Serwinski et al.
(p-phenylene); no OH band observed. Crystallography: deep
blue prism, monoclinic P21/c (No. 14) lattice; a ) 9.730(1) Å, b
) 9.960(1) Å, c ) 14.294(1) Å, â ) 101.36(1)°, V ) 1358.07(10)
Å3, Z ) 4, Dcalc ) 1.342 Mg/m3; 1727 unique reflections with I
> 2σ(I) were modeled with 182 parameters to yield the
structure with R1 ) 0.0431, wR2 ) 0.1252. See the Supporting
Information for further details of the crystal analysis. This
structure has been deposited at the Cambridge Crystal-
lographic Databank Centre, CCDC deposition no. 232910.
P h otolysis of 14 to 7. A MTHF solution of 14 was subjected
to 3-fold freeze-pump-thaw degassing, frozen at 77 K, and
photolyzed for 30-180 s with a 1000 W xenon arc lamp
through a Pyrex filter. ESR (9.559 GHz, MTHF, 77 K): 1230
(wk), 1830 (s ) strong), 3390 (s, remnant 14), 5225, 6056 G.
UV-vis (MTHF, λmax, nm, 77 K): 320, 445 (wk), 486, 528, 578.
1-Hydr oxy-2-(4-azidoph en yl)ben zim idazole-3-oxide (15).
A mixture of 0.14 g (1.02 mmol) of o-benzoquinone-1,2-
dioxime13b and 0.13 g (0.91 mmol) of 4-azidobenzaldehyde was
stirred in 6 mL of absolute ethanol. Next, 0.69 g of 48% HBr
was added to the mixture and the temperature increased to
33-35 °C. The blood-red mixture was stirred at this temper-
ature under argon for 48 h with aluminum foil wrapping to
avoid having direct light shine on the reaction. The solution
was cooled to room temperature and 20 mL of distilled water
added, which caused a precipitate. This solid was filtered and
washed with 30 mL of distilled water and then with 30 mL of
ethanol to yield a light beige solid. Neutralization of the filtrate
with 5% aqueous sodium bicarbonate yielded a little precipi-
tate, which was washed with water and ethanol and then
combined with the first precipitate. The combined solids were
dried under vacuum with minimum exposure to room light,
to yield 0.09 g (38%) of product with that decomposes upon
heating above 260 °C. IR (KBr, cm-1): 3447 (OH str), 2119
(N3 stretch). 1H NMR(CDCl3/CF3COOH, MHz): δ8.08 (d, 2 H,
J ) 8.84 Hz), 7.76 (m, 2 H), 7.65 (m, 2 H), 7.27 (d, 2 H, J )
8.84 Hz).
to cool to room temperature over 20 h. The reaction was
filtered, and the brown solid was washed with a solution of
20 mL of methanol in 50 mL of water. The solid was air-dried
to give formazan 17, which was suitable for use in the next
synthetic step.
Formazan 17 (0.47 g, 1.4 mmol) was placed in 20 mL of
dimethylformamide and then treated with 0.16 g (0.5 mmol)
of Ba(OH)2‚ 8H2O, followed by 2.9 g (19.0 mmol) of BaO. Next,
4.0 mL (5.75 g, 33.6 mmol) of benzyl bromide was added
dropwise. The reaction was stirred at 0 °C for 2 h and then
allowed to warm to room temperature for 1 h. The reaction
was green at this point. The reaction was filtered, poured into
50 mL of toluene, and back-extracted with water. The organic
layer could be evaporated to give a crude, dark green solid,
which could be dissolved in methanol and allowed to cool in a
refrigerator to yield green-black needles of verdazyl 19. Mp:
146-148 °C. Anal. Calcd for C26H20N7: C, 72.54; H, 4.68; N,
22.78. Found: C, 72.01; H, 4.83; N, 21.99. ESR (9.78 GHz,
benzene): nonet, aN ) 5.4 G (4 N). UV-vis (MTHF, λmax, nm):
290, 310, 320, 410, 442, 740 (broad). Crystallography: ir-
regular green-black needle; monoclinic P21/c (No. 14) lattice;
a ) 6.5406(1) Å, b ) 13.1924(3) Å, c ) 6.5406(1) Å, â )
95.0885(9)°, V ) 2216.67(9) Å3, Z ) 4, Dcalc ) 1.290 Mg/m3;
3559 unique reflections with I > 2σ(I) were modeled with 380
parameters to yield the structure with R1 ) 0.0761, wR2
)
0.1731. See the Supporting Information for further details of
the crystal analysis. This structure has been deposited at the
Cambridge Crystallographic Databank Centre, CCDC deposi-
tion no. 232913.
P h otolysis of 19 to 9. A MTHF solution of 19 was subjected
to 3-fold freeze-pump-thaw degassing, frozen at 77 K, and
photolyzed for 2 min with a 1000 W xenon arc lamp through
a Pyrex filter. ESR (9.561 GHz, MTHF, 77 K): 1380 (v wk),
1830 (s ) strong), 3430 (s, remnant 19), 5380, 6200 G. UV-
vis (MTHF, λmax, nm, 77 K): 300, 370, 400 (shoulder), 504,
553, 650 (broad).
2-(4-Azid op h en yl)ben zim id a zole-3-oxid e-1-oxyl (16). A
mixture of 15 mg (0.057 mmol) of 15 and 2.2 mL of 0.1 M
aqueous NaIO4 was stirred for 15 min. Then, 5 mL of
dichloromethane was added, followed by 2 mL of 5% aqueous
NaHCO3. The mixture was stirred for another 5 min. The pale
green-yellow dichloromethane layer separated from the mix-
ture, washed with aqueous saturated NH4Cl, and dried over
anhydrous MgSO4. Evaporation of the solvent gave brownish
solid product (6 mg, 40%, mp 138-141 °C). ESR (9.8 GHz):
aN(CHCl3) ) 4.51 G (2N), aN(MTHF) ) 4.39 G (2N), aN(CCl4)
) 4.18 G (2N). IR (CCl4, cm-1): 2120 (N3 stretch). High-
resolution MS-EI (m/z): 266.07 [266.0678 calculated for
2-(3-Azid op h en yl)-1,3-d ih yd r oxyl-4,4,5,5-tetr a m eth yl-
2H-im id a zolin e (20). A mixture of 1.01 g (4.08 mmol) of 2,3-
bis(hydroxylamino)-2,3-dimethylbutane hydrogen sulfate and
1.01 g (6.78 mmol) of 3-azidobenzaldehyde (see the Supporting
Information for synthesis) was stirred in 35 mL of methanol
containing 2 mL of triethylamine under argon with protection
from light for 42 h. The reaction was filtered, and the filtrate
was evaporated completely to yield a yellow, viscous oil that
was diluted with distilled water to give a solid. The solid was
washed with distilled water dried in air with protection from
direct room light to give 0.56 g (53%) of a slightly yellow solid.
Mp: 140-143 °C. IR (KBr, cm-1): 3410 (OH str), 3010 (CH
str), 2910 (CH str), 2110 (N3 stretch). 1H NMR (CDCl3) δ: 7.25
(s, 1 H), 7.1-7.3 (m, 2 H), 6.98 (m, 1H), 5.35 (br s, 2H), 4.68
(s, 1 H), 1.07 (s, 6 H), 1.06 (s, 6 H).
C
13H8N5O2]. UV (MTHF, λmax, nm): 250, 305, 315, 475.
P h otolysis of 16 to 8. A MTHF solution of 16 was subjected
to 3-fold freeze-pump-thaw degassing, frozen at 77 K, and
photolyzed for 3 min with a 1000 W xenon arc lamp through
a Pyrex filter. ESR (9.559 GHz, MTHF, 77 K): 1060 (wk), 1840
(s ) strong), 3400 (s, remnant 16), 5060, 5890, 6600 G (wk).
UV-vis (MTHF, λmax, nm 77 K): 320, 445 (wk), 486, 528, 578.
1-(4-Azid op h en yl)-3,5-d ip h en ylver d a zyl (19). Phenyl
hydrazine (1.0 mL, 10 mmol) was dissolved in 20 mL of
pyridine at 0 °C, and 4-azidobenzaldehyde (1.3 mL, 1.59 g, 11
mmol) was added slowly to the reaction with stirring. The red
solution was stirred at 0 °C for 1 h, following which 1 g of ice
containing 1.0 mL of glacial acetic acid was added. The result
was solution A, which contained the phenylhydrazone of
4-azidobenzaldehyde.
Aniline (1.0 mL, 1.0 g, 11 mmol) was dissolved in a solution
made up of 1 mL of distilled water, 1 g of ice, and 2 mL of
concd HCl and cooled to 0 °C. This solution was treated
dropwise with a solution of 0.76 g (11 mmol) of sodium nitrite
in 3 mL of water, keeping the reaction temperature at 0 °C.
The result was solution B, which was stirred at 0 °C.
Solution B was added slowly dropwise to solution A,
maintaining the reaction temperature at 0 °C for 1 h. The
reaction was then heated to 60 °C for 15 min and then allowed
2-(3-Azid op h en yl)-4,4,5,5-tetr a m eth yl-2H-im id a zolin e-
1-oxid e-3-oxyl (21). To a 100 mL three-necked round-bot-
tomed flask was added 0.113 g (0.409 mmol) of 20 and 15 mL
of dichloromethane. The solution was stirred under argon
while 15 mL of a 0.101 M sodium periodate solution was added.
The reaction turned deep blue and was stirred for 5 min. The
layers were separated, and the aqueous phase was extracted
with 10 mL of dichloromethane. The organic layers were
combined, washed with saturated ammonium chloride (3 ×
10 mL), and dried over anhydrous magnesium sulfate. The
solvent was evaporated, and the product was chromatographed
on silica with a solvent system of 80/20 hexane/ethyl acetate
(Rf ) 0.14, dark blue). Yield: 0.065 g (58%) of azure crystals.
Mp: 80-81 °C. Anal. Calcd for C13H16N5O2: C, 56.92; H, 5.58;
N, 25.53. Found: C, 56.85; H, 5.86; N, 25.43. UV (CHCl3, λmax
-
(ꢀ), nm,): 256 (11 000), 293 (3700), 366 (7600), 582 (308), 619
(280). IR (KBr, cm-1): 3025 (sharp, arom C-H str), 2924 and
2850 (sharp, aliphatic C-H str), 2120 (N3 stretch). MS (EI,
m/z): 274.13 (C13H16N5O2 ) M), 259.98 (M - 14), 246.12 (M
- 28), 240.98 (M - 34). ESR (9.591 GHz, CH2Cl2): pentet, aN
) 7.48 G (2 N). Crystallography of R-phase: irregular deep
5258 J . Org. Chem., Vol. 69, No. 16, 2004