A simple and efficient resolution of (±)-4,12-dihydroxy[2.2]paracyclophane

The hamburger-shape photocatalyst: thioxanthone-based chiral [2.2]paracyclophane for enantioselective visible-light photocatalysis of 3-methylquinoxalin-2(1H)-one and styrenes

A new thioxanthone-based photocatalyst with a [2.2]paracyclophane skeleton and planar chirality has been developed. The catalyst has been successfully applied in the visible light-mediated enantioselective aza Paternò-Büchi reactions of quinoxalinone and styrenes to produce azetidines. The structures of the catalyst derivatives were unequivocally determined by their single crystal X-ray crystallography analysis.

Enantiopure planar chiral [2.2]paracyclophanes: Synthesis and applications in asymmetric organocatalysis

This short review focuses on enantiopure planar chiral [2.2]paracyclophanes (pCps), a fascinating class of molecules that possess an unusual three-dimensional core and intriguing physicochemical properties. In the first part of the review, different synthetic strategies for preparing optically active pCps are described. Although classical resolution methods based on the synthesis and separation of diastereoisomeric products still dominate the field, recent advances involving the kinetic resolution of racemic compounds and the desymmetrization of meso derivatives open up new possibilities to access enantiopure key intermediates on synthetically useful scales. Due to their advantageous properties including high configurational and chemical stability, [2.2]paracyclophanes are increasingly employed in various research fields, ranging from stereoselective synthesis to material sciences. The applications of [2.2]paracyclophanes in asymmetric organocatalysis are described in the second part of the review. While historically enantiopure pCps have been mainly employed by organic chemists as chiral ligands in transition-metal catalysis, these compounds can also be used as efficient catalysts in metal-free reactions and may inspire the development of new transformations in the near future.

Highly Enantioselective Asymmetric Transfer Hydrogenation: A Practical and Scalable Method To Efficiently Access Planar Chiral [2.2]Paracyclophanes

We report herein a general, practical method based on asymmetric transfer hydrogenation (ATH) to control the planar chirality of a range of substituted [2.2]paracyclophanes (pCps). Our strategy enabled us to perform both the kinetic resolution (KR) of racemic compounds and the desymmetrization of centrosymmetric meso derivatives on synthetically useful scales. High selectivities (up to 99% ee) and good yields (up to 48% for the KRs and 74% for the desymmetrization reactions) could be observed for several poly-substituted paracyclophanes, including a series of bromine-containing molecules. The optimized processes could be run up to the gram scale without any loss in the reaction efficiencies. Because of its broad applicability, the ATH approach appears to be the method of choice to access planar chiral pCps in their enantiopure form.

Synthesis of paracyclophanes with planar and central chirality: kinetic resolution of [2.2]paracyclophane aldimines via palladium-catalyzed addition of arylboronic acids

Kinetic resolution of [2.2]paracyclophane aldimines was achieved through a palladium-catalyzed enantioselective arylation, providing access to chiral paracyclophanes with planar and central chirality as well as the recovered chiral aldimines.

[2.2]Paracyclophane-derived monodentate phosphoramidite ligands for copper-catalyzed asymmetric conjugate addition of diethylzinc to substituted chalcones

Copper-catalyzed asymmetric conjugate addition of diethylzinc to chalcones could be realized by using [2.2]paracyclophane-derived monodentate phosphoramidite ligands. The excellent yield and enantioselectivity (up to 98% yield and 95% enantiomeric excess) could be realized with low catalyst loading of 1.0 mol % and low ligand loading of 1.2%.

12,12′-[2,2′-Oxybis(ethane-2,1-diyl)bis(oxy)]bis[(Rp)-4-bromo[2.2]paracyclophane]

The title compound, C₃₆H₃₆Br₂O₃, was synthesized from (R_p)-4-bromo-12-hy­droxy[2.2]paracyclo­phane and oxydiethane-2,1-diyl bis­(4-methyl­benzene­sulfonate). The crystal packing exhibits a short O⋯Br inter­action [Br⋯O = 3.185 (3) Å] and a weak inter­molecular C—H⋯O contact.