tert-butyl 5-hydroxy-1H-indazole-1-carboxylate

The title compound, C(26)H(26)N(2)O(2)S, was prepared by the reaction of thio-phene-2,5-dicarboxylic acid and 2-amino-4-tert-butyl-phenol. One of the tert-butyl groups is disordered over two conformations, with occupancies of 0.539 (1) and 0.461 (2). The two 1,3-benzoxazole rings are almost planar, with dihedral angles of 0.83 (18) and 1.64 (17)° between the five- and six-membered rings. The thio-phene ring makes dihedral angles of 21.54 (19) and 4.49 (18)° with the planes of the five-membered oxazole rings. The crystal packing is controlled by π-π stacking inter-actions involving the thio-phene and benzene rings, with a centroid-centroid distance of 3.748 (2) Å.

The angles within the benzene ring in the title compound, C(30)H(49)N(3)O, ranging from 116.34 (16) to 124.18 (16)°, reflect the presence of electron-donating and electron-withdrawing substituents. The angles at the two electron-donating tert-butyl substituents are smaller than 120°, at the electron-withdrawing eth-oxy substituent larger than 120°, and at the imine substituent equal to 119.59 (16)°. The latter does not reflect the electron-donating nature of the imine group due to the presence of other substituents.

In the mol-ecule of the title compound, C(28)H(32)N(2), the benzimidazole ring system is almost planar [maximum deviation = 0.0221 (15) Å] and forms dihedral angles of 85.86 (4) and 32.09 (6)° with the benzene rings. In the crystal structure, mol-ecules are linked into chains running parallel to the a axis by inter-molecular C-H⋯N hydrogen bonds. The methyl groups of a tert-butyl group are rotationally disordered over two positions with refined site-occupancy factors of 0.636 (4) and 0.364 (4).