3-Benzyl-3-hydroxy-2-phenyl-3H-indole 1-oxide

The asymmetric unit of the title compound, C21H17NO2, contains two crystallographically independent molecules of similar geometry. The indole ring systems form dihedral angles of 8.30 (5) and 9.58 (5)° with the attached phenyl rings, and 56.96 (5) and 57.68 (5)° with the aromatic rings of the respective benzyl groups. The molecular conformations are stabilized by intramolecular C—H⋯O hydrogen bonds. In the crystal structure, centrosymmetrically related pairs of molecules are linked into dimers through pairs of intermolecular O—H⋯O hydrogen bonds, generating 12-membered rings with R 2 2(12) motifs. The dimers are further linked into a three-dimensional network by C—H⋯O interactions.

The asymmetric unit of the title compound, C 21 H 17 NO 2 , contains two crystallographically independent molecules of similar geometry. The indole ring systems form dihedral angles of 8.30 (5) and 9.58 (5) with the attached phenyl rings, and 56.96 (5) and 57.68 (5) with the aromatic rings of the respective benzyl groups. The molecular conformations are stabilized by intramolecular C-HÁ Á ÁO hydrogen bonds. In the crystal structure, centrosymmetrically related pairs of molecules are linked into dimers through pairs of intermolecular O-HÁ Á ÁO hydrogen bonds, generating 12membered rings with R 2 2 (12) motifs. The dimers are further linked into a three-dimensional network by C-HÁ Á ÁO interactions.
Financial support from the Universitá Politecnica delle Marche and the Universitá degli Studi di Parma is gratefully acknowledged.
Although the most used nitrones in cyclization reactions are acyclic, several papers have appeared in the last two decades describing cycloaddition reactions with cyclic nitrones (Pisaneschi et al., 2002;Jones et al., 2000;Bernotas et al., 1999;Ali & Wazeer, 1988). Significant advances have been described in the use of nitrones derived from sugars and aminoacids for the synthesis of interesting biological compounds including aminoacids, amino alcohols and nucleoside analogs (Merino, 2005).
The asymmetric unit of the title compound ( Fig. 1) contains two crystallographically independent molecules with similar geometry. The indole ring systems including the N1 and N2 atoms form dihedral angles of 8.30 (5) and 9.58 (5)°, respectively, with the attached phenyl rings, and 56.96 (5) and 57.68 (5)°, respectively, with the aromatic ring of the benzyl groups.

Experimental
A solution of benzylmagnesium bromide (20 mmoles in 30 ml of dried THF, obtained from 0.46 g of magnesium and 2.54 g of benzyl chloride in a current of argon) was added to a solution of 2-phenylisatogen (10 mmoles, 2.23 g in 50 ml of dried THF; Bond & Hooper, 1974), at room temperature and under magnetic stirring. After the addition, the reaction mixture was kept at room temperature for 2 h, then it was poured into 10% aqueous NH 4 Cl (100 ml) solution. The mixture was extracted with chloroform (2 × 50 ml) and the separated organic layer was dried on Na 2 SO 4 and evaporated to dryness. The residue was treated with diethyl ether to give a white solid corresponding to the expected nitrone, which was separated by filtration KBr with a Perkin-Elmer MGX1 spectrophotometer equipped with Spectra Tech. 1 H NMR spectrum was recorded on a Gemini Varian 200 MHz. Mass spectrum was recorded on a Carlo Erba QMD 1000 mass spectrometer in positive electron impact (EI) mode. Single crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution at room temperature.