2-Quinolyl- and 1-isoquinolylnitrenes: Ring expansion and ring opening in heteroarylnitrenes

Article abstract of DOI:10.1021/jo026439m

Argon matrix photolysis of tetrazolo[1,5-a]quinoline 8 and tetrazolo[5,1-a]isoquinoline 7 causes nitrogen elimination and ring expansion to 1,3-diazabenzo[d]cyclohepta-l,2,4,6-tetraene 13. The photolysis of tetrazolo[5,1-a]isoquinoline 7 also causes ring opening to o-cyanophenylketenimine 22. Mechanisms of ring opening of heteroarylnitrenes are discussed.

Full text of DOI:10.1021/jo026439m

2-Qu in olyl- a n d 1-Isoqu in olyln itr en es: Rin g Exp a n sion a n d Rin g
Op en in g in Heter oa r yln itr en es
Chris Addicott, Ales Reisinger, and Curt Wentrup*
Department of Chemistry, School of Molecular and Microbial Sciences, The University of Queensland,
Brisbane, Queensland 4072, Australia
wentrup@uq.edu.au
Received September 11, 2002
Argon matrix photolysis of tetrazolo[1,5-a]quinoline 8 and tetrazolo[5,1-a]isoquinoline 7 causes
nitrogen elimination and ring expansion to 1,3-diazabenzo[d]cyclohepta-1,2,4,6-tetraene 13. The
photolysis of tetrazolo[5,1-a]isoquinoline 7 also causes ring opening to o-cyanophenylketenimine
22. Mechanisms of ring opening of heteroarylnitrenes are discussed.
In tr od u ction
spectroscopy.6 The ring expansion of 1 to 2 under solution
photolysis conditions is of synthetic value as a means of
preparation of diazepine derivatives.7
The interconversion of 2-pyridylnitrenes 1 and 3 via
1,3-diazacyclohepta-1,2,4,6-tetraenes 2 under conditions
of flash vacuum thermolysis (FVT) has been established
by 15N and substituent labeling.1,2 In particular, complete
nitrogen scrambling is observed in the 2-cyanopyrrole (4),
glutacononitrile (5), and 2-aminopyridine (6) products
following FVT of 15N-labeled 2-pyridyl azide. 2-Cyanopy-
rrole 4 is the major product of this reaction, but some
3-cyanopyrrole is often obtained as a result of thermal
1,5-sigmatropic shifts of H and CN groups in 4. Com-
pound 5 is a minor product, but the analogous ring
opening of isoquinolylnitrene is important, as demon-
strated in the present paper. 2-Aminopyridine 6 is due
to hydrogen abstraction by the (triplet) nitrene, and
hence its yield is pressure dependent. Seven-membered-
ring carbodiimides of type 2 can be isolated at low
temperatures (77 K suffices in many cases) following
these FVT reactions, and they can also be photochemi-
cally generated in low-temperature matrices. They have
been directly observed and characterized by IR spectro-
scopy.3-5 The dibenzo derivative of 2 was shown to
dimerize at -40 °C to afford a diazete derivative, which
was characterized by X-ray crystallography.3 Formation
of the triplet nitrene 1 under both FVT and matrix
photolysis conditions has been ascertained by ESR
The benzologues of 1, 2-quinolylnitrene 12 and 1-iso-
quinolylnitrene 11, can be generated by FVT of the
tetrazoles 7 and 8. First, mild FVT of 7 and 8 at 150 °C
with isolation of the products at 77 K affords the azides
9 and 10, respectively, which are readily observed by IR
spectroscopy. At 380 °C a new absorption near 2000 cm-1
assigned to carbodiimide 13 appeared.3 Above 500 °C this
species started disappearing again, being replaced by the
final products 15 and 16,3 and these were isolated in 40
and 25% yields, respectively.8 The formation of these two
products in the same ratio from both precursors (7 and
8) suggests the presence of a common intermediate,
presumably isoquinolylnitrene 11, which subsequently
ring opens to the vinylnitrene 14 at temperatures above
500 °C. A 1,2-H shift in 14 would lead to o-cyanophenyl-
acetonitrile 15 (perhaps via the ketenimine 22; see
(1) For reviews of carbene and nitrene rearrangements, see: (a)
Wentrup, C. Top. Curr. Chem. 1976, 62, 173-251. (b) Wentrup, C. Adv.
Heterocycl. Chem. 1981, 28, 231-361. (c) Wentrup, C. In Azides and
Nitrenes; Scriven, E. F. V., Ed.; Academic: New York, 1984; Chapter
8, pp 395-433. (d) Platz, M. S. Acc. Chem. Res. 1995, 28, 487-492. (e)
Gritsan, N. P.; Platz, M. Adv. Phys. Org. Chem 2001, 36, 255-304.
(2) Crow, W. D.; Wentrup, C. Chem. Commun. 1969, 1387.
(3) Wentrup, C.; Winter, H.-W. J . Am. Chem. Soc., 1980, 102, 6159.
(4) Wentrup, C.; The´taz, C.; Tagliaferri, E.; Lindner, H. J .; Kitschke,
B.; Reisenauer, H. P.; Winter, H.-W. Angew. Chem., Int. Ed. Engl. 1980,
19, 566.
(6) Kuzaj, M.; Lu¨erssen, H.; Wentrup, C. Angew. Chem., Int. Ed.
Engl. 1986, 25, 480.
(7) Reisinger, A.; Koch, R.; Wentrup, C. J . Chem. Soc., Perkin Trans.
1 1998, 2247.
(5) Evans, R. A.; Wong, M. W.; Wentrup, C. J . Am. Chem. Soc. 1996,
118, 4009.
(8) Wentrup, C. Tetrahedron 1971, 27, 367.
10.1021/jo026439m CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/23/2003
1470
J . Org. Chem. 2003, 68, 1470-1474

2-Quinolyl- and 1-Isoquinolylnitrenes
below), and aromatic CH insertion to 16.
Further evidence for the conversion of a quinolylni-
trene (18) to an isoquinolylnitrene (20) was given by FVT
of 8-phenyl tetrazolo[1,5-a]quinoline 17. The product 21
was isolated in 73% yield, and it is reasonable to
formulate its formation via ring expansion to the cyclic
carbodiimide 19.9
F IGURE 1. (a) IR spectrum of tetrazolo[5,1-a]isoquinoline in
Ar matrix; (b) calculated IR spectrum of 1,3-diazabenzocyclo-
hepta-1,2,4,6-tetraene 13 (A) (the peak at 2016 cm-1 is
attenuated by a factor of 2); (c) result of 2 h of broadband
irradiation of the matrix in part a. Calculated IR spectra of
(d) s-Z- and (e) s-E-2-(2-iminovinyl)benzonitrile 22 (B) (the
peaks at 2047 and 2043 cm-1 are attenuated by 20% and 10%,
respectively). All calculations are at the B3LYP/6-31G* level,
scaled by 0.9613. Inset: 2010-2070 cm-1. A ) 2020 cm-1. B
) 2041 cm-1. Shoulders are present at 2049, 2052, 2059, and
2071 cm-1. Abscissa in wavenumbers.
Simple sublimation with Ar matrix isolation affords the
matrix-isolated tetrazole (Figure 1a), and only at tem-
peratures above 150 ° C is the azide 9 obtained. Photoly-
sis of 7 (λ > 260 nm) gave rise to new absorptions at 2020,
2041, 2071, 2158, 2238, and 3305 cm-1 (Figure 1c). New
bands in the fingerprint region appeared as well (757,
763, 932, 936, and 948 cm-1). This spectrum is analyzed
as the composite of two compounds, the cyclic carbodi-
imide 13 (2020 cm-1) and the open-chain ketenimine 22
(inter alia 2041, 2238, and 3305 cm-1). The experimental
IR spectra are in good agreement with the calculated
spectra of 13 and the s-Z and s-E forms of 22 (Figure
1b,d,e). As shown below, it is possible to obtain 13 almost
pure from tetrazoloquinoline.
The triplet nitrenes 11 and 12 have been observed by
Ar matrix ESR spectroscopy in both the FVT reactions
and the matrix photolysis reactions of the corresponding
tetrazoles 7 and 8. Further photolysis of these matrices
caused the development of ESR signals typical of a
carbene, which may have been the triplet benzodiazacy-
cloheptatrienylidene (a triplet state of 13).6
We have now investigated the matrix photochemistry
of 7 and 8 in detail and report that both undergo ring
expansion to carbodiimide 13, and 1-isoquinolylnitrene
11 undergoes ring opening as well.
Resu lts
The absorption at 2041 cm-1 is characteristic of an
acyclic ketenimine.10 The shoulders on the 3305- (NH)
and 2041-cm-1 (CdCdNH) bands suggest that the matrix
may contain more than one conformer of 22. The 2238-
Ma tr ix P h otolysis of Tetr a zolo[5,1-a ]isoqu in olin e
7. Compound 7 exists in the tetrazole form in the solid
form in KBr as evidenced by the absence of IR absorp-
tions due to the azido group in the 2100-cm-1 region.
(9) Wentrup, C.; The´taz, C.; Gleiter, R. Helv. Chim. Acta 1972, 55,
2633. See also: Brown, R. F. C.; Smith, R. J . Aust. J . Chem. 1972, 25,
607.
(10) J acox, M. E.; Milligan, D. E. J . Am. Chem. Soc. 1963, 85, 278.
J acox, M. E. Chem. Phys. 1979, 43, 157. Finnerty, J .; Mitschke, U.;
Wentrup, C. J . Org. Chem. 2002, 67, 1084.
J . Org. Chem, Vol. 68, No. 4, 2003 1471

Addicott et al.
TABLE 1. Exp er im en ta l a n d Ca lcu la ted IR Ba n d s
(cm -1) for 22 (B3LYP /6-31G*, sca led by 0.9613)
exptl
417 w, 421 w
452 w, 458 w
557 w, 559 w
605 w, 609 w
635 w, 636 w
763 m
calcd for s-Z-22
calcd for s-E-22
400, 409
455
559
591
-
748
823
411
451
554
603
627
747
826 w, 830 w
837 w, 843 w
932 m, 936 m, 938 m,
941 m, 948 m
1043 w
850
969
962
1027
1104
1182
1295
1444
1469
1063
1111
1121 w
1166 w, 1169 w
1293 w
1274, 1283
1434
1460 w
1493 w
1477
1573 w
1553
1605 w
1589
2047
1591
2041 m, 2049 w, 2059 w,
2071 w
2043
2238 w
3295 w, 3301 w, 3305 w,
3308 w, 3309 w
2245
3319
2246
3301
TABLE 2. Exp er im en ta l a n d Ca lcu la ted IR Ba n d s
(cm -1) for 13 (B3LYP /6-31G*, sca led by 0.9613)
exptl
calcd
exptl
calcd
420 w
411
455
476
521
579
651
691
743
799
822
944
1026
1064
1141 w
1178 w
1207 w
1257 w
1285 w
1296 w
1358 w
1448 w
1473 w
1599 w
1603 w
2020 s
1122
1158
1192
1239
1277
1290
1346
1431
1454
1578
1590
2016
467 w
485 w
535 w
598 w
668 w
705 w
757 m
815 w
841 w
958 w
1039 w
1085 w, 1089 w
cm-1 band (CN) is slightly broadened, probably for the
same reason. All calculations were performed at the
B3LYP/6-31G* level of theory, and no significant changes
occurred for 22 at the B3LYP/6-311++G** level. The
data are compiled in Tables 1 and 2.
Ma tr ix P h otolysis of Tetr a zolo[1,5-a ]qu in olin e 8.
As in the previous case, sublimation and co-deposition
with Ar at 25 K afforded the matrix-isolated tetrazole 8
(Figure 2a), and sublimation through an oven at 150 °C
gave the azide 10.3 Photolysis of 8 with λ > 260 nm for
1 h produced carbodiimide 13 as shown by the excellent
agreement between experimental and calculated IR
bands (Figure 2 and Table 2).
F IGURE 2. (a) IR spectrum of tetrazolo[1,5-a]quinoline in Ar
matrix; (b) results of 1 h of broadband irradiation; and (c)
calculated spectrum of 1,3-diazabenzocyclohepta-1,2,4,6-tet-
raene 13 (A) at the B3LYP/6-31G* level, scaled by 0.9613 (the
peak at 2016 cm-1 is attenuated by a factor of 2). Inset: 2000-
2090 cm-1. A ) 2020 cm-1. B ) 2047 cm-1. Two slightly weaker
peaks are present at 2041 and 2060 cm-1. Abscissa in wave-
numbers.
different species absorbing at 2158 cm-1 (especially from
the isoquinoline) suggests the presence of isocyanide
functions. C-(o-Isocyanophenyl)ketenimine, formed by
ring cleavage of 13, is a possibility for the former set of
bands. The calculated spectra are given in the Supporting
Information. o-(Isocyanomethyl)benzonitrile, formed by
photoisomerization11 of 22, is a possibility for the 2158-
cm-1 species. However, the weakness of these minor
peaks makes any assignment hazardous.
Weak bands are seen at 2041, 2047, and 2060 cm-1 in
Figure 2. These correspond to the wavenumbers assigned
to 22 in Figure 1, but the relative intensities are different,
possibly because a different mixture of conformers and/
or sites is produced. The weakness of these bands makes
a firm assignment impossible, but since we know from
FVT chemistry that the nitrenes do interconvert ther-
mally (see the Introduction), a partial rearrangement of
12 to 11 via 13 and consequential ring opening to 22
would not be surprising under photolysis conditions.
Only a few weak bands remain unassigned in the
spectra of photolysis of 7 and 8. Very weak bands at 2124
and 2128 cm-1 (especially from the quinoline) and a
Th er m a lly P r od u ced Ca r bod iim id e 13. We have
ascertained that the same carbodiimide 13 is produced
thermally and photochemically by carrying out Ar matrix
isolations of the products of FVT of 7 and 8 over the
temperature range 430-730 °C. The absorptions of 13
were identical with those reported in Table 2. The results
obtained previously3 with neat isolation at 77 K were
confirmed.
1472 J . Org. Chem., Vol. 68, No. 4, 2003

2-Quinolyl- and 1-Isoquinolylnitrenes
Carbodiimide 13 absorbs at 2007 cm-1 in the neat state
at 77 K. 15N labeling of the carbodiimide function is
expected to result in a significant lowering of the wave-
number.12 We prepared the 1(3)-15N labeled tetrazoles 7
and 8 by reactions of 2-chloroquinoline and 1-chloroiso-
quinoline with potassium azide labeled on one terminal
nitrogen atom.13 FVT of these compounds afforded the
carbodiimide 13, absorbing at 1999.5 ( 1 cm-1 when
produced from labeled 7, and at 1998.5 ( 1 cm-1 when
produced from labeled 8 (neat, 77 K). FVT of a mixture
of labeled 7 and 8 confirmed that the absorption maxima
of the two 15N-isotopomeric carbodiimides, 1- and 3-15N-
13 are separated by 1 cm-1, in excellent agreement with
the calculated difference (1 cm-1 at the B3LYP/6-31G*
level). The calculated spectra are shown in the Support-
ing Information.
with initial formation of â-styrylnitrene and C-phen-
ylketenimine was proposed.15a We have shown that the
matrix photolysis of â-styryl azide in Ar matrix at 313
nm for 30 min indeed produces a ketenimine absorbing
at 2023 cm-1 16
.
Discu ssion
The results clearly show that both the quinolyl and the
isoquinolyl systems give rise to the ring-expanded car-
bodiimide 13, presumably via the nitrenes 11 and 12
which can be observed (in their triplet states) by ESR
spectroscopy.6 In analogy with calculations on related
systems,14 the ring expansion of the quinolylnitrene may
take place via the azirine 23, but the azirine 24 derived
from isoquinolylnitrene is expected to be a transition
state rather than an intermediate. Both 23 and 24 are
expected to be significantly higher in energy than 13,14
and we have no direct experimental evidence for either
of them.
The formation of 15, 16, and 21 from the appropriate
quinolines 8 and 18 demonstrates that the cyclic carbo-
diimide 13 can isomerize to 1-isoquinolylnitrene 11, at
least under FVT conditions. Since at most traces of 22
are formed in the matrix photolysis of 8, the reaction
essentially stops at the ring expansion stage, 13, under
matrix photolysis conditions.
We have recently discovered an important type of ring
opening (Type 1) involving nitrile ylide intermediates and
taking place in heteroarylnitrenes and heteroarylcar-
benes or their ring-expanded equivalents under matrix
photolysis conditions, e.g. 25 in the 2-pyrazinylnitrene/
4-pyrimidylnitrene/1,3,5-triazacyclohepta-1,2,4,6-tetra-
ene system:17
Analogous Type 1 ring-opening reactions also take place
in 2-quinoxalylnitrene,18 1-quinazolylnitrene,18 3-quinolyl-
ni-trene, and other nitrenes and carbenes,19 as well as
3-pyridazinylnitrene where the ring-opened ylide is a
stable diazo compound, 3-diazo-2-butenoic nitrile.20 Type
1 ring opening is energetically very favorable because
ylides are relatively stable intermediates, and it always
takes place under matrix photolysis conditions whenever
(11) Ketenimine undergoes matrix photochemical isomerization to
methyl isocyanide. Maier, G.; Schmidt, C.; Reiusenauer, H. P.; Endlein,
E.; Becker, D.; Eckwert, J .; Hess, B. A., J r.; Schaad, L. J . Chem. Ber.
1993, 126, 2337.
(12) Donnelly, T.; Dunkin, I. R.; Norwood, D. S. D.; Prentice, A.;
Shields, C. J .; Thomson, P. C. P. J . Chem. Soc., Perkin Trans. 2 1985,
307.
(13) Wentrup, C.; The´taz, C. Helv. Chim. Acta 1976, 59, 256.
(14) Kuhn, A.; Vosswinkel, M.; Wentrup, C. J . Org. Chem., 2002,
67, 9023.
(15) (a) Boyer, J . H.; Krueger, W. E.; Mikol, G. J . J . Am. Chem. Soc.
1967, 89, 5504. (b) Isomura, K.; Kobayashi, S.; Taniguchi, S. Tetra-
hedron Lett. 1968, 3499.
The formation of ketenimine 22 suggests ring opening
of isoquinolylnitrene to the vinylnitrene 14 followed by
a 1,2-H shift. Under thermal conditions in the gas phase,
22 would rearrange to the observed FVT product 15. The
thermolysis of â-styryl azide is known to afford phenyl-
acetonitrile and indole.15 The solution photolysis produces
phenylacetonitrile via 3-phenyl-2-azirine.15 A mechanism
J . Org. Chem, Vol. 68, No. 4, 2003 1473

Addicott et al.
1090 m, 1038 w, 1034 w, 1033 w, 1025 w, 1018 w, 1015 w,
1009 w, 1003 w, 999 w, 993 w, 989 w, 988 m, 985 w, 958 w,
902 w, 899 w, 897 w, 876 w, 811 w, 809 w, 796 s, 795 s, 775 w,
752 w, 748 m, 712 m, 696 w, 633 w, 571 w, 569 w, 518 w, 517
w, 507 w, 417 m, 409 w.
it is structurally possible. Type 1 ring opening to a nitrile
ylide is not structurally possible in 11, 12, or 13, and also
not in 2-pyridylnitrene 1. Therefore, the energetically
more expensive ring opening via vinylnitrene-type inter-
mediates, e.g 14 (Type 2), occurs instead. This is also a
major reaction channel in 3-isoquinolylnitrene,18 where
it succeeds ring expansion, and in 2-pyrimidylnitrenes.19
Ring opening now emerges as a common ultimate fate of
heteroaromatic nitrenes, and sometimes carbenes, espe-
cially under photolysis conditions, where it may compete
with or follow ring expansion. Ring contraction is a
common ultimate fate under thermal conditions, some-
times with ring opening competing and reversible ring
expansion occurring.
Irradiation (λ > 260 nm, 2 h) gave rise to 13 and 22: IR
(Ar, 10 K) (cm-1) 3579 w, 3575 w, 3568 w, 3309 w, 3308 w,
3305 w, 3301 w, 3295 w, 3088 w, 3072 w, 3068 w, 3045 w,
2238 w, 2161 w, 2158 w, 2153 w, 2150 w, 2140 w, 2128 w,
2123 w, 2071 w, 2059 w, 2053 w, 2049 w, 2041 m, 2028 m,
2025 m, 2020 s, 2008 w, 1992 w, 1983 w, 1978 w, 1959 w, 1955
w, 1949 w, 1929 w, 1919 w, 1676 w, 1605 w, 1594 w, 1573 w,
1561 w, 1555 w, 1502 w, 1493 w, 1486 w, 1473 w, 1465 w,
1464 w, 1460 w, 1458 w, 1453 w, 1448 w, 1442 w, 1437 w,
1418 w, 1412 w, 1386 w, 1357 w, 1331 w, 1314 w, 1308 w,
1304 w, 1296 w, 1293 w, 1289 w, 1286 w, 1285 w, 1270 w,
1268 w, 1266 w, 1262 w, 1257 w, 1251 w, 1240 w, 1225 w,
1222 w, 1219 w, 1213 w, 1211 w, 1208 w, 1198 w, 1194 w,
1178 w, 1173 w, 1169 w, 1166 w, 1141 w, 1129 w, 1121 w,
1114 w, 1102 w, 1097 w, 1092 w, 1089 w, 1085 w, 1043 w,
1025 w, 1021 w, 1017 w, 984 w, 983 w, 979 w, 976 w, 971 w,
964 w, 958 w, 948 m, 941 m, 938 m, 936 m, 932 m, 927 w, 920
w, 918 w, 885 w, 872 w, 869 w, 850 w, 843 w, 840 w, 837 w,
830 w, 826 w, 818 w, 815 w, 814 w, 810 w, 807 w, 773 w, 766
w, 763 m, 757 m, 749 w, 747 w, 744 w, 742 w, 740 w, 715 w,
708 w, 705 w, 657 w, 636 w, 635 w, 609 w, 605 w, 598 w, 559
w, 557 w, 554 w, 535 w, 467 w, 464 w, 458 w, 452 w, 428 w,
421 w, 417 w.
Tetr a zolo[1,5-a ]qu in olin e 8. This compound was sub-
limed at 60-64 °C in a stream of Ar for 10 min onto a KBr
window at 31 K. The matrix was cooled to 10 K and the
infrared spectrum recorded: IR (Ar, 10 K) (cm-1) 3475 w, 3081
w, 3066 w, 1963 w, 1929 w, 1897 w, 1849 w, 1816 w, 1627 m,
1620 s, 1612 w, 1579 w, 1566 m, 1543 m, 1533 w, 1468 w,
1464 w, 1459 w, 1455 m, 1452 w, 1419 m, 1412 w, 1370 w,
1367 w, 1335 w, 1326 w, 1292 w, 1282 w, 1261 w, 1235 w,
1231 w, 1223 w, 1222 w, 1164 w, 1162 w, 1144 w, 1133 w,
1129 w, 1095 w, 1081 w, 1067 w, 1039 w, 1020 w, 991 w, 970
w, 949 w, 869 w, 817 s, 815 s, 768 w, 755 s, 702 w, 698 w, 697
w, 630 w, 556 w, 515 w, 472 w, 440 w, 418 w.
Irradiation (λ > 260 nm, 1 h) gave rise to predominantly
13: IR (Ar, 10 K) (cm-1) 3492 w, 2240 w, 2158 w, 2128 w, 2123
w, 2060 w, 2047 w, 2041 w, 2020 s, 2008 w, 1992 w, 1965 w,
1918 w, 1603 w, 1599 w, 1473 w, 1448 w, 1386 w, 1358 w,
1314 w, 1305 w, 1296 w, 1291 w, 1289 w, 1285 w, 1257 w,
1251 w, 1245 w, 1222 w, 1207 w, 1196 w, 1193 w, 1178 w,
1141 w, 1129 w, 1124 w, 1089 w, 1085 w, 1039 w, 1018 w, 988
w, 958 w, 945 w, 923 w, 841 w, 815 w, 808 w, 767 w, 762 w,
757 m, 740 w, 738 w, 715 w, 705 w, 668 w, 662 w, 643 w, 598
w, 570 w, 566 w, 535 w, 485 w, 467 w, 420 w, 418 w.
Tetr a zolo[5,1-a ]isoqu in olin e-1(3)-15N (50 a tom % 15N).
To a mixture of 1-chloroisoquinoline (19.3 mg; 0.118 mmol)
and terminally 15N-labeled sodium azide13 (8.2 mg; 0.126 mmol;
50 atom % 15N) was added 1 mL of 50% aqueous EtOH and
two drops of 10% aqueous EtOH containing 78 mmol of HCl
per 100 mL. The solution was stirred in a closed flask at 100
°C for 20 h. Colorless crystals separated on cooling to room
temperature, yield 7.8 mg (39%), mp 142-145 °C (mp of the
corresponding unlabeled material: 145-146 °C).
Com p u ta tion a l Deta ils
Standard DFT calculations were performed with the Gauss-
ian 98 suite of programs.21 Vibrational spectra were computed
with the B3LYP/6-31G* method. A scaling factor of 0.9613 was
used for frequencies.22
Exp er im en ta l Section
Gen er a l. The starting tetrazoles 7 and 8 and the 15N-
labeled 8 were prepared according to the literature.23-25 The
apparatus for matrix isolation was as previously described.26
A 1000-W high-pressure Xe/Hg lamp was used for photolysis.
Ma tr ix Isola tion a n d P h otolyses: Tetr a zolo[5,1-a ]-
isoqu in olin e 7. This compound was sublimed at 55-56 °C
in a stream of Ar for 25 min onto a KBr window at 31 K. The
matrix was cooled to 10 K and the infrared spectrum re-
corded: IR (Ar, 10 K) (cm-1) 3541 w, 3449 w, 3136 w, 3100 w,
3086 w, 3070 w, 2150 w, 2141 w, 1971 w, 1942 w, 1915 w,
1859 w, 1832 w, 1726 w, 1719 w, 1647 m, 1600 w, 1566 w,
1562 w, 1532 w, 1522 s, 1517 m, 1488 w, 1485 w, 1456 s, 1430
m, 1407 w, 1400 w, 1393 m, 1383 w, 1332 w, 1315 w, 1301 w,
1292 w, 1263 w, 1256 w, 1251 w, 1240 w, 1236 w, 1220 w,
1218 w, 1209 w, 1203 w, 1168 w, 1163 w, 1162 w, 1142 w,
1140 w, 1124 w, 1122 w, 1114 w, 1112 w, 1109 w, 1107 m,
(16) Freiermuth, B.; Wentrup, C. Unpublished results, The Univer-
sity of Queensland, 1989.
(17) Addicott, C.; Wong, M. W.; Wentrup, C. J . Org. Chem. 2002,
67, 8538.
(18) Vosswinkel. M. PhD Thesis, Universities of Queensland and
Bochum, 2003, in preparation.
(19) Bednarek, P.; Mitschke, U.; Wentrup, C. Unpublished results,
The University of Queensland, 2000-2002.
(20) Wentrup, C.; Crow, W. D. Tetrahedron 1970, 26, 4915. Wentrup,
C.; Crow, W. D. Tetrahedron 1971, 27, 1566
(21) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
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Ack n ow led gm en t. The support of this work by the
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We thank Hans-Wilhelm Winter for the experiments on
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Su p p or tin g In for m a tion Ava ila ble: Tables of Cartesian
coordinates, absolute energies, and IR spectra of all calculated
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O026439M
1474 J . Org. Chem., Vol. 68, No. 4, 2003