Atropisomerism in 4-(2-Thienyl)-4H-1, 2, 4-triazole Derivatives

3-Aminomethyl-4-[3-o-chlorobenzoyl)-5-ethylthiophen-2-yl]-5-methyl-4H-1, 2, 4-triazole (I), the hydrolytically ring-opened derivative of etizolam, which is one of the 1, 4-diazepine antianxiety drugs, was investigated from the stereochemical point of view. In order to isolate atropisomeras of compound I, its carbonyl group was reduced to a chiral secondary alcohol. The resulting compounds were resolved successfully into two comonents (IIa and IIb) by silica-gel column chromatography. The structures of atropisomeric IIa and IIb. possessing rotational differences about the single bond between the thiophene and triazole rings, were confirmed by X-ray crystallographic analysis. The interconversion behavior between them was also examined.