Lodomesitylene-catalyzed oxidative cleavage of carbon-carbon double and triple bonds using m-chloroperbenzoic acid as a terminal oxidant

Full text of DOI:10.1021/ja808829t

Published on Web 01/09/2009
Iodomesitylene-Catalyzed Oxidative Cleavage of Carbon-Carbon Double and
Triple Bonds Using m-Chloroperbenzoic Acid as a Terminal Oxidant
Kazunori Miyamoto,† Yoshihisa Sei,‡ Kentaro Yamaguchi,‡ and Masahito Ochiai*,†
Graduate School of Pharmaceutical Sciences, UniVersity of Tokushima, 1-78 Shomachi, Tokushima 770-8505,
Japan, and Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri UniVersity, 1314-1 Shido,
Sanuki, Kagawa, 769-2193, Japan
Received November 11, 2008; E-mail: mochiai@ph.tokushima-u.ac.jp
Transition metal-catalyzed oxidative cleavage of carbon-carbon
multiple bonds has emerged as a powerful tool in organic synthesis.1
High-valent oxometals, mostly of Ru, Os, Mn, Mo, W, and Re, were
used catalytically as reactive oxygen transfer agents to the multiple
bonds.2 We report herein for the first time the organocatalytic version
of the oxidative cleavage reactions. Our method involves use of
iodomesitylene as an effective organocatalyst, which generates an
active aryl(hydroxy)-λ3-iodane 5 in situ, and m-chloroperbenzoic acid
(m-CPBA) as a terminal oxidant under metal-free conditions.3
Recently, we developed an aryl-λ3-iodane-based method for C-C
double bond cleavage, yielding carbonyl compounds, in which a
combination of stoichiometric iodosylbenzene and HBF4 in the
presence of water generates an activated iodosylbenzene monomer as
an ozone equivalent and serves as a safety alternative to ozonolysis,
because of the environmentally friendly nature of aryl-λ3-iodanes.4,5
The method involves syn vicinal dihydroxylation of olefins through
an initial electrophilic anti addition of aryl-λ3-iodanes, followed by a
nucleophilic displacement of the hyper-leaving λ3-iodanyl group by
water with inversion of configuration (Scheme 1).6,7 Subsequent
oxidative glycol fission by λ3-iodanes, probably via the intervention
of cyclic dialkoxy-λ3-iodanes, affords carbonyl compounds.
11, and 12). It is noted that pentamethyl- and p-methoxyiodobenzenes
gave significant amounts of tarry matter, while sterically demanding
2,4,6-tri-tert-butyliodobenzene showed high catalytic efficiency for the
oxidative cleavage.
Table 1. Iodoarene-Catalyzed Oxidative Cleavage of Olefin 1a
yield (%)b
entry
ArI
(equiv) m-CPBA (equiv) time (h)
2
3
1
2
3
4
5
6
7
8
9
-
2.2
2.2
2.2
2.2
3.1
3.1
3.1
3.1
3.1
3.1
3.1
3.1
3.1
3.1
2.5
2
2.5
2.5
5
-
-
PhI
PhI
PhI
PhI
PhI
PhI
(2.2)
(0.3)
(0.1)
(0.1)
(0.05)
(0.01)
(0.01)
(0.01)
(0.01)
(0.01)
(0.01)
72
5
57 29
36 36
-
-
-
-
-
-
-
-
-
-
91 (88)
93 (85)
86 (75)c
18 (23)c
91 (85)c
83 (81)c
94 (83)c
96 (88)c
35 (36)c
93 (89)c
7
24
4-MeOC6H4I
4-MeC6H4I
24
24
30
22
14
48
24
10 4-ClC6H4I
11 3,5-Me2C6H3I
12 2,4,6-Me3C6H2I
13 2,3,4,5,6-Me5C6I (0.01)
14 2,4,6-tBu3C6H2I (0.01)
Scheme 1
a Conditions: 1/ArI/m-CPBA/48% aq HBF4 (2.2 equiv)/CH2Cl2-
b
HFIP-H2O 9:3:1/room temperature/N2. 1H NMR yields. Parentheses
are isolated yields after methylation with TMSCHN2. c Yields of 4:
5-6% (entries 7-10, 13, and 14), 3% (entry 11), and <1% (entry 12).
Exposure of phenylcyclohexene 1 to iodobenzene (1 mol %),
m-CPBA (3.1 equiv), and aqueous HBF4 (2.2 equiv) in CH2Cl2-
hexafluoroisopropanol (HFIP)-H2O (9:3:1) at room temperature re-
sulted in a facile cleavage of the double bond to afford ꢀ-keto acid 3
in a high yield, being isolated as a methyl ester (75%) after treatment
with TMSCHN2 (Table 1, entry 7). Adipic acid monophenyl ester (4)
(5%)wasobtainedasabyproduct,probablyproducedviaBaeyer-Villiger
oxidation of 3 with m-CPBA. Increase in the catalyst loading to 5
mol % inhibited the byproduct formation, with an increased yield of
3 (93%) (entry 6). The reaction provided no evidence for the double
bond cleavage without the organocatalyst (entry 1). Separate experi-
ments indicate that most of the keto acid 3 obtained is formed via
oxidation of the initially formed keto aldehyde 2 by m-CPBA under
the acidic conditions (Supporting Information, Scheme S1).
After extensive studies on the reactions, we finally found that
iodomesitylene serves as the most efficient organocatalyst and the 1
mol % catalyst afforded an 96% yield of the acid 3 with only trace
amount of the byproduct 4 (entry 12). Introduction of methyl groups
on iodobenzene catalyst seems to enhance the rates of oxidation to
reactive aryl-λ3-iodanes, which, in turn, suppresses the unfavorable
Baeyer-Villiger oxidation of 3 by m-CPBA (compare entries 7, 9,
Table 2 demonstrates that cyclopentenes and cyclohexenes with
alkyl or aryl substituents on the double bond are catalytically cleaved
smoothly in good to high yields with iodomesitylene (1 mol %)/
CH2Cl2-HFIP-H2O/room temperature (method A), while unsubsti-
tuted five- to seven-membered cycloalkenes afforded only moderate
yields of diesters. Oxidative scission of 1-decene is sluggish under
the conditions, affording a low yield of methyl nonanoate (19%) even
after 48 h and formation of a large amount of decane-1,2-diol (54%)
was detected (Table 2, entry 13). Changing the solvent to MeCN-
H2O (9:1), heating at 50 °C, and use of 10 mol % of iodomesitylene
(method B) improved the efficiency of the reaction and afforded the
ester in 67% yield. Method B resulted in an efficient cleavage of E-
and Z-disubstituted as well as trisubstituted olefins (entries 14-17).
Reactive tetrasubstituted olefin 2,3-dimethyl-2-butene afforded 69%
yield of acetone using 1 mol % of iodomesitylene (method A). Our
cleavage reaction tolerates various kinds of functionalities such as
carboxylic acid, hydroxy group, amide, and sulfonamide. 11-Tetrade-
cenyl acetate undergoes both deprotection of the acetoxy group and
the double bond cleavage at once (entry 21).
It is noted that both aliphatic and aromatic alkynes were smoothly
cleaved to carboxylic acids under our organocatalytic conditions
(method B), without no evidence for formation of R-dicarbonyl
† University of Tokushima.
‡ Tokushima Bunri University.
9
1382 J. AM. CHEM. SOC. 2009, 131, 1382–1383
10.1021/ja808829t CCC: $40.75
2009 American Chemical Society

C O M M U N I C A T I O N S
Table 2. Iodomesitylene-Catalyzed Oxidative Cleavage of Olefins
rapid disappearance of the olefin within 10 min, with the formation of
a large amount of decane-1,2-diol. The subsequent gradual decrease
of the diol was accompanied by the formation of nonanoic acid.
Interestingly, the organocatalyst was found to be rapidly oxidized to
the iodane 5 by m-CPBA. These results indicate that a slow step in
the catalytic cycle for the cleavage of 1-decene is probably an oxidative
scission of the 1,2-diol derived from the olefin. Furthermore, kinetic
measurements for the cleavage of trans-1,2-cyclohexanediol with the
hydroxyiodane 8 suggested a rapid pre-equilibrium formation of a
cyclic dialkoxy-λ3-iodane such as 7, followed by its rate-limiting
decomposition to dialdehyde (Figure S4).
Scheme 2
In summary, we have developed an efficient method for organo-
catalytic oxidative cleavage of carbon-carbon multiple bonds as an
environmentally friendly, safe alternative to ozonolysis.
Supporting Information Available: Experimental details, Schemes
S1 and S2, and Figures S1-S4. This material is available free of charge
via the Internet at http://pubs.acs.org.
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a Method A: iodomesitylene (1 mol %)/m-CPBA/48% aq HBF4 (2.2
equiv)/CH2Cl2-HFIP-H2O 9:3:1/room temperature/N2. Method B:
iodomesitylene (10 mol %)/m-CPBA/48% aq HBF4 (2.2 equiv)/
c
MeCN-H2O 9:1/50 °C/N2. b m-CPBA. 1H NMR yields. Parentheses are
isolated yields of diketones or methyl esters obtained after methylation
with TMSCHN2. For structures of products, see Scheme S2.
d Iodomesitylene (10 mol %). e E:Z ) 3:7. f GC yields. g E:Z ) 72:28.
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afforded high yields of nonanoic acid and formic acid (entry 24 and
Figure S1).
Scheme 2 depicts a catalytic cycle for the olefin cleavage, which
involves in situ generation of tetracoordinated squareplanar hydroxy-
λ3-iodane 5 as a reactive species.4,9 The iodane 5 undergoes oxidative
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6] 8 and trans-1,2-cyclohexanediol in dichloromethane detected a peak
assignable to the corresponding cyclic dialkoxy-λ3-iodane ·18-crown-6
complex (Figure S2). Time course for the catalytic cleavage of
1-decene under the conditions of method B (Figure S3) revealed a
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