Suppressing Inversion of a Chiral Polycyclic Aromatic Aza Monkey Saddle by Molecular Editing

Abstract

Chiral polycyclic aromatic hydrocarbons with monkey saddle topology are a fascinating class of negatively curved compounds. To make the monkey-saddles valuable building blocks for chirality-assisted synthesis (CAS) approaches, the inversion barriers between the two possible enantiomers need to be high enough to prevent interconversion under CAS conditions. By molecular editing, aza monkey saddles were converted to the corresponding chromene monkey saddles that are configurationally stable even at temperatures of 220 °C over a period of 47 days. Their structures were studied by single X-ray diffraction and enantiomers were separated to study the chiroptical properties. Furthermore, mechanistic assumptions of the formation of the chromene monkey saddles by DFT calculations are discussed.