Nitrenes, Azirenes, and Diradicals
Tetrazolo[1,5-b]isoquinoline-15N/3-Azidoisoquinoline-15N 22T′/
22A′. Labeled 3-aminoisoquinoline (0.171 g, 1.18 mmol) was
dissolved in 7 mL of DCM and cooled to 5-7 °C, affording a
yellow suspension. A suspension of MSH (0.280 g, 1.30 mmol) in
7 mL of DCM was cooled to 5 °C and added to the above
suspension at 5 °C with stirring. The DCM was previously freed
of acid by passing it through a column of basic alumina. When a
clear lemon solution had formed, stirring was stopped, and the
solution was allowed to stand for 1 h, after which time a precipitate
had formed. After addition of 2 mL of diethyl ether, the mixture
was allowed to stand at 5 °C for 12 h. The product was filtered,
washed thoroughly with diethyl ether, and dried in vacuo to afford
319 mg (0.88 mmol, 75.0%) of a yellow solid: mp 170-172 °C.
This material was dissolved in 6 mL of acetic acid (50%), and a
cold solution of 97 mg (1.41 mmol) of sodium nitrite in 2 mL of
water was added dropwise at 0-5 °C. After the mixture had been
stirred in ice in the dark for 2 h, the crude product (48 mg, 32%)
was filtered and purified by vacuum sublimation to yield 13 mg
(9%) of 22T′/22A′: mp 126-128 °C. Unlabeled tetrazole 22T/22A
was obtained in the same manner: mp 126-128 °C; lit.9b mp 122
°C.
1603 w, 1523 s, 1448 w, 1359 vw, 1219 m, 917 w, 848 vw, 793
vw, 768 w, 757 w, 744 w, 630 w, 615 w, and 586 w cm-1. On
subsequent warming, the bands of azirene disappeared between 110
and 140 K.
Argon Matrix Photolysis of 3-Azidoisoquinoline-15N 22A′. The
tetrazole/azide mixture was sublimed at 46-49 °C (2 × 10-6 mbar)
over 2 h and 15 min and codeposited in argon (flow rate about 4
mbar/min): IR (Ar matrix, 7 K) ν 3069, 2330, 2293, 2207, 2182,
2175, 2154 (all vw), 2143 w, 2133 vs, 2116 w, 2111 w, 2105 vw,
1636 m, 1595 m, 1588 vw, 1585 w, 1498 vw, 1496 vw, 1450 vw,
1444 sh, 1443 m, 1438 vw, 1349 m, 1345 sh, 1344 sh, 1340
vw, 1294 vw, 1288 w, 1286 m, 1279 vw, 1274 w, 1270 w, 1236
vw, 1232 w, 1228 m, 1225 vw, 1222 vw, 1193 vw, 1191 w, 1145,
1136, 1107, 1103, 1016, 958, 952, 890, 875, 873, 845, 791, 777,
748, 681, 606, 526, and 468 (all vw) cm-1
.
The azide was then photolyzed with light of λ > 300 nm. The
progress of the photolysis was followed in discrete intervals. After
10.5 min, the azide had almost disappeared, and only a negligible
amount of final photolysis product 17 was present. The bands of
15N-labeled azirines 24′ and 24′′ were observed: IR (Ar matrix, 7
K) ν 1731 vw, 1724 vw, 1717 vw, 1711 w, 1574 vw, 1529 s,
1521 w, 1465 vw, 1448 w, 1446 w, 1356 vw, 1349 vw, 1291 vw,
1216 sh, 1213 m, 1203 br w, 1170 vw, 966 vw, 964 vw, 914 w,
913 w, 910 vw, 908 sh, 844 vw, 842 vw, 836 vw, 834 sh, 792 vw,
790 vw, 766 vw, 762 w, 756 w, 741 vw, 636 vw, 633 vw, 614 vw,
596 vw, 593 w, 591, 589, 587, 555, and 553 (all vw) cm-1 (Figure
4).
Argon Matrix Photolysis of 3-Azidoisoquinoline 22A. The
tetrazole/azide mixture 22T/22A was sublimed at 45-55 °C (3.3
× 10-6 mbar) and codeposited in argon (flow rate about 3 mbar/
min). The condensate consisted only of 3-azidoisoquinoline 22A,
as evidenced by comparison with the IR spectrum of the solid
tetrazole/azide mixture: IR (Ar matrix, 7 K) ν 3069, 3048, 2345,
2301, 2244, 2215 (all vw), 2191 w, 2185 w, 2147 w (N3), 2139 vs
(N3), 2122 s (N3), 2091 w, 1636 s, 1627 m, 1598 m, 1593 s, 1584 m,
1578 w, 1573 vw, 1495 w, 1457 vw, 1450 m, 1444 s, 1440 m,
1400 vw, 1351 s, 1345 sh, 1340 vw, 1302 w, 1299 m, 1293 s,
1291 m, 1282 w, 1280 w, 1275 m, 1270 m, 1245 w, 1243, 1241,
1239, 1237 (all m), 1197 sh, 1194 w, 1150 sh, 1147 w, 1142 sh,
1138 sh, 1136 vw, 1109 w, 1107 w, 1080 vw, 1016 vw, 961 br w,
958 w, 953 w, 931 vw, 892 w, 889, 886, 883, 880, 877 (all vw),
875 w, 873 w, 848, 845, 801, 796, 780, 753 (all vw), 749 m, 682
After 42 min, the filter was removed, and the sample was exposed
to broad-band UV light. After 5 h and 15 min, only minor amounts
of azirines were visible. The dominant bands in the spectrum are
assigned to two 15N-labeled o-cyanophenylketenimines 17′ and 17′′:
IR (Ar matrix, 7 K) ν 3316 vw, 3313 w, 3300 w, 3290 vw, 2235
vw, 2231 vw, 2208 vw, 2201 vw, 2068 vw, 2050 m, 2040 s, 2032 s,
2025 s, 2013 s, 2006 s, 1573 vw, 1495 w, 1491 m, 1465 vw, 1462
vw, 1460 vw, 1344 br w, 1303 vw, 1080 vw, 956 w, 948 s, 939 s,
937 s, 934 s, 933 s, 930 s, 928 s, 926 s, 916 m, 914 m, 884 w, 850
vw, 841 vw, 832 vw, 827 w, 765 w, 760 m, 757 m, 755 m, 598
vw, 606 w, 526 vw, 472 vw, and 468 w cm-1
.
For quantitative, time-dependent IR measurements, 22A was
irradiated in discrete intervals. Initially, the condensate was
photolyzed with light of λ > 300 nm. After 6.5 min photolysis,
the starting material was fully converted, leading to a spectrum
that presented only negligible amounts of secondary photolysis
product 17. The dominating bands originate from 7bH-azireno[3,2-
c]isoquinoline 24: IR (Ar matrix, about 7 K) ν 1733 w, 1726 m,
1723 m (all CdN), 1574 w, 1529 s (CdN), 1466 w, 1449 m,
1356 w, 1292 w, 1290 w, 1214 m, 1203 br w, 1172 vw, 969 vw,
967 vw, 914 w, 846 vw, 839 br vw, 792 w, 791 sh, 766 vw, 763 w,
756 w, 742 br w, 637 vw, 635 w, 632 sh, 615 w, 596 w, 593 vw,
591 vw, 588 vw, 586 vw, 584 vw, 556 sh, and 554 vw cm-1 (Figure
1B).
After removal of the filter, the sample was subjected to broad-
band photolysis for 605 min (high-pressure Hg/Xe lamp). This
resulted in a slow decay of the bands of azirene and a gradual
increase of the bands of o-cyanophenylketenimine 17, to which
the major bands in the final spectrum are ascribed: IR (Ar matrix,
7 K) ν 3316 sh, 3313 w, 3307 w, 3297 vw (all NH), 2236 w, 2232 w
(all CdN), 2055 w, 2049 m, 2040 s, 2031 m, 2022 s, 2016 m (all
CdCdN), 1573 vw, 1492 m, 1465 w, 1464 w, 1460 m, 1418 w,
1411 w, 1346 w, 1341 br w, 1303 vw, 1085 br vw, 1083 vw, 955 w,
951 m, 949 m, 942 m, 937 m, 935 m, 933 s, 928 m, 916 w, 851
vw, 828 w, 765 w, 761 m, 758 m, 755 m, 607 vw, 464 vw, 420 w
cm-1 (Figure 1C). A set of weak bands at 2264, 1590, 1554, 1286,
1265, 1209, 884, 736, 720, and 600 cm-1 is ascribed to 1-cyano-
1H-isoindole 26 (Figure S3 in the Supporting Information).
Photolysis of Neat 3-Azidoisoquinoline 22A. Azide was
sublimed at 46-48 °C (2 × 10-6 mbar) over a 2.5 h period and
deposited neat, without Ar. Azide was then photolyzed (λ > 300
nm) for 8 min, which yielded the IR spectrum of neat azirene 24
(Figure S2 in the Supporting Information): IR (neat, 7 K) ν 1723 w,
vw, 464 vw, 457 vw, and 420 w cm-1
.
Preparative FVT of 3-Azidoisoquinoline 22A: FVT/Argon
Matrix Isolation of 3-Azidoisoquinoline 22A. The tetrazole/azide
mixture was sublimed at 70-75 °C (5 × 10-5 mbar) over a period
of 2 h and 20 min, and the vapor was passed through a FVT tube
at 500-550 °C. The thermolysate was codeposited in Ar (flow rate
about 3 mbar/min) and consisted entirely of 2H-1-cyanoisoindole
27 as evidenced by comparison with a pure, isolated sample: IR
(Ar matrix, 15 K) ν 3480 vs, 2224 vw, 2219 s, 2209 vw, 1660 br
vw, 1590 w, 1453 m, 1410 m, 1386 m, 1311 m, 1304 w, 1240 m,
1137 m, 1110 m, 1105 m, 1045 w, 995 w, 769 m, 750 m, 632 w,
595 w, 589 m, 553 m, 529 w, 476 w, and 427 w cm-1
.
Preparative FVT of 3-Azidoisoquinoline-15N 22A′. Over 2 h,
a sample of 200 mg of 22T′/22A′ was sublimed at 40-50 °C (10-2
mbar) into the quartz tube of the FVT apparatus held at 550 °C.
The product of FVT was isolated on a coldfinger cooled in liquid
N2. At the end of the thermolysis, the isolated substance was
dissolved in acetone and purified by thick layer chromatography
on silica gel, eluting with diethyl ether. Only one band eluted with
isolable quantities of a substance. This material dissolved in acetone
to give a green solution. Evaporation of the solvent and sublimation
at 80 °C (10-2 mbar) afforded 160 mg (96%) of white crystals: mp
130-132 °C dec; mp for unlabeled material 130-132 °C; lit.22
mp 132-134 °C; MS m/z 143 (100%), 144 (10%); IR (KBr) ν
3260 s, 2930 w, 2200 s (C14N), 2180 s (C15N, same intensity as
2200 cm-1 band), 1450 m, 1410 m, 1400, s, 1285 m, 1315 m,
1240 s, 1135 s, 1110 s, 765 s, 755 s, 730 s cm-1 13C NMR (acetone-
;
d6) δ 90.3 (m), 115.5 (m), 117.5 (d, JNC ) 14 Hz), 117.5 (s), 125.2
(s), 118.4, 122.3, 122.9, 125.9, 131.5 (d, JNC ) 4 Hz); 15N NMR
(22) Brown, R. F. C.; Smith, R. J. Aust. J. Chem. 1972, 25, 607.
J. Org. Chem. Vol. 74, No. 3, 2009 1177