METHOXY(2-PYRIDYL)KETENE
523
1
5. Photolysis of 12 does not generate 15, but instead
W). In all cases, irradiation afforded the following bands:
2283 (w), 2124 (s), 1737 (w), 1662 (m), 1592 (m), 1567
(w), 1484 (m), 1472 (m), 1439 (m), 1410 (w), 1384 (w),
1368 (w), 1286 (w), 1214 (m), 1198 (w), 1150 (w), 1055
formaldehyde and 2-pyridylketene (4), largely in the s-E-
form, s-E-4, presumably by fragmentation of methoxy-
carbonyl(2-pyridyl)carbene (14). Photolysis of s-Z-15
results in extrusion of CO and formation of 2-acetylpy-
ridine, presumably by rearrangement of methoxy(2-
pyridyl)carbene (19).
À1
(w), 775 (w) cm .
Photolysis of methoxy-(2-pyridyl)ketene (s-Z-15).
Flash vacuum thermolysis of 12 at 500°C generated
ketene 15, predominantly in the s-Z form, s-Z-15, which
was co-deposited on the spectroscopic window at 7 K.
Irradiation using the unfiltered light of the 1000 W Hg–
Xe lamp or the low-pressure Hg lamp (l = 254 nm) gave
EXPERIMENTAL
3
-(Methoxycarbonyl)-1,2,3-triazolo[1,5-a]pyridine
À1
(12)
CO (2139 cm ) and 2-acetylpyridine; IR (Ar, 7 K), ꢀ
1
À1
712, 1361, 1295, 1285, 1241, 950, 779, 591 cm .
This compound was prepared according to the litera-
4
,11
4
ture;
m.p. 136°C (lit. 138–141°C); GC–MS, m/z 177;
2-Acetylpyridine. A sample of 2-acetylpyridine was
sublimed at 0°C and deposited with Ar for matrix
isolation at 23 K. IR (Ar, 23 K), ꢀ 3500 (w broad), 3063
(w), 3016 (w), 1712 (vs), 1619 (v), 1590 (w), 1572 (w),
1439 (m), 1422 (w), 1413 (w), 1361 (vs), 1301 (w), 1295
(m), 1286 (s), 1241 (s), 1102 (m), 1044 (w), 996 (w), 950
1
3
H NMR (400.1 MHz, CDCl ), ꢁ 8.80 (ddd, J 7.0 Hz,
J7,5 1.0 Hz, J
.9 Hz, J4 1.1 Hz, J 1.1 Hz 1H, H-4), 7.52 (ddd,
J5,4 8.9 Hz, J 6.8 Hz, J 0.9 Hz 1H, H-5), 7.52
ddd, J6 6.9 Hz, J 6.9 Hz, J 1.2 Hz 1H, H-6),
.00 (s, 3H, OCH3); C NMR (100.6 MHz, CDCl ), ꢁ
61.7 (CO), 135.1 (C-3a), 129.2 (C-3, C-7), 125.9 (C-4),
19.2 (C-5), 116.4 (C-6), 52.0 (OCH ); IR (Ar, 28 K), ꢀ
3
7,6
4
5
3
1.0 Hz 1H, H-7), 8.24 (ddd, J
7,4
4,5
4
5
8
,6
4,7
3
3
4
5,6
5,7
3
3
,7 6,5 6,4
4
(
13
À1
4
1
1
2
(m), 779 (m), 740 (w), 622 (w), 591 (s) cm .
3
3
962 (w), 1758 (w), 1719 (s), 1645 (w), 1550 (w), 1533
Computational procedure
(
1
s), 1528 (s), 145 4 (m), 1442 (w), 1417 (w), 1376 (w),
329 (m), 1271 (s), 1256 (m), 1229 (vs), 1163 (w), 1138
Density functional theory calculations were carried out
12
(
(
3
w), 1074 (vs), 1004 (w), 814 (w), 792 (w), 775 (w), 749
using the Gaussian 98 series of programs. Geometry
optimizations, vibrational frequencies and thermochem-
istry were examined with the B3LYP method using the
À1
w), 682 (w) cm . Anal. Calcd for C H N O : C 54.2, H
8
7 3 2
.9, N 23.72%. Found: C 54.42, H 4.08, N 23.16%.
6
–31G* basis set. All wavenumbers were scaled by a
13
factor of 0.9613.
Cartesian coordinates, absolute
Matrix isolation experiments
energies and imaginary frequencies of transition states
are presented in the Supplementary Information, avail-
able at the epoc website at http://www.wiley.com/epoc.
Flash vacuum thermolysis. Triazolopyridine 12 (ca
1
0 mg portions) was subjected to FVT over the
temperature range 400–600°C. The sublimation tem-
perature was 60–75°C. The product was isolated in an Ar
matrix at ca 23 K, and spectra were recorded at 7 K. At
Acknowledgements
4
1
00°C, mainly starting material 12 (1719, 1229,
This research was supported by the Australian Research
Council. We are indebted to the University of Queens-
land for a scholarship for H.G.A.
À1
074 cm ) and a small amount of Z-methoxy-(2-
À1
pyridyl)ketene (s-Z-15) (2114 cm ) were observed. A
mixture of 12 and Z-15 was obtained at 450°C. The
formation of s-Z-15 was essentially complete at 500°C.
The intensity of bands belonging to carbon dioxide
À1
À1
REFERENCES
(
2345 cm ) and carbon monoxide (2139 cm ) in-
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1
2
3
. Kuhn A, Pl u¨ g C, Wentrup C. J. Am. Chem. Soc. 2000; 122: 1945–
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(
2-pyridyl)ketene 15: IR (Ar, 7 K), see Table 2.
2
002; 1366–1368.
. Pl u¨ g C, Kuhn A, Wentrup C. Eur. J. Org. Chem. 2002; 2683–2685.
Matrix photolysis of 12. Compound 12 was deposited
with Ar on the spectroscopic window at 23 K and the
window was cooled to 7–10 K before commencing
irradiation. The photolysis was carried out with the light
of a 1000 W high-pressure Hg–Xe lamp, either unfiltered
or at 313 nm selected with a monochromator (bandwidth
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1
5
. Maas G. In Methoden der Organischen Chemie (Houben-Weyl),
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Copyright 2003 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2003; 16: 519–524