due to a combination of poor crystal quality and considerable
thermal motion, particularly in the methyl substituents.
Triradical 4: Slow evaporation from a 1 : 1 DCM–n-hexane
mixture gave yellow prisms, mp >180 ЊC (slow decomp.); EI MS
Mϩ 580.35497 (1.82 ppm from mass calc. for C37H46N3O3);
g = 2.00582, aN = 14.1 G (toluene-d8, 293 K).
Experimental
5-(4Ј,4Ј,5Ј,5Ј-Tetramethyl-1Ј-oxido-3Ј-oxylimidazolin-2Ј-yl)-
1,1,3,3-tetramethylisoindolin-2-yloxyl (9) and
5-(4Ј,4Ј,5Ј,5Ј-tetramethyl-1Ј-oxylimidazolin-2Ј-yl)-
1,1,3,3-tetramethylisoindolin-2-yloxyl (10)
NMR Spectra were recorded on a Varian Unity 300 spectro-
meter. EPR spectra were recorded on a Brüker ESP 300E EPR
spectrometer (X-band, ∼9.2 GHz) using an EIP 548B micro-
wave frequency counter and a Brüker O35M gaussmeter for
microfrequency calibration.
To a solution of 5-formyl-1,1,3,3-tetramethylisoindolin-2-yl-
oxyl (8, 90 mg, 412 µmol, 1 equiv.) in MeOH (2 cm3) was added
2,3-bis(hydroxyamino)-2,3-dimethylbutane (85 mg, 574 µmol,
1.4 equiv.). The mixture was stirred at room temperature for
22 h whereupon the solvent was removed under vacuum. The
residue was taken up in CHCl3 (3 cm3), cooled to 0 ЊC then
NaIO4 (180 mg, 842 µmol) in H2O (2 cm3) was added with
stirring over 5 min. The solution was stirred at 0 ЊC for a further
15 min. The mixture was diluted with H2O (3 cm3) and
extracted with CHCl3 (3 × 10 cm3). The combined organic
extracts were washed with sat. NaCl (2 × 15 cm3), dried over
anhydrous Na2SO4, filtered, and evaporated to dryness. Chrom-
atography (SiO2; 40 : 60 : 0.2 EtOAc–n-hexane–MeOH) gave
iminyl aminoxyl 10 (32 mg, 97 µmol, 24%) followed by nitronyl
aminoxyl 9 (18 mg, 52 µmol, 13%).
Nitronyl aminoxyl 9: Slow evaporation from a 1 : 1 DCM–n-
hexane mixture gave dark blue prisms, mp 209 ЊC (decomp.); EI
MS Mϩ 345.205330 (Ϫ0.3 ppm from calc. for C19H27N3O3); g =
2.00677, aN(1) = 14.4 G, aN(2) = 7.2 G, aN(3) = 7.2 G (toluene-d8,
293 K).
Iminyl aminoxyl 10: Recrystallisation from n-hexane gave
orange–red clusters, mp 199–201 ЊC (Found: C, 69.1; H, 8.4; N,
12.8. C19H27N3O2 requires C, 69.3; H, 8.3; N, 12.8%); g =
2.00516, aN(1) = 14.1 G, aN(2) = 9.4 G, aN(3) = 4.7 G (toluene-d8,
293 K).
Bis(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (2)
To a solution of 1 (1.00 g, 5.26 mmol, 1 equiv.) in CH2Cl2
(10 cm3) was added AlCl3 (2.80 g, 21.0 mmol, 4 equiv.). The
mixture was stirred at room temperature under an atmosphere
of argon for 24 h. The dark red mixture was poured slowly onto
ice with stirring. The layers were separated and the aqueous
portion was extracted with CHCl3 (3 × 5 cm3). The combined
organics were washed with sat. NaCl (10 cm3), dried over
anhydrous Na2SO4, filtered, and evaporated to dryness. Chrom-
atography (SiO2; 40 : 60 : 0.5 EtOAc–n-hexane–MeOH) gave
starting material 1 (662 mg, 3.48 mmol) followed by biradical 2,
which was recrystallised as fine yellow crystals from hexane
(163 mg, 0.416 mmol, 16%), mp 156 ЊC (decomp.) (Found:
C, 76.3; H, 8.5; N, 6.4. C25H32N2O2 requires C, 76.5; H, 8.2;
N, 7.1%); m/z 392 (100%), 377 (75%), 362 (40%), 347 (71%),
332 (34%), 317 (12%) (fused ring N-containing compounds
frequently give poor combustion analysis and so high reso-
lution EI MS was also run); EI MS found Mϩ 392.245929
(1.1 ppm from calc. mass for C25H32N2O2); g = 2.00580, aN
14.0 G (toluene-d8, 293 K).
=
1,1-Bis(1Ј,1Ј,3Ј,3Ј-tetramethylisoindolin-2Ј-yloxyl-5Ј-yl)ethane
(3)
To a solution of 1 (1.00 g, 5.26 mmol, 1 equiv.) in 1,2-
dichloroethane (10 cm3) was added AlCl3 (2.80 g, 21.0 mmol, 4
equiv.). The mixture was stirred at room temperature under an
atmosphere of argon for 24 h. The dark red mixture was poured
slowly onto ice with stirring. The layers were separated and the
aqueous portion was extracted with CHCl3 (3 × 5 cm3). The
combined organics were washed with sat. NaCl (10 cm3), dried
over anhydrous Na2SO4, filtered, and evaporated to dryness.
Chromatography (SiO2; 40 : 60 : 0.5 EtOAc–hexane–MeOH)
gave starting material 1 (550 mg, 2.89 mmol) followed by the
biradical 3, which was recrystallised as yellow hexagonal prisms
by slow evaporation from a cyclohexane–dichloromethane
(1 : 1) solution (155 mg, 0.382 mmol, 15%), mp 218 ЊC (dec.);
EI MS Mϩ 406.262124 (Ϫ0.2 ppm from calc. mass for
C26H34N2O2); g = 2.00582, aN = 14.0 G (toluene-d8, 293 K).
N,NЈ-Dibenzylpyromellitimide (12)
To a stirred solution of pyromellitic dianhydride (11, 9.6 g,
0.044 mol, 1 equiv.) in glacial AcOH (50 mL) was added drop-
wise benzylamine (14.6 mL, 0.134 mol, 1.5 equiv.). A white
precipitate rapidly formed and the mixture was stirred for a
further 30 min at room temperature. The white precipitate was
collected by vacuum filtration to yield N,NЈ-dibenzyl-
pyromellitimide (12, 15.7 g, 0.0396 mol, 90%). Recrystallisation
from toluene gave colourless needles, mp 301–302 ЊC (Found:
C, 72.6; H, 4.1; N, 7.1. C24H16N2O4 requires C, 72.7; H, 4.1;
1
N, 7.1%); H NMR (CDCl3) δ 4.85 (s, 4H, CH2), 7.32–7.43
(m, 10H, ArH), 8.25 (s, 2H, ArH).
2,6-Dibenzyl-1,2,3,5,6,7-hexahydro-1,1,3,3,5,5,7,7-
octamethylbenzo[1,2-c:4,5-cЈ]dipyrrole (13)
Tris(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yl)methane (4) and
chlorobis(1Ј,1Ј,3Ј,3Ј-tetramethylisoindolin-2Ј-yloxyl-5Ј-yl)-
methane (5)
Magnesium turnings (19.6 g, 0.81 mol, 16 equiv.) and a few
crystals of iodine were placed in a flame dried Grignard appar-
atus under a positive pressure of Ar. Anhydrous Et2O (∼300
mL) and a few drops of iodomethane were added to initiate the
reaction. The remaining iodomethane (51.0 mL, 0.81 mol, 16
equiv. total) and anhydrous Et2O (1.5 L total) were added to
maintain a constant rate of reaction. When addition of the
reagents was complete the mixture was stirred until all activity
subsided. Ether was removed by distillation until the temper-
ature of the mixture reached 80 ЊC. A solution of N,NЈ-
dibenzylpyromellitimide (12, 20.0 g, 0.050 mmol, 1 equiv.) in
anhydrous toluene (1 L) was added to the methyl Grignard
solution (∼60 ЊC) at a rate which maintained a constant tem-
perature. When addition was complete, solvent was distilled
until the temperature of the reaction mixture reached 110 ЊC.
The reaction mixture was refluxed for two hours, then concen-
trated by distillation. After cooling, the reaction was diluted
with hexane fraction (1.5 L) and mixed thoroughly. The result-
ant purple slurry was vacuum filtered through Celite and the
To a solution of 1 (2.00 g, 10.5 mmol, 1 equiv.) in CHCl3
(20 cm3) was added AlCl3 (4.63 g, 34.7 mmol, 3.3 equiv.). The
mixture was stirred at room temperature under an atmosphere
of argon for 24 h. The dark green mixture was poured slowly
onto ice with stirring. The layers were separated and the
aqueous portion was extracted with CHCl3 (3 × 20 cm3). The
combined organics were washed with sat. NaCl (50 cm3), dried
over anhydrous Na2SO4, filtered, and evaporated to dryness.
Chromatography (SiO2; 20 : 20 : 60 : 0.5 DCM–EtOAc–n-
hexane–MeOH) gave starting material 1 (444 mg, 2.34 mmol)
followed by biradical 5 (82 mg, 0.190 mmol, 3.6%) then triradical
4 (533 mg, 0.918 mmol, 26%).
Biradical 5: Recrystallisation from n-hexane gave yellow
needles, mp 180–182 ЊC; EI MS Mϩ 426.20835 (2.22 ppm from
mass calc. for C25H31N2O2Cl); g = 2.00582, aN = 13.9 G
(toluene-d8, 293 K).
536
J. Chem. Soc., Perkin Trans. 2, 2002, 533–537