2,4,5,7-Tetranitrofluorenone Oximate for the Naked-Eye Detection of H-Bond Donors and the Chiroptical Sensing of Enantiopure Reagents

Hydrogen bonding greatly influences rates and equilibrium positions of chemical reactions, conformations, and sometimes even stereochemistry. This study reports on tetranitrofluorenone oximate, a novel dye capable of naked-eye detection of hydrogen-bond donating species (HBDs) and of rapid determination of H-bond donation strength by hypsochromic shift monitoring. In addition, the molecule possesses atropisomeric conformations, of M and P configuration, as evidenced in solid and solution state studies by X-ray diffraction and electronic circular dichroism (ECD), respectively. In the latter case, enantiopure bis-thioureas were the most effective HBDs to promote a chiral induction (diastereoselective recognition, Pfeiffer effect); the ECD results being rationalized by time-dependent density functional theory (TDDFT) calculations. Based on these experiments, bis-thioureas were used as chiral reagents in asymmetric 1,3-dipolar cycloadditions of structurally-related nitrones; the ECD sensing of the stereoinduction between bis-thioureas and the oximate serving as an indirect method of selection of the most effective HBD for asymmetric synthesis.

Automated summary

Hydrogen bonding plays a significant role in chemical reactions, conformation, and stereochemistry. This study introduces a novel dye, tetranitrofluorenone oximate, which can visually detect hydrogen-bond donating species and quickly determine the strength of hydrogen bonding by monitoring hypsochromic shifts. The molecule also exhibits atropisomeric conformations, and enantiopure bis-thioureas are found to be the most effective hydrogen bond donors for chiral induction, as demonstrated by electronic circular dichroism and time-dependent density functional theory calculations. Furthermore, bis-thioureas are used as chiral reagents in asymmetric 1,3-dipolar cycloadditions, with the electronic circular dichroism sensing of stereoinduction serving as an indirect method to select the most effective hydrogen bond donor for asymmetric synthesis.