Peroxidation of 3,4-dihydro-1,4-benzoxazin-2-ones

Article abstract of DOI:10.1039/c9cc09778c

The sp³-C-H peroxidation of 3,4-dihydro-1,4-benzoxazin-2-ones was achieved under mild and simple catalyst-free reaction conditions. A range of biologically important alkylated benzoxazinone peroxides are synthesized in high yield with a good functional group tolerance. The C(sp³)-OO bond was constructed efficiently and could be further converted into C(sp³)-C(sp³), C(sp³)-C(sp²), C(sp³)-C(sp), C-P and CO bonds by late-stage functional group transformations.

Full text of DOI:10.1039/c9cc09778c

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DOI: 10.1039/C9CC09778C
COMMUNICATION
Peroxidation of 3,4-Dihydro-1,4-benzoxazin-2-ones
a
a
a
a
Jie Wang, Xiazhen Bao, Jiayuan Wang and Congde Huo*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
3
6
The sp -C-H peroxidation of 3,4-dihydro-1,4-benzoxazin-2-ones was compounds and pharmaceuticals. As an important albumen in
achieved under mild and simple catalyst-free reaction conditions. A benzoxazinone family, the preparation methodology of 3,4-
range of biologically important alkylated benzoxazinone peroxides dihydro-1,4-benzoxazin-2-one derivatives is relatively rare.
are synthesized in high yield with a good functional group Actually, in 2008, the simple 3-position unsubstituted 3,4-
3
tolerance. C(sp )-OO bond was constructed efficiently and could be dihydro-1,4-benzoxazin-2-ones was first synthesized by Kikelj et
further converted into C(sp )-C(sp ), C(sp )-C(sp ), C(sp )-C(sp), C-P al. Direct functionalization of the sp -C-H bond, which refers to
3
3
3
2
3
7
3
and C=O bond by late stage functional group transformations.
substitution of an existing hydrogen atom with a carbon or
hetero atom group, has attracted much attention recently. On
this basis, C-H functionalization of 3-unsubstituted 3,4-dihydro-
Peroxides are wildly existed structure motifs in natural products
1
and pharmaceutical agents. Natural products with peroxide
1
,4-benzoxazin-2-ones is a significant and meaningful research
units have caused widespread concerns due to their distinct
chemical and biological properties. And peroxide bond (C-OO)
has been regarded as a key pharmacophore in medicinal
chemistry in the past decades. For example, Artemisinin
field to provide complex and biologically active benzoxazinone
derivatives. In 2016, our group for the first time developed an
3
2
efficient oxidative C(sp )–C(sp ) bond formation method to
8a
deliver 3-arylated 3,4-dihydro-1,4-benzoxazin-2-ones.
In
(qinghaosu), isolated from a herb (sweet wormwood) employed
2
017, we described an iron-catalyzed oxidative
in Chinese traditional medicine, has been approved for the
dehydrogenative coupling reaction of 3,4-dihydro-1,4-
benzoxazin-2-ones with malonic esters or ketones to construct
2
treatment of P. falciparum malaria. Another example is
Peroxyferolide, isolated from the leaves of L. tulipifera, which
3
3
8b
C(sp )–C(sp ) bonds. In 2018, we also contribute a copper
catalyzed oxidative phosphonation of 3,4-dihydro-1,4-
3
shows antitumor activities. Peroxides can also be applied as
initiators for radical reactions, as synthetic intermediates in
8c
benzoxazin-2-ones through an oxidative Pudovik reaction.
4
organic synthesis and as energetic materials. For examples,
Although we have developed a few practical methods to
construct new C-C and C-P bond to deliever 3-substituted 3,4-
dihydro-1,4-benzoxazin-2-one derivatives through the oxidative
dehydrogenative coupling strategy, we are still seeking a more
general method for the C-H functionalizations of 3,4-dihydro-
peroxides can be readily transformed to ketone, alcohol, and
epoxy compounds. Therefore, the development of new
methods for the synthesis of organic peroxides has been
stimulated due to their great potential as drug candidates and
useful synthetic units, preferably from readily available starting
1
,4-benzoxazin-2-ones. Encouraged by the importance of
5
materials. However, the synthesis, isolation, and storage of the
peroxide and benzoxazinone moieties, we became interested in
preparing molecules containing both groups. And also, the
oxygenation of C-H bonds adjacent to nitrogen of amines is one
of the most attractive strategies for the synthesis of biologically
organic compounds with peroxide group always have some
difficulties due to the weak oxygen−oxygen bonds.
1
,4-Benzoxazinone motif constitutes privileged structure unit
that can be constantly found in bio-active molecules. They are
also useful building blocks in the synthesis of complex organic
9
active nitrogen compounds. Herein, as a part of our research
on atom-economical synthetic methodology, we reported an
efficient peroxidation of 3,4-dihydro-1,4-benzoxazin-2-ones
with TBHP enabled by a radical process. A range of 3-peroxide
substituted 3,4-dihydro-1,4-benzoxazin-2-ones were obtained
under extremely simple catalyst-free reaction conditions. To
highlight the synthetic application, various late stage functional
a. Gansu International Scientific and Technological Cooperation Base of Water-
Retention Chemical Functional Materials; College of Chemistry and Chemical
Engineering, Northwest Normal University, Lanzhou, Gansu 730070, China. E-mail:
huocongde1978@hotmail.com
Electronic Supplementary Information (ESI) available: [Experimental procedures
and characterization data]. See DOI: 10.1039/x0xx00000x
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COMMUNICATION
Journal Name
group transformations of benzoxazinone peroxide derivatives
were developed.
Scheme 2. Peroxidation of 3,4-Dihydro-1,4-benzoxazin-2-onesa,b View Article Online
DOI: 10.1039/C9CC09778C
R2
2
R
N
N
DC
E,
OOR3
3
R1
+
R OOH
R1
Scheme 1. Screening of Reaction Conditions
O
O
Ar,
70o
O
O
1
2
3
Bn
N
Bn
N
C
t
a,b
OO Bu
conditions
tBuOOHc
+
N
O
OOCMe3
O
N
OOCMe2Ph
O
N
OOtBu
O
N
OOtBu
O
O
O
O
O
1a
2a
3aa
O
O
O
3
aa (84%)
3ab (81%)
3ba (89%)
3ca (75%)
Entry
Solvent
Temp
Atmosphere
yield
o
o
o
o
o
o
o
o
o
o
o
o
o
1
2d
DCE
DCE
70
70
70
70
70
70
70
70
70
60
80
70
70
C
C
C
C
C
C
C
C
C
C
C
C
C
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
air
O2
84%
73%
72%
57%
45%
21%
-
t
t
t
t
N
O
OO Bu
N
OO Bu
N
OO Bu
N
O
OO Bu
3
CHCl3
MeCN
EtOAc
EtOH
THF
4
O
O
O
O
O
O
3da (80%)
3ea (87%)
3fa (84%)
3ga (68%)
5
6
O
7
O
O
O
8
DMF
-
9
toluene
DCE
-
t
t
t
t
N
O
OO Bu
N
OO Bu
N
OO Bu
N
O
OO Bu
10
11
12
13
70%
65%
68%
62%
O
O
O
O
O
O
DCE
3
ha (82%)
3ia (85%)
3ja (78%)
3ka (81%)
DCE
DCE
F3CO
O
F
a
b
Reaction Conditions: 1a (0.2 mmol), 2a (0.4 mmol), solvent (2 mL), 8 h. Isolated
t
N
O
OO Bu
t
t
t
N
O
OO Bu
N
OO Bu
N
O
OO Bu
c
d
yields. 5-6 M in decane. 70% in Water.
O
O
O
O
O
3la (68%)
3ma (67%)
3na (88%)
3oa (84%)
The study was initiated by investigating the reaction of 3,4-
dihydro-1,4-benzoxazin-2-one 1a with TBHP 2a in DCE under
argon atmosphere without any catalyst. To our delight, as
shown in Scheme 1, when the mixture was heated at 70 °C for
Cl
Br
I
OOtBu
O
OOtBu
N
OOtBu
O
OOtBu
O
N
O
N
O
N
O
8
(
h, the desired product 3aa was isolated in excellent yield
Scheme 1, entry 1). The use of water solution of TBHP, instead
of TBHP in decane, was found to be less effective (Scheme 1,
entry 2). The use of other solvents such as CHCl (72%), MeCN
57%), EtOAc (45%) and EtOH (21%) was found to be less
O
O
3
pa (88%)
3qa (80%)
3ra (75%)
3sa (81%)
3
(
t
N
OO Bu
t
N
OOtBu
O
t
N
O
OO Bu
N
OO Bu
productive then DCE (84%) (Scheme 1, entries 3-6). And THF,
O
O
O
O
N
H
O
DMF and toluene were inactive for this transformation (Scheme
3ta (80%)
3
ua (85%)
3va (69%)
3
wa (78%)
o
1
, entries 7-9). Varying of temperature suggested that 70 C was
the best choice for the reaction (Scheme 1, entries 10-11).
Changing the argon atmosphere to O or air atmosphere
F
2
t
t
F
N
OOtBu
O
Cl
N
OOtBu
O
N
OO Bu
N
OO Bu
resulted in lower efficiency (Scheme 1, entries 12-13). Thus, it
was determined that using DCE as solvent at 70 °C under argon
atmosphere were the optimal reaction conditions (84%).
With the optimized reaction conditions established in hand, we
than examined the application of this peroxidation method by
using various substrates. Firstly, beside TBHP, hydroperoxide
N
H
O
N
H
O
N
H
N
H
3
xa (80%)
3ya (82%)
3za (70%)
3z'a (76%)
a
o
b
Reaction Conditions: 1 (0.2 mmol), 2 (0.4 mmol), DCE (2 mL), 70 C, Ar, 3 h-8 h.
Isolated yields.
2
PhMe C-OOH was also suitable substrate for this C-OO bond To highlight the synthetic application, late stage functional
formation reaction (Scheme 2, 3ab). However, tert-butyl group transformations of peroxidic 3,4-dihydro-1,4-benzoxazin-
peroxide, dibenzoyl peroxide and hydrogen peroxide are not 2-ones were developed (Scheme 3). Generally catalyzed by
suitable substrates for this transformation. We than utilized the simple iron salts or copper salts, the coupling reaction of 3aa
standard reaction conditions to the coupling of a series of N- with dimethyl malonate, cyclohexanone and 2-methyl-1,3-
3
3
substituted benzoxazinones 1a-1r and aromatic ring substituted dioxolane gave the corresponding C(sp )-C(sp ) formation
benzoxazinones 1s-1v with TBHP. Delightly, the protocol was products 4, 5 and 6 respectively. The coupling reaction of 3aa
well tolerated for different kinds of substituted substrates to with N,N-dimethylaniline and indole gave the corresponding
3
2
afford 3-peroxyl products in high yields (Scheme 2, 3ba-3va). It C(sp )-C(sp ) formation products 7 and 8 efficiently. The
is worth mentioning that quinoxalinone derivatives 1w-1z’ were coupling reaction of 3aa with ethynylbenzene gave the
3
suitable substrates under these reaction conditions too corresponding C(sp )-C(sp) formation product 9 successfully.
(Scheme 2, 3wa-3z’a).
The coupling reaction of 3aa with dimethyl phosphonate gave
the corresponding C(sp )-P bond formation product 10
3
2
| J. Name., 2012, 00, 1-3
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COMMUNICATION
smoothly. 3aa can be easily transformed to dione 11 in high Some control experiments were conducted to eVlieuwcAidrtaictleeOntlhinee
yield too. Additionally, to further demonstrate the practicality mechanism of this peroxidation (SchemeD4ObI-:d10)..1W03h9e/Cn92C.C00e97q7u8iCv
of this peroxidation reaction, we conducted a gram-scale of radical scavenger such as TEMPO, BHT or diphenylethene was
experiment of 1a with TBHP under the standard catalyst-free added to the reaction, the yield of 3aa decreased significantly,
reaction conditions. As shown in Scheme 4a, the scale-up which suggests the possibility of a radical pathway. And as
synthesis of compound 3aa was afforded in 79% yield.
shown in Scheme 1 (entries 12 & 13), the efficiency of the
reaction decreased under air or O atmosphere. These results
2
Scheme 3. Late-stage transformationa
also point to radical process due to the radical feature of oxygen
molecule. We then tried to confirm the formation of radical
intermediate A and the tert-BuOO radical. For this purpose, the
peroxidation of benzoxazinones 1a was carried out under the
standard reaction conditions and radical trapping agent BHT (2
equiv) was added after 1 hour (Scheme 5, lower half). In this
case, The BHT adducts B, C, D, E could be detected by HRMS.
O
OMe
OMe
Bn
N
O
O
O
4
(88%)
Bn
N
Bn
N
O
O
O
OMe
OMe
O
O
O
O
1
1 (81%)
5 (75%)
- tBuOH
O
Scheme 5. Proposed mechanism

O
(1)
tBuOOH
tBuO
O
HP
+
OH
Bn
N
O
P
O
Bn
N
Bn
N
O
O
O
t
O
OO Bu
O
O
tBuO or OH
tBuOOH
OOtBu
+
tBuOH or H2O
O
O
O
O
O
O
(2)
+
6
(81%)
10 (81%)
3aa
O
Bn
N
Bn
N
(3) tBuO or OH
+
tBuOH or
2
H O
NH
NMe2
+
NMe2
Bn
N
O
O
O
O
t
1a
A
Bn
N
O
O
Bn
Bn
N
O
O
7 (73%)
N
OO Bu
Bn
N
NH
(4)
t
+
OO Bu
9
(67%)
O
O
O
O
O
O
A
3aa
8
(80%)
radical intermediates captured by BHT
(
detected by HRMS after 1 h under standard reaction conditions and 2 equiv of BHT)
a
o
t
reaction conditions for products 4-11:4: Fe(OTf)
2
(10 mol %), MeCN, 60 C, 4 h; 5:
O Bu
OH
C
B
o
o
Fe(OTf)
2
(10 mol %), DCM, 70 C, 3 h; 6: Cu(OAc)
2
(5 mol %), DCE, 60 C, Ar, 6 h; 7:
(5 mol %), MeCN, 60 C, 2 h; 9: CuBr (10 mol
(10 mol %), MeCN, 70 C, 5 h; 11: CuBr (5 mol %),
o
C19H33O2
C15H25O2
HCl (10 mol %), MeCN, rt, 6 h; 8: FeCl
%
2
[
M+H] m/z 293.2475
[M+H] m/z 237.1849
found 237.1846
o
o
), DCM, 60 C, 8 h; 10: Cu(OAc)
2
found 293.2469
O
O
2
MeNO , rt, 9 h.
t
OO Bu
E
D
O
C30H36NO3
M+H] m/z 458.2690
found 458.2685
Scheme 4. Scale-up experiment and radical trapping experiments.
C19H33O3
M+H] m/z 309.2424
found 309.2423
N
[
O
Bn
[
Bn
N
Bn
N
t
O
DCE (30 ml), Ar, 70 o
OO Bu
C
+
tBuOOH
a)
O
O
overnight
9%
O
O
O
1
a (1.2 g)
2a (1.8 mL)
3aa (1.3 g)
7
Although the detailed reaction pathway still remains to be
clarified, a radical involved reaction mechanism is illustrated as
shown in Scheme 5. Firstly, TBHP 2a broke its O-O bond when
o
heated to 70 C and tert-butoxyl radical and hydroxyl radical
Bn
N
Bn
N
t
OO Bu
BHT (2 equiv)
were induced in the system (equation 1). Next, tert-butoxyl
radical or hydroxyl radical reacts with TBHP to generate tert-
butylperoxy radical through hydrogen abstraction (equation 2).
At the same time, the H atom adjacent to the nitrogen atom of
the benzoxazinone 1a was abstracted by the tert-butoxyl radical
or hydroxyl radical to form radical intermediate A (equation 3).
Finally, radical A was trapped by the tert-butylperoxy radical to
give the desired product 3aa (equation 4).
In summary, a highly efficient and practical catalyst-free
oxidative C−H functionalization of 3,4-dihydro-1,4-benzoxazin-
2-ones was developed, which provides a possibility for the
synthesis of potentially bio-active peroxidic benzoxazinone
derivatives from easily available starting materials. The method
is applicable to a diverse set of substrates and the
corresponding products are typically isolated in excellent
b)
+
+
+
tBuOOH
O
O
O
O
DCE, Ar, 70 oC
O
O
1a
2a
3aa
0%
Bn
N
Bn
t
N
OO Bu
TEMPO (2 equiv)
c)
tBuOOH
O
DCE, Ar, 70 oC
O
O
1a
2a
3aa
20%
Bn
N
Bn
N
1
,1-diphenylethylene
t
OO Bu
(2 equiv)
tBuOOH
d)
O
DCE, Ar, 70 oC
2%
O
O
1a
2a
3aa
2
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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3
3
316–5319; (f) H. Yu and J. Shen, Org. Lett., 201Vi4ew, 1Ar6ti,cl3e 2O0nl4in–e
DOI: 10.1039/C9CC09778C
832–3835; (g) S. Iwata, T. Hata and H. Urabe, Adv. Synth.
chemical yields. The resulting peroxide products could be
further transformed into various substituted 3,4-dihydro-1,4-
benzoxazin-2-ones in good to excellent yields. This peroxidation
reaction can be upscalable to grams. A radical process was
involved in this reaction, and the radical intermediate can be
captured by BHT. Further investigations on the mechanism and
synthetic application of these reactions are ongoing in our
group.
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Conflicts of interest
There are no conflicts to declare.
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