Ruthenium-catalyzed asymmetric transfer hydrogenation of [2.2]paracyclophanecarboxaldehydes via kinetic resolution.

Planar-chiral [2.2]paracyclophanes occupy a privileged position in asymmetric catalysis and materials science. However, straightforward and scalable access to enantioenriched [2.2]paracyclophane scaffolds remains a formidable challenge. Herein, we disclose an efficient ruthenium-catalyzed asymmetric transfer hydrogenation of [2.2]paracyclophanecarboxaldehydes via kinetic resolution. Utilizing a formic acid-triethylamine azeotrope as the hydrogen source, this operationally simple protocol affords the recovered planar-chiral aldehydes and the corresponding chiral alcohols with excellent selectivity factors (s up to 165.1) and a broad substrate scope. Moreover, synthetic elaborations, including a decagram-scale preparation and the construction of novel planar-chiral PNO- and PPN-tridentate ligands, present these optically active molecules as promising chiral building blocks.