Helicenes synthesis and their Potential Applications

Review Article

Abstract

Helicenes represent a class of polycyclic compounds characterized by an angular configuration, resulting in a helical conformation. These compounds can feature ortho-fused aromatic or heteroaromatic rings. In instances where an alkyl hexane exhibits more than five aromatic rings (n > 5), distinct consistent enantiomers, P (left-handed) and M (right-handed), may emerge. The intrinsic chiral structure of helicenes, combined with extended p-conjugation, yields notable electrical circular dichroism (ECD) spectra and substantial optical rotations (ORs). Hexapole helicenes, synthesized through (2+2+2) cyclic reactions of aryne precursors generated by palladium, consist of six [5] helicene substructures, resulting in potential 20 stereoisomers. Selectively obtaining HH-1, the second isomeric form, HH-2, becomes the more stable isomer through quantitative isomerization (HH2) under heat conditions, as predicted by density functional theory (DFT) calculations. Chiral high-performance liquid chromatography (HPLC) effectively separates HH-2's two enantiomers. Kinetic investigations into the isomerization, based on DFT calculations, HPLC, and H1 NMR absorption spectroscopy from HH-1 to HH-2, along with an enantiomerically accelerated racemization of enantiomerically purified HH-2, were conducted. In this review, the most recent developments in this area of study are outlined