4-(Benzofuran-2-yl)-2-(3-(4-fluorophenyl)-3,3a,4,5-tetrahydro-2H-benzo[g]indazol-2-yl)thiazole was prepared from reaction of 3-(4-fluorophenyl)-3,3a,4,5-tetrahydro-2H-benzo[g] indazole-2-carbothioamide with 2-bromoacetylbenzofuran in ethanol under reflux for 4 h. The solid obtained on cooling was recrystallized from dimethylformamide to give colourless crystals of the title compound (Mp 218–219°C) [1].

All hydrogen atoms were placed in calculated positions and refined using a riding model. Methine C—H bonds were fixed at 1.00 Å and methylene C—H bonds at 0.99 Å. Aromatic C—H distances were set to 0.95 Å. U_iso for all hydrogens were set to 1.2 times the U_eq for the atoms they are bonded to.

Thiazole ring system has been found in vitamin B₁. Many thiazole derivatives show various biological activities such as antibacterial, antifungal, antiallergic and anti-HIV properties [2, 3, 4]. Convenient syntheses of thiazole derivatives involve reactions of aryl ketones with a N,N-diformylaminomethyl substituent in chloroform in the presence of excess triethylamine and phosphorus pentasulfide at 60°C [5], of isocyanides containing active methylene with carbodithioates in dimethylformamide in the presence of excess sodium hydride at room temperature [6], of thioureas with propargyl bromides in dimethylformamide in the presence of potassium carbonate under microwave condition [7], of N-bromosuccinimide with β-keto esters in the presence of thiourea in aqueous acetone at 50°C [8], of aldehydes with 2-amino(thio)phenols and aldehydes in aqueous ethanol in the presence of using samarium trifluoromethanesulfonate 55°C [9], and of β-diketones with 2-aminothiophenols in the presence of a Brønsted acid as a catalyst [10].

The asymmetric unit of the title crystal structure comprises one molecule of C₂₈H₂₀FN₃OS (cf. the Figure). All lengths and angles are in the expected ranges. In the molecule, the benzofuran and thiozole groups are planar with a twist angle of 11.93(7)° about the bond between them. The tetrahydrobenzoindazole group is also almost planer with C(1), C(8) and C(13) being only 0.22–0.53 Å apart from the plane calculated for the rest of the group. In the crystal structure, inversion related pairs of molecules are linked by two weak C—H⋯N interactions with C6⋯N1 = 3.508(2) Å, C—H⋯N = 170.8°. The benzofuran groups of neighbouring molecules are involved in π−π interaction with a centroid-to-centroid distance of 3.69 Å.

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