3-tert-Butyl-7-azadioxindole was prepared from lithiation of 2-pivaloylaminopyridine with 2.1 mole equivalents of n-BuLi for 15 min at –78 °C and 2 h at 0 °C in anhydrous tetrahydrofuran followed by reaction with carbon monoxide for 2 h [1]. Crystallization of the crude product using a mixture of diethyl ether and ethyl acetate (in 1:2 ratio by volume) gave the title compound as colourless crystals in 62% yield [1].

H atoms were placed in calculated positions and refined using a riding model, with U_iso(H) set to 1.2U_eq(C) and C—H and N—H distances of 0.93 and 0.86 Å, respectively. The exceptions were the methyl (C—H = 0.96 Å) and hydroxyl (O—H = 0.86 Å) groups which were allowed to rotate around the C—C bond (HFIX 137 in SHELX[4]) and C—O bond (HFIX 147), with U_iso(H) set to 1.5U_eq(C/O).

Azaindoles represent an important class of pharmacologically active compounds [2, 3]. The asymmetric unit of the title structure comprises two independent molecules. The two molecules are linked by N—H⋯N (angle = 144.5°, N⋯N distance = 2.936(3) Å) and N—H⋯O (angle = 150.5°, C⋯O distance = 2.835(3) Å) hydrogen bonds forming rings which can be classified by the R₂²(8) graph set. Additional O—H⋯O (angle = 165.7°, O⋯O distance = 2.989(3) Å) and O—H⋯N (angle = 163.2°, O⋯N distance = 2.802(3) Å) hydrogen bonds lead to the formation of a three-dimensional network.

The authors extend their appreciation to the College of Applied Medical Sciences Research Center and the Deanship of Scientific Research at King Saud University for their funding of this research.