P. Rey et al.
2,4-Bis(hydroxylamino)-2,4-dimethylpentane (17): Dinitro compound 15
(5 g, 26 mmol) was dissolved in THF (100 mL). Zn powder (3.5 g) was
added to this solution and the mixture was cooled to ca 108C in a ice
bath. NH4Cl (10 g) in H2O (40 mL) was then added dropwise, with stir-
ring, at such a rate that the temperature did not exceeded 158C. The re-
action mixture was stirred 3 h more at room temperature and filtered,
the THF was evaporated under vacuum, and the resulting semi-solid
compound was extracted with CH2Cl2 (3100 mL). The organic phase
was dried over Na2SO4 and concentrated to give a white powder (3.2g,
76%). M.p. 108–1178C; 1H NMR (200 MHz, 208C, CDCl3): d = 1.16 (s,
12H; CH3), 1.52(s, 2H; CH 2) ppm. Indirect characterization of 17 was
provided by the N,N’-dihydroxyhexahydropyrimidine derivatives.
Tris
A
ACHTREUNG
yl-4,4,6,6-pyrimidinyl-3-oxide-1-oxyl] (19): Anhydrous [Cu
ACHTREUNG
(456 mg, 1 mmol) was dissolved in n-heptane and the mixture was
warmed to 508C. Solid 8d (266 mg, 1 mmol) was added to this solution
and stirring was continued for 15 min at 508C. The blue solution was fil-
tered and allowed to stand in the dark for two days. The dark green crys-
tals that formed (443 mg, 67%) were collected, washed with cold heptane
(10 mL), and dried. M.p. 124–1258C; elemental analysis (%) calcd for
C58H42F36N6O20Cu3: C 34.51, H 2.08, F 33.92, N 4.17, O 15.87, Cu 9.45;
found: C 34.38, H 1.97, N 4.23, Cu 9.61. The structure was confirmed by
X-ray diffraction.
N,N’-Dihydroxy-hexahydropyrimidines 18: Crude bis(hydroxylamine) 17
(0.40 g, 2.5 mmol) and p-toluenesulfonic acid (PTSA; 0.1 g, 0.53 mmol)
were dissolved in chloroform (20 mL), and benzaldehyde (0.27 g,
2.5 mmol) was added in five portions over a period of 5 h at reflux and
with stirring. The pale yellow solution was cooled to room temperature,
diluted with diethyl ether (100 mL), washed with saturated Na2CO3 (3
20 mL), and then dried over Na2SO4. Concentration gave a crude yellow
liquid (600 mg) that was purified by chromatography on silica (Et2O/pe-
troleum ether 1:1), giving the condensed bis(hydroxylamine) 18c as a
white, powder-like solid (473 mg, 77%). M.p. 838C; 1H NMR (200 MHz,
208C, CDCl3): d = 1.12(s, 6H; CH 3), 1.17 (s, 6H; CH3), 1.52(s, 2H;
CH2), 4.58 (s, 1H; CH); elemental analysis (%) calcd for C14H22N2O2: C
67.23, H 8.80, N 11.21, O 12.78; found: C 67.36, H 8.72, N 11.28. Crystals
suitable for X-ray analysis were obtained by slow evaporation from
Et2O/CH2Cl2.
Acknowledgements
P. B. thanks the RØgion Rhône-Alpes-Direction de l’Economie, du Tour-
isme, de la Recherche et de la Technologie for financial support.
[1] For reviews, see: a) V. I. Ovcharenko, R. Z. Sagdeev, Uspekhi
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Compounds 18a (73%, M.p. 898C), 18d (83%, M.p. 1428C), 18e (75%,
M.p. 1778C), 18 f (79%, M.p. 1788C), 18g (67%, M.p. 1088C), and 18h
(87%, M.p. 1258C) were prepared similarly.
If the aldehyde was added in one portion, a large proportion of the prod-
uct was a bis-nitrone, arising from the addition of two molecules of alde-
hyde to one molecule of bis(hydroxylamine). Portionwise addition of the
aldehyde minimizes this unwanted byproduct.
Nitronyl Nitroxides (8)
Alkyl-substituted: Solid NaIO4 (230 mg, 2.1 mmol) was added to 18a
(100 mg, O.53 mmol) in a ice-cooled mixture of CH2Cl2 (20 mL) and satu-
rated NaHCO3 (20 mL). Stirring was continued for 30 minutes, and the
deeply colored organic phase was dried over Na2SO4 and evaporated
under vacuum. The solid was chromatographed on Al2O3 (CH2Cl2/diethyl
ether) to give 8a (55 mg, 56%). M.p. 1048C; elemental analysis (%)
calcd for C9H17N2O2: C 58.38, H 9.19, N 15.14, O 17.30; found: C 58.24,
H 9.23, N 15.08.
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1989, 22, 392–398; b) A. Caneschi, D. Gatteschi, P. Rey, Progr.
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Aromatic-substituted: Dropwise addition of mCPBA (140 mg, 0.81 mmol)
in CH2Cl2 (10 mL) to 18c (100 mg, 0.4 mmol) in a mixture of CH2Cl2
(20 mL) and saturated NaHCO3 (20 mL) gave a dark blue solution. After
a further 15 minutes of stirring at room temperature the organic phase
was washed again with saturated Na2CO3 (220 mL) and then dried over
Na2SO4. Concentration and chromatography on alumina (diethyl ether)
gave nitroxide 8c as a blue solid (64%). M.p. 139–1408C; elemental anal-
ysis (%) calcd for C14H19N2O2: C 68.02, H 7.69, N 11.34; found: C 67.90,
H 7.84, N 11.09.
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All the other pyrimidyl nitroxides—8g/8h and 8d–f—were prepared by
these two procedures. Their properties are reported in Table 1 and
Table 2; satisfactory analyses were obtained and their crystal structures
(except for 8g/8h) can be found in the Supporting Information.
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4,4,6,6-Tetramethyl-2-(p-nitrophenyl)pyrimidinyl-1-oxyl (7d): Diluted
HCl (0.1n) was added dropwise to a solution of NaNO2 (4 g) in H2O
(50 mL). The resulting NO gas was bubbled through a solution of nitron-
yl nitroxide 8d (100 mg, 0.34 mmol) in CH2Cl2 (30 mL) until TLC
showed the disappearance of the purple starting material. The solution
was dried over Na2SO4 and concentrated under vacuum. The resulting
solid was chromatographed on Al2O3 (diethyl ether/petroleum ether 1:1)
to give imino nitroxide 7d (90 mg, 96%). M.p. 1218C; elemental analysis
(%) calcd for C14H18N3O3: C 60.87, H 6.52, N 15.22, O 17.40; found: C
60.69, H 6.61, N 15.29.
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Chem. Eur. J. 2006, 12, 5134 – 5141