.
(6-(Hydroxymethyl)pyridin-2-yl)(4-(trifluoromethyl)phenyl)-
methanone (4c): yellow oil; Rf = 0.66 (hexanes/ethyl acetate, 50/50
v/v); 1H NMR (400 MHz, CDCl3) δ 8.13 (d, J = 8 Hz, 2H), 8.02 (d, J
= 7.6 Hz, 1H), 7.94 (t, J = 7.6 Hz, 1H), 7.75 (d, J = 8 Hz, 2H), 7.51 (d,
J = 7.6 Hz, 1H), 4.83 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 192.6,
158.7, 152.9, 139.3, 138.2, 134.0, 131.2, 125.3, 125.2, 123.8, 123.6,
64.1; IR (neat) 3451, 2922, 1672, 1589, 1322, 760 cm−1; HRMS (m/
z) [M + H]+ calcd for C14H11NO2F3 282.0742, found 282.0748.
(6-(Hydroxymethyl)pyridin-2-yl)(4-methoxyphenyl)methanol
(3d): white solid; mp 116 °C; Rf = 0.18 (hexanes/ethyl acetate, 50/50
(4-(Hydroxymethyl)phenyl)(pyridin-2-yl)methanol (1n): yellow
solid; mp 62−63 °C; Rf = 0.20 (hexanes/ethyl acetate, 50/50 v/v);
1H NMR (400 MHz, CDCl3) δ 8.53 (d, J = 4.8 Hz, 1H), 7.61 (td, J =
1.2 Hz, J = 7.8 Hz, 1H), 7.27−7.37 (m, 4H), 7.12−7.21 (m, 2H), 5.72
(s, 1H), 4.63 (s, 2H); 13C NMR (100 MHz, CDCl3): δ 161.0, 147.9,
142.7, 140.7, 137.1, 127.3, 122.6, 121.5, 74.9, 65.1; IR (neat) 3301,
3135, 2917, 2887, 2841, 2734, 1062, 1001, 761 cm−1; HRMS (m/z)
[M + H]+ calcd for C13H14NO2 216.1025, found 216.1026.
(4-(Hydroxymethyl)phenyl)(pyridin-2-yl)methanone (2n): color-
1
v/v); H NMR (400 MHz, CDCl3) δ 7.55 (t, J = 7.6 Hz, 1H), 7.17−
7.23 (m, 2H), 7.12 (d, J = 7.6 Hz, 1H), 6.99 (d, J = 7.6 Hz, 1H), 6.75−
6.81 (m, 2H), 5.66 (s, 1H), 4.70 (s, 2H), 3.70 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 160.8, 159.4, 158.1, 137.9, 135.1, 128.4, 120.1, 119.4,
114.1, 74.8, 64.6, 55.4; IR (neat) 3355, 2923, 2361, 1604, 1510, 1244,
1032, 740 cm−1; HRMS (m/z) [M + H]+ calcd for C14H16NO3
246.1130, found 246.1135.
(6-(Hydroxymethyl)pyridin-2-yl)(4-methoxyphenyl)methanone
1
1
(4d): colorless oil; Rf = 0.48 (hexanes/ethyl acetate, 50/50 v/v); H
less oil; Rf = 0.20 (hexanes/ethyl acetate, 70/30 v/v); H NMR (400
NMR (400 MHz, CDCl3) δ 8.00−8.07 (m, 2H), 7.80−7.90 (m, 2H),
7.44 (d, J = 6.8 Hz, 1H), 6.89−6.97 (m, 2H), 4.81 (s, 2H), 3.85 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 192.1, 163.7, 158.3, 154.4,
137.9, 133.5, 128.8, 123.2, 122.8, 113.6, 64.1, 55.6; IR (neat) 3394,
2248, 1656, 1594, 1319, 1259, 913, 739 cm−1; HRMS (m/z) [M + H]+
calcd for C14H14NO3 244.0974, found 244.0973.
MHz, CDCl3) δ 8.71 (d, J = 3.6 Hz, 1H), 8.02 (d, J = 8 Hz, 3H), 7.90
(t, J = 7.6 Hz, 1H), 7.49 (d, J = 6.8 Hz, 1H), 7.45 (d, J = 8 Hz, 2H),
4.74 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 193.7, 155.1, 148.6,
146.6, 137.3, 135.3, 131.3, 126.3, 126.2, 124.7, 64.5; IR (neat) 3375,
2925, 2861, 1662, 1606, 1577, 1414, 1311, 745 cm−1; HRMS (m/z)
[M + H]+ calcd for C13H12NO2 214.0868, found 214.0870.
(4-Chlorophenyl)(6-(hydroxymethyl)pyridin-2-yl)methanol (3e):
white solid; mp 121 °C; Rf = 0.30 (hexanes/ethyl acetate, 50/50 v/
v); 1H NMR (400 MHz, CDCl3) δ 7.64 (t, J = 8.0 Hz, 1H), 7.25−7.33
(m, 4H), 7.21 (d, J = 7.6 Hz, 1H), 7.06 (d, J = 8.0 Hz, 1H), 5.75 (s,
1H), 4.77 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 160.0, 158.4,
141.4, 138.1, 133.8, 128.8, 128.5, 120.0, 119.7, 74.6, 64.5; IR (neat)
(6-(Hydroxymethyl)pyridin-2-yl)phenylmethanol (3a): yellow oil;
Rf = 0.28 (hexanes/ethyl acetate, 50/50 v/v); H NMR (400 MHz,
CDCl3) δ 7.49−7.57 (m, 1H), 7.16−7.31 (m, 5H), 7.11 (d, J = 7.6 Hz,
1H), 7.01 (d, J = 8.0 Hz, 1H), 5.70 (s, 1H), 4.68 (s, 2H); 13C NMR
(100 MHz, CDCl3) δ 160.4, 158.2, 142.8, 137.9, 128.7, 128.5, 128.0,
127.1, 120.1, 119.5, 75.2, 64.5; IR (neat) 3376, 2923, 2859, 1712,
1
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3359, 1588, 1326, 1268, 756 cm−1; HRMS (m/z) [M + H]+ calcd for
C13H13NO2Cl 250.0635, found 250.0635.
2007, 50, 219. (c) Wetzel, M.; Gargano, E. M.; Hinsberger, S.;
Marchais-Oberwinkler, S.; Hartmann, R. W. Eur. J. Med. Chem. 2012,
47, 1. (d) Wang, X.; Wang, D. Z. Tetrahedron 2011, 67, 3406.
(e) Zhang, W.; Liu, M.; Wu, H.; Ding, J.; Cheng, J. Tetrahedron Lett.
2008, 49, 5336.
(3) (a) Zhang, J.; Wang, Z.; Wang, Y.; Wan, C.; Zheng, X.; Wang, Z.
Green Chem. 2009, 11, 1973. (b) De, H. J.; Abbaspour, T. K.; Maes, B.
U. W. Angew. Chem., Int. Ed. 2012, 51, 2745. (c) Pieber, B.; Kappe, C.
O. Green Chem. 2013, 15, 320. (d) Hsu, S.-F.; Plietker, B.
ChemCatChem 2013, 5, 126.
(4) (a) Alamsetti, S. K.; Muthupandi, P.; Sekar, G. Chem. Eur. J.
2009, 15, 5424. (b) Alamsetti, S. K.; Sekar, G. Chem. Commun. 2010,
46, 7235.
(5) Bertrand, J. A.; Kelley, J. A.; Vassian, E. G. J. Am. Chem. Soc. 1969,
91, 2394.
(6) Muetterties, E. L. J. Am. Chem. Soc. 1968, 90, 5097.
(7) After the reaction, the dioxane was evaporated and the cobalt
product was isolated by adding ether (4 × 5 mL) to the resulting
residue followed by centrifuging to remove the product ketone 2. The
resulting cobalt residue was characterized by powder XRD. The
recovered cobalt product is very similar to other recovered cobalt
products (Figure 5a). See the Figure 3 in the Supporting Information
for the powder XRD spectra for this recovered cobalt product.
(8) For oxidation reactions using molecular oxygen/air, see:
(a) Nishiyama, Y.; Nakagawa, Y.; Mizuno, N. Angew. Chem., Int. Ed.
2001, 40, 3639. (b) Soule, J.-F.; Miyamura, H.; Kobayashi, S. J. Am.
Chem. Soc. 2011, 133, 18550. (c) Fries, P.; Halter, D.; Kleinschek, A.;
Hartung, J. J. Am. Chem. Soc. 2011, 133, 3906.
(9) After the addition of sodium acetate, within 10 min the reaction
mixture turned into a gel form. To turn this into a homogeneous
solution, the reaction tube was shaken by hand until it became
homogeneous (around 1 min).
(10) Couve-Bonnaire, S.; Carpentier, J.-F.; Mortreux, A.; Castanet, Y.
Tetrahedron 2003, 59, 2793.
(4-Chlorophenyl)(6-(hydroxymethyl)pyridin-2-yl)methanone
(4e): white solid; mp 116 °C; Rf = 0.66 (hexanes/ethyl acetate, 50/50
1
v/v); H NMR (400 MHz, CDCl3) δ 7.89−8.03 (m, 4H), 7.44−7.51
(m, 3H), 4.84 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 192.2, 158.5,
153.4, 139.7, 138.2, 134.6, 132.5, 128.7, 123.6, 123.5, 64.1; IR (neat)
3412, 2923, 2854, 1663, 1583, 849, 756 cm−1; HRMS (m/z) [M + H]+
calcd for C13H11NO2Cl 248.0478, found 248.0478.
(6-(Hydroxymethyl)pyridin-2-yl)(p-tolyl)methanol (3f): yellow oil;
1
Rf = 0.28 (hexanes/ethyl acetate, 50/50 v/v); H NMR (400 MHz,
CDCl3) δ 7.62 (t, J = 7.6 Hz, 1H), 7.25 (d, J = 8.0 Hz, 2H), 7.18 (d, J
= 7.6 Hz, 1H), 7.13 (d, J = 7.6 Hz, 2H), 7.08 (d, J = 8.0 Hz, 1H), 5.74
(s, 1H), 4.77 (s, 2H) 2.32 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
160.7, 158.1, 140.0, 137.7, 129.4, 127.1, 120.0, 119.3, 75.2, 64.6, 21.3;
IR (neat) 3355, 2923, 2361, 1604, 1510, 1244, 1032, 740 cm−1; HRMS
(m/z) [M + H]+ calcd for C14H16NO2 230.1181, found 230.1184.
(6-(Hydroxymethyl)pyridin-2-yl)(p-tolyl)methanone (4f): colorless
oil; Rf = 0.48 (hexanes/ethyl acetate, 50/50 v/v); 1H NMR (400 MHz,
CDCl3) δ 7.84 (d, J = 8.0 Hz, 2H), 7.77 (d, J = 4.4 Hz, 2H), 7.36 (t, J
= 4.4 Hz, 1H), 7.18 (d, J = 8.0 Hz, 2H), 4.72 (s, 2H), 2.33 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 193.4, 158.5, 154.1, 144.0, 137.7, 133.5,
131.1, 129.0, 123.2, 122.9, 64.1, 21.8; IR (neat) 3394, 2248, 1656,
1594, 1319, 1259, 913, 739 cm−1; HRMS (m/z) [M + H]+ calcd for
C14H14NO2 228.1025, found 228.1028.
ASSOCIATED CONTENT
* Supporting Information
■
S
Figures, tables, and CIF files giving NMR spectra of ketones
and secondary alcohols, powder XRD data for the recovered
cobalt product, and crystallographic data for 8a,b and 8a′. This
material is available free of charge via the Internet at http://
pubs.acs.org. CCDC 781092 (crystal A) and 789671 (crystal B)
also contain supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
(11) De, H. J.; Abbaspour, T. K.; Maes, B. U. W. Angew. Chem., Int.
Ed. 2012, 51, 2745.
(12) Froimowitz, M.; Gu, Y.; Dakin, L. A.; Nagafuji, P. M.; Kelley, C.
J.; Parrish, D.; Deschamps, J. R.; Janowsky, A. J. Med. Chem. 2007, 50,
219.
(13) Ghorai, P.; Kraus, A.; Keller, M.; Gotte, C.; Igel, P.; Schneider,
E.; Schnell, D.; Bernhardt, G.; Dove, S.; Zabel, M.; Elz, S.; Seifert, R.;
Buschauer, A. J. Med. Chem. 2008, 51, 7193.
(14) Maerten, E.; Sauthier, M.; Mortreux, A.; Castanet, Y.
Tetrahedron 2006, 63, 682.
AUTHOR INFORMATION
Corresponding Author
*E-mail for G.S.: gsekar@iitm.ac.in.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the DST (Project No. SB/S1/OC-72/2013) New
Delhi for financial support. I.K. and S.K.A. thank the CSIR of
India for research fellowships. We thank Dr. Babu Varghese
(SAIF, IIT Madras) and Mr. V. Ramkumar for XRD
measurements.
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