Metal-Free [4+2] Annulation of Arylalkynes with tert-Butyl Nitrite through C(sp2)-H Oxidation to Assemble Benzo[e][1,2]oxazin-4-ones

Article abstract of DOI:10.1002/adsc.201500656

A metal-free radical-mediated [4+2] annulation of internal arylalkynes with tert-butyl nitrite (t-BuONO) is presented for the synthesis of benzo[e][1,2]oxazin-4-ones through the addition of t-BuONO across the C-C triple bond, hydration, isomerization and aromatic C(sp²)-H oxidation cascades. The ¹⁸O-labeling experiment shows that two oxygen atoms in the product system are from water.

Full text of DOI:10.1002/adsc.201500656

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DOI: 10.1002/adsc.201500656
Metal-Free [4+2] Annulation of Arylalkynes with tert-Butyl
2
À
Nitrite through C(sp ) H Oxidation to Assemble
Benzo[e][1,2]oxazin-4-ones
a
a,
a,b,
Xu-Heng Yang, Ren-Jie Song, * and Jin-Heng Li *
a
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan
University, Changsha 410082, Peopleꢀs Republic of China
Fax: (+86)-731-8871-3642; phone: (+86)-731-8871-3642; e-mail: srj0731@hnu.edu.cn or jhli@hnu.edu.cn
State Key Laboratory of Applied Organic Chemistry Lanzhou University, Lanzhou 730000, Peopleꢀs Republic of China
b
Received: July 8, 2015; Revised: August 11, 2015; Published online: December 9, 2015
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201500656.
Abstract: A metal-free radical-mediated [4+2] an-
nulation of internal arylalkynes with tert-butyl ni-
trite (t-BuONO) is presented for the synthesis of
benzo[e][1,2]oxazin-4-ones through the addition of
t-BuONO across the CꢀC triple bond, hydration,
Scheme 1. Radical-mediated [4+2] annulation.
2
isomerization and aromatic C(sp )ÀH oxidation cas-
1
8
cades. The O-labeling experiment shows that two
oxygen atoms in the product system are from water.
Herein, we report a new metal-free radical-mediat-
ed [4+2] annulation protocol to assemble benzo[e]-
[1,2]oxazin-4-ones (Scheme 1), in which internal aryl-
alkynes serve as 4-carbon units for reaction with t-
BuONO through the formation of a C=O double
bond, a C=N double bond and a CÀO single bond.
Keywords: alkynes; benzoxazines; cycloaddtion; ni-
trites; radical reaction
[5]
This method achieves the addition of t-BuONO
across the CꢀC triple bond, followed by a hydration,
2
[6]
The cycloaddition reaction has become one of the isomerization and aromatic C(sp )ÀH oxidation se-
most important methods in synthesis to build diverse quence, and represents the first example of O-arylox-
[7]
[
1,2]
carbo- and heterocyclic systems.
proaches, annulations with alkynes occupy a privileged Notably, the products, benzoxazines, are important
Among these ap- ime ether skeleton construction via CÀH oxidation.
[
1,2]
position and have been well exploited.
many classic approaches suffer from the cost of the products, pharmaceuticals and materials.
catalytic systems, harsh reaction conditions and/or Our studies began with an investigation of reaction
However, heterocyclic scaffolds that occur in many natural
[8]
limited substrate scope. Alternatively, the transition conditions for the [4+2] annulation of 1,2-diphenyl-
2
metal-catalyzed aromatic C(sp )ÀH functionalization ethyne (1a) with t-BuONO (Table 1). Extensive
strategy, in combination with subsequent annulation screening of various reaction parameters, including
with alkynes, has become particularly attractive be- the effect of reaction temperature, nitrites, solvents
cause it avoids the prior preparation of activated sub- and H O, revealed that the reaction of alkyne 1a with
2
strates with the associated reduction of chemical 5 equiv. of t-BuONO and 4 equiv. of H O in DMSO
2
waste generated, thereby streamlining organic synthe- at 1008C for 12 h was optimal to furnish the desired
[2–4]
[9]
sis in a more step- and atom-economic fashion.
benzoxazine 2a in 66% yield (entry 1). The results
One typical class of these transformations is the [4+2] showed that the reaction temperature affected the re-
annulation of substrates containing cleavable CÀH/ action: the yield of 2a decreased from 66% at 1008C
[
3]
[4]
NÀY (Y=H, O, N) bonds, CÀH/OÀH bonds, or to 28% at 808C and to 51% at 1208C (entries 1–3).
[
5]
CÀH bond/CÀC p-bonds with alkynes leading to di- While a decrease in the loading of t-BuONO to
verse heterocycles. However, the majority of these 3 equiv. was not beneficial to the formation of benz-
transformations are also restricted by the requirement oxazine 2a (34% yield; entry 4), the addition of
for expensive metal catalytic systems.
8 equiv. t-BuONO gave the identical results to that
with 5 equiv. t-BuONO (entry 5). Subsequently, three
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Xu-Heng Yang et al.
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[
a]
Table 1. Screening for the optimal reaction conditions.
Entry
Variation from the standard conditions
Isolated yield [%]
[
b]
1
2
3
4
5
6
7
8
9
1
1
1
1
none
at 808C
at 1208C
66
28
51
34
68
35
trace
trace
63
12
61
44
62
t-BuONO (3 equiv.)
t-BuONO (8 equiv.)
n-AmONO (5 equiv.) instead of t-BuONO
AgNO (5 equiv.) instead of t-BuONO
Fe(NO ) (5 equiv.) instead of t-BuONO
2
3
3
DMF instead of DMSO
toluene instead of DMSO
0
1
2
3
H O (5 equiv.) in anhydrous DMSO
2
H O (2 equiv) in anhydrous DMSO
2
[c]
none for 24 h
[a]
Reaction conditions: 1a (1 mmol), t-BuONO (5 equiv.), H O (4 equiv.) and anhydrous DMSO (1 mL) at 1008C under an
2
argon atmosphere for 12 h.
Some by-products, including benzil (3a) (18% yield), were observed.
[
[
b]
c]
1a (1 g, 5.7 mmol).
other nitrites, namely n-AmONO, AgNO2 and oxyphenyl)ethane-1,2-dione in the presence of t-
Fe(NO ) , were examined (entries 6–8). Switching the BuONO. For unsymmetrical internal diarylalkynes
3
3
nitrite to n-AmONO decreased the yield to 35% 1e–i, 1k and 1m–t, benzoxazines 2e–t were construct-
(
entry 6). However, both AgNO and Fe(NO ) had ed, and several substituents, namely Me, MeO, CN, t-
2
3 3
no reactivity (entries 7 and 8). The effect of solvents Bu, Ph, Cl and NO , on the aromatic ring were well
2
was also tested (entries 9 and 10): DMF (entry 9) was tolerated. Notably, two chemoselective products were
found to show the same reactivity as DMSO, but tolu- formed within the annulation process and the chemo-
ene was less effective (entry 10). It should be noted selectivity depended on the substitution effect of the
that a further increase in the loading of H O from aryl groups. The electronic effect and the sterically
2
4
(
equiv. to 5 equiv. slightly reduced the yield hindered effect of substituents affected the chemose-
entry 11). However, the annulation was suppressed lectivity. For examples, diarylalkynes 1h, 1j and 1o
by decreasing the loading of H O to 2 equiv. (en- having a methoxy-substituted phenyl group and
2
tries 11 and 12). These results suggested that H O a phenyl group mainly underwent the [4+2] annula-
2
plays an important role in the annulation process. It tion on the phenyl group rather than the methoxy-
was noted that this reaction was applicable to substituted phenyl group, building 2h, 2j and 2o in
a 1 gram (5.7 mmol) reaction of substrate 1a, thus fur- good yields, and their reactivity decreased from para
nishing 2a in 62% yield (entry 13).
to meta to ortho substitution in terms of yield. A simi-
We next decided to explore the feasibility of this lar chemoselectivity was obtained from o-methyl-sub-
4+2] annulation protocol with respect to internal ar- stituted alkyne 1g or o-cyano-substituted alkyne 1i
[
ylalkynes 1 (Table 2). In the presence of t-BuONO, (2g and 2i). Owing to the similar electronic properties
various symmetrical internal diarylalkynes 1b, 1c and between a phenyl group and p-alkyl-substituted
1
f were smoothly converted into 2b, 2c and 2f in phenyl group, a mixture of isomers 2k/2l and 2m/2n
good yields. However, using 1,2-bis(2-chlorophenyl)e- was formed form the corresponding alkynes 1k and
thyne 1d as substrate, only the de-chloro product 3- 1m. Furthermore, the steric hindrance effect of 1m
(
2-chlorophenyl)-4H-benzo[e][1,2]oxazin-4-one
2d shifts the chemoselectivity toward the [4+2] annula-
was obtained under the standard conditions. Unfortu- tion on the p-t-Bu-substituted phenyl group (2m and
nately, 1,2-bis(2-methoxyphenyl)ethyne was not a suit- 2n). Diarylalkynes 1o and 1p, bearing an electron-rich
able substrate and was converted to 1,2-bis(2-meth- p-substituted aryl group and a phenyl group, favored
3
850
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Metal-Free [4+2] Annulation of Arylalkynes with tert-Butyl Nitrite
[a]
Table 2. Variation of the alkynes (1).
[
a]
Reaction conditions: 1 (1 mmol), t-BuONO (5 equiv.), H O (4 equiv.) and DMSO (1 mL) at 1008C under
2
an argon atmosphere for 12 h. For unsymmetrical internal arylalkynes, some the other chemoselective
products were observed by GC-MS analysis, but most were not isolated. The isolated chemoselective ratio
is also given in parenthesis.
A de-Cl product 3-(2-chlorophenyl)-4H-benzo[e][1,2]oxazin-4-one (2d) was obtained.
Only 1,2-bis(2-methoxyphenyl)ethane-1,2-dione (3e) was isolated with 68% yield.
The other product, 1-cyclopropyl-2-phenylethane-1,2-dione (3x), was obtained in 35% yield.
[
[
[
b]
c]
d]
the [4+2] annulation on the phenyl group, giving 2o benzene 1aa were not suitable substrates to furnish
and 2p in moderate yield. For diarylalkynes 1q–t, the desired products 2z and 2aa.
bearing an electron-deficient substituted aryl group
As shown in Eq. (1), terminal arylalkynes 1ab and
and a phenyl group, the [4+2] annulation on the Ph 1ac underwent sequential dimerization of alkynes and
group had precedence over the electron-deficient sub- annulation with t-BuONO to afford isoxazoles 4ab
stituted Ph group (2q–t).
and 4ac, not the expected benzoxazines 2.
Use of diarylalkynes 1u–w with a naphthalen-1-yl
group, a pyridin-2-yl group or a thiophen-2-yl group
successfully furnished 2u–w in moderate yields with
excellent chemoselectivity. Gratifyingly, the [4+2] an-
nulation protocol could be applicable to alkyl-substi-
tuted arylalkyne 1x and electron-poor arylalkyne 1y,
albeit assembling 2x and 2y in lower yields. However,
both (bromoethynyl)benzene 1z and (iodoethynyl)-
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Xu-Heng Yang et al.
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1
8
To understand the mechanism, an O-labeling ex- this new annulation strategy are currently underway
[
10]
18
periment was conducted.
Two O atoms were in- in our laboratory.
troduced into the benzoxazine system in the presence
1
2
8
of 4 equiv. H O and anhydrous DMSO according to
1
3
the GC-MS and C NMR analysis [Eq. (2)].
Experimental Section
General Considerations
1
13
The H and C NMR spectra were recorded in CDCl sol-
3
vent on a NMR spectrometer using TMS as internal stan-
dard. LR-MS was performed on a GC-MS instrument and
HR-MS was measured on an electrospray ionization (ESI)
apparatus using time-of-flight (TOF) mass spectrometry. All
melting points are uncorrected.
Typical Experimental Procedure for the Annulation
of Arylalkynes (1) with tert-Butyl Nitrite and Water
The mechanism outlined in Scheme 2 was proposed
[
5,8c,11]
for the [4+2] annulation.
Initially, decomposition
of t-BuONO with H O into HNO and t-BuOH readi- To a Schlenk tube were added arylalkynes 1 (1.0 mmol),
2
2
H O (4.0 equiv.), tert-butyl nitrite (5.0 equiv.) and DMSO
ly occurs under heating, and then HNO is quickly
2
2
[
5,11]
(1 mL). Then the tube was charged with argon, and the mix-
ture was stirred at 1008C for the indicated time (about 12 h)
until complete consumption of starting material as moni-
tored by TLC and/or GC-MS analysis. After the reaction
was finished, the reaction mixture was washed with brine.
The aqueous phase was re-extracted with ethyl acetate. The
combined organic extracts were dried over Na SO , concen-
converted into NO , NO and H O.
Subsequently,
2
2
the addition of NO across the CꢀC triple bond af-
2
fords radical intermediate A, followed by isomeriza-
tion of intermediate A which produces intermediate
B or C. Finally, cyclization of intermediate C through
the CÀO bond-forming takes place to give product 2a
2
4
[
8c,11d]
with the aid of t-BuONO.
Notably, within the an- trated under vacuum, and the resulting residue was purified
nulation process intermediate A can also react with by silica gel column chromatography (hexane/ethyl ace-
H O to form benzil (3a).
tate=10:1) to afford the desired benzo[e][1,2]oxazin-4-ones
2
2
.
In summary, we have developed a new metal-free
radical-mediated [4+2] annulation of arylalkynes with
t-BuONO for the synthesis of benzo[e][1,2]oxazin-4-
ones. Importantly, this method allows the formation
3
-Phenyl-4H-benzo[e][1,2]oxazin-4-one
(2a): 1 yield:
147.2 mg (66%); white solid; mp 128.4–129.58C; H NMR
(
400 MHz, CDCl ): d= 8.22–8.19 (m, 1H), 7.95–7.89 (m,
3
2
1
1
H), 7.81–7.77 (m, 1H), 7.57–7.49 (m, 4H), 7.47–7.40 (m,
2
of the C(sp )ÀO bonds to access the O-aryloxime
13
H); C NMR (100 MHz, CDCl ): d=168.1, 162.0, 157.9,
2
3
ether skeletons through the C(sp )ÀH oxidation, and
35.6, 130.6, 129.9, 129.3, 128.4, 125.5, 125.5, 120.3, 116.3; IR
À1
represents a significant synthetic utilization of internal
(KBr): n=1687, 1583, 1375 cm ; HR-MS (ESI): m/z=
+
arylalkynes for the [4+2] annulation process. Further 224.0713, calcd. for C H NO [M+H] : 224.0706.
1
4
9
2
[
12] 1
studies on the detailed mechanism and applications of
Benzil (3a):
H NMR (400 MHz, CDCl ): d=8.04–7.92
3
(
m, 4H), 7.73–7.61 (m, 2H), 7.52 (t, J=7.6 Hz, 4H);
1
3
C NMR (100 MHz, CDCl ): d=194.6, 134.9, 133.0, 129.9,
3
1
1
29.0; IR (KBr): n=1720, 1596, 1581, 1449, 1324, 1210,
175, 873, 717, 685 cm .
À1
7-Methyl-3-p-tolyl-4H-benzo[e][1,2]oxazin-4-one
(2b):
yield: 160.7 mg (64%); white solid; mp 126.4–127.78C;
1
H NMR (400 MHz, CDCl ): d=8.06 (d, J=8.0 Hz, 1H),
3
7
8
.83 (d, J=8.0 Hz, 2H), 7.29 (d, J=7.2 Hz, 3H), 7.22 (d, J=
.4 Hz, 1H), 2.51 (s, 3H), 2.42 (s, 3H); C NMR (100 MHz,
13
CDCl ): d=168.0, 162.1, 157.8, 147.3, 140.7, 129.2, 129.1,
3
1
3
27.2, 127.1, 125.2, 118.1, 115.6, 22.2, 21.5; IR (KBr): n=
055, 1685, 1631, 1458, 1349, 1288, 1225, 785, 748, 695 cm ;
À1
HR-MS (ESI): m/z=252.1026, calcd. for C H NO [M+
1
6
13
2
+
H] : 252.1019.
-Methoxy-3-(4-methoxyphenyl)-4H-enzo[e][1,2]oxazin-4-
one (2c): yield: 203.8 mg (72%); white solid; mp 165.9–
7
1
1
9
6
66.78C; H NMR (400 MHz, CDCl ): d=8.09 (d, J=
3
.2 Hz, 1H), 7.93 (d, J=6.8 Hz, 2H), 7.03–6.96 (m, 3H),
.84 (d, J=2.0 Hz, 1H), 3.94 (s, 3H), 3.87 (s, 3H); C NMR
1
3
(
100 MHz, CDCl ): d=167.3, 165.4, 164.1, 161.5, 157.4,
3
132.3, 131.0, 127.2, 122.4, 116.2, 113.8, 97.1, 56.1, 55.4; IR
Scheme 2. Possible mechanism.
(KBr): n=3075, 2948, 2836, 1688, 1596, 1284, 1187, 1131,
3
852
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Metal-Free [4+2] Annulation of Arylalkynes with tert-Butyl Nitrite
À1
9
78, 746 cm ; HR-MS (ESI): m/z=284.0906, calcd. for
121.8, 120.3, 116.8, 116.3, 114.2, 55.4; IR (KBr): n=3066,
+
À1
C H NO [M+H] : 284.0917.
2942, 1681, 1588, 1293, 1179, 1134, 983, 751, 723 cm ; HR-
1
6
13
4
+
3
-(2-Chlorophenyl)-4H-benzo[e][1,2]oxazin-4-one
(2d):
MS (ESI): m/z=254.0809, calcd. for C H NO [M+H] :
1
5
11
3
yield: 123.4 mg (48%); white solid; mp 118.3–119.68C;
254.0812.
3-p-Tolyl-4H-benzo[e][1,2]oxazin-4-one and 7-methyl-3-
phenyl-4H-benzo[e][1,2]oxazin-4-one (2k/2l): yield:
1
H NMR (400 MHz, CDCl ): d=8.20–8.18 (m, 1H), 7.83–
3
7
7
.79 (m, 1H), 7.56 (d, J=8.4 Hz, 1H), 7.53–7.50 (m, 1H),
.48- 7.43 (m, 3H), 7.42–7.38 (m, 1H); C NMR (100 MHz,
13
1
156.5 mg (66%); white solid; H NMR (400 MHz, CDCl ):
3
CDCl ): d=166.9, 162.0, 159.6, 135.9, 133.9, 131.3, 131.2,
d=8.20–8.18 (m, 1H), 8.08 (d, J=8.0 Hz, 0.56H), 7.93–7.89
(m, 1H), 7.83 (d, J=8.0 Hz, 2H), 7.79–7.75 (m, 1H), 7.53–
7.47 (m, 2.76H), 7.46–7.39 (m, 1H), 7.30 (d, J=8.0 Hz,
3
1
3
29.8, 129.7, 126.8, 125.8, 125.4, 120.0, 116.4; IR (KBr): n=
056, 2934, 1658, 1554, 1283, 1181, 1156, 956, 757, 721 cm ;
À1
HR-MS (ESI): m/z=258.0325, calcd. for C H ClNO [M+
2.62H), 7.27–7.21 (m, 0.85H), 2.52 (s, 1.70H), 2.43 (s, 3H);
14
8
2
+
13
H] : 258.0316.
,2-Bis(2-methoxyphenyl)ethane-1,2-dione (3e): yield:
C NMR (100 MHz, CDCl ): d=168.2, 167.8, 162.1, 162.0,
3
1
157.9, 157.8, 147.5, 140.9, 135.5, 130.5, 130.0, 129.3, 129.2,
129.1, 128.3, 127.3, 127.0, 125.5, 125.4, 125.2, 120.2, 118.1,
116.3, 115.7, 22.2, 21.5; IR (KBr): n=3050, 1687, 1625, 1460,
1
1
83.6 mg (68%); H NMR (400 MHz, CDCl ): d=8.08 (d,
3
J=7.6 Hz, 1H), 7.57 (t, J=8.0 Hz, 1H), 7.12 (t, J=7.6 Hz,
13
À1
1
H), 6.95 (d, J=7.6 Hz, 1H), 3.59 (s, 3H); C NMR
1416, 1291, 1229, 932, 757. 692 cm ; HR-MS (ESI): m/z=
+
(
100 MHz, CDCl ): d=192.4, 160.3, 135.5, 130.4, 123.4,
238.0869, calcd. for C H NO [M+H] : 238.0863.
3
15 11
2
1
21.3, 112.5, 55.9.
3-(4-tert-Butylphenyl)-4H-benzo[e][1,2]oxazin-4-one and
7-tert-butyl-3-phenyl-4H-benzo[e][1,2]oxazin-4-one (2m/2n):
yield: 214.8 mg (77%); yellow solid; H NMR (400 MHz,
3-(Thiophen-2-yl)-4H-thieno[2,3-e][1,2]oxazin-4-one (2f):
1
yield: 119.9 mg (51%); yellow solid; mp 153.6–154.78C;
1
H NMR (400 MHz, CDCl ): d=8.32–8.31 (m, 1H), 7.90 (d,
CDCl ): d=8.20–8.17 (m, 1H), 8.13–8.08 (m, 2H), 7.96–7.90
3
3
J=5.2 Hz, 1H), 7.59–7.57 (m, 1H), 7.23 (d, J=5.6 Hz, 1H),
(m, 4H), 7.89–7.85 (m, 2H), 7.77–7.73 (m, 1H), 7.55–7.45
(m, 13H), 7.43–7.37 (m, 1H), 1.39 (s, 17H), 1.36 (s, 9H);
13
7
1
.20–7.17 (m, 1H); C NMR (100 MHz, CDCl ): d=166.5,
62.9, 152.0, 136.1, 132.0, 131.0, 130.1, 127.6, 120.5, 117.1; IR
3
1
3
C NMR (100 MHz, CDCl ): d=168.2, 167.7, 162.2, 161.9,
3
(
7
KBr): n=3097, 1665, 1617, 1477, 1425, 1281, 1030, 945, 762,
160.4, 157.8, 157.7, 153.8, 135.5, 130.4, 130.1, 129.3, 129.0,
128.3, 127.0, 125.4, 125.4, 125.3, 125.0, 123.8, 120.2, 118.0,
116.2, 112.2, 35.7, 34.8, 31.1, 30.7; IR (KBr): n=2964, 1662,
À1
16 cm ; HR-MS (ESI): m/z=235.9842, calcd. for
+
C H NO S [M+H] : 235.9834.
1
0
5
2 2
À1
3
-o-Tolyl-4H-benzo[e][1,2]oxazin-4-one
58.8 mg (67%); white solid; mp 124.6–125.88C; H NMR
400 MHz, CDCl ): d=8.19–8.17 (m, 1H), 7.82–7.78 (m,
(2g):
yield:
1621, 1460, 1442, 1285, 1228, 955, 757, 693 cm ; HR-MS
1
+
1
(
(ESI): m/z=280.1335, calcd. for C H NO [M+H] :
1
8
17
2
280.1332.
3
1
3
1
1
1
2
H), 7.55 (d, J=8.4 Hz, 1H), 7.46–7.29 (m, 5H), 2.30 (s,
3-(4-Methoxyphenyl)-4H-benzo[e][1,2]oxazin-4-one (2o):
yield: 172.1 mg (68%); white solid; mp 127.2–128.58C;
13
H); C NMR (100 MHz, CDCl ): d=167.7, 162.1, 161.0,
3
1
37.4, 135.8, 130.5, 130.0, 129.8, 129.6, 125.7, 125.6, 125.4,
H NMR (400 MHz, CDCl ): d=8.20–8.18 (m, 1H), 7.95 (d,
3
19.9, 116.4, 19.9; IR (KBr): n=3052, 1678, 1631, 1455,
J=8.8 Hz, 2H), 7.80–7.72 (m, 1H), 7.52 (d, J=8.8 Hz, 1H),
À1
424, 1287, 1226, 927, 752, 688 cm ; HR-MS (ESI): m/z=
7.42 (t, J=7.6 Hz, 1H), 7.01 (d, J=8.8 Hz, 2H), 3.87 (s,
+
13
38.0858, calcd. for C H NO [M+H] : 238.0863.
3H); C NMR (100 MHz, CDCl ): d=168.5, 162.0, 161.6,
15
11
2
3
3
-(2-Methoxyphenyl)-4H-benzo[e][1,2]oxazin-4-one (2h):
157.2, 135.5, 130.9, 125.5, 125.3, 122.3, 120.2, 116.3, 113.9,
55.4; IR (KBr, cm ): 3065, 2927, 1678, 1587, 1285, 1178,
À1
yield: 146.8 mg (58%); white solid; mp 110.1–111.68C;
H NMR (400 MHz, CDCl ): d=8.18–8.16 (m, 1H), 7.80–
.75 (m, 1H), 7.55–7.45 (m, 2H), 7.45–7.35 (m, 2H), 7.10–
.01 (m, 2H), 3.81 (s, 3H); C NMR (100 MHz, CDCl ):
1
1117, 969, 741, 718; HR-MS (ESI): m/z=254.0819, calcd. for
3
+
7
7
C H NO [M+H] : 254.0812.
1
5
11
3
13
3-(Biphenyl-4-yl)-4H-benzo[e][1,2]oxazin-4-one
(2p):
3
d=167.3, 162.0, 159.8, 158.0, 135.5, 131.7, 130.6, 125.4, 125.4,
yield: 191.4 mg (64%); white solid; mp 187.2–188.38C;
1
1
2
20.7, 119.8, 119.8, 116.3, 111.4, 55.9; IR (KBr): n=3070,
H NMR (400 MHz, CDCl ): d=8.22–8.20 (m, 1H), 8.03 (d,
3
À1
938, 1684, 1593, 1295, 1182, 1125, 975, 746, 721 cm ; HR-
J=8.4 Hz, 2H), 7.80–7.76 (m, 1H), 7.72 (d, J=8.4 Hz, 2H),
7.67–7.61 (m, 2H), 7.54 (d, J=8.4 Hz, 1H), 7.51–7.43 (m,
+
MS (ESI): m/z=254.0817. calcd. for C H NO [M+H] :
15
11
3
1
3
254.0812.
3H), 7.41–7.36 (m, 1H); C NMR (100 MHz, CDCl ): d=
3
2-(4-Oxo-4H-benzo[e][1,2]oxazin-3-yl)benzonitrile
(2i):
168.2, 162.0, 157.6, 143.4, 140.3, 135.6, 129.7, 128.9, 128.8,
yield: 126.5 mg (51%); white solid; mp 193.5–194.78C;
127.8, 127.2, 127.1, 125.5, 125.5, 120.3, 116.3; IR (KBr): n=
3046, 1687, 1613, 1460, 1344, 1207, 1122, 953 760, 691 cm ;
1
À1
H NMR (400 MHz, CDCl ): d=8.21 (d, J=8.0 Hz, 1H),
3
7
7
1
1
1
.86–7.82 (m, 2H), 7.78–7.72 (m, 2H), 7.67–7.57 (m, 2H),
HR-MS (ESI): m/z=300.1024, calcd. for C H NO [M+
H] : 300.1019.
2
0
13
2
13
+
.49 (t, J=7.6 Hz, 1H); C NMR (100 MHz, CDCl ): d=
3
66.8, 162.1, 157.3, 136.2, 133.6, 133.0, 132.5, 131.0, 130.4,
3-(4-Chlorophenyl)-4H-benzo[e][1,2]oxazin-4-one
(2q):
26.2, 125.4, 120.2, 117.3, 116.5, 113.0; IR (KBr): n=3079,
yield: 141.4 mg (55%); white solid; mp 152.5–153.38C;
À1
1
675, 1611, 1455, 1291, 1205, 1128, 950, 781, 700 cm ; HR-
H NMR (400 MHz, CDCl ): d=8.20–8.17 (m, 1H), 7.91 (d,
3
+
MS (ESI): m/z=249.0664, calcd. for C H N O [M+H] :
2
J=8.4 Hz, 2H), 7.83–7.74 (m, 1H), 7.53 (d, J=8.4 Hz, 1H),
15
8
2
2
1
3
49.0659.
7.48–7.42 (m, 3H); C NMR (100 MHz, CDCl ): d=167.9,
3
3-(3-Methoxyphenyl)-4H-benzo[e][1,2]oxazin-4-one (2j):
161.9, 156.8, 136.9, 135.8, 130.6, 128.6, 128.4, 125.7, 125.4,
yield: 154.4 mg (61%); white solid; mp 116.4–117.58C;
120.2, 116.3; IR (KBr): n=3046, 1672, 1591, 1459, 1339,
1
À1
H NMR (400 MHz, CDCl ): d=8.21–8.18 (m, 1H), 7.82–
1206, 1147, 930, 824, 757 cm ; HR-MS (ESI): m/z=
3
+
7
7
.74 (m, 1H), 7.57–7.50 (m, 2H), 7.48–7.37 (m, 3H), 7.09-
258.0323, calcd. for C H ClNO [M+H] : 258.0316.
1
4
8
2
13
.03 (m, 1H), 3.87 (s, 3H); C NMR (100 MHz, CDCl ):
3-(4-Nitrophenyl)-4H-benzo[e][1,2]oxazin-4-one
(2r):
3
d=168.0, 161.9, 159.4, 157.7, 135.6, 131.1, 129.4, 125.5, 125.5,
yield: 142.1 mg (53%); yellow solid; mp 163.2–164.48C;
Adv. Synth. Catal. 2015, 357, 3849 – 3856
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
3853

Xu-Heng Yang et al.
COMMUNICATIONS
1
À1
H NMR (400 MHz, CDCl ): d=8.42–8.38 (m, 2H), 8.23–
.20 (m, 1H), 7.97–7.88 (m, 2H), 7.61–7.50 (m, 3H);
1610, 1460, 1330, 1141, 1061, 968, 929, 758 cm ; HR-MS
3
+
8
(ESI): m/z=188.0711, calcd. for C H NO [M+H] :
1
1
9
2
13
C NMR (100 MHz, CDCl ): d=167.3, 161.3, 158.3, 151.6,
188.0706.
3
1
31.2, 129.3, 128.8, 128.6, 128.0, 123.3, 119.3, 112.9; IR
1-Cyclopropyl-2-phenylethane-1,2-dione
60.9 mg (35%); white solid; mp 117.1–118.48C; H NMR
(3x): 1 yield:
(KBr): n=3078, 2925, 1659, 1618, 1361, 1350, 1202, 908, 759,
À1
6
89 cm ; HR-MS+ (ESI): m/z=269.0553, calcd. for
(400 MHz, CDCl
3
): d=8.00–7.98 (m, 2H), 7.68–7.61 (m,
C H N O [M+H] : 269.0557.
1H), 7.50 (t, J=7.6 Hz, 2H), 2.58–2.52 (m, 1H), 1.34–1.31
1
4
8
2
4
1
3
4-(4-Oxo-4H-benzo[e][1,2]oxazin-3-yl)benzonitrile (2s):
(m, 2H), 1.22–1.16 (m, 2H); C NMR (100 MHz, CDCl ):
3
yield: 116.6 mg (47%); white solid; mp 148.2–149.38C;
d=202.6, 192.3, 134.5, 132.1, 130.2, 128.8, 18.6, 13.2; IR
(KBr): n=1715, 1588, 1579, 1452, 1331, 1217, 1183, 868, 721,
689 cm .
1
H NMR (400 MHz, CDCl ): d=8.30 (d, J=8.0 Hz, 1H),
3
À1
7
.92–7.89 (m, 3H), 7.66–7.64 (m, 1H), 7.59–7.47 (m, 3H);
1
3
C NMR (100 MHz, CDCl ): d=167.3, 160.9, 158.3, 131.2,
Ethyl 4-oxo-4H-benzo[e][1,2]oxazine-3-carboxylate (2y):
3
1
129.3, 128.9, 128.6, 127.5, 127.1, 122.3, 121.4, 118.7, 116.7; IR
yield: 105.2 mg (48%); yellow oil; H NMR (400 MHz,
CDCl ): d=8.17–8.15 (m, 1H), 7.85–7.81 (m, 1H), 7.57 (d,
(
7
KBr): n=3075, 1678, 1624, 1462, 1289, 1213, 1131, 945, 782,
06 cm ; HR-MS+ (ESI): m/z=249.0667, calcd. for
3
À1
J=8.4 Hz, 1H), 7.50–7.44 (m, 1H), 4.53–4.47 (m, 2H), 1.44
1
3
(
t, J=7.2 Hz, 3H); C NMR (100 MHz, CDCl ): d=165.2,
C H N O [M+H] : 249.0659.
3
1
5
8
2
2
1
1
1
61.5, 160.1, 153.1, 136.3, 126.4, 125.2, 120.7, 116.5, 63.1,
3-(3-Nitrophenyl)-4H-benzo[e][1,2]oxazin-4-one
(2t):
4.0; IR (KBr): n=3087, 2993, 1736, 1670, 1609, 1450, 1376,
yield: 115.3 mg (43%); yellow solid; mp 128.6–129.58C;
À1
1
240, 1166, 979 cm ; HR-MS (ESI): m/z=220.0611, calcd.
H NMR (400 MHz, CDCl ): d=9.07 (d, J=2.8 Hz, 1H),
3
+
for C H NO [M+H] : 220.0604.
8
1
1
1
1
2
.61–8.58 (m, 1H), 7.97–7.89 (m, 2H), 7.70 (d, J=9.6 Hz,
11
9
4
13
p-Tolyl(5-p-tolylisoxazol-3-yl)methanone (4ab):1 yield:
H), 7.57–7.50 (m, 3H); C NMR (100 MHz, CDCl ): d=
3
1
13.6 mg (41%); white solid; mp 110.3–111.88C; H NMR
67.4, 164.3, 158.0, 144.6, 131.4, 129.8, 129.4, 128.6, 128.6,
(
400 MHz, CDCl ): d=8.26 (d, J=8.4 Hz, 2H), 7.74 (d, J=
22.6, 119.7, 118.5. IR (KBr): n=3063, 2975, 1664, 1573,
3
À1
8.4 Hz, 2H), 7.32 (d, J=8.4 Hz, 4H), 6.98 (s, 1H), 2.45 (s,
258, 1186, 1196, 934, 756, 714 cm ; HR-MS (ESI): m/z=
13
+
3H), 2.42 (s, 3H); C NMR (100 MHz, CDCl ): d=185.5,
3
69.0563, calcd. for C H N O [M+H] : 269.0557.
14
8
2
4
1
1
70.8, 162.5, 145.1, 141.1, 133.3, 130.8, 129.8, 129.3, 125.9,
3-(Naphthalen-2-yl)-4H-benzo[e][1,2]oxazin-4-one (2u):
24.1, 99.7, 21.8, 21.5; IR (KBr): =3140, 1650, 1604, 1508,
yield: 152.9 mg (56%); white solid; mp 104.6–104.98C;
À1
1
1442, 1243, 1183, 893, 757, 674 cm ; HR-MS (ESI): m/z=
2
H NMR (400 MHz, CDCl ): d=8.23–8.21 (m, 1H), 8.01 (d,
3
+
78.1182, calcd. for C H NO [M+H] : 278.1176.
18 15 2
J=8.0 Hz, 1H), 7.96–7.89 (m, 1H), 7.87–7.82 (m, 1H), 7.74
(4-Methoxyphenyl)[5-(4-methoxyphenyl)isoxazol-3-yl]me-
(
d, J=8.4 Hz, 1H), 7.65–7.56 (m, 3H), 7.54–7.46 (m, 3H);
1
3
thanone (4ac): yield: 114.7 mg (37%); white solid; mp
C NMR (100 MHz, CDCl ): d=168.1, 162.2, 160.5, 135.9,
3
1
1
28.5–128.68C; H NMR (400 MHz, CDCl ): d=8.44–8.31
3
1
1
1
33.6, 131.6, 130.8, 128.6, 128. 4, 127.5, 126.8, 126.3, 125.8,
(
m, 2H), 7.82–7.73 (m, 2H), 7.07–6.96 (m, 4H), 6.90 (s, 1H),
25.6, 125.1, 125.0, 120.0, 116.5; IR (KBr): n=3050, 1663,
1
3
À1
3.91 (s, 3H), 3.88 (s, 3H); C NMR (100 MHz, CDCl ): d=
3
611, 1459, 1293, 1205, 1132, 920, 796, 774 cm ; HR-MS
+
184.2, 170.5, 164.4, 162.7, 161.4, 133.2, 128.8, 127.6, 119.6,
(ESI): m/z=274.0871, calcd. for C H NO [M+H] :
18
11
2
1
1
14.5, 113.9, 98.9, 55.6, 55.4; IR (KBr): n=3079, 2945, 2833,
274.0863.
À1
668, 1584, 1467, 1287, 891, 736, 668 cm ; HR-MS (ESI): m/
3
-(Pyridin-2-yl)-4H-benzo[e][1,2]oxazin-4-one (2v): yield:
+
1
z=310.1081, calcd. for C18
H
15NO
4
[M+H] : 310.1074.
1
07.5 mg (48%); yellow solid; mp 133.4–133.68C; H NMR
(
(
(
400 MHz, CDCl ): d=8.82 (d, J=4.4 Hz, 1H), 8.23–8.20
3
m, 1H), 7.94 (d, J=8.0 Hz, 1H), 7.90–7.78 (m, 2H), 7.59
13
d, J=8.4 Hz, 1H), 7.49–7.44 (m, 2H); C NMR (100 MHz,
CDCl ): d=167.7, 162.0, 157.3, 150.1, 149.1, 136.6, 135.8,
3
Acknowledgements
1
1
25.8, 125.4, 125.4, 124.8, 120.7, 116.4; IR (KBr): n=1682,
À1
596, 1356 cm ; HR-MS (ESI): m/z=225.0663, calcd. for
We thank the Natural Science Foundation of China (Nos.
21402046, 21172060 and 21472039), Specialized Research
Fund for the Doctoral Program of Higher Education (No.
20120161110041), and Hunan Provincial Natural Science
Foundation of China (No. 13JJ2018). Dr. R.-J. Song. also
thanks the Fundamental Research Funds for the Central Uni-
versities.
+
C H N O [M+H] : 225.0659.
1
3
8
2
2
3-(Thiophen-2-yl)-4H-benzo[e][1,2]oxazin-4-one
(2w):
yield: 116.8 mg (51%); yellow solid; mp 158.4–159.88C;
1
H NMR (400 MHz, CDCl ): d=8.27–8.25 (m, 1H), 8.21–
3
8
7
.19 (m, 1H), 7.79–7.75 (m, 1H), 7.59–7.50 (m, 2H), 7.44–
.40 (m, 1H), 7.19–7.17 (m, 1H); C NMR (100 MHz,
13
CDCl ): d=167.2, 161.8, 152.5, 135.6, 131.2, 130.9, 130.6,
3
1
1
27.5, 125.5, 125.4, 119.6, 116.4; IR (KBr): n=3095, 1661,
À1
612, 1474, 1419, 1277, 1030, 949, 758, 712 cm ; HR-MS
+
(ESI): m/z=230.0277, calcd. for C H NO S [M+H] : References
12
7
2
2
30.0270.
3
-Cyclopropyl-4H-benzo[e][1,2]oxazin-4-one (2x): yield:
[1] For selected reviews: a) Advances in Cycloaddition,
Vols. 1–6, JAI, Greenwich, CT, 1988–1999; b) W. Car-
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Wiley-VCH, Weinheim, 2002; d) G. Masson, C. Lalli,
1
6
(
(
9.2 mg (37%); white solid; mp 98.6–99.48C; H NMR
400 MHz, CDCl ): d=8.11 (d, J=8.0 Hz, 1H), 7.79–7.66
m, 1H), 7.42 (d, J=8.4 Hz, 1H), 7.37 (t, J=7.6 Hz, 1H),
.51–2.45 (m, 1H), 1.16–1.12 (m, 2H), 1.10–1.06 (m, 2H);
C NMR (100 MHz, CDCl ): d=168.4, 161.9, 161.5, 135.4,
25.1(2C), 118.5, 116.2, 9.0, 8.2; IR (KBr): n=3086, 1655,
3
2
13
3
1
3
854
asc.wiley-vch.de
ꢁ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2015, 357, 3849 – 3856

COMMUNICATIONS
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