X-ray crystallographic structure of a novel enantiopure chiral isothiourea with potential applications in enantioselective synthesis

The synthesis of a chiral isothiourea, namely, (4aR,8aR)-3-phenyl-4a,5,6,7,8,8a-hexahydrobenzo[4,5]imidazo[2,1-b]thiazol-9-ium bromide, C₁₅H₁₇N₂S⁺·Br⁻, with potential organocatalytic and anti-inflammatory activity is reported. The preparation of the heterocycle of interest was carried out in two high-yielding steps. The hydrobromide salt of the isothiourea of interest provided suitable crystals for X-ray diffraction analysis, the results of which are reported. Salient observations from this analysis are the near perpendicular arrangement of the phenyl ring and the mean plane of the heterocycle. This conformational characteristic may be relevant with regard the stereoselectivity induced by the chiral isothiourea in asymmetric reactions. Furthermore, evidence was found for the existence of an S…Br⁻ halogen bond.