J. CHEM. RESEARCH (S), 1997 287
Table 2 Physical data for compounds 4–f
max(KBr)/cmꢀ1
Compound 4 CtO
v
d (ppm) (CDCl3–TMS)
a
b
c
1762
1768
1758
1H 2.46 (s, 3 H, CH3), 7.42–8.31 (m, 4 H, Ar-H)
13C 20.85 (CH3), 116.21, 125.90, 127.65, 127.86 (4 CH), 135.96 (C10), 145.98 (C5), 158.97 (CO), 159.74
(C2)
1H 7.24–8.35 (m, 9 H, Ar-H)
13C 116.62, 126.80, 127.73, 127.86, 128.02, 128.26, 129.81 (9 CH), 132.13 (C-Ph), 135.96 (C10), 146.46
(C5), 156.52 (C2), 158.80 (CO)
1H 1.38 (t, 3 H, CH3), 2.77 (q, 2 H, CH2), 7.38–8.21 (m, 4 H, Ar-H)
13C 9.44 (CH3), 27.36 (CH2), 116.17, 125.82, 127.29, 127.49 (4 CH), 135.55 (C10), 145.73 (C5), 158.68
(CO), 163.08 (C2)
d
e
1755
1762
1H 7.45–8.42 (m, 5 H, C2-H, Ar-H)
13C 118.86, 127.08, 128.64, 129.20 (4 CH), 136.61 (C10), 145.45 (C5), 149.73 (C2), 158.36 (CO)
1H 1.24 (t, 3 H, CH3), 1.83 (sextet, 2 H, CH2), 2.72 (t, 2 H, CH2), 7.32–8.28 (m, 4 H, Ar-H)
13C 13.47, 19.50, 36.52 (3C-aliphatic), 116.78, 126.43, 127.98, 128.26 (4 CH), 136.28 (C 10), 146.38
(C5), 159.66 (CO), 163.00 (C2)
f
1765
1H 1.02 (t, 3 H, CH3), 1.22–1.98 (m, 4 H, 2CH2), 2.79 (t, 2 H, CH2), 7.38–8.35 (m, 4 H, Ar-H)
13C 13.72, 22.23, 28.17, 34.49 (4C-aliphatic), 116.90, 126.56, 128.02, 128.31 (4 CH), 136.33 (C10),
146.51 (C5), 159.26 (CO), 163.24 (C2)
The structures of compounds 4a–f were confirmed by IR,
mmol) and trimethyl orthoformate (8.49 g, 80 mmol) contained in
a tall beaker was placed in the microwave oven and the beaker was
covered with a stemless funnel and irradiated for 5 min at 210 W
and then for 1 min at 385 W. The reaction mixture was allowed to
cool to room temperature and the resultant residue recrystallised
from dry heptane to afford the pure 4H-3,1-benzoxazin-4-one
(moisture sensitive, very hygroscopic) in 76% yield.
1H and 13C NMR spectral analyses (Table 2) and their physi-
cal properties were identical with those of authentic samples
prepared by reported procedures.6
In conclusion, we have demonstrated that orthoesters and
anthranilic acid condense under conventional thermal heat-
ing or microwave irradiation, providing an efficient and con-
venient synthesis of 2-substituted 3,1-benzoxazin-4-ones. In
this method, orthoesters serve as a ‘one-atom linchpin’ to
form the corresponding benzoxazin-4-one. The extension of
this reaction to the synthesis of other heterocycles is currently
under investiation.
Received, 17th January 1997; Accepted, 21st April 1997
Paper E/7/00411G
References
Experimental
1 C. Parkanyi, H. L. Yuan, B. H. E. Stromberg and A. Evenzahav,
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5250, at 2450 MHz. Melting points are uncorrected. For safety
reasons all the experiments with microwave ovens should be per-
formed in an efficient hood in order to avoid contact with vapours.
All products (except 4f) are known compounds and their physical
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Preparation of 2-Substituted 4H-3,1-benzoxazin-4-ones under
Classical Heating. General Procedure with 2-n-Butyl-4H-3,1-
benzoxazin-4-one (4f).sA stirred mixture of anthranilic acid
(2.74 g, 20 mmol) and trimethyl orthovalerate (6.49 g, 40 mmol)
was heated under reflux for 1.5 h. After this time the reaction
mixture was cooled to 0 °C and the white precipitate thus obtained
was filtered off and recrystallized from heptane to give colourless
needles of 4f in 75% yield.
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General Procedure under Microwave Irradiation with 4H-3,1-
Benzoxazin-4-one (4d).sA mixture of anthranilic acid (2.74 g, 20