2-[1-(tert-Butoxycarbonyl)pyrrolidin-2-yl]-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide

In the title compound, C16H28N3O4, the plane of the pyrrolidine ring system is twisted with respect to the plane of the nitronyl nitroxide unit, making a dihedral angle of 79.80 (6)°. The crystal structure is stabilized by C—H⋯O hydrogen bonds.

In the title compound, C 16 H 28 N 3 O 4 , the plane of the pyrrolidine ring system is twisted with respect to the plane of the nitronyl nitroxide unit, making a dihedral angle of 79.80 (6) . The crystal structure is stabilized by C-HÁ Á ÁO hydrogen bonds.

Comment
Nitronyl nitroxide radical is a class of important functionalized molecule, which has characteristics of magnetism, anticancer, antiradiation and antioxidation, etc (Iqbal, et al., 2009;Qin, et al., 2009;Tanaka, et al., 2007;Soule, et al., 2007). The title compound has been be used for coordination with many metalcations, such as Mn 2+ , Cu 2+ and Ni 2+ leading to form some molecule based magentic materials. The molecular structure of the title compound is shown in Fig1. The pyrrolidine ring and the nitronyl nitroxide ring are twisted with respect to each other making a dihedral angle of 79.80 (6)°. The crystal structure is stabilized by C-H···O hydrogen bonds (Table 1).
Experimental 2,3-Dimethyl-2,3-bis(hydroxylamino) butane (1.48 g, 10.0 mmol) and tert-butyl-2-(hydroxymethyl) pyrrolidine-1carboxylate (2.01 g, 10.0 mmol) were dissolved in methanol (Ullman, et al., 1974). The reaction was stirred for 15 h at reflux temperature, then cooled to room temperature and filtered. The white powder was washed by methanol and suspended in a mixed solution of dichloromethane (30.0 ml) and water (30.0 ml). Then the reaction mixture was added to an aqueous solution of NaIO 4 and stirred for 15 min in ice bath to give a blue solution. The aqueous phase was extracted with CH 2 Cl 2 and the organic layer was combined and dried over MgSO 4 . Then the solvent was removed to give a dark red residue which was purified by a flash column chromatography with the elution of n-hexane/ ethyl acetate (1:3) to yield the title compound (I) as a dark blue powder. Single crystals of compound (I) were obtained from the mixed solution of n-heptane and dichloromethane (the ratio of volume is 1 to 1).

Refinement
In both structures all the H atoms were discernible in the difference Fourier maps. However, they were constrained by riding model approximation. C-H methyl =0.96 Å; C-H aryl =0.93 Å; U iso H methyl and U iso H aryl are 1.5 U eq (C) and 1.2 U eq (C), respectively.
supplementary materials sup-2 Figures Fig. 1. Molecular structure of the title compound (I), showing the atom labeling scheme. Displacement ellipsoids are drawn at the 30% probability level.