Oxidative Cycloaddition of Aldoximes with Maleimides using Catalytic Hydroxy(aryl)iodonium Species

Article abstract of DOI:10.1002/adsc.201600331

A mild catalytic procedure for the efficient oxidative cyclization of aldoximes with maleimides mediated by hypervalent iodine(III) active species has been developed. This catalytic cyclization affords the corresponding pyrrolo-isoxazole products in generally good yields. The catalytic cycle involves active hydroxy(aryl)iodonium species generated in situ from 2-iodobenzoic acid as precatalyst and m-chloroperoxybenzoic acid (m-CPBA) as terminal oxidant in the presence of trifluoromethanesulfonic acid. The presence of active hydroxy(aryl)iodonium species in this reaction has been confirmed by ESI-mass spectrometry and¹H NMR spectroscopy. (Figure presented.) .

Full text of DOI:10.1002/adsc.201600331

UPDATES
DOI: 10.1002/adsc.201600331
Oxidative Cycloaddition of Aldoximes with Maleimides using
Catalytic Hydroxy(aryl)iodonium Species
a,
a
a
b
Akira Yoshimura, * Khiem C. Nguyen, Gregory T. Rohde, Akio Saito,
c
a,
Mekhman S. Yusubov, and Viktor V. Zhdankin *
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA
a
Fax : (+1)-218-726-7394; e-mail: ayoshimu@d.umn.edu or vzhdanki@d.umn.edu
b
Division of Applied Chemistry, Institute of Engineering Tokyo University of Agriculture and Technology, Koganei, Tokyo
84-8588, Japan
The Tomsk Polytechnic University, 634050 Tomsk, Russia
1
c
Received: March 25, 2016; Revised: April 19, 2016; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600331.
Abstract: A mild catalytic procedure for the effi-
cient oxidative cyclization of aldoximes with male-
ACHTUNGTRENNUNGi mides mediated by hypervalent iodine(III) active
a later work, Yan and co-workers have reported the
catalytic hypervalent iodine(III)-mediated cyclization
of aldoximes with alkenes or alkynes under similar
[
7b,c]
species has been developed. This catalytic cycliza-
tion affords the corresponding pyrrolo-isoxazole
products in generally good yields. The catalytic
cycle involves active hydroxy(aryl)iodonium species
generated in situ from 2-iodobenzoic acid as preca-
talyst and m-chloroperoxybenzoic acid (m-CPBA)
as terminal oxidant in the presence of trifluorome-
thanesulfonic acid. The presence of active hydroxy-
conditions.
We have recently reported a novel hy-
pervalent iodine reagent, IBA-OTf, which was pre-
pared from 2-iodosylbenzoic acid and trifluorometh-
AHCTUNGTRENNUNG
[
8]
with nitriles. However, to the best of our knowledge,
the cyclization reaction of aldoximes with maleimides
using hypervalent iodine(III) compounds has not
been previously reported.
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(aryl)iodonium species in this reaction has been
1
confirmed by ESI-mass spectrometry and H NMR
Herein, we report the first catalytic hypervalent io-
dine(III)-mediated oxidative cyclization reaction of
aldoximes with maleimides using hydroxy(aryl)iodoni-
um active species generated in situ from 2-iodobenzo-
ic acid and m-CPBA in the presence of trifluorome-
thanesulfonic acid. The products of this reaction, bicy-
clic pyrrolo-isoxazoles, belong to an important struc-
tural class, which is commonly found in bioactive
spectroscopy.
Keywords: cyclization; heterocycles; iodine; iodoni-
um species; oxidation; pyrrolo-isoxazoles
[
1b,9]
compounds and natural products.
Several research
The oxidative cyclization of aldoximes and alkenes or groups have previously reported the synthesis of pyr-
alkynes is an important chemical transformation lead- rolo-isoxazoles from aldoximes and maleimides in
[10]
ing to heterocyclic compounds with oxygen and nitro- two steps using various chlorinating reagents, such
[
10a,b]
[10c–e]
gen in the ring, which are commonly found in biologi- as chloramine-T,
N-chlorosuccinimide (NCS),
[
10f]
cally active compounds, medicinal synthons and natu- N-tert-butyl-N-chlorocyanamide,
ral products. Among the known procedures for the chlorite (NaOCl).
and sodium hypo-
Minakata and co-workers have
[1]
[10g–i]
oxidative cyclization of aldoximes with alkenes or al- reported a procedure for the preparation of pyrrolo-
kynes, particularly important are the procedures uti- isoxazoles from aldoximes with N-phenylmaleimide
lizing stoichiometric amounts of organohypervalent using the stoichiometric hypoiodite species generated
[
2–7]
[11]
iodine(III) reagents,
such as (diacetoxyiodo)ben- in situ from the NaI-t-BuOCl combination.
[3]
[4]
zene,[ iodosylbenzene, [hydroxy(tosyloxy)]iodoben-
In the initial experiments, we investigated the oxi-
5]
[6]
zene, and [bis(trifluoroacetoxy)iodo]benzene. Pre- dative cyclization of aldoximes with maleimides using
viously, our group has first found that catalytic hyper- stoichiometric amounts of a hypervalent iodine(III)
valent iodine(III) species, generated in situ from io- reagent (IBA-TfOH 3). We have found that the reac-
doarenes and Oxone, could promote the oxidative tion of benzaldoxime 1a (1 equiv.), maleimide 2a (1.5
[
7a]
cyclization of aldoximes with alkenes or alkynes. In to 5 equiv.), and reagent 3 (1.2 equiv.) in dichlorome-
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Table 1. Optimization of the catalytic cyclization of benzal-
[a]
doxime 1a with maleimide 2.
Scheme 1. Oxidative cyclization of benzaldoxime and malei-
mide using IBA-TfOH.
thane at room temperature afforded pyrrolo-isoxazole
4
a in moderate to high yields (Scheme 1). Motivated
by these results, we then attempted to develop a cata-
lytic cyclization reaction of aldoximes with male- Entry
Solvent
CH Cl
Aryl iodide
5 (equiv.)
TfOH
(equiv.)
4a
[%]
[
b]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
imides using in situ generated hypervalent iodine(III)
species. In a search for optimized catalytic conditions,
we investigated reactions of benzaldoxime 1a
[c]
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
none
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
0.6
none
1.2
1.2
none
100 (85)
75
100
2
2
2
2
2
2
2
2
2
CH Cl
5a (0.1)
5b (0.1)
5c (0.1)
5d (0.1)
5e (0.1)
5f (0.1)
5g (0.1)
5a (0.1)
5a (0.1)
5a (0.1)
5a (0.1)
5a (0.1)
5a (0.05)
5a (0.1)
5a (0.1)
5a (0.1)
5a (0.1)
2
(
(
1 equiv.) and maleimide 2 (5 equiv.) with m-CPBA
1.5 equiv.) as a terminal oxidant in the presence of
[c]
CH Cl
2
CH Cl
2
[
c]
c]
c]
c]
trifluoromethanesulfonic acid (TfOH) using catalytic
amounts of different aromatic iodides 5 as precata-
lysts in various solvents (Table 1; for additional details
see Table S1 in the Supporting Information). In the
absence of aryl iodide, the formation of pyrrolo-isoxa-
zole 4a was not observed (Table 1, entry 1). Screening
of various aryl iodides has indicated that 2-iodobenzo-
ic acid 5a and 2-iodo-5-methylbenzoic acid 5c are the
most effective precatalysts in this catalytic reaction
CH Cl
78[
2
CH Cl
85
2
[
CH
CH Cl
Cl
2
95[
95
2
(CH Cl)
96 (82)
2
2
[c]
0
1
2
3
4
5
heptane
methanol
CHCl3
66
[c,d]
–
[c]
95
95
86
93
72
90
71
[c]
[c]
[c]
EtOAc
CH Cl
2
2
2
2
2
2
(
entries 2–8). Since 2-iodobenzoic acid 5a is a readily
CH Cl
2
available commercial product, we decided to use it as 16[
CH Cl
2
e]
[c]
[c]
a precatalyst in our following studies. Out of several 17
CH Cl
2
[
e,f]
solvents tested, dichloromethane was found to be the 18
CH Cl
2
best solvent in this reaction (entries 3, 9–13). Decreas-
ing the amount of 2-iodobenzoic acid 5a from 10 to
[a]
Reaction conditions: benzaldoxime 1a (1 equiv.), male-
imide 2a (5 equiv.), m-CPBA (1.5 equiv.), aryl iodide 5
0–0.1 equiv.) and TfOH (0–1.2 equiv.) in various solvent
at room temperature for 24 h.
Yields of product 4a determined from H NMR spectra
of reaction mixtures are shown (numbers in parentheses
show isolated yields of 4a).
Benzaldoxime 1a was recovered from the reaction mix-
ture.
Trace amount of product 4a was detected, but the yield
could not be calculated.
At 408C.
After 4 h.
AHCTUNGTRENNUNG
5
mol% leads to decreased yields of the product 4a
(
(
entry 14). In the presence of catalytic amounts of
[b]
1
TfOH or in the absence of TfOH, the product yield
was also lower (entries 15 and 16). Warming the reac-
tion mixture to 408C and shortening the reaction time
to 4 h did not improve the yields (entries 17 and 18).
Using the optimized reaction conditions and 2-io-
dobenzoic acid 5a as the precatalyst, we have investi-
gated the conversion of various substituted aldoximes
[
[
c]
d]
[e]
[f]
1
(
to the respective pyrrolo-isoxazole derivatives
Table 2). In general, the reactions of substituted aro-
matic aldoximes 1 with electron-withdrawing or elec-
tron-donating substituents in the aromatic ring and tive gave product 4b only in a moderate yield, proba-
maleimide 2a gave the corresponding products 4a–j in bly, due to a partial oxidation of the methyl group, or
good yields. In the reaction of sterically hindered the oxidation of the electron-rich aromatic ring
ortho-substituted aldoximes with maleimide, the re- during the reaction. The reaction of an aliphatic ald-
spective products 4e and 4f were also obtained in
ACHTUNGTRENNUoGN xime with maleimide afforded the respective product
good yields. However, the reaction of the tolyl deriva- 4k only in a relatively low yield. Under similar condi-
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[a]
Table 2. Catalytic hypervalent iodine-mediated oxidative cyclization of aldoximes 1 and maleimides 2.
[
a]
Reaction conditions: benzaldoxime 1 (1 equiv.), maleimide 2 (5 equiv.), m-CPBA (1.5 equiv.), 2-iodobenzoic acid 5a
0.1 equiv.) and TfOH (1.2 equiv.) in dichloromethane at room temperature for 24 h. Isolated yields are shown in paren-
theses.
(
tions, the reaction of cinnamaldehyde oxime produced Information). The presence of stoichiometric TfOH is
product 4l in 70% yield. The reaction of benzaldox- essential in this reaction; the special blank experi-
ime 1a with N-methylmaleimide 2b under these cata- ments have demonstrated that in the absence of
lytic conditions also gave the corresponding N-substi- TfOH 2-iodobenzoic acid 5a reacts with m-CPBA to
tuted pyrrolo-isoxazole 4m in good yield. Compared produce 2-iodosylbenzoic acid (IBA), which is then
to the previously reported procedure of oxidative cy- converted to IBA-OTf 3 by subsequent reaction with
cloaddition of aldoximes and N-phenyl-substituted TfOH. Furthermore, the reaction of benzaldoxime 1a
maleimides using stoichiometric t-BuOI generated and maleimide 2a with stoichiometric hydroxy(aryl)-
[
8]
from the NaI-t-BuOCl combination, our catalytic pro-
ACHTUNGTRENNGNUi odonium triflate (IBA-OTf ) 3 afforded product 4a
cedure gives comparable or higher yields of pyrrolo- in high yield (Scheme 1). As expected, the reaction of
[11]
isoxazoles.
Moreover, our procedure allows us to maleimide 2a with the protected benzaldoxime, O-
synthesize the parent N-unsubstituted products (4a– methylbenzaldoxime, under optimized conditions
4
l), which cannot be obtained by using stochiometric failed to produce product 4a. This result indicates that
[11]
t-BuOI as the oxidant.
The structure of one of the ligand exchange between the aldoxime and the
these products, pyrrolo-isoxazole 4c, was character- hydroxyl group of the activated hypervalent io-
ized by X-ray crystallography (see the Supporting In-
formation for details).
ACHTUNGTRENNUNG
In order to clarify the mechanism of this catalytic mide 2a under the same conditions, only a trace
reaction, we have performed several control experi- amount of product 4 was detected, and the starting
ments (see the Supporting Information for details). material, acetophenone oxime, could be recovered
Most likely, this reaction involves the hydroxy(aryl)io- from the reaction mixture. This result suggests that
donium species as active species generated from 2-io- the oxidation step of aldoxime to nitrile oxide using
dobenzoic acid 5a and m-CPBA in the presence of activated ioACHTUNGTRENNUNG
[
3–7]
TfOH. We were able to confirm the presence of hy- tion.
droxy(aryl)iodonium species in the reaction mixture
1
by ESI-mass spectrometry and H NMR spectroscopy previously reported reactions of aldoximes using stoi-
(
see the spectra in Sections 4 and 5 of the Supporting chiometric iodine(III) reagents, we propose a catalytic
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aqueous Na S O (5 mL) and then saturated NaHCO3
2
2
3
(
5 mL) were added, and the mixture was extracted with
ethyl acetate. The organic phase was dried over anhydrous
Na SO and concentrated under reduced pressure. Purifica-
2
4
tion by column chromatography (hexane-ethyl acetate=3:1
to 1:1) afforded analytically pure pyrrolo-isoxazole 4.
CCDC 1470155 contains the supplementary crystallo-
graphic data for this paper (compound 4c). These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
Acknowledgements
This work was supported by research grants from the Nation-
al Science Foundation (CHE-1262479), Russian Science
Foundation (RSF-16-13-10081), and by the Asahi Glass
Foundation.
References
Scheme 2. Proposed mechanism for the oxidative cyclization
of aldoxime and maleimide.
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Experimental Section
Typical Procedure
2-Iodobenzoic acid 5a (6.2 mg, 0.025 mmol), maleimide 2a
(
121 mg, 1.25 mmol), mCPBA (65 mg, 0.375 mmol), and tri-
fluoromethanesulfonic acid (45 mg, 0.300 mmol) were added
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UPDATES
6
Oxidative Cycloaddition of Aldoximes with Maleimides
using Catalytic Hydroxy(aryl)iodonium Species
Adv. Synth. Catal. 2016, 358, 1 – 6
Akira Yoshimura,* Khiem C. Nguyen, Gregory T. Rohde,
Akio Saito, Mekhman S. Yusubov, Viktor V. Zhdankin*
Adv. Synth. Catal. 0000, 000, 0 – 0
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÞÞ
These are not the final page numbers!