Copper-catalyzed C-N bond formation/rearrangement sequence: Synthesis of 4H-3,1-benzoxazin-4-ones

Article abstract of DOI:10.1021/jo400515y

A facile and efficient copper-catalyzed method for the synthesis of 4H-3,1-benzoxazin-4-one derivatives has been developed. This procedure is based on a tandem intramolecular C-N coupling/rearrangement process. This method would provide a new and useful strategy for construction of N-heterocycles.

Full text of DOI:10.1021/jo400515y

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Article
Copper-Catalyzed C-N Bond Formation / Rearrangement
Sequence: Synthesis of 4H-3,1-Benzoxazin-4-ones
Zhi-Yuan Ge, Qiong Ming Xu, Xiang-Dong Fei, Ting Tang, Yong-Ming Zhu, and Shun-Jun Ji
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/jo400515y • Publication Date (Web): 12 Apr 2013
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Copper-Catalyzed C-N Bond Formation / Rearrangement Sequence:
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Synthesis of 4H-3,1-Benzoxazin-4-ones
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Zhi-Yuan Ge,† Qiong-Ming Xu,† Xiang-Dong Fei,† Ting Tang,† Yong-Ming Zhu,*,† and
Shun-Jun Ji‡
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† College of Pharmaceutical Sciences, Soochow University, Suzhou, 215123, People’s Republic of China
E-mail: zhuyongming@suda.edu.cn
‡ College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123, China
ABSTRACT: A facile and efficient copper-catalyzed method for the synthesis of
4H-3,1-benzoxazin-4-one derivatives has been developed. This procedure is based on a
tandem intramolecular C-N coupling / rearrangement process. This method would provide a
new and useful strategy for construction of N-heterocycles.
INTRODUCTION
4H-3,1-Benzoxazin-4-ones are a class of fused heterocycles that are of interest to organic
chemists owing to their biological activities.1-8 For instance, some of 2-substituted
4H-3,1-benzoxazin-4-ones act as chymotrypsin inactivators (Ⅰ),1 HSV-1 protease inhibitors
(Ⅱ),2 and inhibitors of human leukocyte elastase (Ⅲ),3 cathepsin G,4 C1r serine protease5 and
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human chymase.6 Besides, compound Ⅳ, shown in Figure 1, has the ability to lower the level
of plasma cholesterol and triglyceride.7 Moreover, Cetilistat (Ⅴ), a novel lipase inhibitor, was
reported to be used as an anti-obesity remedy.8 In addition, 2-substituted
4H-3,1-benzoxazin-4-ones are useful synthetic intermediates for the synthesis of
pharmaceutically active compounds.9 Therefore, it is not surprising that there is an ever
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increasing
number
of
synthetic
approaches
toward
the
preparation
of
4H-3,1-benzoxazin-4-one derivatives, especially 4H-3,1-benzoxazin-4-ones substituted in the
2-position.10-17 Among these methodologies, cyclization of anthranilic acid or N-acylanthranilic
acid, and ring transformation of isatoic anhydride are most popular.11 Other notable methods
include oxidation of 2-aryl-3H-indol-3-ones, 2-phenyl-3-oxo-3H-indole 1-oxide, or
2-aryl-4H-benzo[d][1,3]oxazines,12 thermolysis of benzo[d][1,2,3]triazin-4(3H)-ones or isatoic
anhydride,13 electrochemical cyclization of o-trichloroacetylanilides,14 cyclization of
2-ureidobenzoic
acids,
alkyl
2-ureidobenzoates,
or
2-ureidobenzamides,15
palladium-catalyzed carbonylation with CO,16 and palladium-catalyzed cyclization of
azidoalkynes.17 Some of these methods still suffer from either harsh reaction conditions or
hazardous materials. Consequently, we are making an effort to investigate a further efficient
method for the synthesis of this class of N-heterocycles.
Very recently, our group reported
a
novel copper(I)-catalyzed reaction of
1-(2-halophenyl)-1,3-diones,18 which involves a rearrangement process as a key step. We
hypothesized that the similar strategy might be applicable to prepare benzoxazinones from
N-acyl-2-halobenzamides. In a continuation to our interest in copper-catalyzed tandem
cyclization reactions, herein, we would like to report a new strategy for the synthesis of
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2-substituted benzoxazinones via a copper-catalyzed reaction of N-acyl-2-halobenzamides.
Figure 1. Structures of Some Bioactive 2-Substituted 4H-3,1-Benzoxazin-4-ones.
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RESULTS AND DISCUSSION
We initially investigated the reaction conditions by employing N-phenyl-2-iodobenzamide
(1a) as the model substrate (Table 1). Considering that 2-picolinic acid was used as the best
ligand of CuI in our previous study,18 we tested the reaction in the presence of CuI (10 mol %),
2-picolinic acid (20 mol %), and K2CO3 (2 equiv) in anhydrous toluene (5 mL) at 120 °C , and a
42% yield of the desired product was obtained after 6 h (Table 1, entry 1). Then, several
ligands and a ligand-free condition were tested in this reaction, and a comparable yield was
obtained in the absence of ligand (Table 1, entries 2-4). Base screening tests revealed that
K3PO4, in comparison with other bases, produced 2a by the yield increased to 60% (Table 1,
entries 5-9). Analytical results showed that benzoic acid was a major by-product. Considering
that adventitious moisture might result in the generation of benzoic acid in the reaction, we
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tested several drying agents, and a 81% yield was obtained in the presence of CaCl2 (Table 1,
entries 10-13). Other solvents, such as o-xylene, 1,4-dioxane, and THF, proved to be less
effective (Table 1, entries 14-16). A comparison of catalysts showed that CuI was superior to
the others (Table 1, entries 17-19). Based on these considerations, our products could be
easily obtained from 1a in the presence of CuI (10 mol %), K3PO4 (2 equiv), and CaCl2 (2
equiv) in anhydrous toluene (5 mL) within a sealed tube under nitrogen at 120 °C for 6h.
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Table 1: Optimizations of Conditions for Benzoxazinone Synthesis a
entry catalyst
ligand b
base
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
NaOtBu
NaOAc
KF
solvent c
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
additive yield(%) d
1
2
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
L1
L2
L3
-
-
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36
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42
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0
-
3
-
4
-
5
-
-
6
-
-
7
-
-
0
8
-
-
25
60
63
9
-
K3PO4
K3PO4
-
10
-
MS 4 Å
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CuI
CuI
-
-
-
-
-
-
-
-
-
K3PO4
K3PO4
K3PO4
K3PO4
toluene
toluene
toluene
o-xylene
MgSO4
CaO
69
65
81
75
65
58
73
71
70
CuI
CaCl2
CaCl2
CaCl2
CaCl2
CaCl2
CaCl2
CaCl2
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CuI
CuI
K3PO4 1,4-dioxane
CuI
K3PO4
K3PO4
K3PO4
K3PO4
THF
CuBr
CuCl
Cu(OAc)2
toluene
toluene
toluene
aAll reactions were run with 1a (0.5 mmol) , catalyst (0.05 mmol) , ligand
(0.1 mmol) , base (1.0 mmol) , additive (1.0 mmol) and solvent (5 mL)
under nitrogen in a sealed tube for 6h. bL1: 2-picolinic acid, L2:
c
(±)-trans-1,2-diaminocyclohexane, L3: 1,10-phenanthroline. The reaction
temperature: 1,4-dioxane and toluene were at 120 °C, o-xylene was at
150 °C , and THF was at 70 °C. dIsolated yield.
To evaluate the scope and generality of the methodology, different substrates with varying
substituents were synthesized and investigated under the standard reaction conditions, and
the results are summarized in Tables 2 and 3. Substrates bearing both electron-rich and
electron-poor aromatic groups on R2 generated the desired products in moderate to good
yields (2b-2h). Similar results were obtained when R2 was furanyl (2i and 2j), and a lower yield
was observed when it was thiophen-2-yl (2k). The reaction proceeded smoothly to give the
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desired products in moderate yields, as for a variety of substrates with alkyl and alkenyl
substituents on R2 (2l-2o). It was also of note that electronic properties of R1 had no significant
effect on this reaction, and desired products were obtained in good yields (2p-2t).
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Table 2: copper-catalyzed reaction of substituted N-acyl-2-iodobenzamide a
2a 81% b
2b 90% b
2c 83% b
2g 53% b
2k 36% b c
2d 84% b
2e 77% b
2f 60% b
2h 70% b
2i 64% b
2j 59% b
2l 42% b
2n 67% b
2o 53% b
2p 75% b
2m 61% b
2q 87% b
2r 84% b
2s 79% b d
2t 85% b
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aThe reactions were performed in a sealed tube with 1 (0.5
mmol), CuI (0.05 mmol), K3PO4 (1.0 mmol), and CaCl2 (1.0
mmol) in toluene (5 mL) at 120 °C under nitrogen for 6 h.
bIsolated yield. c80% conversion, 140 °C , 48 h. d140 °C , 20 h.
As illustrated in Table 3, when the substrate was changed from iodoarene to bromoarene,
a slightly lower yield was observed (2a). Various substituted N-benzoyl-2-bromobenzamides
were also examined, and the target products were produced in moderate yields (2u-2y). We
found that 2y was generated in a good yield when 1-(1-bromonaphthalen-2-yl) was the
substituent on substrate 1y probably owing to the weak aromaticity of the naphthalene ring.
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Table 3: copper-catalyzed reaction of substituted N-benzoyl-2-bromobenzamide a
2a 65% b
2u 61% b
2v 60% b
2y 78% b
2w 53% b
2x 65% b
aThe reactions were performed in a sealed tube
with 1 (0.5 mmol), CuI (0.05 mmol), K3PO4 (1.0
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mmol), and CaCl2 (1.0 mmol) in toluene (5 mL) at
120 °C under nitrogen for 6 h. bIsolated yield.
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On the basis of the above experimental results and related reports,13c,17 a plausible
mechanism for this reaction was depicted in Scheme 1. Copper iodide would activate
N-benzoyl-2-iodobenzamide (1a) to generate a copper(I) complex A, which would then
produce N-benzoyl benzazetone (B) via the C−N coupling process. Immediately, release of
ring strain led to the ketene compound C via the C−N bond cleavage. Ring closure of C would
then yield the target product 2a.
Scheme 1. Postulated Reaction Mechanism.
CONCLUSION
In summary, we have developed an efficient and rapid method for the synthesis of
4H-3,1-benzoxazin-4-one derivatives from easily available N-acyl-2-halobenzamides. Key step
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of this transformation is the C-N bond formation / rearrangement sequence. Considering mild
reaction conditions and a wide functional-group tolerance, this protocol is expected to be
beneficial to organic synthesis.
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EXPERIMENTAL SECTION
General Remarks. Chemicals and reagents were purchased from commercial suppliers and
used without special instructions. All anhydrous solvents used in the reactions were dried and
freshly distilled. Thin-layer chromatography (TLC) was performed using silica HSGF254 plates.
Melting points were determined without correction on a digital melting-point apparatus. 1H and
13C NMR spectra were obtained from a solution in CDCl3 with tetramethylsilane (TMS) as
internal standard using a 400/101 MHz (1H/13C) or 300/75 MHz (1H/13C) spectrometer, δ in
parts per million (ppm), and J in hertz (Hz). Infrared (IR) spectra were recorded in KBr tablets,
and wavenumbers in cm-1. HRMS analyses were carried out on an electrospray ionization (ESI)
apparatus using time-of-flight (TOF) mass spectrometry.
General procedure for the synthesis of compounds 2a-2y. A sealed tube was charged
with a magnetic stir bar, substrate 1 (0.5 mmol),19 CuI (0.05 mmol, 10 mg), K3PO4 (1.0 mmol,
212 mg), CaCl2 (1.0 mmol, 111 mg) and anhydrous toluene (5 mL). The tube was purged with
nitrogen gas, and stirred at 120 °C for the indicated time. After completion of reaction, the
mixture was filtered through a short plug of celite, and washed with EtOAc (2×3mL). The
combined filtrates were concentrated on a rotary evaporator and purified on a silica gel column
using petroleum ether/EtOAc as eluent to give the pure target product.
Characterization Data of the Isolated Compounds. 2-Phenyl-4H-3,1-benzoxazin-4-one
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(2a).17 From substrate N-benzoyl-2-iodobenzamide, yield 78% (87 mg); from substrate
N-benzoyl-2-bromobenzamide, yield 65% (73 mg). White solid, m.p. 108 – 110 °C . 1H NMR
(400 MHz, CDCl3) δ 8.30 – 8.28 (m, 2H), 8.22 (d, J = 7.7 Hz, 1H), 7.81 (t, J = 7.4 Hz, 1H), 7.67
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(d, J = 7.9 Hz, 1H), 7.58 – 7.55 (m, 1H), 7.52-7.48 (m, 3H). C NMR (101 MHz, CDCl3) δ
159.7, 157.2, 147.1, 136.7, 132.7, 130.3, 128.8, 128.7, 128.4, 128.4, 127.3, 117.1. IR (KBr): ν
= 1764, 1617, 1472, 1316, 1259, 1062, 1009, 762, 682, 629 cm-1. LRMS (ESI): m/z calcd for
C14H10NO2 [M + H]+, 224.1; found, 224.1.
2-p-Tolyl-4H-3,1-benzoxazin-4-one (2b).17 Yield 90% (107 mg). White solid, m.p. 138 –
140 °C . 1H NMR (400 MHz, CDCl3) δ 8.23 – 8.18 (m, 3H), 7.81 (t, J = 7.3 Hz, 1H), 7.66 (d, J =
8.0 Hz, 1H), 7.49 (t, J = 7.4 Hz, 1H), 7.30 (d, J = 7.7 Hz, 2H), 2.43(s, 3H). 13C NMR (101 MHz,
CDCl3) δ 159.8, 157.4, 147.2, 143.5, 136.6, 129.6, 128.7, 128.4, 128.1, 127.5, 127.2, 117.0,
21.8. LRMS (ESI): m/z calcd for C15H12NO2 [M + H]+, 238.1; found, 238.1.
2-(4-Methoxyphenyl)-4H-3,1-benzoxazin-4-one (2c).17 Yield 83% (105 mg). White solid, m.p.
144 – 145 °C. 1H NMR (300 MHz, CDCl3) δ 8.19 (t, J = 9.0 Hz, 3H), 7.76 (t, J = 7.7 Hz, 1H),
13
7.60 (d, J = 8.0 Hz, 1H), 7.44 (t, J = 7.5 Hz, 1H), 6.95 (d, J = 8.7 Hz, 2H), 3.86 (s, 3H). C
NMR (101 MHz, CDCl3) δ 163.3, 159.8, 157.1, 147.4, 136.5, 130.3, 128.6, 127.7, 127.0, 122.5,
116.7, 114.2, 55.5. LRMS (ESI): m/z calcd for C15H12NO3 [M + H]+, 254.1; found, 245.1.
2-(3,4,5-Trimethoxyphenyl)-4H-3,1-benzoxazin-4-one (2d).11d Yield 84% (132 mg). White
solid, m.p. 179 – 181 °C. 1H NMR (400 MHz, CDCl3) δ 8.20 (d, J = 7.7 Hz, 1H), 7.80 (t, J = 7.4
Hz, 1H), 7.65 (d, J = 7.9 Hz, 1H), 7.55 – 7.46 (m, 3H), 3.98 (s, 6H), 3.95 (s, 3H). 13C NMR (101
MHz, CDCl3) δ 159.6, 156.7, 153.2, 147.0, 142.0, 136.6, 128.6, 128.1, 127.0, 125.2, 116.7,
105.4, 61.0, 56.4. LRMS (ESI): m/z calcd for C17H16NO5 [M + H]+, 314.1; found, 314.1.
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2-(4-Fluorophenyl)-4H-3,1-benzoxazin-4-one (2e).12d Yield 77% (93 mg). White solid, m.p.
176 – 177 °C. 1H NMR (400 MHz, CDCl3) δ 8.30 (dd, J = 8.1, 5.7 Hz, 2H), 8.22 (d, J = 7.7 Hz,
1H), 7.82 (t, J = 7.5 Hz, 1H), 7.66 (d, J = 8.1 Hz, 1H), 7.51 (t, J = 7.5 Hz, 1H), 7.18 (t, J = 8.5 Hz,
2H). 13C NMR (75 MHz, CDCl3) δ 167.3, 163.9, 159.4, 156.2, 146.9, 136.6, 130.8, 130.7,
128.6, 128.3, 127.2, 126.4, 126.4, 116.8, 116.2, 115.9. LRMS (ESI): m/z calcd for C14H9FNO2
[M + H]+, 242.1; found, 242.1.
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2-(4-(Trifluoromethyl)phenyl)-4H-3,1-benzoxazin-4-one (2f).16h Yield 60% (87 mg). White
solid, m.p. 127 – 128 °C. 1H NMR (400 MHz, CDCl3) δ 8.57 (s, 1H), 8.48 (d, J = 7.7 Hz, 1H),
8.24 (d, J =7.7 Hz, 1H), 7.87 – 7.81 (m, 2H), 7.71 (d, J = 8.0 Hz, 1H), 7.65 (t, J = 7.7 Hz, 1H),
7.55 (t, J = 7.4 Hz, 1H). 13C NMR (75 MHz, CDCl3) δ 159.2, 155.7, 147.4, 146.6, 136.9, 131.7,
131.4, 131.3, 131.2, 129.5, 129.1, 129.1, 128.9, 128.8, 127.5, 125.3, 125.3, 122.0, 120.0,
117.1, 112.8, 112.4. LRMS (ESI): m/z calcd for C15H9F3NO2 [M + H]+, 292.1; found, 292.1.
2-(2-Chlorophenyl)-4H-3,1-benzoxazin-4-one (2g).11c Yield 53% (68 mg). White solid, m.p.
135 – 137 °C. 1H NMR (400 MHz, CDCl3) δ 8.25 (d, J = 7.7 Hz, 1H), 7.90 (d, J = 7.5 Hz, 1H),
7.85 (t, J = 7.6 Hz, 1H), 7.71 (d, J = 8.0 Hz, 1H), 7.57 (t, J = 7.5 Hz, 1H), 7.52(d, J = 7.8 Hz,
13
1H), 7.46 (t, J = 7.4 Hz, 1H), 7.40 (t, J = 7.3 Hz, 1H). C NMR (101 MHz, CDCl3) δ 159.2,
156.5, 146.4, 136.7, 133.4, 132.4, 131.5, 131.1, 130.3, 129.0, 128.6, 127.4, 127.0, 117.0.
LRMS (ESI): m/z calcd for C14H9ClNO2 [M + H]+, 258.0; found, 258.0.
2-(Naphthalen-1-yl)-4H-3,1-benzoxazin-4-one (2h).11e Yield 70% (96 mg). Yellow solid, m.p.
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118 – 120 °C. H NMR (400 MHz, CDCl3) δ 9.14 (d, J = 8.6 Hz, 1H), 8.30 – 8.24 (m, 2H),
8.01(d, J = 8.1 Hz, 1H), 7.89 (d, J = 8.0 Hz, 1H), 7.82 (t, J = 7.5 Hz, 1H), 7.75 (d, J = 7.9 Hz,
1H), 7.63 (t, J = 7.6 Hz, 1H), 7.56 – 7.50 (m, 3H). 13C NMR (101 MHz, CDCl3) δ 159.7, 157.6,
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146.8, 136.6, 134.1, 133.3, 130.8, 130.1, 128.9, 128.6, 128.5, 127.9, 127.4, 126.9, 126.4,
125.8, 124.8, 117.0. LRMS (ESI): m/z calcd for C18H12NO2 [M + H]+, 274.1; found, 274.1.
2-(Furan-2-yl)-4H-3,1-benzoxazin-4-one (2i).10a Yield 64% (68 mg). Yellow solid, m.p. 95 –
96 °C. 1H NMR (400 MHz, CDCl3) δ 8.20 (d, J = 7.6 Hz, 1H), 7.80 (t, J = 7.4 Hz, 1H), 7.72 –
7.67 (m, 2H), 7.49 (t, J = 7.3 Hz, 1H), 7.37 – 7.33 (m, 1H), 6.61 (s, 1H). 13C NMR (101 MHz,
CDCl3) δ 158.6, 149.8, 147.1, 146.7, 144.4, 136.8, 128.8, 128.3, 127.2, 117.2, 116.9, 112.6.
LRMS (ESI): m/z calcd for C12H8NO3 [M + H]+, 214.0; found, 214.0.
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2-(Furan-3-yl)-4H-3,1-benzoxazin-4-one (2j). Yield 59% (63 mg). White solid, m.p. 71 –
73 °C. 1H NMR (400 MHz, CDCl3) δ 8.21 – 8.10 (m, 2H), 7.76 (t, J = 7.6 Hz, 1H), 7.56 (d, J =
8.0 Hz, 1H), 7.50 (s, 1H), 7.45 (t, J = 7.5 Hz, 1H), 6.95 (s, 1H). 13C NMR (101 MHz, CDCl3) δ
159.1, 153.3, 146.8, 146.4, 144.4, 136.5, 128.5, 128.0, 126.7, 119.7, 116.9, 109.0. IR (KBr): ν
= 1766, 1635, 1604, 1397, 1163, 1006, 875, 769, 688, 595 cm-1. HRMS (ESI): m/z calcd for
C12H7NNaO3 [M + Na]+, 236.0318; found, 236.0318.
2-(Thiophen-2-yl)-4H-3,1-benzoxazin-4-one (2k). Yield 36% (41 mg). White solid, m.p. 124 –
126 °C . 1H NMR (400 MHz, CDCl3) δ 8.22 (d, J = 7.8 Hz, 1H), 7.98 – 7.96 (m, 1H), 7.81 (t, J =
7.6 Hz, 1H), 7.65 – 7.61 (m, 2H), 7.49 (t, J = 7.5 Hz, 1H), 7.18 (t, J = 3.9 Hz, 1H). 13C NMR (75
MHz, CDCl3) δ 159.2, 153.9, 147.2, 136.8, 134.3, 132.6, 132.0, 128.9, 128.5, 128.1, 127.0,
116.8. HRMS (ESI): m/z calcd for C12H8NO2S [M + H]+, 230.0270; found, 230.0276.
2-tert-Butyl-4H-3,1-benzoxazin-4-one (2l).17 Yield 42% (43 mg). White solid, m.p. 124 –
125 °C. 1H NMR (400 MHz, CDCl3) δ 8.20 (d, J = 7.7 Hz, 1H), 7.79 (t, J = 7.6 Hz, 1H), 7.60 (d,
J = 8.0 Hz, 1H), 7.50 (t, J = 7.5 Hz, 1H), 1.41 (s, 9H). 13C NMR (75 MHz, CDCl3) δ 168.4, 160.4,
146.7, 136.5, 128.4, 128.2, 127.1, 116.9, 38.1, 27.8. LRMS (ESI): m/z calcd for C12H14NO2 [M
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+ H]+, 204.1; found, 204.1.
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2-Adamantyl-4H-3,1-benzoxazin-4-one (2m). Yield 61% (86 mg). White solid, m.p. 94 –
96 °C. 1H NMR (400 MHz, CDCl3) δ 8.18 (d, J = 7.7 Hz, 1H), 7.78 (t, J = 7.4 Hz, 1H), 7.59 (d, J
= 8.0 Hz, 1H), 7.48 (t, J = 7.5 Hz, 1H), 2.11 (s, 3H), 2.08 (s, 6H), 1.82 – 1.74 (m, 6H). 13C NMR
(75 MHz, CDCl3) δ 167.8, 160.4, 146.8, 136.4, 128.4, 128.1, 127.0, 117.1, 39.8, 39.4, 36.5,
28.0. IR (KBr): ν = 2904, 2850, 1756, 1632, 1606, 1451, 1210, 1037, 1003, 765, 685, 620 cm-1.
HRMS (ESI): m/z calcd for C18H19NNaO2 [M + Na]+, 304.1308; found, 304.1321.
(E)-2-Styryl-4H-3,1-benzoxazin-4-one (2n).16c Yield 67% (84 mg). White solid, m.p. 144 –
146 °C. 1H NMR (400 MHz, CDCl3) δ 8.16 (d, J = 7.7 Hz, 1H), 7.80 – 7.73 (m, 2H), 7.57 – 7.53
(m, 3H), 7.44 (t, J = 7.4 Hz, 1H), 7.40 – 7.33 (m, 3H), 6.73 (d, J = 16.1 Hz, 1H). 13C NMR (101
MHz, CDCl3) δ 159.2, 157.2, 147.0, 141.9, 136.5, 134.6, 130.3, 129.0, 128.6, 128.1, 128.0,
126.9, 118.8, 116.9. LRMS (ESI): m/z calcd for C16H12NO2 [M + H]+, 250.1; found, 250.1.
2-(Prop-1-en-2-yl)-4H-3,1-benzoxazin-4-one (2o). Yield 53% (50 mg). White solid, m.p. 92 –
93 °C. 1H NMR (400 MHz, CDCl3) δ 8.24 – 8.18 (m, 1H), 7.83 – 7.76 (m, 1H), 7.67 – 7.60 (m,
1H), 7.54 – 7.47 (m, 1H), 6.35 (s, 1H), 5.71 (s, 1H), 2.17 (s, 3H). 13C NMR (75 MHz, CDCl3) δ
159.6, 157.5, 146.8, 136.5, 135.8, 128.6, 128.5, 127.5, 124.3, 117.2, 18.9. HRMS (ESI): m/z
calcd for C11H10NO2 [M + H]+, 188.0706; found, 188.0704.
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7-Chloro-2-phenyl-4H-3,1-benzoxazin-4-one (2p).11g Yield 75% (97 mg). White solid, m.p.
180 – 182 °C. 1H NMR (400 MHz, CDCl3) δ 8.32 – 8.26 (m, 2H), 8.16 (d, J = 8.3 Hz, 1H), 7.69
(s, 1H), 7.63 – 7.56 (m, 1H), 7.56 – 7.40 (m, 3H). 13C NMR (75 MHz, CDCl3) δ 158.9, 158.4,
148.2, 143.1, 133.2, 130.0, 129.9, 128.9, 128.9, 128.6, 127.1, 115.5. LRMS (ESI): m/z calcd
for C14H9ClNO2 [M + H]+, 258.0; found, 258.0.
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6-Chloro-2-phenyl-4H-3,1-benzoxazin-4-one (2q).17 Yield 87% (112 mg). White solid, m.p.
152 – 153 °C. 1H NMR (400 MHz, CDCl3) δ 8.31 – 8.26 (m, 1H), 8.26 – 8.24 (m, 1H), 8.16 (d, J
= 2.4 Hz, 1H), 7.73 (dd, J = 8.6, 2.4 Hz, 1H), 7.64 – 7.54 (m, 2H), 7.50 (m, 2H). 13C NMR (101
MHz, CDCl3) δ 158.5, 157.4, 145.6, 136.9, 133.9, 133.0, 129.9, 128.9, 128.9, 128.4, 128.0,
118.2. LRMS (ESI): m/z calcd for C14H9ClNO2 [M + H]+, 258.0; found, 258.0.
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6-Fluoro-2-phenyl-4H-3,1-benzoxazin-4-one (2r).17 Yield 84% (101 mg). White solid, m.p.
130 – 131 °C. 1H NMR (400 MHz, CDCl3) δ 8.27 (d, J = 7.5 Hz, 2H), 7.87 (dd, J = 7.5, 2.2 Hz,
1H), 7.73 – 7.67 (m, 1H), 7.61 – 7.45 (m, 4H). 13C NMR (75 MHz, CDCl3) δ 163.1, 159.8, 158.9,
158.9, 156.6, 156.6, 143.6, 143.6, 132.8, 130.0, 129.7, 129.6, 128.9, 128.3, 125.0, 124.7,
118.4, 118.3, 114.2, 113.8. LRMS (ESI): m/z calcd for C14H9FNO2 [M + H]+, 242.1; found,
242.1.
6,7-Dimethoxy-2-phenyl-4H-3,1-benzoxazin-4-one (2s).11f Yield 79% (112 mg). White solid,
m.p. 197 – 198 °C. 1H NMR (400 MHz, CDCl3) δ 8.23 (d, J = 7.3 Hz, 2H), 7.58 – 7.40 (m, 4H),
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7.06 (s, 1H), 4.01 (s, 3H), 3.97 (s, 3H). C NMR (101 MHz, CDCl3) δ 159.4, 156.6, 156.4,
149.6, 143.3, 132.3, 130.4, 128.7, 128.0, 109.6, 108.1, 107.5, 56.6, 56.4. LRMS (ESI): m/z
calcd for C16H14NO4 [M + H]+, 284.1; found, 284.1.
8-Methyl-2-phenyl-4H-3,1-benzoxazin-4-one (2t). Yield 85% (101 mg). White solid, m.p. 121
– 123 °C. 1H NMR (400 MHz, CDCl3) δ 8.26 (d, J = 6.6 Hz, 2H), 8.01 (d, J = 7.1 Hz, 1H), 7.59
(d, J = 6.4 Hz, 1H), 7.51 (d, J = 6.0 Hz, 1H), 7.46 (d, J = 6.5 Hz, 2H), 7.35 – 7.29 (m, 1H), 2.59
(s, 3H). 13C NMR (101 MHz, CDCl3) δ 160.1, 155.8, 145.2, 137.3, 136.2, 132.4, 130.5, 128.7,
128.2, 127.7, 126.1, 116.9, 17.1. HRMS (ESI): m/z calcd for C15H12NO2 [M + H]+, 238.0863;
found, 238.0869.
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7-Fluoro-2-phenyl-4H-3,1-benzoxazin-4-one (2u).11g Yield 61% (74 mg). White solid, m.p.
150 – 152 °C. 1H NMR (400 MHz, CDCl3) δ 8.35 – 8.21 (m, 3H), 7.62 – 7.56 (m, 1H), 7.55 –
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7.48 (m, 2H), 7.34 (d, J = 9.1 Hz, 1H), 7.22 (t, J = 8.4 Hz, 1H). C NMR (75 MHz, CDCl3) δ
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169.6, 166.2, 158.7, 158.4, 149.7, 149.5, 133.1, 131.6, 131.4, 129.9, 128.9, 128.56, 116.9,
116.6, 113.7, 113.6, 113.5, 113.2. LRMS (ESI): m/z calcd for C14H9FNO2 [M + H]+, 242.1; found,
242.1.
6-Methoxy-2-phenyl-4H-3,1-benzoxazin-4-one (2v).17 Yield 60% (76 mg). White solid, m.p.
137 – 139 °C. 1H NMR (400 MHz, CDCl3) δ 8.25 (d, J = 7.3 Hz, 2H), 7.62 – 7.56 (m, 2H), 7.55
13
– 7.44 (m, 3H), 7.36 (d, J = 7.3 Hz, 1H), 3.90 (s, 3H). C NMR (101 MHz, CDCl3) δ 159.9,
159.3, 155.3, 141.2, 132.3, 130.4, 128.8, 128.8, 128.0, 126.0, 117.8, 108.7, 56.0. LRMS (ESI):
m/z calcd for C15H12NO3 [M + H]+, 254.1; found, 245.1.
6,7-Methylenedioxy-2-phenyl-4H-3,1-benzoxazin-4-one (2w).16f Yield 53% (71 mg). Yellow
solid, m.p. 185 – 187 °C. 1H NMR (400 MHz, CDCl3) δ 8.25 (d, J = 7.4 Hz, 2H), 7.59 – 7.44 (m,
4H), 7.05 (s, 1H), 6.13 (s, 2H). 13C NMR (101 MHz, CDCl3) δ 159.3, 156.5, 155.0, 148.2, 145.1,
132.5, 130.3, 128.8, 128.2, 111.3, 106.3, 105.6, 102.8. LRMS (ESI): m/z calcd for C15H10NO4
[M + H]+, 268.1; found, 268.1.
6-Methyl-2-phenyl-4H-3,1-benzoxazin-4-one (2x).17 Yield 65% (77 mg). White solid, m.p.
136 – 138 °C. 1H NMR (400 MHz, CDCl3) δ 8.30 – 8.22 (m, 2H), 7.99 (d, J = 11.2 Hz, 1H), 7.63
– 7.40 (m, 5H), 2.44 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 159.8, 156.4, 144.8, 138.7, 137.8,
132.4, 130.4, 128.8, 128.2, 127.0, 116.7, 21.4. LRMS (ESI): m/z calcd for C15H12NO2 [M + H]+,
238.1; found, 238.1.
2-Phenyl-4H-naphtho[1,2-d][1,3]oxazin-4-one (2y).17 Yield 78% (107 mg). Yellow solid, m.p.
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180 – 182 °C. 1H NMR (400 MHz, CDCl3) δ 8.91 (d, J = 7.7 Hz, 1H), 8.37 (d, J = 7.5 Hz, 2H),
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8.03 (d, J = 8.6 Hz, 1H), 7.85 – 7.75 (m, 2H), 7.71 – 7.62 (m, 2H), 7.60 – 7.48 (m, 3H). C
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NMR (101 MHz, CDCl3) δ 159.9, 158.0, 146.0, 137.2, 132.8, 130.4, 130.2, 129.2, 128.8, 128.5,
128.4, 128.0, 127.4, 125.4, 122.4, 112.9. LRMS (ESI): m/z calcd for C18H12NO2 [M + H]+, 274.1;
found, 274.1.
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ACKNOWLEDGMENT
We gratefully acknowledge the financial support by PAPD (A Project Funded by the Priority
Academic Program Development of Jiangsu Higher Education Institutions) and NSFC
(National Natural Science Foundation of China, 21172162).
1
Supporting Information: copies of H, 13C NMR spectra. This material is available free of
charge via the Internet at http://pubs.acs.org/.
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