NBu4NI-catalyzed α-benzoxylation of ketones with terminal aryl alkenes

Article abstract of DOI:10.1002/ejoc.201500233

A metal-free protocol for the α-benzoxylation of ketones has been developed by using terminal aryl alkenes as an arylcarboxy surrogate. Moderate to good yields were attained for a variety of propiophenones and acetophenones by using tetra-n-butylammonium iodide (TBAI) as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant under ambient reaction conditions. An efficient synthesis for the α-benzoxylation of aryl ketones has been developed by using terminal aryl alkenes as the arylcarboxy surrogate. The products were obtained in moderate to good yields for a broad scope of substrates. Tetra-n-butylammonium iodide (TBAI) and tert-butyl hydroperoxide (TBHP) were employed as the catalyst and oxidant, respectively.

Full text of DOI:10.1002/ejoc.201500233

Job/Unit: O50233
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FULL PAPER
DOI: 10.1002/ejoc.201500233
nBu4NI-Catalyzed α-Benzoxylation of Ketones with Terminal Aryl Alkenes
Buddhadeb Mondal,[a] Subas Chandra Sahoo,[a] and Subhas Chandra Pan*[a]
Keywords: Synthetic methods / Ketones / Alkenes / Radicals
A metal-free protocol for the α-benzoxylation of ketones has
been developed by using terminal aryl alkenes as an aryl-
carboxy surrogate. Moderate to good yields were attained
for a variety of propiophenones and acetophenones by using
tetra-n-butylammonium iodide (TBAI) as the catalyst and
tert-butyl hydroperoxide (TBHP) as the oxidant under
ambient reaction conditions.
the α-acyloxylation of ketones by using N-methyl-O-benz-
oylhydroxylamine[10a] and later developed an asymmetric
version.[10b] The chiral amine catalyzed α-benzoxylation of
ketones was independently disclosed by the List and
Bencivenni groups.[11] Ochai and co-workers developed an
iodobenzene-catalyzed α-acetoxylation of ketones by using
m-chloroperbenzoic acid.[12] An excellent method for the
(hypo)iodite-catalyzed direct α-acyloxylation of carbonyl
compounds with carboxylic acids was developed by
Ishihara and co-workers.[13] Recently, Cheng et al. used the
combination of TBAI and TBHP for the development of
the α-acyloxylation of ketones in which benzylic alcohols
were used as a carboxylic acid surrogate.[3g] With regard to
functional group transformations, employing a surrogate is
useful and often necessary. Recently, Patel and co-workers
demonstrated the use of aryl alkenes as an arylcarboxy
surrogate under metal and metal-free conditions.[3f,14]
Herein, we have used aryl alkenes as an arylcarboxy
surrogate for the α-benzoxylation of ketones and obtained
good yields for a variety of ketones under metal-free condi-
tions.
Introduction
The last decade has witnessed a surge of interest in the
use of metal-free processes to perform a variety of organic
transformations. These processes sometimes complement
metal-catalyzed methods and are preferred because of their
potential for industrial, economic, and environmental
benefits. In addition, they are often carried out under non-
inert conditions.[1] Besides a plethora of organocatalysts, a
few metal-free catalysts such as iodine, iodide salts, and
organoammonium iodides have also been utilized.[2] These
catalysts are often employed in combination with an oxi-
dant and generally follow a single-electron transfer (SET)
mechanism. Herein, we report a simple method for the α-
benzoxylation of ketones in which terminal aryl olefins are
used as an arylcarboxy surrogate, tetra-n-butylammonium
iodide (TBAI) as the catalyst, and tert-butyl hydroperoxide
(TBHP) as the oxidant.[3,4]
The α-acyloxylation of ketones is an essential transfor-
mation in organic chemistry. The products are valuable
building blocks,[5] and the α-hydroxy carbonyl functionality
is present in an enormous number of both naturally
occurring and synthetic molecules.[6] The value of this pro-
cess has triggered an array of research groups to focus on
the synthesis of the α-acyloxy ketone functionality. Al-
though the traditional approach for the preparation of α-
acyloxy ketones is by a substitution reaction of α-halo carb-
onyl compounds[7] or the oxidative coupling of carbonyl
compounds with heavy metal oxidants,[8] the more attract-
ive approach is to use derivatives of ketones and carboxylic
acids directly. In 1998, Ohfune developed a copper-cata-
lyzed insertion of α-diazo ketones into carboxylic acids.[9]
Tomikson and co-workers reported a general approach to
Results and Discussion
We started our investigation by mixing styrene (1a,
0.5 mmol), propiophenone (2a, 1.0 mmol), I2 (0.2 equiv.),
and TBHP (70% aqueous solution, 6 equiv.) in ethyl acetate
as the solvent. After heating at 80 °C for 24 h, no product
formation had occurred (Table 1, Entry 1). Similarly, the
addition of KI as the catalyst could not promote the reac-
tion (Table 1, Entry 2). Pleasingly, replacing I2 with TBAI
resulted in 45% yield of the desired α-benzoxylated product
3aa (Table 1, Entry 3). Other oxidants such as K2S2O8 and
di-tert-butyl peroxide (DTBP) failed to bring about the re-
action (Table 1, Entries 4 and 5). To improve the product
yield, we screened a variety of solvents. A higher yield was
obtained by using acetonitrile as the solvent (Table 1, En-
try 6). Chlorobenzene as the solvent also provided a similar
yield of the product (Table 1, Entry 7). Finally, benzonitrile
[a] Department of Chemistry, Indian Institute of Technology
Guwahati,
Assam 781039, India
E-mail: span@iitg.ernet.in
www.iitg.ernet.in/span
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500233.
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B. Mondal, S. C. Sahoo, S. C. Pan
FULL PAPER
was found to be the best solvent and provided the product Table 2. α-Benzoxylation of different propiophenone derivatives.[a]
in 58% yield (Table 1, Entry 8). We then turned our
attention towards changing the equivalents of TBHP.
Gratifyingly, the yield was enhanced by using 7 equiv. of
TBHP, and product 3aa was obtained in 65% yield
(Table 1, Entry 9). A further increase in the equivalents of
TBHP did not enhance the yield of 3aa, and, in fact, the
Entry
Ar
R
Product
% Yield[b]
yield decreased (Table 1, Entry 10). Also, TBAI or TBHP
alone was insufficient for product formation (Table 1, En-
tries 11–12). Performing the reaction at higher temperature
(90 °C) or using of smaller amount of TBAI (10 mol-%)
resulted in a lower yield of product.
1
2
3
4
5
6
7
8
9
C6H5
Me
Me
Me
Me
Me
Me
Me
Me
Et
3aa
3ab
3ac
3ad
3ae
3af
3ag
3ah
3ai
65
54
56
52
59
50
60
58
49
4-MeC6H4
4-MeOC6H4
4-ClC6H4
4-BrC6H4
3-ClC6H4
3-BrC6H4
thiophenyl
valerophenone
Table 1. Optimization of the reaction conditions.[a]
[a] Reagents and conditions: 1a (0.5 mmol) and 2a–2i (1.0 mmol)
in benzonitrile (2 mL) under an open atmosphere. [b] Isolated yield
after silica gel column chromatography.
Entry Catalyst
Oxidant
Solvent
% Yield[b]
styrenes were also submitted to the reaction conditions
(Table 3, Entries 6–8), and 3-chlorostyrene was found to be
the best substrate, providing 62% yield of product 3ia. A
slightly lower yield was observed with ortho-substituted
styrene 2j, which is possibly a consequence of steric factors
(Table 3, Entry 9). Delightfully, 1- and 2-vinylnaphthalene
can also be employed in our reaction, and the products
were obtained in moderate yields (Table 3, Entries 10 and
11).
1
2
I2
KI
TBHP
TBHP
TBHP
K2S2O8
DTBP
TBHP
TBHP
TBHP
TBHP[c]
TBHP[d]
–
EtOAc
EtOAc
EtOAc
EtOAc
EtOAc
MeCN
PhCl
PhCN
PhCN
PhCN
PhCN
PhCN
0
0
45
0
3
4
5
6
7
8
9
10
11
12
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
–
0
50
51
58
65
54
0
Table 3. α-Benzoxylation of different aryl olefins with propiophen-
TBHP
0
one.[a]
[a] Reagents and conditions: 1a (0.5 mmol) and 2a (1.0 mmol) in
solvent (2 mL) under an open atmosphere. [b] Isolated yield after
silica gel column chromatography. [c] TBHP (7 equiv.) was em-
ployed. [d] TBHP (8 equiv.) was employed.
With the optimized conditions in hand, we focused on
the scope of the reaction. Initially, propiophenone deriva-
tives 2a–2i were treated with styrene (1a, Table 2), and a Entry Ar
Product
% Yield[b]
variety of electron-rich and electron-poor aryl substituents
were well-tolerated under our reaction conditions. In par-
ticular, different para-substituted propiophenones provided
products 3ab–3ae in good yields (Table 2, Entries 2–5).
Products 3af and 3ag, which have meta substituents on the
aryl group were also isolated in acceptable yields (Table 2,
Entries 6 and 7). Significantly, ketone 2h, which has a
heteroaryl functionality, was also employed, and product
3ah was isolated in 58% yield (Table 2, Entry 8). Finally,
the aliphatic part of the ketone was varied, and valerophe-
none (2i) provided product 3ai in a moderate yield of 49%
(Table 2, Entry 9).
1
2
3
4
5
6
7
8
4-MeC6H4
4-MeOC6H4
4-ClC6H4
4-BrC6H4
4-FC6H4
3-MeC6H4
3-MeOC6H4
3-ClC6H4
2-MeC6H4
1-naphthyl
2-naphthyl
3ba
3ca
3da
3ea
3fa
3ga
3ha
3ia
58
55
53
63
50
50
45
62
35
51
48
9
10
11
3ja
3ka
3la
[a] Reagents and conditions: 1b–1l (0.5 mmol) and 2a (1.0 mmol)
in benzonitrile (2 mL) under an open atmosphere. [b] Isolated yield
after silica gel column chromatography.
Next, the scope of the olefin substrate was investigated,
and the results are summarized in Table 3. As can be seen,
We then proceeded to employ a variety of acetophenones
different substituents on the phenyl group of styrene did in our reaction, as they were less studied by Ishihara and
not change the outcome of the reaction very much. Initially, Cheng. Our reaction conditions were found to be suitable
different para-substituted styrene derivatives were screened, for the range of acetophenones 2j–2o (Table 4). Aceto-
and moderate to good yields were obtained (Table 3, En- phenone (2j) was submitted to the reaction with styrene,
tries 1–5). Interestingly, 4-bromostyrene (1e) provided 63% and after 36 h, the desired product 3aj was afforded in 50%
yield of the desired product. Different meta-substituted yield (Table 4, Entry 1). Electron-rich para-substituted
2
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α-Benzoxylation of Ketones with Terminal Aryl Alkenes
acetophenones 2k and 2l resulted in moderate yields of their perester was treated with ketone 2a, the desired α-benzoxyl-
respective products (Table 4, Entries 2 and 3). However, ation product 3ka was isolated in 57% yield. Thus, it can
electron-poor acetophenones underwent the reaction be envisaged that styrene under the influence of TBAI/
slowly, and lower yields were obtained (Table 4, Entries 4 TBHP is transformed into either benzoic acid or a tert-
and 5). Pleasingly, 2-acetonaphthone was also found to be butyl perester through phenyl glyoxal and benzaldehyde
a suitable ketone and delivered product 3ao in 43% yield intermediates (Scheme 1).[3f] Meanwhile, in the presence of
(Table 4, Entry 6).
a formed tert-butoxy radical, α-carbonyl radical 4 is
generated.[15] Then, the reaction between α-carbonyl radical
4 and the tert-butyl perester radical provides product 3aa.
This substitution should occur through an attack of 4 onto
the oxygen atom of the carbonyl unit of the perester to form
a highly stabilized benzylic as well as a double-heteroatom-
stabilized radical followed by the subsequent fragmentation
of the tert-butoxy radical. Alternatively, radical 4 could be
oxidized into cation intermediate 5, similar to the reports
of Yu and Zhu.[3c,4f] The occurrence of having a positive
charge α to a carbonyl group has already been reported,[16]
though such a cation is seemingly unstable. Finally, the
reaction between cation 5 and the carboxylate anion[17] af-
fords the product (Scheme 1). Taking into account earlier
reports and the stabilities of the intermediates, it appears
that the substitution of the tert-butyl perester by radical 4
is more plausible.
Table 4. α-Benzoxylation of different acetophenones.[a]
Entry
Ar
Product
% Yield[b]
1
2
3
4
5
6
C6H5
3aj
3ak
3al
3am
3an
3ao
50
40
42
32
30
43
4-MeC6H4
4-MeOC6H4
4-BrC6H4
4-FC6H4
2-Naphthyl
[a] Reagents and conditions: 1a (0.5 mmol) and 2j–2o (1.0 mmol)
in benzonitrile (2 mL) under an open atmosphere. [b] Isolated yield
after silica gel column chromatography.
Our next attempt was to employ a variety of aryl alkenes
with acetophenone, and the outcomes of these reactions are
shown in Table 5. Different electron-rich and electron-poor
para-substituted styrenes afforded the desired products in
moderate yields (Table 5, Entries 1–3). Styrene 2g, with its
meta substitution, could also be employed, and 3gj was iso-
lated in 40% yield (Table 5, Entry 4). A moderate yield of
50% for product 3lj was obtained by using 2-vinylnaphthal-
ene (Table 5, Entry 5).
Table 5. α-Benzoxylation of different aryl olefins with acetophe-
none.[a]
Entry
Ar
Product
% Yield[b]
1
2
3
4
5
4-MeC6H4
4-ClC6H4
4-BrC6H4
3-MeC6H4
2-naphthyl
3bj
3dj
3ej
3gj
3lj
38
35
38
40
50
[a] Reagents and conditions: 1 (0.5 mmol) and 2j (1.0 mmol) in ben-
zonitrile (2 mL) under an open atmosphere. [b] Isolated yield after
silica gel column chromatography.
Scheme 1. The proposed mechanism.
A few experiments were carried out to understand the
mechanism of the reaction. After the addition of 50 mol-%
of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), a dimin-
ished yield of 35% was observed for product 3aa. This sug-
gests that a possible radical pathway may be operating in
Conclusions
In summary, we have developed a metal-free protocol for
this reaction.[3g] In addition, we found that replacing styr- the α-benzoxylation of ketones by using aryl alkenes as the
ene with benzoic acid provided 3aa in 65% yield under our reactants. Under the reaction conditions with TBAI as the
reaction conditions. Similarly, when 1-naphthyl tert-butyl catalyst and TBHP as the oxidant, aryl alkenes are con-
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B. Mondal, S. C. Sahoo, S. C. Pan
FULL PAPER
= 4.8 Hz, 1 H), 7.99 (d, J = 6.0 Hz, 2 H), 8.08–8.10 (m, 2 H) ppm.
13C NMR (150 MHz, CDCl3): δ = 17.2, 55.6, 71.8, 114.2, 125.9,
127.5, 128.5, 130.0, 131.0, 133.4, 164.0, 166.1, 195.2 ppm. HRMS
(ESI+): calcd. for C17H17O4 [M + H]+ 285.1121; found 285.1121.
verted into the desired coupling partners, namely, an aryl-
carboxy group or an aryl tert-butyl perester. This conver-
sion can be considered an alternative to an ozonolysis reac-
tion in which the C=C bond cleavage of styrene affords
benzaldehyde. Our α-benzoxylation method is probably
more expensive than the earlier transformations described
above, but it is useful in the case that the required styrene
is readily available. Nevertheless, this protocol provides a
mild and convenient approach for the α-benzoxylation of
ketones.
1-(4-Chlorophenyl)-1-oxopropan-2-yl Benzoate (3ad):[13] White solid
(75 mg, 52% yield); m.p. 110–112 °C. 1H NMR (400 MHz,
CDCl3): δ = 1.65 (d, J = 6.8 Hz, 3 H), 6.12 (q, J = 3.9 Hz, 1 H),
7.45–7.47 (m, 5 H), 7.92–7.94 (m, 2 H), 8.01 (d, J = 8.8 Hz, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 17.5, 71.9, 128.6, 129.0,
129.3, 130.0, 130.1, 131.4, 133.5, 140.2, 166.1, 195.8 ppm.
1-(4-Bromophenyl)-1-oxopropan-2-yl Benzoate (3ae): White solid
1
(98 mg, 59% yield); m.p. 87–89 °C. H NMR (400 MHz, CDCl3):
δ = 1.65 (d, J = 6.8 Hz, 3 H), 6.12 (q, J = 4.8 Hz, 1 H), 7.40–7.56
(m, 2 H), 7.57–7.63 (m, 4 H), 7.64–7.87 (m, 2 H), 8.07 (d, J =
7.6 Hz, 1 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 17.2, 71.9,
128.6, 128.9, 130.0, 130.1, 131.5, 132.0, 132.3, 133.5, 166.1,
196.0 ppm. HRMS (ESI+): calcd. for C17H14BrO3 [M + H]+
333.0121; found 333.0130.
Experimental Section
General Methods: Chemicals and solvents were purchased from
commercial suppliers and used without further purification. The
1H NMR spectroscopic data were recorded with 400 and 600 MHz
spectrometers. The 13C NMR spectroscopic data were recorded
with 100 and 150 MHz spectrometers. Chemical shifts were re-
ported in parts per million (ppm). The residual solvent was used
1-(3-Chlorophenyl)-1-oxopropan-2-yl Benzoate (3af): Yellow sticky
1
oil (72 mg, 50% yield). H NMR (400 MHz, CDCl3): δ = 1.66 (d,
J = 7.2 Hz, 3 H), 6.11 (q, J = 7.2 Hz, 1 H), 7.40–7.54 (m, 3 H),
7.55–7.59 (m, 2 H), 7.85–7.87 (m, 1 H), 7.88–7.97 (m, 1 H), 7.98–
8.09 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 17.2, 72.1,
126.7, 128.2, 128.6, 128.8, 130.0, 130.3, 133.6, 133.7, 135.3, 136.2,
168.1, 195.9 ppm. HRMS (ESI+): calcd. for C17H14ClO3 [M +
H]+ 289.0626; found 289.0624.
1
as an internal reference for H NMR (for CHCl3, δ = 7.260 ppm),
and the solvent was used as an internal refererence for 13C NMR
(for CDCl3, δ = 77.23 ppm). The multiplicity of each signal was
reported by using the following abbreviations: s (singlet), d (doub-
let), t (triplet), q (quartet), m (multiplet), dd (doublet of doublet),
br. s (broad singlet). Coupling constants were reported in Hertz
(Hz). HRMS spectra were recorded by using the ESI mode.
1-(3-Bromophenyl)-1-oxopropan-2-yl Benzoate (3ag): White solid
1
(100 mg, 60% yield); m.p. 69–71 °C. H NMR (400 MHz, CDCl3):
General Procedure for α-Benzoxylation Reaction: A mixture of aryl
alkene 1 (0.5 mmol), ketone 2 (1 mmol), Bu4NI (36.9 mg, 20 mol-
%), and TBHP (70% aqueous solution, 480 μL, 3.5 mmol) in
PhCN (2 mL) were added to an oven-dried round-bottomed flask
that was fitted with a condenser. The reaction mixture was vigor-
ously stirred in a preheated oil bath at 80 °C for 24–36 h under air.
The reaction mixture was cooled to room temperature, and the
mixture was extracted with ethyl acetate (3ϫ 3 mL). The combined
ethyl acetate layers were washed successively with a saturated solu-
tion of sodium thiosulfate (2ϫ 5 mL), dried with anhydrous
Na2SO4, and filtered. The solvent was evaporated under reduced
pressure to give the crude mixture, which was purified by column
chromatography on silica gel (60–120/100–200 mesh size, petroleum
ether/ethyl acetate) to afford the desired product 3.
δ = 1.66 (d, J = 7.2 Hz, 3 H), 6.11 (q, J = 4.0 Hz, 1 H), 7.31–7.41
(m, 3 H), 7.46 (d, J = 7.6 Hz, 1 H), 7.71 (d, J = 7.2 Hz, 1 H), 7.90
(d, J = 6.4 Hz, 1 H), 7.92–8.13 (m, 2 H), 8.22 (s, 1 H) ppm. 13C
NMR (150 MHz, CDCl3): δ = 17.2, 72.4, 123.4, 126.3, 127.1, 128.6,
130.0, 130.6, 131.7, 133.0, 133.6, 136.7, 166.1, 195.4 ppm. HRMS
(ESI+): calcd. for C17H14BrO3 [M + H]+ 333.0121; found 333.0129.
1-Oxo-1-(thiophen-2-yl)propan-2-yl Benzoate (3ah): Colorless oil
1
(74.4 mg, 58% yield). H NMR (400 MHz, CDCl3): δ = 1.71 (d, J
= 6.8 Hz, 3 H), 5.97 (q, J = 7.2 Hz, 1 H), 7.14–7.16 (m, 1 H), 7.45
(t, J = 7.6 Hz, 2 H), 7.56–7.61 (m, 1 H), 7.69 (d, J = 4.8 Hz, 1 H),
7.87 (d, J = 3.6 Hz, 1 H), 8.10 (d, J = 7.2 Hz, 2 H) ppm. 13C NMR
(150 MHz, CDCl3): δ = 17.8, 73.0, 126.3, 127.9, 128.5, 130.0, 132.9,
133.5, 134.6, 140.6, 166.0, 189.7 ppm. HRMS (ESI+): calcd. for
C14H13O3S [M + H]+ 261.0580; found 261.0588.
1-Oxo-1-phenylpropan-2-yl Benzoate (3aa): White solid (82.5 mg,
1
1-Oxo-1-phenylpentan-2-yl Benzoate (3ai): Colorless oil (69.2 mg,
65% yield); m.p. 92–94 °C. H NMR (400 MHz, CDCl3): δ = 1.67
1
49% yield). H NMR (400 MHz, CDCl3): δ = 1.00 (t, J = 7.6 Hz,
(d, J = 7.2 Hz, 3 H), 6.21 (q, J = 7.2 Hz, 1 H), 7.42–7.51 (m, 4 H),
7.55–7.59 (m, 2 H), 7.61–8.01 (m, 2 H), 8.09 (d, J = 7.6 Hz, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 17.4, 72.0, 128.6, 128.7,
129.0, 129.7, 130.0, 133.4, 133.7, 134.7, 166.1, 196.9 ppm. HRMS
(ESI+): calcd. for C16H15O3 [M + H]+ 255.1016; found 255.1034.
3 H), 1.54–1.63 (m, 2 H), 1.99 (q, J = 5.6 Hz, 2 H), 6.11 (q, J =
4.8 Hz, 1 H), 7.43–7.51 (m, 4 H), 7.55–7.61 (m, 2 H), 8.01 (d, J =
7.2 Hz, 2 H), 8.10 (d, J = 6.8 Hz, 2 H) ppm. 13C NMR (150 MHz,
CDCl3): δ = 13.9, 19.1, 33.7, 75.7, 128.6, 128.9, 129.3, 130.0, 132.3,
133.4, 133.7, 135.1, 166.4, 196.7 ppm. HRMS (ESI+): calcd. for
C18H19O3 [M + H]+ 283.1329; found 283.1328.
1-Oxo-1-p-tolylpropan-2-yl Benzoate (3ab): White solid (72.4 mg,
1
54% yield); m.p. 84–86 °C. H NMR (400 MHz, CDCl3): δ = 1.66
1-Oxo-1-phenylpropan-2-yl 4-Methylbenzoate (3ba): White solid
(78 mg, 58% yield); m.p. 66–68 °C. H NMR (400 MHz, CDCl3):
(d, J = 7.2 Hz, 3 H), 2.41 (s, 3 H), 6.19 (q, J = 6.8 Hz, 1 H), 7.28
(d, J = 8.0 Hz, 2 H), 7.42–7.46 (m, 2 H), 7.55–7.58 (m, 1 H), 7.59–
7.91 (m, 2 H), 7.92–8.10 (m, 2 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 17.5, 21.9, 72.0, 128.5, 128.8, 129.6, 129.8, 130.0,
132.1, 133.4, 144.7, 166.1, 196.4 ppm. HRMS (ESI+): calcd. for
C17H17O3 [M + H]+ 269.1172; found 269.1190.
1
δ = 1.66 (d, J = 7.2 Hz, 3 H), 2.41 (s, 3 H), 6.18 (q, J = 6.8 Hz, 1
H), 7.22–7.25 (m, 2 H), 7.43–7.49 (m, 3 H), 7.50–8.01 (m, 4
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 17.3, 21.8, 71.9, 126.3,
128.5, 128.7, 128.9, 129.2, 130.0, 133.6, 144.1, 166.2, 197.0 ppm.
HRMS (ESI+): calcd. for C17H17O3 [M + H]+ 269.1172; found
269.1190.
1-(4-Methoxyphenyl)-1-oxopropan-2-yl Benzoate (3ac): White solid
(79.5 mg, 56% yield); m.p. 96–98 °C. 1H NMR (400 MHz, CDCl3):
δ = 1.66 (d, J = 4.8 Hz, 3 H), 3.87 (s, 3 H), 6.18 (q, J = 4.8 Hz, 1
1-Oxo-1-phenylpropan-2-yl 4-Methoxybenzoate (3ca):[3g] White
1
H), 6.95 (d, J = 6.0 Hz, 2 H), 7.44 (t, J = 4.8 Hz, 1 H), 7.57 (t, J solid (72.2 mg, 55% yield). H NMR (600 MHz, CDCl3): δ = 1.65
4
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α-Benzoxylation of Ketones with Terminal Aryl Alkenes
(d, J = 6.6 Hz, 3 H), 3.86 (s, 3 H), 6.17 (q, J = 7.2 Hz, 1 H), 6.92
(d, J = 8.4 Hz, 2 H), 7.30 (d, J = 7.8 Hz, 2 H), 7.45–7.53 (m, 3 H),
(d, J = 7.2 Hz, 1 H), 8.91 (d, J = 9.0 Hz, 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 17.4, 72.1, 124.6, 125.9, 126.4, 126.6, 128.0,
8.04 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 128.6, 129.0, 130.8, 131.5, 133.7, 133.8, 133.9, 134.6, 167,
17.3, 55.4, 72.1, 114.0, 122.1, 127.6, 128.7, 128.9, 132.1, 133.6,
163.8, 165.8, 197.1 ppm.
197.0 ppm.
1-Oxo-1-phenylpropan-2-yl 2-Naphthoate (3la): White solid (73 mg,
48% yield); m.p. 97–99 °C. H NMR (600 MHz, CDCl3): δ = 1.73
1
1-Oxa-1-phenylpropan-2-yl 4-Chlorobenzoate (3da):[3g] White solid
1
(d, J = 6.6 Hz, 3 H), 6.28 (q, J = 6.6 Hz, 1 H), 7.48–7.51 (m, 2 H),
7.53–7.55 (m, 1 H), 7.56–7.59 (m, 2 H), 7.60–7.87 (m, 2 H), 7.88–
7.95 (m, 1 H), 7.96–8.04 (m, 2 H), 8.08–8.10 (m, 1 H), 8.97 (s,1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 17.4, 72.2, 125.4, 126.8,
127.9, 128.3, 128.5, 128.7, 128.9, 129.5, 130.0, 131.6, 132.6, 133.7,
134.6, 135.8, 166.3, 196.9 ppm. HRMS (ESI+): calcd. for C20H17O3
[M + H]+ 305.1172; found 305.1169.
(76.3 mg, 53% yield). H NMR (400 MHz, CDCl3): δ = 1.67 (d, J
= 7.2 Hz, 3 H), 6.19 (q, J = 7.2 Hz, 1 H), 7.40–7.44 (m, 2 H), 7.46–
7.51 (m, 2 H), 7.55–7.62 (m, 1 H), 7.97–8.03 (m, 4 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 17.4, 72.3, 128.5, 128.6, 128.9, 130.0,
131.4, 133.8, 134.5, 139.9, 165.2, 196.6 ppm.
1-Oxo-1-phenylpropan-2-yl 4-Bromobenzoate (3ea):[3g] White solid
1
(104.6 mg, 63% yield). H NMR (400 MHz, CDCl3): δ = 1.66 (d,
2-Oxo-2-phenylethyl Benzoate (3aj):[5d] White solid (60 mg, 50%
yield). 1H NMR (400 MHz, CDCl3): δ = 5.59 (s, 2 H), 7.45–7.53
(m, 4 H), 7.58–7.64 (m, 2 H), 7.96–7.99 (m, 2 H), 8.13–8.16 (m, 2
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 66.6, 128.0, 128.6,
128.7, 129.0, 130.1, 130.4, 133.5, 134.0, 166.2, 196.7 ppm.
J = 7.2 Hz, 3 H), 6.19 (q, J = 6.8 Hz, 1 H), 7.47–7.58 (m, 2 H),
7.59–7.61 (m, 3 H), 7.93–8.01 (m, 4 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 17.4, 72.3, 128.5, 128.6, 129.0, 130.0, 131.5, 131.9,
133.8, 134.5, 165.4, 196.6 ppm.
1-Oxo-1-phenylpropan-2-yl 4-Fluorobenzoate (3fa):[3g] White solid
1
2-Oxo-2-p-tolylethyl Benzoate (3ak): Colorless sticky oil (50.8 mg,
40% yield). H NMR (400 MHz, CDCl3): δ = 2.43 (s, 3 H), 5.56
(68 mg, 50% yield). H NMR (400 MHz, CDCl3): δ = 1.67 (d, J =
1
4.4 Hz, 3 H), 6.20 (q, J = 5.2 Hz, 1 H), 7.12 (t, J = 8.8 Hz, 2 H),
(s, 2 H), 7.35–7.38 (m, 2 H), 7.47 (t, J = 8.0 Hz, 2 H), 7.58–7.61
(m, 1 H), 7.86 (t, J = 2.0 Hz, 2 H), 7.88–8.15 (m, 2 H) ppm. 13C
NMR (150 MHz, CDCl3): δ = 21.9, 66.5, 128.1, 128.6, 129.3, 129.7,
130.1, 130.4, 133.4, 145.0, 166.2, 191.8 ppm. HRMS (ESI+): calcd.
for C16H15O3 [M + H]+ 255.1016; found 255.1033.
7.46–7.51 (m, 3 H), 7.98–8.01 (m, 2 H), 8.09–8.11 (m, 2 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 17.3, 72.1, 115.7 (d, JC,F
=
22 Hz), 128.5, 128.6, 128.8 (d, JC,F = 32 Hz), 130.0, 132.5, 133.4,
133.8, 165.0 (d, JC-F = 29 Hz), 167.4, 196.7 ppm.
1-Oxo-1-phenylpropan-2-yl 3-Methylbenzoate (3ga): Colorless
sticky oil (67 mg, 50% yield). 1H NMR (600 MHz, CDCl3): δ =
1.67 (d, J = 7.2 Hz, 3 H), 2.39 (s, 3 H), 6.20 (q, J = 6.6 Hz, 1 H),
7.32 (t, J = 7.2 Hz, 1 H), 7.48 (t, J = 7.8 Hz, 3 H), 7.88–7.92 (m,
2 H), 8.00 (d, J = 7.8 Hz, 3 H) ppm. 13C NMR (150 MHz, CDCl3):
δ = 17.3, 21.4, 72.0, 123.4, 127.2, 128.4, 128.7, 128.9, 130.0, 130.5,
133.7, 134.2, 138.3, 166.3, 197.0 ppm. HRMS (ESI+): calcd. for
C17H17O3 [M + H]+ 269.1172; found 269.1175.
2-(4-Methoxyphenyl)-2-oxoethyl Benzoate (3al): Light brown solid
(56.7 mg, 42% yield); m.p. 94–96 °C. 1H NMR (400 MHz, CDCl3):
δ = 3.88 (s, 3 H), 5.53 (s, 2 H), 6.97 (d, J = 8.8 Hz, 2 H), 7.43–7.48
(m, 3 H), 7.94–7.97 (m, 2 H), 8.09–8.11 (m, 1 H), 8.13–8.15 (m, 1
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 55.7, 66.4, 114.2, 127.5,
128.6, 130.1, 130.3, 131.6, 133.4, 164.2, 166.2, 190.7 ppm. HRMS
(ESI+): calcd. for C16H15O4 [M + H]+ 271.0965; found 271.0964.
2-(4-Bromophenyl)-2-oxoethyl Benzoate (3am):[5e] Yellow sticky oil
(51 mg, 32% yield). 1H NMR (400 MHz, CDCl3): δ = 5.52 (s 2 H),
7.61–7.67 (m, 5 H), 7.81–7.97 (m, 2 H), 7.99 (d, J = 8.8 Hz, 2
H) ppm. 13C NMR (150 MHz, CDCl3): δ = 66.6, 126.4, 128.3,
129.5, 130.2, 131.6, 132.1, 132.5, 133.1, 165.5, 191.2 ppm.
1-Oxo-1-phenylpropan-2-yl 3-Methoxybenzoate (3ha): Yellow oil
(64 mg, 45% yield). H NMR (400 MHz, CDCl3): δ = 1.67 (d, J =
1
7.2 Hz, 3 H), 3.83 (s, 3 H), 6.19 (q, J = 6.8 Hz, 1 H), 7.11 (d, J =
6.0 Hz, 1 H), 7.35 (t, J = 7.6 Hz, 1 H), 7.48 (t, J = 7.6 Hz, 2 H),
7.56–7.59 (m, 2 H), 7.61–7.68 (m, 1 H), 7.70–8.01 (m, 2 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 17.3, 55.6, 72.2, 114.4, 120.0,
122.5, 128.7, 128.9, 129.6, 130.9, 133.7, 134.6, 159.7, 166.0,
2-(4-Fluorophenyl)-2-oxoethyl Benzoate (3an): Light yellow solid
1
(38.7 mg, 30% yield). H NMR (400 MHz, CDCl3): δ = 5.53 (s, 2
196.9 ppm. HRMS (ESI+): calcd. for C17H17O4 [M
285.1121; found 285.1121.
+
H]+
H), 7.12–7.21 (m, 4 H), 7.47 (t, J = 7.6 Hz, 1 H), 7.98–8.02 (m, 2
H), 8.12–8.17 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
66.5, 115.9 (d, JC,F = 88 Hz), 126.3, 128.6, 130.1, 130.8 (d, JC,F
2.0 Hz), 132.7, 132.8, 133.6, 165.0, 167.5, 190.7 ppm.
=
1-Oxo-1-phenylpropan-2-yl 3-Chlorobenzoate (3ia): Brown solid
(90 mg, 62% yield); m.p. 81–83 °C. H NMR (400 MHz, CDCl3):
1
δ = 1.68 (d, J = 6.8 Hz, 3 H), 6.20 (q, J = 7.2 Hz, 1 H), 7.37–7.43
(m, 1 H), 7.45–7.52 (m, 2 H), 7.55 (d, J = 7.6 Hz, 1 H), 7.58–7.63
(m, 1 H), 7.96–8.01 (m, 3 H), 8.07 (s 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 17.4, 72.4, 128.1, 128.6, 129.0, 129.9, 130.0,
131.4, 133.4, 133.8, 134.4, 134.7, 164.9, 196.5 ppm. HRMS (ESI+):
calcd. for C16H14ClO3 [M + H]+ 289.0626; found 289.0624.
2-(Naphthalen-2-yl)-2-oxoethyl Benzoate (3ao): Sticky oil (62.4 mg,
43% yield). H NMR (400 MHz, CDCl3): δ = 5.47 (s, 2 H), 7.41–
1
7.46 (m, 1 H), 7.48 (t, J = 4.0 Hz, 2 H), 7.63 (d, J = 7.2 Hz, 2 H),
7.72 (d, J = 8.4 Hz, 2 H), 7.75–7.77 (m, 2 H), 7.78–7.87 (m, 1 H),
8.09 (d, J = 8.4 Hz, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ =
66.7, 124.2, 125.5, 127.2, 128.0, 128.6, 128.7, 129.0, 129.7, 130.1,
130.4, 131.8, 133.5, 134.2, 166.2, 192.2 ppm. HRMS (ESI+): calcd.
for C19H15O3 [M + H]+ 291.1016; found 291.1017.
1-Oxo-1-phenylpropan-2-yl 2-Methylbenzoate (3ja):[3g] Colorless
sticky oil (47 mg, 35% yield). 1H NMR (600 MHz, CDCl3): δ =
1.65 (d, J = 7.2 Hz, 3 H), 2.59 (s, 3 H), 6.19 (q, J = 6.6 Hz, 1 H),
7.23–7.26 (m, 2 H), 7.39–7.41 (m, 1 H), 7.42–7.50 (m, 2 H), 7.58–
7.59 (m, 1 H), 7.61–8.01 (m, 3 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 17.3, 21.8, 71.9, 125.9, 128.7, 129.0, 130.0, 131.0,
131.8, 132.4, 133.7, 134.7, 140.6, 167.1, 197.0 ppm.
2-Oxo-2-phenylethyl 4-Methylbenzoate (3bj): Sticky oil (42.3 mg,
1
38% yield). H NMR (400 MHz, CDCl3): δ = 2.40 (s, 3 H), 5.59
(s, 2 H), 7.23–7.45 (m, 2 H), 7.47–7.52 (m, 4 H), 7.96–7.99 (m, 3
H) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.9, 66.6, 126.3, 128.0,
128.6, 129.0, 130.1, 133.5, 134.0, 144.2, 166.2, 192.4 ppm. HRMS
(ESI+): calcd. for C16H15O3 [M + H]+ 255.1016; found 255.1033.
1-Oxo-1-phenylpropan-2-yl 1-Naphthoate (3ka):[3g] White solid
1
(77.5 mg, 51% yield). H NMR (600 MHz, CDCl3): δ = 1.72 (d, J
2-Oxo-2-phenylethyl 4-Chlorobenzoate (3dj):[5d] Colorless solid
= 6.6 Hz, 3 H), 6.33 (q, J = 6.6 Hz, 1 H), 7.47–7.59 (m, 4 H), 7.60– (48 mg, 35% yield). 1H NMR (400 MHz, CDCl3): δ = 5.59 (s, 2
7.62 (m, 2 H), 7.88 (d, J = 7.8 Hz, 1 H), 8.03–8.06 (m, 3 H), 8.30 H), 7.44–7.53 (m, 4 H), 7.58–7.64 (m, 1 H), 7.95–7.98 (m, 2 H),
Eur. J. Org. Chem. 0000, 0–0
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B. Mondal, S. C. Sahoo, S. C. Pan
FULL PAPER
8.09–8.15 (m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 66.7,
128.0, 128.6, 129.0, 130.1, 131.5, 133.5, 134.2, 140.2, 165.4,
192.0 ppm.
Jiang, Y. Cheng, C. Zhu, Chem. Commun. 2012, 48, 979–981;
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mun. 2014, 50, 12880–12883.
2-Oxo-2-phenylethyl 4-Bromobenzoate (3ej):[5d] White solid
1
(60.5 mg, 38% yield). H NMR (400 MHz, CDCl3): δ = 5.58 (s, 2
H), 7.45–7.58 (m, 3 H), 7.60–7.63 (m, 2 H), 7.95–8.01 (m, 3 H),
8.14 (d, J = 7.2 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
66.7, 128.0, 128.6, 129.1, 130.1, 131.6, 132.0, 133.5, 134.1, 165.5,
192.0 ppm.
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2-Oxo-2-phenylethyl 3-Methylbenzoate (3gj): Colorless oil (50.8 mg,
1
40% yield). H NMR (400 MHz, CDCl3): δ = 2.38 (s, 3 H), 5.58
(s, 2 H), 7.40–7.53 (m, 5 H), 7.97 (d, J = 7.6 Hz, 1 H), 8.06–8.15
(m, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 21.4, 66.6, 127.0,
127.3, 128.0, 128.6, 128.7, 129.0, 130.1, 133.5, 134.0, 138.4, 166.4,
192.3 ppm. HRMS (ESI+): calcd. for C16H15O3 [M
255.1016; found 255.1030.
+
H]+
2-Oxo-2-phenylethyl 2-Naphthoate (3lj): White solid (72.5 mg, 50%
1
yield); m.p. 110–112 °C. H NMR (400 MHz, CDCl3): δ = 5.65 (s,
2 H), 7.49–7.61 (m, 5 H), 7.86–7.92 (m, 3 H), 8.10–8.16 (m, 3 H),
8.73 (d, J = 8.8 Hz, 1 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
66.7, 125.5, 126.8, 127.0, 127.9, 128.0, 128.4, 128.6, 129.0, 129.6,
130.1, 131.8, 133.5, 134.0, 135.8, 166.3, 192.3 ppm. HRMS (ESI+):
calcd. for C19H15O3 [M + H]+ 291.1016; found 291.1017.
Acknowledgments
This work is supported by the Science & Engineering Research
Board (SERB), India (grant number SR/FT/CS-81/2011) and the
Ministry of Human Resource Development (grant number 5-7/
2014-TS-VII) under the Centre of Excellence in FAST). The au-
thors thank the CIF of the Indian Institute of Technology for the
use of the instrumental facility.
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Received: February 17, 2015
Published Online: ᭿
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Job/Unit: O50233
/KAP1
Date: 02-04-15 13:29:01
Pages: 7
α-Benzoxylation of Ketones with Terminal Aryl Alkenes
α-Acyloxylation Reaction
B. Mondal, S. C. Sahoo,
S. C. Pan* ......................................... 1–7
nBu4NI-Catalyzed α-Benzoxylation of
Ketones with Terminal Aryl Alkenes
An efficient synthesis for the α-benzoxyl-
ation of aryl ketones has been developed
by using terminal aryl alkenes as the aryl-
carboxy surrogate. The products were ob-
tained in moderate to good yields for a
broad scope of substrates. Tetra-n-butyl-
ammonium iodide (TBAI) and tert-butyl
hydroperoxide (TBHP) were employed as
the catalyst and oxidant, respectively.
Keywords: Synthetic methods / Ketones /
Alkenes / Radicals
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