A Comparison of the Flash Vacuum Pyrolysis Products of Some N-Acylbenzotriazoles and N-Acylbenzisoxazolones

Article abstract of DOI:10.1071/CH99037

The flash vacuum pyrolysis (f.v.p.) products of 2-(1H-benzotriazol-1-ylcarbonyl)benzonitrile, methyl 2-(1H-benzotriazol-1-ylcarbonyl)benzoate and 1-(2-chloromethylbenzoyl)-1H-benzotriazole and the corresponding benzisoxazolones have been characterized. The benzotriazole derivatives gave compounds whose origin suggests the predominance of radical processes. At lower temperatures the benzisoxazolones gave benzoxazole products consistent with a singlet carbene intermediate, but which had triplet diradical properties at higher temperatures, leading to the formation of acridine from the chloromethyl compound. The major low-temperature f.v.p. product from the (chloromethylbenzoyl)benzisoxazolone was indolo[1,2-b]benzoxazole.

Full text of DOI:10.1071/CH99037

C S I R O P U B L I S H I N G
Australian Journal
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Volume 52, 1999
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Aust. J. Chem., 1999, 52, 775–780
.
A Comparison of the Flash Vacuum Pyrolysis Products of
Some N -Acylbenzotriazoles and N -Acylbenzisoxazolones
Mehdi M. Baradarani,A,B Jabbar Khalafy A,B and Rolf H. Prager A
A
Chemistry Department, Flinders University of South Australia,
G.P.O. Box 2100, Adelaide, S.A. 5001.
B
Permanent address: Chemistry Department, Urmia University,
Urmia 57154, Iran.
The ash vacuum pyrolysis (f.v.p.) products of 2-(1H -benzotriazol-1-ylcarbonyl)benzonitrile, methyl
2-(1H -benzotriazol-1-ylcarbonyl)benzoate and 1-(2-chloromethylbenzoyl)-1H -benzotriazole and the cor-
responding benzisoxazolones have been characterized. The benzotriazole derivatives gave compounds
whose origin suggests the predominance of radical processes. At lower temperatures the benzisoxa-
zolones gave benzoxazole products consistent with a singlet carbene intermediate, but which had triplet
diradical properties at higher temperatures, leading to the formation of acridine from the chloromethyl
compound. The major low-temperature f.v.p. product from the (chloromethylbenzoyl)benzisoxazolone
was indolo[1,2-b]benzoxazole.
Introduction
In a recent paper1 we examined the ash vacuum
pyrolysis (f.v.p.) products of some (ortho-substituted)
benzylbenzisoxazolones and the corresponding benzo-
triazoles, and found that the products of the latter
were consistent with the intermediacy of diradicals.
These pathways were most marked in the case of the 2-
methoxycarbonylbenzyl analogue. We had hoped that
the N -benzylbenzisoxazolones would undergo ther-
mal decomposition by processes involving carbenoid
intermediates,2 but elimination to the imines was
clearly the rst step in their thermal reactions (Scheme
1). In order to avoid such elimination reactions, and
to attempt to nd any evidence for cyclizations of
the type shown in Scheme 2, we have prepared the
acyl compounds (1)–(6), and herein report their f.v.p.
products, and a cursory examination of some photolysis
products.
on mass and n.m.r. spectrometric evidence and its
acidity, and would represent the rst member of a
new heterocyclic system. Compound (8), remarkably
stable at 600 , is believed to be formed by radical
recombination of the rst formed diradical from (1),
followed by addition of benzotriazole, itself formed by
fragmentation of (1) (Scheme 3). The alternative zwit-
terionic intermediate (9), postulated in some thermal
liquid phase reactions,4,8 appears unlikely to us under
the f.v.p. conditions employed.
The ester (2) underwent extensive decomposition
under the pyrolysis conditions, and the only charac-
terized product was the oxazole (10) (42%).
The triazole (3) underwent f.v.p. to give acridine
hydrochloride (65%), with only traces of two other
Discussion
The 1-acyltriazoles (1)–(3) were prepared in high
yield by treating the sodium salt of the benzotriazole
with the corresponding acid chloride in tetrahydrofuran;
only in the case of (3) was the N 1 acylated material
accompanied by about 10% of the N 2 acylated isomer,3
readily separated by crystallization. Previous work on
the pyrolytic reactions of acylated benzotriazoles has
always given low yields of products.4–7 F.v.p. of com-
pound (1) at 520 gave a mixture of oxazole (7) (16%),
and 33% of a compound to which we have tentatively
assigned the isoindolo[1,2-d] [1,2,3,5]benzotetraazepine
structure (8). The structure of (8) is based only
Manuscript received 22 March 1999
᭧ CSIRO 1999
0004-9425/99/080775$ 05.00
10.1071/CH99037

776
M. M. Baradarani, J. Khalafy and R. H. Prager
to the amidyl radical centre rather than to the aryl
radical centre leading to (12), presumably for entropic
reasons, as the bond strengths of N–H and Ar–H are
comparable. In the event, no chlorophthalimidine (13)
could be found by g.c.–m.s. investigation.
As has been previously observed,2 the acylbenzisox-
azolones, also prepared from their sodium salts and
the corresponding acid chlorides in tetrahydrofuran,
underwent f.v.p. at lower temperatures, and more
cleanly, than the benzotriazoles. The benzisoxazolones
(4) and (5) gave the oxazoles (7) and (10) in 72
and 83% yields respectively at 550 . The benzisoxa-
zolone (6) gave the oxazole (14) in 11% yield at 520 ;
the major product (59%) was the novel tetracycle
products. Evidence to be presented below suggests
that the acridine is a product of the triplet diradical
(11) (Scheme 4). The diradical (11), formed by loss
of nitrogen, appears to prefer hydrogen atom transfer

F.V.P. of N -Acylbenzotriazoles and N -Acylbenzisoxazolones
777
isoindolo[2,1-b]benzoxazole (16). While the syntheses
of the nitrogen,9 sulfur10 and selenium11 analogues
(17)–(19) have been reported, and indeed they enjoy
some industrial applications,12 (16) does not appear to
have been described. By analogy with the preparation
of (18),10 we suggest that, under the f.v.p. conditions,
the relatively weak base (14) is converted into the salt
(15), which is deprotonated under the high vacuum
conditions (Scheme 5).
temperatures now gives predominantly a triplet car-
bene/diradical, leading to hydrogen atom transfer as
observed with the benzotriazole. Finally, we wondered
whether similar intermediates might be formed on
photolysis in solution. When (6) was photolysed at
300 nm in acetone, conditions that favour oxazole for-
mation from acylisoxazolones,13 two compounds could
be isolated; these were identi ed as phthalide (60%)
and anthranilic acid (53%). These products could be
expected from the diradical produced by homolysis
of the N–O bond, which abstracts hydrogen from
the solvent acetone (Scheme 6), but no acridine was
obtained in this case. When the solvent was changed
to acetonitrile, the photolysis products were a compli-
cated mixture, in which only three components could
be unambiguously identi ed, namely phthalide (38%),
oxazole (14) (17%), and 2-chloroaniline (4%). The
absence of reduction products in this case suggests
to us that the products are arising from the carbene
intermediate, as suggested in Scheme 7. While the
formation of the phthalimidine (20) might have been
expected, no evidence for its presence could be found by
g.c.–m.s. The photolysis of N -benzoyltriazoles14 gener-
ally leads mainly to hydrogen abstraction or cyclization
to phenanthridin-6(5H )-one via radical intermediates
(Scheme 8).
When the f.v.p. of (6) was conducted at 650 , the
product distribution was markedly di erent to that at
520 , above. While a trace of oxazole (14) was detected,
the tetracycle (16) was now only a minor product
(11%), the major product being acridine hydrochloride.
This observation suggests that pyrolysis at the higher
In conclusion, this work supports the conclusions
of Yonezawa,15 who suggests that the decomposition
of triazoles, under both thermal and photochemical

778
M. M. Baradarani, J. Khalafy and R. H. Prager
of sodium hydride (80 mg, 60% suspension in oil, washed with
dry tetrahydrofuran (2 ml)) in dry tetrahydrofuran (3 ml).
After 10 min a solution of 2-chloromethylbenzoyl chloride
(378 mg, 2 mmol) in dry tetrahydrofuran (4 ml) was added,
and the mixture was stirred at 25 for 24 h. Dichloromethane
(20 ml) was added, and the mixture washed with water (20 ml),
dried, and the solvent removed. Recrystallization of the solid
residue from ethanol removed c. 10% of the N 2 substituted
isomer, and gave the title compound as white needles (450 mg,
83%), m.p. 144 (Found: C, 61 7; H, 3 6; N, 15 4%; M+
,
conditions, occurs by both singlet and triplet pathways.
The benzisoxazolones generally decompose via singlet
carbenes, at least at relatively low temperatures.
271 0511. C14H10ClN3O requires C, 61 9; H, 3 7; N, 15 5%;
M+ , 271 0512). 1H n.m.r. 4 81, s, 2H; 7 46–7 78, m, 6H;
8 17, dd, J 8 1, 1 2 Hz, 1H; 8 42, dd, J 8 1, 1 2 Hz, 1H.
13C n.m.r. 43 41, 114 64, 120 33, 126 56, 128 09, 130 42,
130 61, 131 06, 131 79, 132 21, 137 64, 146 00, 167 10 (one
Experimental
quaternary C not visible).
1713, 1597, 1483, 1451, 1376,
max
1049, 939, 883 cm 1. Mass spectrum m/z 271 (M, 5%), 243
(23), 242 (42), 241 (44), 208 (100), 180 (24), 179 (25), 154
(29), 152 (83), 124 (65).
Full experimental details were given in the preceding paper in
this series.1 All previously described compounds were identi ed
by direct comparison with authentic materials, and synthesized
by literature procedures.
2-(3-Oxo-1,3-dihydro-2,1-benzisoxazol-1-
ylcarbonyl)benzonitrile (4)
2-(1 H-Benzotriazol-1-ylcarbonyl)benzonitrile (1)
A solution of 2-cyanobenzoyl chloride (166 mg, 1 mmol)
in dichloromethane (4 ml) was added to a suspension of
benzisoxazolone19 (135 mg, 1 mmol) and pyridine (5 drops)
in dry dichloromethane (5 ml). After 3 5 h at room temper-
ature, the mixture was washed with water (2 5 ml), dried
over sodium sulfate, and the solvent removed. The residue
was recrystallized from ethanol to give white needles (210 mg,
To a solution of 1H -benzotriazole (0 6 g, 5 mmol) and
pyridine (7 drops) in dry dichloromethane (6 ml) was added
a solution of 2-cyanobenzoyl chloride16 (0 83 g, 5 mmol) in
dry dichloromethane (12 ml). The mixture was re uxed under
nitrogen for 5 h, cooled, further dichloromethane (20 ml) added,
and the solution washed with water (3 20 ml). Removal of
solvent gave a cream solid which was recrystallized from carbon
tetrachloride to give white needles, m.p. 149 (1 02 g, 82%)
(Found: C, 67 8; H, 3 1; N, 22 6%; M+ , 248 0703. C14H8N4O
requires C, 67 8; H, 3 2; N, 22 6%; M+ , 248 0698). 1H
n.m.r. 7 59, td, J 7 5, 1 2 Hz, 1H; 7 71–7 95, m, 4H; 8 06,
ddd, J 7 0, 1 2, 0 9 Hz, 1H; 8 18, dd, J 8 1, 1 2 Hz, 1H;
80%), m.p. 180 (Found: C, 63 3; H, 2 7; N, 10 4%; M+
264 0535. 15H8N2O3 requires C, 63 2; H, 3 0; N, 10 1%;
M+ , 264 0535). 1H n.m.r.
,
C
7 69–7 93, m, 6H; 7 93, dd,
J 8 1, 1 2 Hz, 1H; 8 28, dd, J 8 1, 1 2 Hz, 1H. 13C n.m.r.
111 99, 115 65, 116 50, 125 90, 126 88, 129 73, 132 13,
132 61, 133 92, 135 00, 136 96, 144 95, 161 02, 163 41 (one
8 42, dd, J 8 1, 1 2 Hz, 1H. 13C n.m.r.
113 05, 114 66,
quaternary C not visible).
1
2240, 1789, 1685, 1600, 1332,
. Mass spectrum m/z 264 (M, 3%), 248
max
116 53, 120 48, 127 01, 131 05, 131 62, 131 79, 132 37,
132 62, 134 05, 135 15, 146 17, 164 52. Mass spectrum m/z
248 (M, 14%), 221 (20), 220 (100), 192 (14), 129 (85), 101
(65), 74 (29).
958, 776, 769 cm
(5), 220 (5), 130 (100), 102 (23), 75 (17).
Methyl 2-(3-Oxo-1,3-dihydro-2,1-benzisoxazol-1-
ylcarbonyl)benzoate (5)
Methyl 2-(1 H-Benzotriazol-1-ylcarbonyl)benzoate (2)
A suspension of benzisoxazolone (135 mg, 1 mmol) and
methyl 2-chlorocarbonylbenzoate (200 mg, 1 mmol) in dichloro-
methane (7 ml) was re uxed under nitrogen for 1 h. The solution
was passed through a short plug of silica. The solid white residue
obtained after evaporation was recrystallized from ethanol to
give white needles (237 mg, 80%), m.p. 122 (Found: C, 64 9;
H, 3 6; N, 4 7%; M+ , 297 0629. C16H11NO5 requires C,
64 6; H, 3 7; N, 4 7%; M+ , 297 0637). 1H n.m.r. 3 76, s,
3H; 7 46, ddd, J 8 1, 7 2, 0 9 Hz, 1H; 7 60, ddd, J 7 2, 1 5,
0 6 Hz, 1H; 7 62, td, J 7 5, 1 5 Hz, 1H; 7 71, td, J 7 5, 1 2
Hz, 1H; 7 86, ddd, J 8 4, 7 5, 1 2 Hz, 1H; 7 92, ddd, J 8 1,
1 2, 0 9 Hz, 1H; 8 1, ddd, J 8 1, 1 2, 0 9 Hz, 1H; 8 27, br
d, J 7 2 Hz, 1H. 13C n.m.r. 52 65, 111 99, 115 09, 125 73,
126 21, 127 91, 128 04, 130 21, 130 77, 133 02, 134 86,
To a solution of 1H -benzotriazole (357 mg, 3 mmol) and pyri-
dine (5 drops) in dry dichloromethane (4 ml) was added a solution
of 2-methoxycarbonylbenzoyl chloride (600 mg, 3 mmol) (made
from methyl hydrogen phthalate17 and thionyl chloride) in dry
dichloromethane (2 ml). The mixture was stirred at 25 under
nitrogen for 24 h. Dichloromethane (20 ml) was added, and
the solution was washed with water (3 20 ml), dried, and the
solvent removed. The resultant solid was recrystallized from
ethanol to give the title compound as pale brown needles, m.p.
113 (718 mg, 85%) (Found: C, 64 2; H, 3 9; N, 15 0%; M+
,
281 0808. C15H11N3O3 requires C, 64 1; H, 3 9; N, 14 9%;
M+ , 281 0801). 1H n.m.r. 3 68, s, 3H; 7 55, ddd, J 8 2,
7 2, 1 0 Hz, 1H; 7 65–7 78, m, 4H; 8 11–8 18, m, 2H; 8 49,
dt, J 8 4, 0 9 Hz, 1H. 13C n.m.r. 52 56, 114 57, 120 27,
126 45, 128 56, 129 40, 130 16, 130 60, 131 01, 131 52,
136 78, 145 86, 163 84, 165 80, 165 92.
1786, 1719,
max
1697, 1465, 1367, 1332, 1288, 972, 754 cm 1. Mass spectrum
m/z 297 (M, 0 2%), 266 (1 6), 222 (1 7), 164 (9 7), 163 (100),
135 (3), 133 (2 5), 104 (4 2), 92 (4 7), 77 (13 3), 76 (9 7), 51
(1 5), 50 (3 4), 44 (6 7).
132 77, 135 51, 146 23, 165 96, 169 56.
1726, 1597,
max
1487, 1442, 1385, 1327, 1290, 1231, 1151, 1083, 1052, 1004,
939, 884, 768, 771, 753, 714 cm 1. Mass spectrum m/z 281
(M, 11%), 222 (16), 162 (100), 104 (9), 91 (11).
1-(2-Chloromethylbenzoyl)benzisoxazol-3(1 H)-one (6)
1-(2-Chloromethylbenzoyl)-1 H-benzotriazole (3)
A solution of benzisoxazolone (405 mg, 3 mmol) in dry
tetrahydrofuran (3 ml) was added to a suspension of sodium
hydride (120 mg, 60% suspension in oil, washed with dry
tetrahydrofuran (2 ml)) in dry tetrahydrofuran (3 ml). After
10 min at room temperature under nitrogen, a solution of
2-chloromethylbenzoyl chloride (567 mg, 3 mmol) in dry tetrahy-
drofuran (3 ml) was added. The mixture was stirred at room
2-Chloromethylbenzoyl chloride was prepared in 87% yield
from phthalide (1 34 g) and triphenylphosphine dichloride (3 3
g) by the method of Burton and Koppes.18 1H n.m.r. 4 90,
s, 2H; 7 42–7 75, m, 3H; 8 28, dd, J 7 75, 1 2 Hz, 1H.
A solution of 1H -benzotriazole (238 mg, 2 mmol) in dry
tetrahydrofuran (4 ml) was added under nitrogen to a suspension

F.V.P. of N -Acylbenzotriazoles and N -Acylbenzisoxazolones
779
temperature for 4 h, dichloromethane (20 ml) added, and the
mixture washed with water (20 ml). The organic phase was
dried, concentrated, and the solution passed through a short
column of silica. The resultant solid was recrystallized from
ethanol to give white needles (623 mg, 77%), m.p. 139 (Found:
C, 62 8; H, 3 6; N, 4 9%; M+ , 287 0353. C15H10ClNO3
requires C, 62 6; H, 3 5; N, 4 9%; M+ , 287 0349). 1H n.m.r.
4 78, s, 2H; 7 42–7 5, m, 2H; 7 53–7 57, m, 2H; 7 64, ddd,
J 8 1, 1 2, 0 9 Hz, 1H; 7 84, td, J 8 1, 1 2 Hz, 1H; 7 93,
ddd, J 7 5, 1 2, 0 9 Hz, 1H; 8 18, br d, J 8 1 Hz, 1H.
13C n.m.r. 43 09, 112 10, 115 35, 125 71, 126 33, 128 34,
128 91, 130 37, 131 61, 131 71, 136 60, 136 62, 145 0, 163 36,
72%), whose spectroscopic data were identical with those of
the compound obtained above.
Pyrolysis at 650 gave the same product, but the yield was
reduced to 38%.
Pyrolysis of Methyl 2-(3-Oxo-1,3-dihydro-2,1-benzoxazol-1-
ylcarbonyl)benzonitrile (5)
Compound 5 (100 mg) was pyrolysed under f.v.p. conditions
(590 , 120 , 0 05 mmHg, 90 min). The product in the cold
trap was dissolved in dichloromethane and ltered through a
plug of silica. The solvent was removed, and the product
(80 mg) was puri ed by radial chromatography (CH2Cl2)/light
petroleum, 1 : 1), to give methyl 2-(benzoxazol-2-yl)benzoate
(10) (71 mg, 83%) as a colourless oil (Found: M+ , 253 0738.
163 68.
1779, 1681, 1601, 1477, 1375, 1333, 1253, 973,
max
752 cm 1. Mass spectrum m/z 289 (M, 0 6%), 287 (M, 1 8),
C
15H11NO3 requires M+ , 253 0739). 1H n.m.r.
3 85, s,
252 (1 2), 155 (47), 153 (100), 134 (18), 105 (53).
3H; 7 35–7 40, m, 2H; 7 54–7 67, m, 3H; 7 77–7 82, m, 2H;
8 04–8 08, m, 1H. 13C n.m.r. 52 6, 110 6, 120 45, 124 64,
125 42, 126 58, 129 30, 130 12, 131 01, 131 16, 132 68,
Pyrolysis of 2-(1 H-Benzotriazol-1-ylcarbonyl)benzonitrile (1)
(i) At 520 . The nitrile (1) (100 mg) was subjected to ash
vacuum pyrolysis (520 , 110 , 0 05 mmHg, 2 h). The contents
of the cold trap were extracted with dichloromethane, to give
2-(benzoxazol-2-yl)benzonitrile (7) (14 mg, 16%), and evapora-
tion of the ethanol extract of the pyrolysis tube gave a yellow
base-soluble oil, tentatively identi ed as 5-(1H -benzotriazol-1-
yl)-5H -isoindolo[1,2-d][1,2,3,5]benzotetrazepin-12-ol(8)(49 mg,
33%). 1H n.m.r. 6 35, t, J 7 Hz, 2H; 6 63, d, J 10 Hz, 2H;
6 92, t, J 10 Hz, 1H; 7 05, d, J 10 Hz, 1H; 7 50, m, 3H;
7 65, m, 3H. 13C n.m.r. 107 5, 114 0, 116 5, 120 0, 120 5,
120 8, 122 5, 125 8, 126 0, 132 8, 133 2, 134 6, 134 8, 135 0,
136 8, 142 0, 152 5, 170 0 (two peaks not observed). Mass
spectrum m/z 367 (M), 341, 257, 217, 203, 136, 81.
141 95, 151 06, 162 15, 168 68.
1733, 1617, 1559, 1454,
max
1443, 1345, 1295, 1242, 1194, 1129, 1100, 1047, 761, 747,
703 cm 1. Mass spectrum m/z 253 (M, 20%), 222 (41), 195
(34), 148 (66), 134 (20), 105 (50), 104 (100), 91 (8), 86 (18),
84 (28), 77 (24), 76 (96), 74 (23), 63 (13), 51 (13), 50 (45).
Pyrolysis of 1-(2-Chloromethylbenzoyl)benzisoxazol-
3(1 H)-one (6)
(i) At 520 .
Isoxazolone (6) was pyrolysed under f.v.p.
conditions (520 , 110 , 0 05 mmHg, 30 min). The crude
product was separated by column chromatography (CH2Cl2),
giving 2-(benzoxazol-2-yl)benzyl chloride (14) (10 mg, 11%) as
a colourless oil, and isoindolo[2,1-b]benzoxazole (16) (43 mg,
59%) as a colourless oil. 2-(Benzoxazol-2-yl)benzyl chloride
(ii) At 650 .
The nitrile (1) was pyrolysed under ash
vacuum pyrolysis conditions (650 , 110 , 0 05 mmHg, 2 h).
The product from the cold trap was puri ed by chromatogra-
phy on silica to give 2-(benzoxazol-2-yl)benzonitrile (7) (25 mg,
32%) as a pale yellow oil (Found: M+ , 220 0637. C14H8N2O
(14) (Found: M+ , 243 0448. C14H10ClNO requires M+
,
243 0450). 1H n.m.r. 5 39, s, 2H; 7 36–7 58, m, 4H; 7 62,
td, J 8 1, 1 2 Hz, 1H; 7 69, dd, J 7 6, 1 2 Hz, 1H; 7 82, td,
J 7 6, 1 2 Hz, 1H; 8 24, dd, J 7 6, 1 2 Hz, 1H. 13C n.m.r.
44 67, 110 59, 115 76, 120 42, 124 61, 125 47, 127 70,
requires M+ , 220 0637). 1H n.m.r.
7 38–7 46, m, 2H;
7 6–7 69, m, 2H; 7 75, td, J 8 1, 1 5 Hz, 1H; 7 83–7 89,
m, 2H; 8 41, dd, J 8 1, 1 5 Hz, 1H. 13C n.m.r.
110 88,
110 92, 117 62, 120 81, 125 0, 126 16, 129 14, 129 7, 131 06,
132 78, 135 06, 141 58, 150 65, 159 46. 2230, 1545,
128 63, 130 09, 131 17, 131 35, 137 42, 142 20, 150 31.
max
1576, 1440, 1266, 1192, 1042, 835, 718 cm 1. Mass spectrum
m/z 245 (M, 34%), 243 (M, 100), 209 (17), 207 (82), 184 (20),
179 (14), 153 (15), 90 (11). Isoindolo[2,1-b]benzoxazole (16)
(Found: M+ , 207 0688. C14H9NO requires M+ , 207 0684).
1H n.m.r. 6 66, s, 1H; 7 35, td, J 8 1, 1 2 Hz, 1H; 7 62–7 82,
m, 4H; 7 97, dd, J 8 1, 1 2 Hz, 1H; 8 12–8 21, m, 2H. 13C
n.m.r. 84 69, 115 12, 119 64, 124 09, 124 71, 125 39, 131 06,
max
1
1543, 1377, 1260, 1032, 815, 738 cm
. Mass spectrum m/z
220 (M, 100%), 192 (12), 178 (30), 151 (30), 128 (9), 92 (18).
Pyrolysis of Methyl 2-(1 H-Benzotriazol-1-
ylcarbonyl)benzoate (2)
The triazole (2) (100 mg) was pyrolysed as above (700 ,
110 , 0 05 mmHg, 1 h). The product was obtained by passing
the dichloromethane washing of the cold trap and pyroly-
sis tube through a short plug of silica, followed by radial
chromatography (CH2Cl2/light petroleum, 1 : 1). Methyl 2-
(benzoxazol-2-yl)benzoate (10) (38 mg, 42%) was isolated as a
colourless oil, with properties identical to those described for
the pyrolysis product of (5), below.
131 26, 131 78, 133 72, 135 92, 138 12, 138 92, 161 30.
max
1602, 1582, 1488, 1464, 1399, 1377, 1353, 1211, 1051, 1019,
1
756 cm
. Mass spectrum m/z 207 (M, 6%), 179 (12), 169
(20), 153 (10), 134 (53), 105 (100), 90 (8), 77 (78).
(ii) At 650 . Pyrolysis as above at 650 led to a product
which was soluble in water, and another which was soluble in
dichloromethane. The latter gave isoindolo[2,1-b]benzoxazole
(16) (10 mg, 14%), identical with the sample obtained above.
The aqueous phase was basi ed with sodium hydroxide and
extracted with dichloromethane to give acridine as yellow crys-
tals, m.p. 100 (39 mg, 62%) (Found: M+ , 179 0725. Calc.
for C13H9N: M+ , 179 0735). The identity was con rmed by
direct comparison of its spectroscopic properties with those of
an authentic sample, and by g.c.–m.s. analysis. 1H n.m.r.
7 45, td, J 7 5, 0 9 Hz, 2H; 7 71, td, J 7 5, 0 9 Hz, 2H; 7 88,
dd, J 8 1, 1 2 Hz, 2H; 8 21, dd, J 8 1, 1 2 Hz, 2H; 8 63,
Pyrolysis of 1-(2-Chloromethylbenzoyl)-1 H-benzotriazole (3)
The triazole (3) was pyrolysed as above (650 , 110 ,
0 05 mmHg, 50 min). The products were obtained by washing
the trap and pyrolysis tube with dichloromethane and water.
The aqueous phase was basi ed with aqueous sodium hydrox-
ide, and then extracted with dichloromethane to give acridine
(42 mg, 62%), m.p. 100 , with spectroscopic data identical in
all respects with those of an authentic sample.
s, 1H. 13C n.m.r.
135 86, 148 90.
125 5, 126 43, 128 05, 129 23, 130 13,
Pyrolysis of 2-(3-Oxo-1,3-dihydro-2,1-benzoxazol-1-
ylcarbonyl)benzonitrile (4)
Photolysis of 1-(2-Chloromethylbenzoyl)benzisoxazol-
3(1 H)-one (6)
The isoxazolone (4) (100 mg) was pyrolysed under f.v.p.
conditions (520 , 110 , 0 05 mmHg, 4 h). A solution of the con-
tents of the cold trap in dichloromethane was chromatographed
on silica to give 2-(benzoxazol-2-yl)benzonitrile (7) (61 mg,
(i) In acetone.
A solution of the benzisoxazolone (6)
(100 mg) in acetone (200 ml) was photolysed through a Pyrex
lter under nitrogen for 24 h. Removal of the solvent and

780
M. M. Baradarani, J. Khalafy and R. H. Prager
5
6
partitioning of the residue between aqueous sodium carbonate
and dichloromethane gave phthalide (29 mg, 60%) in the neu-
tral fraction, and anthranilic acid (25 mg, 53%) in the acidic
fraction. The identity of both compounds was established by
infrared spectroscopy, 1H and 13C n.m.r. spectrometry and
g.c.–m.s. comparison with commercially available samples.
Burgess, E. M., Carithers, R., and McCullagh, L., J. Am.
Chem. Soc., 1968, 90, 1923.
Maquestiau, A., Beugnies, D., Flammag, R., Freiermuth,
B., and Wentrup, C., Org. Mass Spectrom., 1990, 25, 197.
Druliner, J. D., J. Am. Chem. Soc., 1968, 90, 6879.
Hubert, A. J., and Reimlinger, H., Chem. Ber., 1970, 103,
2828.
7
8
(ii) In acetonitrile.
A solution of the benzisoxazolone
9
10
11
12
(6) (50 mg) in acetonitrile (200 ml) was irradiated through
Pyrex under nitrogen for 24 h. Removal of solvent gave a
brown solid which was analysed by 1H n.m.r. spectroscopy
and g.c.–m.s., and was shown to comprise phthalide (9 mg,
38%), 2-(benzoxazol-2-yl)benzyl chloride (14) (7 mg, 17%), and
2-chloroaniline (1 mg, 4%).
Tamborski, C., Prabbu, U. D. G., and Eapen, K. C., J.
Fluorine Chem., 1985, 28, 139.
Babichev, F. S., and Kibirev, V. K., Zh. Obshch. Khim.,
1963, 33, 2000 (Chem. Abstr., 1963, 59, 10019e).
Likhitskaya, V. S., and Babichev, F. S., Ukr. Khim. Zh.,
1969, 35, 746 (Chem. Abstr., 1970, 72, 12654r).
Babichev, F. S., Acta Univ. Debrecen. Ludovico Kossuth
Nominatae, Ser. Phys. Chim., 1966, 12, 73 (Chem. Abstr.,
1967, 67, 43716p).
Acknowledgments
13
Khalafy, J., Svensson, C. E., Prager, R. H., and Williams, C.
M., Tetrahedron Lett., 1998, 39, 5405; Khalafy, J., Prager,
R. H., and Williams, C. M., Aust. J. Chem., 1999, 52, 31.
Meier, H., and Menzel, I., Justus Liebigs Ann. Chem., 1970,
739, 56.
Ohashi, M., Tsujimoto, K., and Yonezawa, T., J. Chem.
Soc., Chem. Commun., 1970, 1089; Tsujimoto, K., Ohashi,
M., and Yonezawa, T., Bull. Chem. Soc. Jpn, 1973, 46,
3605.
Braun, A., and Tcherniac, J., Ber. Dtsch. Chem. Ges.,
1907, 40, 2709.
Eliel, E. L., and Burgstahler, A. W., J. Am. Chem. Soc.,
1949, 71, 2251.
M.M.B. and J.K. are grateful for the granting of
sabbatical leave from Urmia University, I R Iran. The
project was supported by the Australian Research
Council.
14
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