Iron(III) sulfate as terminal oxidant in the synthesis of methyl ketones via wacker oxidation

Article abstract of DOI:10.1021/jo500921j

An efficient and environmentally benign method using Fe(III) sulfate as a terminal oxidant in the synthesis of methyl ketones from terminal olefins via the Wacker process is developed. The methodology offers high selectivity for a Markonikov product, shows good functional group compatibility, involves mild reaction conditions, and is operationally simple. Fe₂(SO ₄)₃ is the sole terminal oxidant in this process. The method holds potential for future applications in organic synthesis.

Full text of DOI:10.1021/jo500921j

Article
pubs.acs.org/joc
Iron(III) Sulfate as Terminal Oxidant in the Synthesis of Methyl
Ketones via Wacker Oxidation
Rodney A. Fernandes* and Dipali A. Chaudhari
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, Maharashtra, India
S
* Supporting Information
ABSTRACT: An efficient and environmentally benign method using Fe(III)
sulfate as a terminal oxidant in the synthesis of methyl ketones from terminal
olefins via the Wacker process is developed. The methodology offers high
selectivity for a Markonikov product, shows good functional group compatibility,
involves mild reaction conditions, and is operationally simple. Fe2(SO4)3 is the
sole terminal oxidant in this process. The method holds potential for future
applications in organic synthesis.
efficient Pd-catalyzed oxidation of terminal olefins to methyl
ketones in an environmentally benign process (Scheme 1). No
INTRODUCTION
■
Many natural products have a methyl ketone moiety, and their
cumulative biological history over many years firmly establishes
that this moiety is of natural origin. Of the several approaches
to introduce methyl ketone unit such as hydration of alkynes,1
Friedel−Crafts acylation,2 Dakin−West reaction,3 and Weinreb
ketone synthesis,4 the Wacker oxidation5−11 is the most familiar
approach. The Cu-mediated conventional Wacker process is
well established on an industrial scale. However, the process
suffers from certain limitations mainly derived from the use of
CuCl2 as a Pd-reoxidant which leads to corrosive reaction
media and forms chlorinated byproducts. The Wacker process
for higher olefins sometimes results in slower reaction,
chlorinated byproducts, and double bond isomerized com-
pounds.12 The catalytic CuCl2 version requires pressurization
of oxygen. To overcome these limitations many modifications
are directed toward developing an alternative reoxidant.9,13 The
direct O2 coupled Wacker oxidation along with coordinating
solvents (DMF, DMA, NMP, or ethylene carbonate) offered a
good alternative.13z,ad Co-catalysts13d,e,g,i,w,ae,af and/or sol-
vents,13q−t,ab nitrogen based ligands,13n,p,y organic oxidants
Scheme 1. Oxidation of Terminal Olefins to Methyl Ketones
(FG = functional group)
aldehyde formation or olefin isomerization was observed.
Fe2(SO4)3 is freely soluble in the CH3CN/H2O (7:1) solvent
system, making this method advantageous and operationally
simple.
RESULTS AND DISCUSSION
■
We first examined various Pd-catalysts and Fe-salts for
oxidation of 1-decene (1b) as a model substrate (Table 1).
With the use of PdCl2 (5 mol %) in a mixture of CH3CN/H2O
(7:1) with Fe2(SO4)3·nH2O (1.5 equiv)15 at 45 °C under N2,
the reaction was complete within 1.5 h giving decan-2-one (2b)
as the sole product in 95% yield (Table 1, entry 1). No trace of
aldehyde was formed. The purification process was mere
filtration of the reaction mixture through a pad of silica gel to
remove water and inorganic byproducts delivering the ketone
product after filtrate concentration in virtually pure form.
Fe(NO3)3·9H2O also worked well delivering 2b in 87% yield
(Table 1, entry 2). Other iron based salts and complexes such
as Fe(C2O4)·2H2O, Fe(OAc)2, Fe(BF4)2·6H2O, Fe(ClO4)2·
xH2O, K3FeCN6, and FeSO4 showed oxidation, however in
lower yields (Table 1, entries 3−8). The normal Fe-oxides such
as Fe2O3 and Fe3O4 (nanoparticles) were unsuccessful for this
oxidation (Table 1, entries 9 and 10). The Fe(II) compounds
are not oxidants but in the reaction media (H2O, 45 °C) may
become oxidized to Fe(III) and then act as terminal oxidants.
(benzoquinone),9,13f,h,j,af organic peroxides,13a,c,x,ac nitrites,13o,af
H2O2,13b KBrO3,13ae O2/TFA,13ag and CrO3
were also
13ah
explored. While many of these modifications offer a wider
scope to Wacker-type oxidation, there is still a need to develop
a cost-effective, mild, environmentally benign, and operationally
simpler method. In 1988, Backvall and Hopkins developed an
̈
iron(II) phthalocyanine based multicomponent catalytic system
for the oxidation of terminal olefins.14a However, acidic media
and tedious workup for removal of polar aprotic solvent DMF
could be disadvantageous. Acid sensitive functionalities also
become an issue. Formation of palladium nanoparticles in
olefin oxidation with iron(III) aqua ions in the presence of the
Pd/ZrO2/SO4 metallic catalyst has been investigated.14b
However, only limited examples have been explored. Use of
iron compounds in natural olefin oxidation is also documen-
ted.14c,d From careful investigation of various available iron salts
as oxidants, we found, to our delight, Fe2(SO4)3 offered an
Received: April 26, 2014
© XXXX American Chemical Society
A
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(Table 1, entry 15). Surprisingly, the reaction was rather slow
when carried out in the presence of air (open flask) and took 30
h to complete giving 2b in 75% yield (entry 16). Screening
different solvents for this oxidation (Table 1, entries 17−21)
revealed that CH3CN/H2O (7:1) was the best solvent mixture
(entry 1). Keeping the PdCl2 catalyst loading at 5 mol % and
changing the concentration of oxidant Fe2(SO4)3·nH2O
showed that the optimum requirement was 1.5 equiv (Table
1, entries 22 and 23). Similarly, with 1.5 equiv of oxidant the
optimum catalyst loading required was 5 mol % (Table 1, entry
1 vs entries 24 and 25). The optimized oxidation conditions
which include the use of PdCl2 (5 mol %), Fe2(SO4)3·nH2O
(1.5 equiv)15 in CH3CN/H2O (7:1) at 45 °C gave the methyl
ketones in good to excellent yields. With these optimized
conditions and operationally simple procedure, we evaluated
the scope and limitations of this method (Table 2).
The long chain inactivated olefins 1-octene, 1-decene, and 1-
tetradecene gave the methyl ketones (2a−c, entries 1−3, Table
2) in 92−95% yields. Terminal dienes also showed comparable
reactivity and gave methyl diketones 2d and 2e in good yields
(entries 4 and 5). The oxidation was compatible with diverse
functional groups: hydroxyl, halide, benzoate, MOM, silyl, ester,
and acid were all tolerated giving the methyl ketone products
with complete Markonikov selectivity in good yields (2f−n,
entries 6−14). No OH group oxidation or deprotection of acid
labile groups was observed. Styrenes are masked precursors for
aryl methyl ketones synthesis through olefin oxidation. Various
aryl substituted styrenes with electron-donating or -with-
drawing groups reacted under the present protocol to give
aryl methyl ketones (2o−t, entries 15−20) in good yields.
Hydroxyl allylated salicylic acid delivered the methyl ketone 2u
in 70% yield (entry 21). Similarly bis-allylated salicylic acids
(with ester and ether functionality) gave the diketones 2v and
2w in 74% and 70% yields, respectively (entries 22 and 23).
Menthyl allyl ether efficiently gave 2x in 66% yield (entry 24).
Classically difficult substrates such as protected allyl and
homoallyl alcohols show a possible coordination of the
neighboring oxygen atom to the Lewis acidic palladium causing
water attack through multiple pathways.13ac,16 Under the
developed procedure these compounds also reacted successfully
(Table 3). Primary allyl alcohols with various protecting
groups: phenyl, benzyl, 4-tert-butylphenyl, 2-naphthyl, 4-
methylbenzoyl, and nitrobenzoyl gave methyl ketones (4a−g,
entries 1−7) in good yields. The acyloin products (4h−j,
entries 8−10) were obtained in good yields without the
formation of otherwise competitive aldehydes due to
heteroatom directed effects. Homoallyl alcohols delivered the
protected β-hydroxy ketone products (4k−o, entries 11−15) in
good yields with complete Markonikov selectivity.
Table 1. Optimization of Reaction Conditions for Oxidation
of 1-Decene
a
Pd-catalyst
(mol %)
yield
(%)
entry
oxidant (equiv)
solvent
t (h)
1
PdCl2 (5)
Fe2(SO4) ·
b 3
CH3CN/H2O 1.5
(7:1)
95
87
52
48
62
72
25
52
43
46
71
86
81
37
nH2O (1.5)
2
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
Pd(OAc)2 (5)
Fe(NO3)3·9H2O CH3CN/H2O 1.5
(1.5) (7:1)
3
Fe(C2O4)·2H2O CH3CN/H2O 16
(1.5) (7:1)
4
Fe(OAc)2 (1.5) CH3CN/H2O 35
(7:1)
5
Fe(BF4)2·6H2O CH3CN/H2O 15
(1.5)
(7:1)
6
Fe(ClO4)2·
xH2O (1.5)
CH3CN/H2O 2.5
(7:1)
7
K3FeCN6 (1.5)
FeSO4 (1.5)
Fe2O3 (1.5)
CH3CN/H2O 27
(7:1)
8
CH3CN/H2O 20
(7:1)
9
CH3CN/H2O 23
(7:1)
10
11
12
13
14
15
Fe3O4 (NP)
(1.5)
CH3CN/H2O 51
(7:1)
Fe2(SO4)3·nH2O CH3CN/H2O 3.5
(1.5) (7:1)
Pd(CF3CO2)2
(5)
Fe2(SO4)3·nH2O CH3CN/H2O
(1.5) (7:1)
4
Pd(dba)2 (5)
Pd(PPh3)4 (5)
−
Fe2(SO4)3·nH2O CH3CN/H2O
(1.5) (7:1)
8
Fe2(SO4)3·nH2O CH3CN/H2O 10
(1.5) (7:1)
d
Fe2(SO4)3·nH2O CH3CN/H2O 18
(1.5) (7:1)
NR
c
16
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (5)
PdCl2 (2)
PdCl2 (10)
Fe2(SO4)3·nH2O CH3CN/H2O 30
(1.5) (7:1)
75
81
24
76
71
71
68
90
71
81
17
18
19
20
21
22
23
24
25
Fe2(SO4)3·nH2O DMF/H2O
(1.5) (7:1)
29
32
36
Fe2(SO4)3·nH2O THF/H2O
(1.5) (7:1)
Fe2(SO4)3·nH2O DMA/H2O
(1.5) (7:1)
Fe2(SO4)3·nH2O CH3CN/H2O 1.5
(1.5) (3:1)
Fe2(SO4)3·nH2O CH3CN/H2O 1.5
(1.5) (1:1)
Fe2(SO4)3·nH2O CH3CN/H2O 18
(1.0) (7:1)
Fe2(SO4)3·nH2O CH3CN/H2O
(2.0) (7:1)
1
Fe2(SO4)3·nH2O CH3CN/H2O 19
(1.5) (7:1)
CONCLUSION
Fe2(SO4)3·nH2O CH3CN/H2O 2.5
(1.5) (7:1)
■
In summary, we have found a mild, efficient, general, and
environmentally benign method to access methyl ketones from
terminal olefins without the use of Cu-salts and molecular
oxygen. Various long chain terminal olefins, dienes, substituted
styrenes, and protected allyl and homoallyl alcohols have been
explored (39 examples). A wide spectrum of functional-group
tolerance, mild reaction conditions, complete Markonikov
selectivity, and use of commercially available Fe2(SO4)3·nH2O
as the sole oxidant are key features of this methodology. Since it
is a mild process with operational simplicity and exclusive
ketone delivery, we expect this method to find broad
application in synthetic chemistry.
a
All reactions were performed with olefin (0.5 mmol), Fe-source
(1.0−2.0 equiv., 0.5−1.0 mmol), Pd-catalyst (2−10 mol %, 0.01−0.05
b
mmol), at 45 °C in solvent (4 mL) under N2. Fe2(SO4)3·nH2O is a
hydrate obtained from Aldrich Chem. Co. with unspecified water
molecules. The amount used is based on Fe2(SO4)3 anhydrous mol wt.
Hence the actual amount of Fe2(SO4)3 present in reaction media
c
would be less than 1.5 equiv. NP = Nanoparticles. Reaction carried
d
out in the presence of air. NR = No reaction.
Changing the Pd-catalyst did not prove better (Table 1, entries
11−14). When no catalyst was used, the reaction did not work
B
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a
Table 2. Synthesis of Methyl Ketones from Terminal Olefins
a
Reaction conditions: Substrate (0.5 mmol), PdCl2 (5 mol %, 0.025 mmol), Fe2(SO4)3·nH2O (1.5 equiv, 0.75 mmol), CH3CN (3.5 mL), H2O (0.5
b
mL), at 45 °C under N2. Substrate (0.5 mmol), PdCl2 (10 mol %, 0.05 mmol), Fe2(SO4)3·nH2O (3.0 equiv, 1.5 mmol), CH3CN (3.5 mL), H2O
(0.5 mL), at 45 °C under N2.
evaporation from CHCl3 on CsBr plates. High-resolution mass spectra
EXPERIMENTAL SECTION
■
(HRMS) were obtained using positive electrospray ionization by the
General Information. Solvents and reagents were purified by
standard methods. Thin-layer chromatography was performed on EM
1
TOF method. The H and 13C NMR anaylses of 2w were at 400 and
125 MHz, respectively.
General Procedure for Oxidation of Terminal Olefins. To a
stirred solution of olefin (0.5 mmol) in CH3CN (3.5 mL) and H2O
250 Kieselgel 60 F254 silica gel plates. The spots were visualized by
staining with KMnO4 or under a UV lamp. H and 13C NMR were
1
recorded with a spectrometer operating at 500 or 400 and 125 or 100
MHz for proton and carbon nuclei, respectively. The chemical shifts
are based on the TMS peak at δ = 0.00 pm for proton NMR and the
CDCl3 peak at δ = 77.00 ppm (t) in carbon NMR. IR spectra were
obtained on an FT−IR spectrometer, and samples were prepared by
(0.5 mL) were added PdCl2 (4.4 mg, 0.025 mmol, 5 mol %) and
Fe2(SO4)3·nH2O (600 mg, 1.5 mmol, 1.5 equiv) at room temperature.
The reaction mixture was warmed to 45 °C and stirred for a specified
time (see Tables 2 and 3) under N2. The reaction mixture was then
filtered through a small pad of silica gel and washed with EtOAc, and
C
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a
Table 3. Oxidation of Protected Allyl and Homoallyl Alcohols
a
Reaction conditions: Substrate (0.5 mmol), PdCl2 (5 mol %, 0.025 mmol), Fe2(SO4)3·nH2O (1.5 equiv, 0.75 mmol), CH3CN (3.5 mL), H2O (0.5
mL), at 45 °C under N2.
the filtrate was concentrated. The residue in some cases contained
virtually pure compound, and no further purification was necessary
(for compounds 2a−c and 2f−h). In other cases the residue was
purified by silica gel column chromatography using petroleum ether/
EtOAc as an eluent to afford the methyl ketones.
6.7 Hz, 2H), 2.38 (t, J = 7.4 Hz, 2H), 2.10 (s, 3H), 1.54−1.50 (m,
4H), 1.37−1.20 (m, 10H); 13C {1H} NMR (100 MHz, CDCl3): δ =
209.6, 63.0, 43.8, 32.7, 29.4, 29.3, 29.27, 29.1, 25.7, 23.8; HRMS (ESI-
TOF) calcd for [C11H22O2 + Na]+ 209.1512, found 209.1510.
16-Hydroxyheptadecane-2-one (2g). Yield (105.3 mg, 78%).
White solid, mp 55−57 °C; IR (CHCl3): νmax = 3402, 2916, 2849,
Octan-2-one (2a):17 Yield (59 mg, 92%). Colorless oil; H NMR
1
1
1709, 1464, 1372, 1163, 1124, 1038, 910, 667 cm−1; H NMR (400
(400 MHz, CDCl3/TMS): δ = 2.41 (t, J = 7.5 Hz, 2H), 2.13 (s, 3H),
1.59−1.52 (m, 2H), 1.32−1.21 (m, 6H), 0.87 (t, J = 6.9 Hz, 3H); 13C
{1H} NMR (100 MHz, CDCl3): δ = 209.5, 43.8, 31.6, 29.8, 28.8, 23.8,
22.5, 14.0.
MHz, CDCl3/TMS): δ = 3.78−3.75 (m, 1H), 2.38 (t, J = 7.4 Hz, 2H),
2.10 (s, 3H), 1.55−1.51 (m, 2H), 1.39−1.38 (m, 2H), 1.35−1.22 (m,
20H), 1.15 (d, J = 6.2 Hz, 3H); 13C {1H} NMR (100 MHz, CDCl3): δ
= 209.4, 68.0, 43.7, 39.3, 29.8, 29.6, 29.5, 29.5, 29.4, 29.3, 29.1, 25.7,
23.8, 23.4; HRMS (ESI-TOF) calcd for [C17H34O2 + Na]+ 293.2451,
found 293.2455.
Decan-2-one (2b):13i Yield (74.2 mg, 95%). Colorless oil; 1H NMR
(400 MHz, CDCl3/TMS): δ = 2.40 (t, J = 7.5 Hz, 2H), 2.11 (s, 3H),
1.55−1.52 (m, 2H), 1.30−1.22 (m, 10H), 0.86 (t, J = 6.9 Hz, 3H); 13C
{1H} NMR (100 MHz, CDCl3): δ = 209.4, 43.8, 31.8, 29.8, 29.3,
29.14, 29.1, 23.8, 22.6, 14.1.
10-Bromodecan-2-one (2h):22a Yield (89.4 mg, 76%). Colorless
oil; IR (CHCl3): νmax = 2931, 2856, 1717, 1459, 1439, 1359, 1259,
1224, 1166, 948, 721, 644 cm−1; 1H NMR (400 MHz, CDCl3/TMS):
δ = 3.39 (t, J = 6.8 Hz, 2H), 2.41 (t, J = 7.4 Hz, 2H), 2.13 (s, 3H),
1.87−1.78 (m, 2H), 1.59−1.51 (m, 2H), 1.42−1.38 (m, 2H), 1.29−
1.23 (m, 6H); 13C {1H} NMR (100 MHz, CDCl3): δ = 209.3, 43.7,
34.0, 32.7, 29.8, 29.2, 29.0, 28.5, 28.0, 23.7; HRMS (ESI-TOF) calcd
for [C10H19BrO + Na]+ 257.0511, found 257.0511.
Tetradecan-2-one (2c):20 Yield (99.3 mg, 94%). Colorless oil; H
1
NMR (400 MHz, CDCl3/TMS): δ = 2.42 (t, J = 7.5 Hz, 2H), 2.14 (s,
3H), 1.58−1.55 (m, 4H), 1.36−1.19 (m, 16H), 0.88 (t, J = 6.8 Hz,
3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 209.3, 43.7, 31.8, 29.7,
29.6, 29.53, 29.5, 29.4, 29.3, 29.25, 29.1, 23.7, 22.6, 14.0.
Decane-2,9-dione (2d):21a Yield (63 mg, 74%). Colorless oil; IR
(CHCl3): νmax = 3019, 2933, 2858, 1717, 1409, 1363, 1168, 1048, 967,
5-Oxohexyl Benzoate (2i):22b Yield (82.6 mg, 75%). Colorless oil;
1H NMR (400 MHz, CDCl3/TMS): δ = 8.04−8.02 (m, 2H), 7.58−
7.53 (m, 1H), 7.46−7.40 (m, 2H), 4.36 (t, J = 6.1 Hz, 2H), 2.51 (t, J =
6.9 Hz, 2H), 2.15 (s, 3H), 1.82−1.70 (m, 4H); 13C {1H} NMR (100
MHz, CDCl3): δ = 208.5, 166.6, 132.9, 130.3, 129.5, 128.3, 64.5, 43.0,
29.9, 28.1, 20.2; HRMS (ESI-TOF) calcd for [C13H16O3 + Na]+
243.0992, found 243.0989.
1
927, 667 cm−1; H NMR (400 MHz, CDCl3/TMS): δ = 2.41 (t, J =
7.4 Hz, 4H), 2.12 (s, 6H), 1.61−1.52 (m, 4H), 1.31−1.25 (m, 4H);
13C {1H} NMR (100 MHz, CDCl3): δ = 209.2, 43.6, 29.9, 28.9, 23.5;
HRMS (ESI-TOF) calcd for [C10H18O2 + Na]+ 193.1199, found
193.1198.
Dodecane-2,11-dione (2e):21b Yield (76.3 mg, 77%). Colorless oil;
IR (CHCl3): νmax = 3017, 2916, 1704, 1406, 1379, 1284, 1165, 1131,
11-(Methoxymethoxy)undecan-2-one (2j):22c Yield (93.3 mg,
81%). Colorless oil; IR (CHCl3): νmax = 3014, 2929, 2856, 1716,
1
1018, 949, 717, 667 cm−1; H NMR (400 MHz, CDCl3/TMS): δ =
2.40 (t, J = 7.4 Hz, 4H), 2.12 (s, 6H), 1.63−1.51 (m, 4H), 1.28−1.23
(m, 8H); 13C {1H} NMR (100 MHz, CDCl3): δ = 209.2, 43.6, 29.7,
29.1, 28.9, 23.6; HRMS (ESI-TOF) calcd for [C12H22O2 + Na]+
221.1512, found 221.1512.
1
1465, 1410, 1361, 1145, 1111, 1043, 919, 667 cm−1; H NMR (400
MHz, CDCl3/TMS): δ = 4.61 (s, 2H), 3.51 (t, J = 6.6 Hz, 2H), 3.35
(s, 3H), 2.41 (t, J = 7.5 Hz, 2H), 2.13 (s, 3H), 1.60−1.54 (m, 2H),
1.28−1.27 (m, 12H); 13C {1H} NMR (100 MHz, CDCl3): δ = 209.3,
96.3, 67.8, 55.0, 43.7, 29.8, 29.7, 29.3, 29.1, 26.1, 23.8; HRMS (ESI-
TOF) calcd for [C13H26O3 + Na]+ 253.1774, found 253.1778.
11-Hydroxyundecan-2-one (2f):17 Yield (79.2 mg, 85%). Colorless
oil; IR (CHCl3): νmax = 3415, 2929, 2855, 1712, 1465, 1363, 1169,
1
1055, 912 cm−1; H NMR (400 MHz, CDCl3/TMS): δ = 3.59 (t, J =
D
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1-(tert-Butyldiphenylsilyloxy)propan-2-one (2k):22d Yield (140.6
mg, 90%). Colorless oil. 1H NMR (400 MHz, CDCl3/TMS): δ = 7.65
(dd, J = 7.2, 0.7 Hz, 4H), 7.44−7.38 (m, 6H), 4.16 (s, 2H), 2.20 (s,
3H), 1.10 (s, 9H); 13C {1H} NMR (100 MHz, CDCl3): δ = 208.5,
135.5, 132.6, 130.0, 127.8, 69.9, 26.7, 26.3, 19.2.
TMS): δ = 8.03 (d, J = 9.0 Hz, 2H), 6.91 (d, J = 9.0 Hz, 2H), 4.82 (s,
2H), 4.61 (s, 2H), 2.28 (s, 3H), 2.21 (s, 3H); 13C {1H} NMR (100
MHz, CDCl3): δ = 204.3, 201.9, 165.3, 161.7, 132.1, 122.6, 114.3,
72.8, 68.6, 26.5, 26.2; HRMS (ESI-TOF) calcd for [C13H14O5 + Na]+
273.0733, found 273.0734.
Ethyl 3-Oxobutanoate (2l):13aa Yield (56.6 mg, 87%). Colorless
oil; 1H NMR (400 MHz, CDCl3/TMS): δ = 4.16 (q, J = 7.2 Hz, 2H),
3.40 (s, 2H), 2.23 (s, 3H), 1.25 (t, J = 7.1 Hz, 3H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 200.6, 167.1, 61.3, 50.1, 30.1, 14.0.
4-Oxopentanoic Acid (2m):22e Yield (47.6 mg, 82%). Colorless oil;
1H NMR (400 MHz, CDCl3/TMS): δ = 2.73 (t, J = 7.2 Hz, 2H), 2.61
(t, J = 7.2 Hz, 2H), 2.18 (s, 3H); 13C {1H} NMR (100 MHz, CDCl3):
δ = 206.6, 178.2, 37.7, 29.8, 27.7.
1-[(1R,2S,5R)-2-Isopropyl-5-methylcyclohexyloxy]propan-2-one
25
(2x). Yield (70 mg, 66%). Colorless oil; [α]D = −73.3 (c = 1.0,
CHCl3); IR (CHCl3): νmax = 3020, 2958, 2928, 2872, 1720, 1457,
1
1370, 1116, 1015, 938, 842, 668 cm−1; H NMR (400 MHz, CDCl3/
TMS): δ = 4.14 (d, J = 16.8 Hz, 1H), 3.93 (d, J = 16.8 Hz, 1H), 3.11
(td, J = 10.6, 4.1 Hz, 1H), 2.28−2.24 (m, 1H), 2.18 (s, 3H), 2.06−2.00
(m, 1H), 1.68−1.61 (m, 2H), 1.37−1.28 (m, 2H), 1.01−0.84 (m, 8H),
0.78 (d, J = 7.0 Hz, 4H); 13C {1H} NMR (125 MHz, CDCl3): δ =
208.0, 80.3, 74.3, 48.0, 40.0, 34.4, 31.4, 26.6, 25.6, 23.2, 22.2, 20.9,
16.1; HRMS (ESI-TOF) calcd for [C13H24O2 + Na]+ 235.1669, found
235.1666.
5-Oxohexanoic Acid (2n):22e Yield (52.7 mg, 81%). Colorless oil;
1H NMR (400 MHz, CDCl3/TMS): δ = 2.53 (t, J = 7.2 Hz, 2H), 2.39
(t, J = 7.2 Hz, 2H), 2.15 (s, 3H), 1.94−1.84 (m, 2H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 208.0, 178.7, 42.3, 32.8, 29.9, 18.5.
1-Phenoxypropan-2-one (4a):24a Yield (57.1 mg, 76%). Colorless
Acetophenone (2o):17 Yield (51 mg, 85%). Pale yellow oil; H
1
1
oil; H NMR (400 MHz, CDCl3/TMS): δ = 7.33−7.28 (m, 2H),
NMR (400 MHz, CDCl3/TMS): δ = 7.97−7.92 (m, 2H), 7.57−7.51
7.02−6.98 (m, 1H), 6.91−6.88 (m, 2H), 4.54 (s, 2H), 2.28 (s, 3H);
13C {1H} NMR (100 MHz, CDCl3): δ = 205.9, 157.6, 129.6, 121.7,
114.4, 72.9, 26.6.
(m, 1H), 7.48−7.41 (m, 2H), 2.60 (s, 3H).
4-Methoxyacetophenone (2p):13ab Yield (48.8 mg, 65%). Color-
1
1-(Benzyloxy)propan-2-one (4b):24b Yield (65.7 mg, 80%).
less oil; H NMR (400 MHz, CDCl3/TMS) δ = 7.94 (d, J = 8.6 Hz,
1
2H), 6.94 (d, = 8.6 Hz, 2H), 3.87 (s, 3H), 2.56 (s, 3H).
4-tert-Butylacetophenone (2q):18 Yield (68.6 mg, 78%). Colorless
oil; 1H NMR (400 MHz, CDCl3/TMS): δ = 7.90 (d, J = 8.7 Hz, 2H),
7.48 (d, J = 8.7 Hz, 2H), 2.58 (s, 3H), 1.34 (s, 9H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 197.9, 156.8, 134.5, 128.3, 125.5, 35.1, 31.0,
26.5.
Colorless oil; H NMR (400 MHz, CDCl3/TMS): δ = 7.38−7.25
(m, 5H), 4.58 (s, 2H), 4.07 (s, 2H), 2.16 (s, 3H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 206.8, 137.0, 128.5, 127.9, 127.0, 75.2, 73.3,
26.4.
1-[4-(tert-Butyl)phenoxy]propan-2-one (4c). Yield (64.7 mg,
1
68%). Colorless oil; H NMR (400 MHz, CDCl3/TMS): δ = 7.32
2-Acetylnaphthalene (2r):23a Yield (49.3 mg, 58%). Colorless oil;
1H NMR (400 MHz, CDCl3/TMS): δ = 8.48 (s, 1H), 8.04 (dd, J =
8.7, 1.7 Hz, 1H), 7.97 (d, J = 8.2 Hz, 1H), 7.92−7.86 (m, 2H), 7.66−
7.53 (m, 2H), 2.73 (s, 3H); 13C {1H} NMR (100 MHz, CDCl3): δ =
198.2, 135.6, 134.5, 132.5, 130.2, 129.5, 128.6, 128.5, 127.8, 126.8,
123.9, 26.7.
(d, J = 8.9 Hz, 2H), 6.82 (d, J = 8.9 Hz, 2H), 4.52 (s, 2H), 2.28 (s,
3H), 1.30 (s, 9H); 13C {1H} NMR (100 MHz, CDCl3): δ = 206.4,
155.5, 144.5, 126.5, 114.0, 73.2, 34.1, 31.5, 26.6; HRMS (ESI-TOF)
calcd for [C13H18O2 + Na]+ 229.1199, found 229.1199.
1-(Napthalen-2-yloxy)propan-2-one (4d):24c Yield (130.6 mg,
81%). White solid, mp 64−66 °C; IR (CHCl3): νmax = 3028, 3056,
2924, 2850, 1732, 1631, 1600, 1509, 1470, 1432, 1390, 1358, 1272,
1259, 1222, 1173, 1122, 1071, 978, 950, 908, 875, 838, 819, 777, 638
4-Phenylacetophenone (2s):23b Yield (63.7 mg, 65%). White solid,
mp 115−117 °C; IR (CHCl3): νmax = 3019, 2923, 1679, 1599, 1404,
1359, 1267, 1119, 1078, 1044, 957, 927, 842, 694, 669 cm−1; 1H NMR
(400 MHz, CDCl3/TMS): δ = 8.04 (d, J = 8.6 Hz, 2H), 7.69 (d, J =
8.6 Hz, 2H), 7.63 (d, J = 7.0 Hz, 2H), 7.50−7.41 (m, 3H), 2.65 (s,
3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 197.8, 145.8, 139.9,
135.8, 128.94, 128.9, 128.2, 127.3, 127.2, 26.6; HRMS (ESI-TOF)
calcd for [C14H12O + Na]+ 219.0780, found 219.0783.
1
cm−1; H NMR (400 MHz, CDCl3/TMS): δ = 7.79 (d, J = 8.8 Hz,
2H), 7.72 (d, J = 8.2 Hz, 1H), 7.48−7.44 (m, 1H), 7.39−7.35 (m,
1H), 7.22 (dd, J = 9.0, 2.6 Hz, 1H), 7.03 (d, J = 2.5 Hz, 1H), 4.66 (s,
2H), 2.33 (s, 3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 205.9,
155.6, 134.2, 129.9, 129.3, 127.7, 126.8, 126.6, 124.2, 118.5, 106.9,
73.0, 26.7; HRMS (ESI-TOF) calcd for [C13H12O2 + Na]+ 223.0730,
found 223.0729.
4-Nitrophenylacetophenone (2t):18 Yield (45.4 mg, 55%). Pale
1
yellow solid, mp 76−78 °C; H NMR (400 MHz, CDCl3/TMS): δ =
2-Oxopropyl 4-Methylbenzoate (4e). Yield (73 mg, 76%).
8.32 (d, J = 8.8 Hz, 2H), 8.11 (d, J = 8.8 Hz, 2H), 2.68 (s, 3H); 13C
{1H} NMR (100 MHz, CDCl3): δ = 196.3, 150.7, 141.6, 129.3, 123.9,
27.0.
1
Colorless oil; H NMR (400 MHz, CDCl3/TMS): δ = 7.97 (d, J =
8.2 Hz, 2H), 7.26 (d, J = 8.1 Hz, 2H), 4.86 (s, 2H), 2.40 (s, 3H), 2.22
(s, 3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 202.1, 165.9, 144.2,
129.9, 129.2, 126.3, 68.6, 26.2, 21.6; HRMS (ESI-TOF) calcd for
[C11H12O3 + Na]+ 215.0679, found 215.0675.
2-(2-Oxopropoxy)benzoic Acid (2u). Yield (68 mg, 70%). Color-
less oil; IR (CHCl3): νmax = 3212, 2919, 1781, 1717, 1600, 1485, 1458,
1418, 1341, 1295, 1252, 1184, 1165, 1095, 1058, 1036, 958, 862, 829,
798, 684, 646 cm−1; 1H NMR (400 MHz, CDCl3/TMS): δ = 8.18 (dd,
J = 7.8, 1.4 Hz, 1H), 7.53 (t, J = 7.2 Hz, 1H), 7.18 (t, J = 7.6 Hz, 1H),
6.91 (d, J = 8.2 Hz, 1H), 4.89 (s, 2H), 2.30 (s, 3H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 201.2, 165.4, 156.3, 134.8, 133.1, 123.0,
118.9, 112.9, 73.6, 26.0; HRMS (ESI-TOF) calcd for [C10H10O4 +
Na]+ 217.0471, found 217.0472.
2-Oxopropyl 2-(2-Oxopropoxy)benzoate (2v). Yield (92.6 mg,
74%). White solid, mp 62−64 °C; IR (CHCl3): νmax = 3020, 2928,
2846, 1728, 1603, 1586, 1491, 1457, 1420, 1364, 1306, 1253, 1180,
1168, 1134, 1097, 1060, 1012, 964, 884, 828, 703, 668 cm−1; 1H NMR
(400 MHz, CDCl3/TMS): δ = 7.96 (dd, J = 7.8, 1.8 Hz, 1H), 7.51−
7.48 (m, 1H), 7.1 (td, J = 7.6, 0.8 Hz, 1H), 6.84 (d, J = 8.3 Hz, 1H),
4.88 (s, 2H), 4.60 (s, 2H), 2.35 (s, 3H), 2.23 (s, 3H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 205.7, 201.7, 164.7, 157.6, 134.3, 132.4,
121.5, 119.5, 113.6, 73.9, 68.6, 26.9, 26.2; HRMS (ESI-TOF) calcd for
[C13H14O5 + Na]+ 273.0733, found 273.0731.
2-Oxopropyl 4-Nitrobenzoate (4f). Yield (67.6 mg, 64%). White
solid, mp 102−104 °C; 1H NMR (400 MHz, CDCl3/TMS): δ = 8.28
(d, J = 9.1 Hz, 2H), 8.23 (d, J = 9.1 Hz, 2H), 4.97 (s, 2H), 2.23 (s,
3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 200.3, 164.0, 150.7,
134.6, 131.0, 123.6, 69.1, 26.1; HRMS (ESI-TOF) calcd for
[C10H9O5N + Na]+ 246.0373, found 246.0379.
2-Oxopropyl 3,5-Dinitrobenzoate (4g):19 Yield (81.8 mg, 61%).
White solid, mp 139−141 °C; IR (CHCl3): νmax = 3093, 3020, 2923,
1735, 1630, 1599, 1547, 1462, 1418, 1345, 1285, 1157, 1075, 1035,
1
923, 905, 669 cm−1; H NMR (400 MHz, CDCl3/TMS): δ = 9.27−
9.25 (m, 1H), 9.24−9.20 (m, 2H), 5.05 (s, 2H), 2.27 (s, 3H); 13C
{1H} NMR (100 MHz, CDCl3): δ = 199.1, 161.9, 148.7, 132.9, 129.7,
122.8, 69.6, 25.9; HRMS (ESI-TOF) calcd for [C10H8O7N2 + Na]+
291.0224, found 291.0230.
1-(tert-Butyldiphenylsilyloxy)-1-phenylpropan-2-one (4h):24d
1
Yield (151.3 mg, 78%). Colorless oil; H NMR (400 MHz, CDCl3/
TMS): δ = 7.66−7.64 (m, 2H), 7.47−7.42 (m, 3H), 7.40−7.32 (m,
5H), 7.31−7.27 (m, 5H), 5.08 (s, 1H), 2.02 (s, 3H), 1.13 (m, 9H);
13C {1H} NMR (100 MHz, CDCl3): δ = 207.7, 138.2, 135.7, 135.6,
132.8, 132.6, 130.0, 129.8, 128.5, 128.1, 127.8, 127.6, 126.2, 81.7, 26.9,
2-Oxopropyl 4-(2-Oxopropoxy)benzoate (2w). Yield (87.5 mg,
70%). White solid, mp 80−82 °C; IR (CHCl3): νmax = 3021, 2928,
1721, 1607, 1583, 1509, 1420, 1371, 1314, 1276, 1170, 1115, 1070,
1
1008, 966, 883, 848, 696, 667 cm−1; H NMR (400 MHz, CDCl3/
E
dx.doi.org/10.1021/jo500921j | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
24.3, 19.3; HRMS (ESI-TOF) calcd for [C25H28O2Si + Na]+ 411.1751,
found 411.1755.
ACKNOWLEDGMENTS
■
2-Oxononan-3-yl Acetate (4i):24e Yield (65.1 mg, 65%). Colorless
oil; 1H NMR (400 MHz, CDCl3/TMS): δ = 4.98 (dd, J = 8.2, 4.6 Hz,
1H), 2.16 (s, 3H), 2.15 (s, 3H), 1.76−1.71 (m, 2H), 1.54−1.25 (m,
8H), 0.88 (t, J = 6.8 Hz, 3H); 13C {1H} NMR (100 MHz, CDCl3): δ =
205.5, 170.7, 78.7, 31.5, 30.2, 28.9, 26.1, 25.1, 22.5, 20.7, 14.0.
2-Oxo-1-phenylpropyl Acetate (4j):24e Yield (71 mg, 74%).
This work is financially supported by the Council of Scientific
and Industrial Research (CSIR) New Delhi [Grant No.
02(0158)/13/EMR-II], India. D.A.C. thanks CSIR for a
research fellowship India.
REFERENCES
■
1
Colorless oil; H NMR (400 MHz, CDCl3/TMS): δ = 7.44−7.38
(1) For representative reviews, see: (a) Beller, M.; Seayad, J.; Tillack,
A.; Jiao, H. Angew. Chem., Int. Ed. 2004, 43, 3368. (b) Alonso, F.;
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Chem., Int. Ed. 2012, 51, 8933.
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(c) Olah, G. A.; Krishnamurti, R.; Prakash, G. K. S. Comprehensive
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339. (d) Bandini, M.; Melloni, A.; Umani-Ronchi, A. Angew. Chem., Int.
Ed. 2004, 43, 550.
(m, 5H), 5.97 (s, 1H), 2.20 (s, 3H), 2.12 (s, 3H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 201.7, 170.3, 133.1, 129.4, 129.1, 128.1, 80.9,
26.1, 20.7.
2-Oxononan-4-yl Acetate (4k):24f Yield (75.1 mg, 75%). Colorless
oil; 1H NMR (400 MHz, CDCl3/TMS): δ = 5.22−5.16 (m, 1H), 2.70
(dd, J = 16.2, 7.4 Hz, 1H), 2.57 (dd, J = 16.2, 5.3 Hz, 1H), 2.13 (s,
3H), 2.01 (s, 3H), 1.54−1.51 (m, 2H), 1.32−1.21 (m, 6H), 0.86 (t, J =
6.8 Hz, 3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 205.8, 170.5,
70.3, 48.0, 34.1, 31.5, 30.4, 24.8, 22.5, 21.1, 14.0.
3-Oxo-1-phenylbutyl Acetate (4l):24g Yield (73.2 mg, 71%).
1
Colorless oil; H NMR (400 MHz, CDCl3/TMS): δ = 7.37−7.28
(m, 5H), 6.18 (dd, J = 8.7, 4.9 Hz, 1H), 3.12 (dd, J = 16.6, 8.7 Hz,
1H), 2.82 (dd, J = 16.7, 4.9 Hz, 1H), 2.15 (s, 3H), 2.04 (s, 3H); 13C
{1H} NMR (100 MHz, CDCl3): δ = 204.7, 169.8, 139.6, 128.6, 128.2,
126.4, 71.6, 49.8, 30.4, 21.0.
(3) (a) Dakin, H. D.; West, R. J. Biol. Chem. 1928, 78, 91.
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(4) Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815.
1-(4-Methoxyphenyl)-3-oxobutyl Acetate (4m). Yield (99.2 mg,
84%). Colorless oil; 1H NMR (400 MHz, CDCl3/TMS): δ = 7.29 (d, J
= 8.7 Hz, 2H), 6.86 (d, J = 8.7 Hz, 2H), 6.13 (dd, J = 8.5, 5.3 Hz, 1H),
3.78 (s, 3H), 3.10 (dd, J = 16.5, 8.5 Hz, 1H), 2.81 (dd, J = 16.5, 5.3
Hz, 1H), 2.14 (s, 3H), 2.01 (s, 3H); 13C {1H} NMR (100 MHz,
CDCl3): δ = 204.8, 169.9, 159.5, 131.6, 128.0, 113.9, 71.3, 55.2, 49.6,
30.4, 21.1; HRMS (ESI-TOF) calcd for [C13H16O4 + Na]+ 259.0941,
found 259.0948.
1-(Naphthalen-1-yl)-3-oxobutyl Benzoate (4n). Yield (122.2 mg,
77%). Colorless oil; IR (CHCl3): νmax = 3062, 3009, 2925, 2854, 1719,
1601, 1584, 1510, 1492, 1451, 1417, 1398, 1363, 1315, 1270, 1176,
1110, 1070, 1058, 1026, 975, 938, 862, 798, 713, 686 cm−1; 1H NMR
(400 MHz, CDCl3/TMS): δ = 8.25 (d, J = 8.4 Hz, 1H), 8.10−8.07
(m, 2H), 7.88 (d, J = 7.6 Hz, 1H), 7.80 (d, J = 8.2 Hz, 1H), 7.64−7.42
(m, 7H), 7.21 (dd, J = 9.0, 4.0 Hz, 1H), 3.40 (dd, J = 16.9, 8.6 Hz,
1H), 3.13 (dd, J = 16.9, 4.1 Hz, 1H), 2.23 (s, 3H); 13C {1H} NMR
(100 MHz, CDCl3): δ = 204.6, 165.3, 135.6, 133.9, 133.1, 129.9,
129.8, 129.6, 129.0, 128.9, 128.7, 126.6, 125.8, 125.3, 123.7, 122.9,
69.9, 49.6, 30.4; HRMS (ESI-TOF) calcd for [C21H18O3 + Na]+
341.1148, found 341.1148.
(5) (a) Smidt, J.; Hafner, W.; Jira, R.; Sedlmeier, J.; Sieber, R.;
Ruttinger, R.; Kojer, K. Angew. Chem. 1959, 71, 176. (b) Smidt, J.;
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Hafner, W.; Jira, R.; Sieber, R.; Sedlmeier, J.; Sabel, A. Angew. Chem.,
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4-(Benzyloxy)-4-(4-nitrophenyl)butan-2-one (4o). Yield (91.3 mg,
61%). Colorless oil; IR (CHCl3): νmax = 3066, 3032, 3008, 2865, 1716,
1606, 1521, 1497, 1415, 1347, 1162, 1096, 1075, 1028, 884, 857, 699
1
cm−1; H NMR (400 MHz, CDCl3/TMS): δ = 8.15 (d, J = 8.8 Hz,
2H), 7.48 (d, J = 8.7 Hz, 2H), 7.27−7.21 (m, 5H), 4.93 (dd, J = 8.4,
4.6 Hz, 1H), 4.32 (d, J = 11.3 Hz, 1H), 4.27 (d, J = 11.3 Hz, 1H), 2.99
(dd, J = 16.5, 8.5 Hz, 1H), 2.57 (dd, J = 16.5, 4.6 Hz, 1H), 2.10 (s,
3H); 13C {1H} NMR (100 MHz, CDCl3): δ = 205.3, 148.9, 147.6,
137.2, 128.4, 127.9, 127.9, 127.5, 123.9, 76.5, 71.5, 51.5, 31.0; HRMS
(ESI-TOF) calcd for [C17H17NO4 + Na]+ 322.1050, found 322.1049.
(g) Backvall, J.-E.; Awasthi, A. K.; Renko, Z. D. J. Am. Chem. Soc. 1987,
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J.-E.; Hopkins, R. B.; Grennberg, H.; Mader, M. M.; Awasthi, A. K. J.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Spectra for compounds 2a−2x and 4a−4o. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: rfernand@chem.iitb.ac.in.
Notes
The authors declare no competing financial interest.
F
dx.doi.org/10.1021/jo500921j | J. Org. Chem. XXXX, XXX, XXX−XXX

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Article
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