Oxidative cleavage of olefins by in situ-generated catalytic 3,4,5,6-tetramethyl-2-iodoxybenzoic acid/oxone

Article abstract of DOI:10.1021/jo502002w

Oxidative cleavage of a variety of olefins to the corresponding ketones/carboxylic acids is shown to occur in a facile manner with 3,4,5,6-tetramethyl-2-iodobenzoic acid (TetMe-IA)/oxone. The simple methodology involves mere stirring of the olefin and catalytic amount (10 mol %) of TetMe-IA and oxone in acetonitrile-water mixture (1:1, v/v) at rt. The reaction mechanism involves initial dihydroxylation of the olefin with oxone, oxidative cleavage by the in situ-generated 3,4,5,6-tetramethyl-2-iodoxybenzoic acid (TetMe-IBX), and oxidation of the aldehyde functionality to the corresponding acid with oxone. Differences in the reactivities of electron-rich and electron-poor double bonds have been exploited to demonstrate chemoselective oxidative cleavage in substrates containing two double bonds.

Full text of DOI:10.1021/jo502002w

Article
pubs.acs.org/joc
Oxidative Cleavage of Olefins by In Situ-Generated Catalytic 3,4,5,6-
Tetramethyl-2-iodoxybenzoic Acid/Oxone
Jarugu Narasimha Moorthy* and Keshaba Nanda Parida
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
S
* Supporting Information
ABSTRACT: Oxidative cleavage of a variety of olefins to the
corresponding ketones/carboxylic acids is shown to occur in a
facile manner with 3,4,5,6-tetramethyl-2-iodobenzoic acid
(TetMe-IA)/oxone. The simple methodology involves mere
stirring of the olefin and catalytic amount (10 mol %) of
TetMe-IA and oxone in acetonitrile−water mixture (1:1, v/v)
at rt. The reaction mechanism involves initial dihydroxylation
of the olefin with oxone, oxidative cleavage by the in situ-
generated 3,4,5,6-tetramethyl-2-iodoxybenzoic acid (TetMe-
IBX), and oxidation of the aldehyde functionality to the corresponding acid with oxone. Differences in the reactivities of electron-
rich and electron-poor double bonds have been exploited to demonstrate chemoselective oxidative cleavage in substrates
containing two double bonds.
alcohols to enones,8d benzylic oxidation and C−H activation,8e
INTRODUCTION
■
etc.
o-Iodoxybenzoic acidpopularly called IBXis a more than a
Our own interest has been centered on exploring new
reactions mediated by IBX/oxone and developing modified
century old oxidation reagent.1 Its cheap availability, ease of
handling, and environmentally benign attributes continue to
IBXs as well as catalytic protocols that simplify the oxidation
attract the attention of chemists for extensive application in a
chemistry using IBX.9 We recently showed that the structurally
variety of oxidative transformations.2 However, the noted
disadvantage of IBX is its insolubility in common organic
puckered and sterically encumbered TetMe-IBXgenerated
catalytically in situ from its precursor iodo acid (i.e., TetMe-IA)
solvents, the root cause of which is traceable to operation of a
number of intermolecular interactions3 that hold molecules
very cohesively in the solid state to preclude solvation from
overcoming the lattice energy. It is soluble only in a highly
polar solvent such as dimethyl sulfoxide (DMSO),4 which is
undesirable from the points of view of difficulty with isolation
of product(s) and tedious workup; to avoid the use of DMSO,
IBX-mediated reactions are performed at elevated temperatures
in a solvent such as ethyl acetate.5 Furthermore, IBX is known
to be explosive on mechanical impact/heating.6 To overcome
these lacunae, development of modified IBXs and catalytic
protocols that allow oxidations at ambient conditions by way of
in situ generation of IBX in the presence of a terminal oxidant
such as oxone is being actively pursued.7 A catalytic protocol
that obviates the use of stoichiometric amounts of IBX was first
introduced by Vinod and co-workers for alcohol oxidations
with catalytic o-iodobenzoic acid and oxone in acetonitrile−
water at 70 °C.7a Subsequently, Ishihara and co-workers
demonstrated oxidation of alcohols using catalytic amounts of
o-iodobenzenesulfonic acid in the presence of oxone in
acetonitrile or nitromethane at 70 °C;7b it is noteworthy that
generation of I(V) species in the presence of a co-oxidant
occurs only at higher temperatures. A variety of reactions
catalyzed by hypervalent iodine catalysts have been reported.8
These include oxidation of phenols to quinones,8b,c α,β-
dehydrogenation of ketones,7b rearrangement of tertiary allylic
in the presence of oxoneoxidizes alcohols to the correspond-
ing carbonyl compounds in acetonitrile−water (1:1, v/v) at
rt.9d The high reactivity of the in situ-generated TetMe-IBX
spurred us to explore oxidative cleavage of olefins to
corresponding carbonyl compounds. The latter is a trans-
formation of paramount importance in organic synthesis. Vinod
et al. showed that olefins can be oxidatively cleaved by using p-
iodobenzoic acid as a catalyst in the presence of oxone at 60 °C,
where [hydroxy(4-carboxyphenyl)iodonium]ion is presumed to
be the active species;10 it is noteworthy that 20 mol % of the
iodo acid was employed, and the oxidative cleavage of aliphatic
olefins using this procedure was found to be too sluggish. A
variety of procedures based on organometallic reagents11 and
metal-free protocols12,13 have been reported in the literature.
While the metal-based reagents are undesirable, metal-free
protocols such as ozone present hazards due to explosive
property as well as operational difficulties.12c,d Noteworthy
methodologies for oxidative cleavage that necessitate stoichio-
metric amounts of the reagents are H2O2 with catalytic
heteropoly acid adsorbed on aluminum, magnesium or zinc
oxide support,13a phenyliodonium diacetate (PIDA),13d etc.
Methodologies involving the use of a stoichiometric amount of
Received: September 3, 2014
Published: October 29, 2014
© 2014 American Chemical Society
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PhIO13b and mCPBA13c in the presence of ArI as a catalyst
have also been developed for oxidative cleavage. We recently
showed that olefins can be oxidatively cleaved by oxone itself
without the use of any catalyst in acetonitrile−water but at
reflux conditions.9h Oxone is a cheap and environmentally
benign stable triple salt. However, its reactivity at high
temperatures limits its application for oxidative cleavage of
electron-rich olefins and substrates bearing sensitive functional
groups. Herein, we report that the high reactivity of TetMe-
IBX, which is generated in situ from its precursor iodo acid (i.e.,
TetMe-IA) in the presence of oxone, in conjunction with the
ability of oxone to carry out dihydroxylation of olefins allows
facile oxidative cleavage of a variety of olefins at room
temperature; indeed, limitations with oxone as the reagent at
high temperatures are overcome due to occurrence of the
reaction cascade at rt. It is also shown that electron-rich olefins
are selectively cleaved in preference to electron-deficient ones.
oxidation of p-bromostyrene was explored with each of these
iodo acids employed in 10 mol % together with 3 equiv of
oxone in acetonitrile−water (1:1, v/v) at rt. Results of these
screening experiments are consolidated in Table 1. While o-
iodobenzoic acid (o-IA) was found to produce the correspond-
ing acid in 20% yield along with the diol in 67% yield after 24 h,
p-iodobenzoic acid (p-IA) led to an insignificant yield of the
acid. However, MeO-IA was found to produce the acid in 74%
yield. While respectable conversion of p-bromostyrene to the
corresponding acid was observed with Me-IA, DiMe-IA, and
DIDA, remarkable reactivity was found for TetMe-IA; the acid
was isolated in 84% yield with a trace amount of the ketol in 12
h. Notably, the formation of only diol was observed without the
added catalyst, and no diol was found to be formed when the
reaction was conducted with the I(V) reagent (i.e., TetMe-IBX;
cf. Supporting Information). It thus emerges that TetMe-IA
undergoes oxidation readily to I(V) species, which has been
shown to be highly reactive for alcohol oxidations from our
previous investigations.9d
Spurred by the results observed with TetMe-IA as a catalyst,
we examined the oxidation of a variety of olefins. The results
are consolidated in Table 2. The parent styrene, under the
employed conditions of oxidation, was found to yield benzoic
acid in 89% isolated yield (Table 2, entry 1); it should be noted
that the reaction of styrene with oxone alone at reflux
conditions leads to poor yield of the benzoic acid over a
period of 14 h.9h The oxidative cleavage with TetMe-IA/oxone
was found to work equally well for a variety of electron-rich as
well as electron-deficient styrenes, leading to the corresponding
benzoic acids in 76−91% yields (entries 2−10). Intriguing
results were observed for o-substituted styrenes in that the
reaction was found to be clean for o-Cl- and o-Br-substituted
styrenes (entries 12 and 13), while o-Me-substituted derivative
led to a mixture of products (entry 14), where o-methylbenzoic
acid was obtained only in 11% yield and o-methylphenylglyox-
ylic acid was isolated in 76% yield. o-Nitrostyrene was found to
react slowly, leading to 52% yield of o-nitrobenzoic acid with
27% of the reactant recovered unreacted. Facile cleavage was
observed for an aliphatic terminal olefin, that is, 1-tridecene
(entry 15). 1,2-Aryl alkyl-substituted olefins yielded good yields
of the cleaved products (entries 16 and 17). However, α-
methylstyrene yielded acetophenone together with benzoic
acid; the latter is an overoxidation product of the ketone (entry
21). Cinnamyl alcohol and cinnamyl bromide were found to
RESULTS AND DISCUSSION
■
At the outset, we set out to identify the iodo acids that allow
generation of hypervalent iodine species upon reaction with
oxone at rt. In Chart 1 are shown a broad set of iodo acids that
Chart 1
were subjected to screening for their ability to produce
hypervalent iodine species in the presence of oxone as a
terminal oxidant and catalyze oxidation of p-bromostyrene, a
representative case. It is noteworthy that the hypervalent iodine
species generated from all the iodo acids in Chart 1 have been
found to be applicable for oxidation of alcohols. Thus, the
Table 1. Results of Catalyst Screening for Oxidative Cleavage of p-Bromostyrene as a Representative Case with Oxone as the
a
Terminal Oxidant in Acetonitrile−Water (1:1) Mixture
a
p-Bromostyrene (0.55 mmol), 10 mol % of the catalyst, and oxone (1.65 mmol) were taken in 10 mL of acetonitrile−water (1:1, v/v) at rt.
b
c
Isolated yield of p-bromobenzoic acid. No reaction.
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a
Table 2. Results of Catalytic Oxidative Cleavage of Olefins by TetMe-IA/Oxone in CH3CN−H2O (1:1) Mixture
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Table 2. continued
a
b
All reactions were carried with 10 mol % of TetMe-IA and oxone in CH3CN−H2O (1:1, v/v) mixture at rt. Isolated yields unless mentioned
c
d
e
otherwise. 27% reactant was recovered. 2-Methylphenylglyoxylic acid was isolated in 76% yield. o-Carboxycinnamic acid was isolated in 8% yield.
f
g
h
Benzoic acid was isolated in 33% yield. Starting compound was recovered in 43% yield. Conversion was ca. 35%, and the corresponding cleaved
i
j
carboxylic acid was isolated in 9% yield. Conversion was ca. 88%, and the corresponding acid derived from cleavage was isolated in 10% yield. 2-
Hydroxy-2-phenylcyclohexanone was isolated in 2% yield. No reaction. 89% reactant was found unreacted.
k
l
a
Table 3. Chemoselective Oxidations Using TetMe-IA and Oxone in CH3CN/H2O
a
b
All reactions were carried out with 10 mol % of TetMe-IA and 3 equiv of oxone in CH3CN−H2O (1:1, v/v) mixture at rt. Isolated yields unless
c
mentioned otherwise. 4-[2-(4-Bromophenyl)ethenyl]benzoic acid was isolated in 11% yield.
yield the corresponding oxidative cleavage products in
respectable yields (entries 18 and 19). Cyclic dodecene and
1,1-diphenylethylene were found to undergo cleavage, leading
to the corresponding diacid and benzophenone in 84 and 85%
yields, respectively (entries 20 and 22). 1-Phenylcyclohexene
reacted with oxone, leading to the ring-opened keto acid in 85%
yield (entry 26). 1,2-Diarylethylenes (i.e., stilbenes) were found
to undergo reaction rather sluggishly, leading to 1,2-diketones
as one of the products; even after 36−38 h, considerable
amounts of starting compounds were recovered unreacted with
low yields of oxidative cleavage products, such as carboxylic
acids (entries 23−25).
While the electron-rich p-methoxycinnamic acid underwent
oxidative cleavage over a period of 36 h to afford p-
methoxybenzoic acid in 86% isolated yield, the unsubstituted
cinnamic acid was found to be unreactive even after 24 h
(entries 29 and 31). While cyclic enone and chalcone were
found to undergo cleavage leading to the corresponding
products in 84 and 86% yields, respectively (entries 27 and 28),
α,β-unsaturated carboxylic acids, nitriles, and esters were found
to be unreactive under the employed conditions (entries 30−
33). Intriguingly, allyl and cinnamyl esters were found to be
unreactive (entries 34−36). 1H NMR monitoring studies of the
reactions of these substrates revealed no evidence for formation
of the dihydroxy intermediates (cf. Figures S37 and S38,
Supporting Information).
As mentioned at the outset, we have recently reported that
oxone itself can be employed to cleave olefins but at the reflux
conditions of acetonitrile−water (1:1, v/v);9h the high
temperature at which the reactions occur with oxone alone is
highly detrimental and renders the protocol limited in its
scope.9h We have shown that this procedure is disadvantageous
for methoxy-substituted arylolefins, olefins that contain benzylic
carbons, and esters. The present protocol involving the use of
TetMe-IA is mild in terms of the reaction conditions.
Consequently, all the drawbacks associated with oxone as the
reagent are overcome. As may be seen from the results in Table
2, substrates that contain methoxy-substituted arenes are not
affected at rt (entries 2, 6, and 29). While alkylarenes lead to
messy reactions with products arising from oxidation of the
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Scheme 1. Mechanism of Oxidative Cleavage of Styrene
Figure 1. 1H NMR monitoring of oxidation of p-bromostyrene with oxone (3 equiv) in CD3CN−D2O (1:1) at rt: (a) 0 h, before addition of oxone,
(b) 2 h after addition of oxone, (c) upon introduction of TetMe-IA, (d) after 4 h, (e) after 8 h, (f) after 14 h.
alkyl groups and esters undergoing hydrolysis at the reflux
conditions with oxone in acetonitrile−water mixture,9h
alkylarenes and ester functionalities are unaffected with the
present protocol at rt (entries 3, 6, 7, 10, and 14).
TetMe-IA as a catalyst in the presence of oxone as a co-oxidant
at rt.
When 6-vinyl-2H-chromen-2-one was employed as the
substrate at the employed reaction conditions, 2-oxo-2H-
chromene-6-carboxylic acid was isolated in 83% yield (Table 3,
entry 1). Clearly, cleavage of the vinyl group occurs with the
cyclic electron-deficient double bond untouched. In a similar
manner, electron-rich double bonds were found to undergo
cleavage in substrates that simultaneously contain a function-
ality such as α,β-unsaturated ester/acid/nitrile; the acids were
produced in 81−90% isolated yields (entries 2−4). The
reaction of 4-bromostilbene was earlier found to be sluggish,
leading to the corresponding benzil, but not the benzoic acid
derived from oxidative cleavage, suggesting thereby that the
latter does not occur at rt. Thus, chemoselective oxidative
cleavage of the isolated double bond in (Z)-1-ethenyl-4-[2-(4-
bromophenyl)ethenyl]benzene was examined. Indeed, the vinyl
double bond underwent cleavage to the corresponding acid
As is evident from the results in Table 2, the oxidative
cleavage is not observed for electron-deficient olefins that
cannot undergo epoxidation followed by ring opening to yield
the corresponding diols (vide infra); notably, the same olefins
do lead to diols in the presence of oxone upon heating.
Capitalizing on the difference in the reactivities of electron-rich
and electron-deficient olefins to undergo epoxidation with
oxone at rt, chemoselective oxidative cleavage of electron-rich
double bonds in the presence of electron-poor double bonds
was explored. Incidentally, there are only a few reports of
chemoselective epoxidation and are virtually unknown with the
exception of reactions employing ozone; even with the latter,
there are only scant reports in the literature.14 In Table 3 are
shown our results of chemoselective cleavage of olefins with
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Scheme 2. Mechanism of Oxidation of o-Methylstyrene
with concomitant oxidation of the stilbene double bond,
leading to 4-[2-(4-bromophenyl)-2-oxoacetyl]benzoic acid in
74% isolated yield when oxone was employed in 5 equiv and
the reaction was run for 30 h. However, when the reaction was
carried out with 3 equiv of oxone and over a period of 18 h, a
mixture of products, namely, (E)-4-[2-(4-bromophenyl)-
ethenyl]benzoic acid (37%) and 4-[2-(4-bromophenyl)-2-
oxoacetyl]benzoic acid (45%), was isolated.
Mechanism of Oxidation of Olefins. It is well-known that
the reaction of olefins with oxone produces epoxides and diols
depending on basic and acidic conditions, respectively.15 As the
solution of oxone in acetonitrile−water (1:1, v/v) is strongly
acidic, pH ≈3−4, the initially formed epoxides should be
expected to open up to afford the corresponding diols (Scheme
1). Indeed, the latter were isolated in a number of cases when
the reactions were stopped midway or when the reactions were
conducted without TetMe-IA as an added catalyst (e.g., entry 9,
Table 1). Further, for o-methylstyrene, 1-o-tolylethane-1,2-diol
was isolated in 87% when the reaction was run without the
catalyst. The fact that the diols are produced by the reaction of
oxone with olefins such as styrene in CH3CN−H2O (1:1, v/v)
has also been shown by us previously.9h
The reaction of p-bromostyrene, a representative olefin, with
TetMe-IA/oxone in CD3CN−D2O (1:1, v/v) as monitored by
1H NMR spectroscopy is shown in Figure 1. As can be seen, the
formation of 1-(4-bromophenyl)ethane-1,2-diol occurs within 2
h after the addition of oxone. Upon introduction of TetMe-IA
to the reaction mixture, one observes the disappearance of the
signals corresponding to the diol with concomitant appearance
of new signals at δ 2.6, 2.8, 8.0, and 8.3, which presumably
correspond to the periodinane complex; evidently, TetMe-IA
undergoes oxidation to I(V) species (i.e., TetMe-IBX) at rt,
which subsequently participates in the oxidation to form a
cyclic periodinane. The signals corresponding to aldehyde and
acid appear gradually, which we believe are a consequence of
decomposition of the periodinane complex (Scheme 1). The
fact that the initially formed aldehyde undergoes oxidation
rapidly to carboxylic acid under the employed reaction
conditions is well-known.16 As the diols are quickly
decomposed oxidatively to aldehydes, which further undergo
rapid oxidation, the formation of diols from the olefins appears
to be rate-determining. The fact that the reactions of electron-
deficient olefins with TetMe-IA/oxone proceed slowly is in
good agreement with this reasoning.
The result observed with o-methylstyrene clearly brings out
the role of sterics (entry 14, Table 2). Oxidative cleavage of this
substrate leads predominantly to o-methylphenylglyoxylic acid
(76%) with o-toluic acid formed only in 11% yield. Clearly, the
sterics prohibit cleavage followed by oxidation. We have
isolated the 1,2-diol and subjected it independently to oxidation
to establish the fact that it is the 1,2-diol which is an
intermediate in the reaction of o-methylstyrene with TetMe-
IA/oxone leading to the glyoxylic acid and o-toluic acid. With 3
equiv of oxone and 10 mol % of TetMe-IA, the reaction of the
1,2-diol at rt led to o-methylglyoxylic acid in 87% isolated yield
along with o-toluic acid as a minor product in 7% yield. This
suggests that the o-methyl group hinders the formation of cyclic
periodinane derived from in situ-generated TetMe-IBX, which
may decompose to o-toluic acid (Scheme 2). We have verified
from an independent experiment that the oxidation of o-
methyl-α-hydroxyacetophenone with TetMe-IA (10 mol
%)/oxone (1.5 equiv) at rt leads to glyoxylic acid and o-toluic
acid in 86 and 4% yields, which attests to the fact that the
sterically hindered acyloins do not decompose predominantly
to o-toluic acid (eq 1); notably, the reaction was found not to
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organic extract was dried over anhyd Na2SO4 and concentrated in
vacuo. The residue was subjected to a short-pad silica gel column
chromatography to isolate pure product(s). All the products were
characterized by their 1H NMR spectral data (cf. Supporting
Information).
occur even after 24 h without the added TetMe-IA catalyst and
with just oxone alone. In contrast, the oxidation of sterically
unhindered diol, that is, 1-(4-bromophenyl)ethane-1,2-diol,
under conditions similar to those employed for o-methylstyrene
led to p-bromobenzoic acid in 91% yield within 8 h (eq 2).
Given that chloro and bromo substituents at o-position do
not influence as that of the methyl group, a subtle difference is
evidently obviating the oxidative cleavage. Otherwise, a range of
olefins including the moderately poor ones are found to be
oxidatively cleaved with TetMe-IA/oxone to the corresponding
acids under mild conditions at rt.
The fact that oxidative cleavage of the diolsgenerated by
the reaction of olefins with oxonedoes not occur at all or
occurs with lower efficiencies with all other iodo acids other
than TetMe-IA in Chart 1 should be understood from the
unique attributes inherent to TetMe-IA. In the latter, the
consecutive methyl groups render the iodo acid to be
sufficiently electron-rich as to facilitate its oxidation with
oxone at rt to I(V) species. We have shown earlier that the
steric relay between the consecutive methyl groups in TetMe-
IBX renders it to be twisted and that the twisting enhances its
solubility in common organic solvents.9d Thus, the room
temperature oxidation of TetMe-IA to TetMe-IBX in
conjunction with enhanced solubility of the latter is responsible
for the facile domino oxidative cleavage of olefins at rt with
catalytically in situ-generated modified IBX and oxone.
Characterization Data of Oxidation Products. Benzoic Acid.9h
Colorless solid; Rf (25% EtOAc/petroleum ether) 0.37; 1H NMR
(CDCl3, 400 MHz) δ 7.49 (t, J = 7.3 Hz, 2H), 7.62 (t, J = 7.8 Hz, 1H),
8.12 (d, J = 7.3 Hz, 2H).
p-Methoxybenzoic Acid.9h Colorless solid; Rf (50% EtOAc/
1
petroleum ether) 0.4; H NMR (500 MHz, CDCl3) δ 3.88 (s, 3H),
6.95 (d, J = 9.0 Hz, 2H), 8.07 (d, J = 9.0 Hz, 2H).
p-Toluic Acid.9h Colorless solid; Rf (25% EtOAc/petroleum ether)
0.37; 1H NMR (CDCl3, 400 MHz) δ 2.44 (s, 3H), 7.4 (d, J = 8.1 Hz,
2H), 8.01 (d, J = 8.1 Hz, 2H).
p-Bromobenzoic Acid.9h Colorless solid; Rf (50% EtOAc/
1
petroleum ether) 0.48; H NMR (CDCl3, 500 MHz) δ 7.62 (d, J =
8.5 Hz, 2H), 7.96 (d, J = 8.5 Hz, 2H).
p-Nitrobenzoic Acid.9h Colorless solid; Rf (10% CH3OH/EtOAc)
0.32; 1H NMR (CDCl3, 400 MHz) δ 8.27 (d, J = 8.8 Hz, 2H), 8.33 (d,
J = 8.8 Hz, 2H).
o-Bromobenzoic Acid.9h Colorless solid; Rf (50% EtOAc/
1
petroleum ether) 0.49; H NMR (CDCl3, 500 MHz) δ 7.38−7.43
(m, 2H), 7.72(d, J = 8.2 Hz, 1H), 8.02 (dd, J1 = 7.3 Hz, J2 = 2.1 Hz,
1H); 13C NMR (CDCl3, 125 MHz) δ 122.6, 127.3, 130.1, 132.5,
133.6, 134.9, 170.8.
Acetophenone.9d Colorless liquid; Rf (10% EtOAc/petroleum
ether) 0.59; 1H NMR (CDCl3, 400 MHz) δ 2.61 (s, 3H), 7.46 (t, J =
7.3 Hz, 2H), 7.54−7.59 (m, 1H), 7.96 (dd, J1 = 8.5 Hz, J2 = 1.4 Hz,
2H).
Benzophenone.9f Colorless solid; Rf (10% EtOAc/petroleum
CONCLUSIONS
■
1
ether) 0.45; H NMR (CDCl3, 400 MHz) δ 7.48 (t, J = 7.8 Hz,
A catalytic protocol that works at rt for oxidative cleavage of
olefins has been developed based on in situ-generated
hypervalent I(V) and oxone. From the screening of a number
of iodo acids that lead to hypervalent I(V) species on oxidation
with oxone in CH3CN−H2O at rt, TetMe-IA was identified as
the reactive catalyst. It has been shown that olefins undergo
facile oxidative cleavage with 10 mol % of TetMe-IA/oxone at
rt. Mechanistically, the olefins undergo initial epoxidation
followed by ring opening to 1,2-diols with oxone as the reagent
in CH3CN−H2O. The in situ-generated I(V) species is
surmised to decompose the diols into carbonyl compounds.
The aldehydes thus produced undergo further oxidation to
acids with oxone. The procedure that involves mere stirring of
the substrate and the catalyst in CH3CN−H2O (1:1, v/v)
mixture at rt with incremental addition of oxone is simple,
convenient, and cost-effective for oxidative cleavage of olefin to
corresponding carbonyl compounds. For substrates that
contain both electron-rich and electron-deficient double
bonds, chemoselective cleavage of electron-rich olefins has
been demonstrated.
4H), 7.59 (t, J = 7.3 Hz, 2H), 7.8 (d, J = 8.2 Hz, 4H).
2-Hydroxy-2-phenylcyclohexanone.9a Colorless liquid; Rf (25%
1
EtOAc/petroleum ether) 0.4; H NMR (400 MHz, CDCl3) δ 1.7−
1.87 (m, 4H), 2.02−2.1 (m, 1H), 2.4−2.45 (m, 2H), 2.97−3.01 (3,
1H), 7.28 (m, 5H).
p-tert-Butylbenzoic Acid.17 Colorless solid; Rf (50% EtOAc/
1
petroleum ether) 0.5; H NMR (CDCl3, 500 MHz) δ 1.35 (s, 9H),
7.49 (d, J = 8.6 Hz, 2H), 8.04 (d, J = 8.6 Hz, 2H).
p-(Benzyloxy)benzoic Acid.18 Colorless solid; Rf (50% EtOAc/
1
petroleum ether) 0.3; H NMR (CDCl3, 400 MHz) δ 5.14 (s, 2H),
7.03 (d, J = 8.5 Hz, 2H), 7.33−7.45 (m, 5H), 8.06 (d, J = 8.5 Hz, 2H);
13C NMR (CDCl3, 125 MHz) δ 70.2, 114.7, 121.2, 127.5, 128.3, 128.7,
132.5, 136.0, 163.4, 171.6.
p-Acetoxybenzoic Acid.19 Colorless solid; Rf (50% EtOAc/
1
petroleum ether) 0.3; H NMR (CDCl3, 400 MHz) δ 2.33 (s, 3H),
7.21 (d, J = 8.6 Hz, 2H), 8.06 (d, J = 8.6 Hz, 2H).
o-Cholrobenzoic acid.20 Colorless solid; Rf (50% EtOAc/
petroleum ether) 0.3; 1H NMR (CDCl3, 400 MHz) δ 7.35−7.38
(m, 1H), 7.46−7.52 (m, 2H), 8.03 (d, J = 8.7 Hz, 1H).
o-Nitrobenzoic Acid.9h Colorless solid; Rf (10% CH3OH/EtOAc)
1
0.31; H NMR (CDCl3, 400 MHz) δ 7.68−7.73 (m, 2H), 7.86−7.92
(m, 2H); 13C NMR (CDCl3, 125 MHz) δ 123.9, 125.9, 130.4, 132.58,
132.6, 148.9, 169.0.
o-Toluic Acid.9h Colorless solid; Rf (25% EtOAc/petroleum ether)
EXPERIMENTAL SECTION
■
1
0.5; H NMR (400 MHz, CDCl3) δ 2.66 (s, 3H), 7.26 (m, 2H), 7.45
Solvents were distilled prior to use, and double distilled water was used
for the reaction. All the reactions were carried out in an open
atmosphere without any precaution. The products were isolated by
column chromatography with a silica gel of 100−200 μm particle size.
NMR spectra were recorded with 400 and 500 MHz spectrometers. IR
spectra were recorded on an FT-IR spectrophotometer. Mass spectral
analyses were carried out with ESI-QTOF instrument.
(m, 1H), 8.06 (dd, J = 7.5 Hz, J1 = 1.8 Hz, 1H).
2-Methylphenylglyoxylic Acid. Colorless solid; Rf (10% CH3OH/
EtOAc) 0.3; mp 279−283 °C (decomp); IR (KBr) cm−1 3432, 2927,
1
1686, 1632; H NMR (DMSO-d6, 500 MHz) δ 2.48 (s, 3H), 7.22−
7.25 (m, 2H), 7.36−7.37 (m, 1H), 7.71−7.73 (m, 1H); 13C NMR
(DMSO-d6, 125 MHz) δ 21.2, 126.0, 131.8, 131.9, 132.0, 134.6, 138.9,
170.8, 199.8; ESI-MS− m/z calcd for C9H7O3 163.0395 [M − H+],
found 163.0395.
General Procedure for the Oxidative Cleavage of Olefins. To
a solution of the olefin (ca. 1.0 mmol) in 10−16 mL of acetonitrile−
water (1:1) mixture was added 10 mol % of TetMe-IA followed by
oxone (2−5 mmol) incrementally over the entire duration of the
reaction. Progress of the reaction in each case was monitored by TLC
analysis. After completion of the reaction as judged from TLC analysis,
the organic matter was extracted with ethyl acetate. The combined
2-Naphthoic Acid.21 Colorless solid; Rf (25% EtOAc/petroleum
ether) 0.5; 1H NMR (400 MHz, CDCl3) δ 7.57−7.63 (m, 2H), 7.92−
7.99 (m, 3H), 8.06 (dd, J = 7.5 Hz, J1 = 1.8 Hz, 1H), 8.73 (s, 1H).
o-Carboxycinnamic Acid.9f Colorless solid; Rf (10% MeOH/
EtOAc) 0.2;1H NMR (acetone-d6, 400 MHz), δ 6.39 (d, J = 15.9 Hz,
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Article
1H), 7.52 (t, J = 7.6 Hz, 1H), 7.62 (t, J = 7.3 Hz, 1H), 7.81 (d, J = 7.6
Hz, 1H), 8.01 (d, J = 7.8 Hz, 1H), 8.55 (d, J = 15.9 Hz, 1H).
6-Phenyl-6-oxohexanoic Acid.9h Colorless solid; Rf (75% EtOAc/
of the oxidations of p-bromostyrene, o-methylstyrene, 1-
(allyloxy)-4-methylbenzene, and (E)-3-(4-bromophenyl)allyl
acetate. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
petroleum ether) 0.4; H NMR (400 MHz, CDCl3) δ1.74−1.81 (m,
4H), 2.42 (t, J = 6.9 Hz, 2H), 3.01 (t, J = 6.9 Hz, 2H), 7.45 (d, J = 7.7
Hz, 1H), 7.54 (d, J = 7.4 Hz, 1H), 7.95 (d, J = 8.7 Hz, 2H).
(E)-4-(3-Methoxy-3-oxoprop-1-enyl)benzoic Acid.22 Colorless
AUTHOR INFORMATION
Corresponding Author
*E-mail: moorthy@iitk.ac.in.
■
1
solid; Rf (50% EtOAc/petroleum ether) 0.5; H NMR (CDCl3, 500
MHz) δ 3.83 (s, 3H), 6.55 (d, J = 16 Hz, 1H), 7.62 (d, J = 8 Hz, 2H),
7.72 (d, J = 16 Hz, 1H), 8.12 (d, J = 8 Hz, 2H).
Notes
(E)-4-(2-Carboxyethenyl)benzoic Acid.23 Colorless solid; Rf (20%
The authors declare no competing financial interest.
1
MeOH/EtOAc) 0.5; H NMR (DMSO-d6, 500 MHz) δ 6.64 (d, J =
16.05 Hz, 1H), 7.63 (d, J = 16.0 Hz, 1H), 7.8 (d, J = 8.3 Hz, 2H), 8.12
(d, J = 8.3 Hz, 2H).
ACKNOWLEDGMENTS
■
3,3-Dimethyl-5-oxohexanoic Acid.24 Colorless solid; Rf (50%
J.N.M. is thankful to the Council of Scientific and Industrial
Research (CSIR), India, for generous financial support. K.N.P.
gratefully acknowledges the senior research fellowship from
CSIR, New Delhi.
1
EtOAc/petroleum ether) 0.5; H NMR (400 MHz, CDCl3) δ 1.11
(s, 6H), 2.14 (s, 3H), 2.45 (s, 2H), 2.58 (s, 2H); 13C NMR (CDCl3,
125 MHz) δ 28.1, 30.0, 32.6, 44.4, 52.2, 177.2, 208.9.
1-(4-Bromophenyl)-2-phenylethane-1,2-dione.25 Yellow solid; Rf
1
(10% EtOAc/petroleum ether) 0.5; H NMR (400 MHz, CDCl3) δ
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■
7.52−7.54 (m, 2H), 7.65−7.7 (m, 3H), 7.84 (d, J = 8.7 Hz, 2H), 7.96
(d, J = 8.7 Hz, 2H).
Dodecanoic Acid.9h Colorless solid; Rf (50% EtOAc/petroleum
ether) 0.5; 1H NMR (400 MHz, DMSO-d6) δ 0.86 (t, J = 6.6 Hz, 3H),
1.2−1.31 (m, 16H), 1.58−1.66 (m, 2H), 2.33 (t, J = 7.5 Hz, 2H).
(E)-4-(2-Cyanoethenyl)benzoic Acid.26 Colorless solid; Rf (50%
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EtOAc/petroleum ether) 0.4; H NMR (DMSO-d6, 500 MHz) δ 6.6
(d, J = 16.6 Hz, 1H), 7.71−7.77 (m, 3H), 7.97 (d, J = 8.6 Hz, 2H).
p-(Methoxycarbonyl)benzoic Acid.27 Colorless solid; Rf (50%
EtOAc/petroleum ether) 0.4; 1H NMR (DMSO-d6, 500 MHz) δ 3.88
(s, 4H), 8.06 (s, 4H).
Dodecanedioic Acid.28 Colorless solid; Rf (10% MeOH/EtOAc)
1
0.4; H NMR (DMSO-d6, 400 MHz) δ 1.21−1.24 (m, 12H), 1.46−
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4-(2-(4-Bromophenyl)-2-oxoacetyl)benzoic Acid. Yellow solid; Rf
(20% MeOH/EtOAc) 0.4; mp >300 °C; IR (KBr) cm−1 1688, 1665;
1H NMR (DMSO-d6, 500 MHz) δ 7.86−7.89 (m, 4H), 8.05 (d, J =
8.05, 2H), 8.13 (d, J = 8.05, 2H); 13C NMR (DMSO-d6, 125 MHz) δ
129.9, 130.53, 130.59, 131.6, 132.1, 133.1, 135.5, 136.85, 166.8, 193.4,
193.8; ESI-MS− m/z calcd for C15H8O4Br 330.9605 [M − H+], found
330.9605.
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1-(4-Bromophenyl)-2-hydroxyethanone.29 Colorless solid; Rf
1
(20% EtOAc/petroleum ether) 0.5; H NMR (400 MHz, CDCl3) δ
4.84 (s, 2H), 7.66 (d, J = 8.7, 2H), 7.78 (d, J = 8.7, 2H).
1-(4-Nitrophenyl)-2-phenylethane-1,2-dione.30 Yellow solid; Rf
(10% EtOAc/petroleum ether) 0.5; 1H NMR (CDCl3, 400 MHz)
7.55 (t, J = 7.8 Hz, 2 H), 7.71 (t, J = 7.3 Hz, 1 H), 7.90 (m, 2 H), 8.17
(m, 2 H), 8.36 (m, 2 H).
(E)-4-[2-(4-Bromophenyl)ethenyl]benzoic Acid.31 Colorless solid;
Rf (25% EtOAc/petroleum ether) 0.5; 1H NMR (CDCl3, 500 MHz) δ
6.64−6.65 (m, 2H), 7.08 (d, J = 8.5 Hz, 2H), 7.31(d, J = 8.5 Hz, 1H),
7.36 (d, J = 8.5 Hz, 2H), 7.97 (d, J = 8.5 Hz, 2H).
2-Oxo-2H-chromene-6-carboxylic Acid. Colorless solid; Rf (50%
EtOAc/petroleum ether) 0.5; mp 251−254 °C, IR (KBr) cm−1 3096,
2929, 1750, 1682, 1622; 1H NMR (DMSO-d6, 500 MHz) δ 6.58 (d, J
= 12.0 Hz, 1H), 7.48 (d, J = 10.8 Hz, 1H), 8.10−8.13 (m, 1H), 8.19
(d, J = 12.0 Hz, 1H), 0.8.35 (d, J = 2.6 Hz, 1H); 13C NMR (DMSO-d6,
125 MHz) δ 117.3, 117.4, 119.2, 127.5, 130.7, 133.0, 144.6, 156.7,
160.0, 166.7; ESI-MS− m/z calcd for C10H5O4 189.0187 [M − H+],
found 189.0181.
4-(2-Phenyl-2-oxoacetyl)benzoic Acid.30 Yellow solid; Rf (10%
1
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8.3 Hz, 2H), 8.14 (d, J = 8.3 Hz, 2H).
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ASSOCIATED CONTENT
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S
* Supporting Information
1H and 13C NMR spectral reproductions for the products of
oxidations and 1H NMR spectral reproductions for monitoring
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Article
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