Synthesis of 2-Alkenyl-4H-3,1-Benzoxazin-4-Ones through HFIP-Mediated Decarboxylative [4+2]-Annulation of Isatoic Anhydrides with Cyclopropenones under Silver Catalysis

Article abstract of DOI:10.1002/adsc.202100489

We herein describes an HFIP-mediated [4+2]-cycloaddition reaction from simple and easily available isatoic anhydrides and cyclopropenones under silver catalysis. This transformation involves the tandem decarboxylative esterification, intermolecular additi

Full text of DOI:10.1002/adsc.202100489

UPDATES
doi.org/10.1002/adsc.202100489
Synthesis of 2-Alkenyl-4H-3,1-Benzoxazin-4-Ones through HFIP-
Mediated Decarboxylative [4+2]-Annulation of Isatoic
Anhydrides with Cyclopropenones under Silver Catalysis
Mengqi Yang,a Jixin Wang,a Weiwei Lv,b Dan Ba,b Guolin Cheng,b,* and
Lianhui Wanga,*
a
School of Medicine, Huaqiao University, Quanzhou, 362021, People’s Republic of China
E-mail: lianhui.wang@hqu.edu.cn
College of Materials Science and Engineering, Huaqiao University, Xiamen 361021, People’s Republic of China
b
E-mail: glcheng@hqu.edu.cn
Manuscript received: April 21, 2021; Revised manuscript received: June 13, 2021;
Version of record online: ■■■, ■■■■
Supporting information for this article is available on the WWW under https://doi.org/10.1002/adsc.202100489
successively reported via palladium-catalyzed cyclo-
carbonylation reaction of o-haloanilines with unsatu-
Abstract: We herein describes an HFIP-mediated
[4+2]-cycloaddition reaction from simple and
rated halides or triflates under an atmosphere of carbon
easily available isatoic anhydrides and cycloprope-
monoxide (Scheme 1a).[4] The other route to access to
nones under silver catalysis. This transformation
2-alkenyl-4H-3,1-benzoxazin-4-ones was recently
involves the tandem decarboxylative esterification,
intermolecular addition, intramolecular substitution,
small ring opening and isomerization processes,
achieved from N-(2-carboxyphenyl)- and N-(2-formyl-
phenyl)acrylamides through the intramolecular cycliza-
tion strategy (Scheme 1b).[5] Despite the progress, the
which allows the rapid assembly of versatile 2-
availability of substrates and required reaction con-
diarylalkenyl-4H-3,1-benzoxazin-4-ones.
ditions (e.g. CO atmosphere, external oxidant, strong
acidic or basic medium, microwave) makes these
synthetic methods of limited utility to some extent.
Keywords: isatoic anhydride; cyclopropenone; hexa-
fluoro-2-propanol; cycloaddition; 4H-3,1-benzoxazin-
Based on our ongoing interest in versatile nitrogen-
containing heterocyclic constructions,[6] we herein wish
4-one
to present an intermolecular synthesis of 2-alkenyl-
substituted 4H-3,1-benzoxazin-4-ones from easily
available isatoic anhydrides and cyclopropenones.[7]
4H-3,1-Benzoxazin-4-ones represent a class of impor- Notably, isatoic anhydrides underwent decarboxylative
tant N-heterocycles of considerable interest, and have esterification in the presence of hexafluoro-2-propanol
been used as versatile and valuable precursors for the
preparation of pharmaceutically active compounds.[1]
As a particularly branch, 2-alkenyl-substituted 4H-3,1-
benzoxazin-4-ones and their derivatives exhibit a
variety of biological activities such as human leuko-
cyte elastase inhibitor, acaricide, fibrosis inhibitor and
antagonist, and therefore have received much attention
in recent years (Figure 1).[2]
In view of their high biological activity, the
construction of common moieties such as alkyl or aryl
substituents at C2 position on the 4H-3,1-benzoxazin-
4-one framework were extensively investigated in the
past decades,[3] whereas the synthesis of 2-alkenyl-
substituted 4H-3,1-benzoxazin-4-ones has been com-
paratively less studied. In this context, one general
approach to 2-alkenyl-4H-3,1-benzoxazin-4-ones was
Figure 1. The representative 2-alkenyl-4H-3,1-benzoxazin-4-
ones and their related derivatives of biological interest.
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Scheme 1. Synthetic protocols of 2-alkenyl-4H-3,1-benzoxazin-4-ones.
(HFIP) to generate the nitrogen anion intermediate in Furthermore, we screened different kinds of solvents
this transformation,[8] which is prone to the [4+2] including PhMe, PhCF3, 1,4-dioxane and MeCN, and
cycloaddition with cyclopropenones through nucleo- found that the expected product 3aa could be obtained
philic attack under silver catalysis to allow the only under the conditions of PhMe and PhCF3
assembly of versatile 2-diarylalkenyl-4H-3,1-benzoxa- (entries 26–30). Finally, the best performance of the
zin-4-one products (Scheme 1).
cycloaddition was observed in 84% yield when 3.0
Our initial experiments were carried out by using equivalents of diphenylcyclopropenone (2a) was
isatoic anhydride (1a, 0.1 mmol) and diphenylcyclo- loaded into the reaction system in three times at
propenone (2a, 0.1 mmol) as the model substrates, as intervals of 2 h (entries 31–32).
shown in Table 1. No reaction was observed in the
Having acquired the optimal reaction conditions
presence of Ag2O as catalyst and Na2CO3 as base in (Table 1, entry 32), we investigated the cycloaddition
°
PhMe at 120 C for 16 h (entry 1), and only trace reaction of isatoic anhydrides 1 with diphenylcyclopro-
amounts of the target product 3aa was obtained penone (2a), as shown in Scheme 2. Generally, isatoic
without silver catalysis (entry 2). To our delight, the anhydrides 1 bearing electron-donating and electron
current decarboxylative cycloaddition proceed withdrawing substituents in different positions of the
smoothly when HFIP was loaded as the efficient phenyl rings were converted into the 2-diphenylalken-
additives,[8] which delivered the 2-alkenyl-4H-3,1- yl-substituted 4H-3,1-benzoxazin-4-one products 3 in
benzoxazin-4-one product 3aa in 27% isolated yield moderate to good yields, in which substrates 1 with
(entry 3). At the same time, the undesired α,β- electron-donating groups behave better reactivity than
unsaturated ester product 4aa from the nucleophilic those with electron-withdrawing groups. Moreover, the
addition of cyclopropenone 2a with HFIP and the reaction of diphenylcyclopropenone (2a) with a variety
spirolactone product 5aa were observed from dimeri-
zation of cyclopropenone 2a in 7% and 5% yields,
respectively, and the similar results were observed in
the following reaction condition screenings as well as
in the substrate scope investigations, which reduced
the efficiency of the desired [4+2] cyclization
processes to some extent. Furthermore, the examina-
tion of other alcohol additives such as i-PrOH, t-BuOH
and Me3COH only generated 3aa in no more than 10%
yields (entries 4–6). Besides, the yield of 3aa was no
further improvement by either increasing or decreasing
the loadings of HFIP, or even in place of PhMe as the
reaction solvent (entries 7–9). Besides, investment of
silver and other metal salts, such as AgOTf,
CF3COOAg, AgOAc, AgNO3, Ag2CO3, Cu(OTf)2,
Cu(OAc)2, CuI, Sc(OTf)3 and FeCl3 proved Ag2O to be
the best (entry 3 vs entries 10–19). With Ag2O as
catalyst, various inorganic and organic bases were next
tested (entries 3 and 20–25), and the experimental
results showed that the current transformation effi-
ciently proceeded in the presence of Na2CO3 (entry 3).
Scheme 2. Substrate scope of isatoic anhydrides 1.
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Table 1. Optimization of the reaction conditions.[a]
°
Entry
Catalyst (x)
Base (y)
Additive (z)
Solvent
T [ C]
3aa [%][b]
1
2
3
4
5
6
7
8
Ag2O (10)
–
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
Na2CO3 (2)
K2CO3 (2)
Cs2CO3 (2)
NaOAc (2)
t-BuONa (2)
Et3N (2)
–
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
HFIP
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
100
N.R.
Trace
27
5
10
4
18
21
N.R.
23
8
10
15
10
N.R.
Trace
4
HFIP (3)
HFIP (3)
i-PrOH (3)
t-BuOH (3)
Me3COH (3)
HFIP (2)
HFIP (4)
–
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
AgOTf (20)
CF3CO2Ag (20)
AgOAc (20)
AgNO3 (20)
Ag2CO3 (10)
Cu(OTf)2 (20)
Cu(OAc)2 (20)
CuI (20)
Sc(OTf)3 (20)
FeCl3 (20)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
Ag2O (10)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30[c]
31[d]
32[d]
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
HFIP (3)
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhMe
PhCF3
1,4-Dioxane
MeCN
PhMe
PhMe
PhMe
6
N.R.
Trace
Trace
Trace
N.R.
Trace
Trace
42
DBU (2)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1)
Na2CO3 (1)
42
N.R.
Trace
56
76
84
[a] Reaction conditions: 1a (0.1 mmol), 2a (0.1–0.3 mmol), Catalyst (10–20 mol%), Base (1.0–2.0 equiv.), HFIP (2.0–5.0 equiv.)
and PhMe (1.0 mL) under N2 for 16 h.
[b] Isolated yields.
[c] 2a (0.3 mmol).
[d] 2a (0.3 mmol) was added three times at intervals of 2 h, and then further reacted for 10 h. HFIP=Hexafluoro-2-propanol.
DBU=1,8-Diazabicyclo[5.4.0]undec-7-ene. N.R.=No reaction.
of the halo-substituted isatoic anhydrides 1 steadily were unambiguously confirmed by X-ray single crystal
delivered the corresponding products 3, which might diffraction.[9]
allow for the late-stage modifications through transi-
In order to further evaluate the scope of this
tion-metal-catalyzed couplings. Unfortunately, hetero- transformation, several substituted cyclopropenones 2
cyclic-type substrates, such as 2H-pyrido[2,3-d][1,3] were tested. As shown in Scheme 3, substrates 2
oxazine-2,4(1H)-dione (1r), 2H-pyrido[3,4-d][1,3] bearing alkyl, fluoro and trifluoromethyl substituents
oxazine-2,4(1H)-dione (1s) and 2H-thieno[2,3-d][1,3] could proceed smoothly with isatoic anhydrides 1
oxazine-2,4(1H)-dione (1t) were failed to deliver the under the standard conditions. In contrast to isatoic
desired annulation products 3ra–ta under the standard anhydrides 1, cyclopropenones 2d and 2e with fluoro
reaction conditions. The structure of compound 3na groups behaved better reactivity than those with alkyl
groups (2b and 2c). To our disappointment, dithio-
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Scheme 5. Proposed mechanism.
Scheme 3. Substrate scope of cyclopropenones 2.
synthetic protocol from isatoic anhydrides 1 (Sche-
phene-substituted cyclopropenone 2g only delivered me 4c).
the corresponding annulation product 3ag in 4% yield.
On the basis of the preliminary experimental results
To gain insight into the mechanism of this cyclo- and the previous literature reports,[5] a plausible
addition reaction, preliminary experiments were con- reaction mechanism is presented in Scheme 5. First,
ducted. As mention above, no target product 3 was isatoic anhydride 1a underwent decarboxylative ester-
formed in the model reaction of 1a and 2a without ification with HFIP to generate intermediate A under
HFIP additives in this catalytic system (Scheme 4a), basic conditions. Subsequently, an intermolecular
and meanwhile, intermediate 6a was always detected nucleophilic attack from intermediate A to the
in the presence of HFIP. Therefore, intermediate 6a carbonyl group of diphenylcyclopropenone 2a with the
was isolated and was further loaded into the cyclo- assistance of silver catalyst gave intermediate C, which
addition with cyclopropenone 2a under silver catalysis immediately underwent an intramolecular nucleophilic
in the absence of HFIP. Thus, the target product 3aa substitution to accomplish the [4+2] cyclization.
was successfully obtained with a yield of 42%, Finally, the three-membered-ring opening and isomer-
indicating 6a as a key intermediate in the present ization processes from the thus formed intermediate D
transformation (Scheme 4b). Besides, the assumptive afforded the desired 2-alkenyl substituted 4H-3,1-
intermediates 2-aminobenzoic acid (7) and 2-amino- benzoxazin-4-one product 3aa.
benzaldehyde (8) instead of isatoic anhydride (1a)
were introduced into the standard reaction conditions, 4H-3,1-benzoxazin-4-one
In order to explore the application of the 2-alkenyl-
products 3, their
and the desired product 3aa was only obtained with 8 fluorescence emission characteristics were preliminar-
in 58% yield, indicating the unique of the present ily investigated. Unfortunately, all the obtained com-
pounds 3 were failed to exhibit characteristics of
aggregation-induced emission (AIE, for selected exam-
ples see the supporting information).[10]
In summary, we have developed an HFIP-mediated
[4+2]-cycloaddition reaction from easily available
isatoic anhydrides and cyclopropenones under silver
catalysis. The reaction involves the successive trans-
formations of decarboxylative esterification of HFIP to
isatoic anhydrides, intermolecular 1,2-addition to
cyclopropenones, intramolecular substitution, small
ring opening and isomerization to afford the 2-alkenyl-
4H-3,1-benzoxazin-4-one products.
Experimental Section
The representative procedure for the preparation of
compounds 3
Isatoic anhydride 1 (0.1 mmol, 1.0 equiv.), HFIP (0.3 mmol,
3.0 equiv.), Ag2O (0.01 mmol, 10 mol%) and Na2CO3
Scheme 4. Preliminary mechanistic studies.
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(0.1 mmol, 1 equiv.) were added sequentially to a flame-dried
Schlenk tube and was dissolved in PhMe (1.0 mL) at room
temperature under N2 atmosphere. Then, cyclopropenone 2
(0.3 mmol, 3.0 equiv.) was added three times at intervals of 2 h
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°
at 100 C. After cyclopropenone 2 was completely added, the
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After reaction completion, the solvent was removed under
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acetate (v/v) afforded the corresponding product 3.
Acknowledgements
This research was supported by the Science and Technology
Project of Quanzhou City (2018 C073R), NSF of China (Nos.
22071068 and 21602064), Outstanding Youth Scientific Re-
search Cultivation Project of Colleges and Universities of
Fujian Province, and the Instrumental Analysis Center of
Huaqiao University.
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Synthesis of 2-Alkenyl-4H-3,1-Benzoxazin-4-Ones through
HFIP-Mediated Decarboxylative [4+2]-Annulation of
Isatoic Anhydrides with Cyclopropenones under Silver
Catalysis
Adv. Synth. Catal. 2021, 363, 1–7
M. Yang, J. Wang, W. Lv, D. Ba, G. Cheng*, L. Wang*