Enantioselective Pd⁰‐Catalyzed C(sp²)–H Arylation for the Synthesis of Chiral Warped Molecules

Abstract

C−H activation‐based ring‐forming methods are a powerful approach for the construction of complex molecular architectures, especially those containing a congested stereocenter. Therefore, this strategy seems perfectly suited to address the synthesis of chiral polycyclic aromatic hydrocarbons (PAHs) and bowl‐shaped molecules, which are important target molecules in the field of organic electronic materials. Herein, we describe an enantioselective Pd0‐catalyzed C(sp2)−H arylation protocol for the synthesis of chiral fluoradenes and other warped molecules, which could serve to the bottom‐up construction of chiral PAHs. The current approach relies on the use of chiral bifunctional phosphine–carboxylate ligands and delivers diverse polycyclic compounds in high yield and with good to excellent enantioselectivity. The chiroptical properties of the obtained products were investigated, and some of them were found to have a strong ellipticity and an emission band located in the visible region.

Design of Chiral NHC‐Carboxylates as Potential Ligands for Pd‐Catalyzed Enantioselective C−H Activation

“…Our group recently showed the beneficial effect of bifunctional ligands in Pd 0 -catalyzed enantioselective desymmetrizing C(sp 2 )À H activation for the synthesis of 5,6-dihydrophenanthridines [20] and chiral warped molecules. [21] The designed phosphine ligands (1) based on a binaphthyl scaffold incorporate a carboxylate group, which acts as the base to promote the CÀ H activation step occurring through the concerted metalation-deprotonation (CMD) mechanism (Figure 1). [22] It is assumed that the high enantioinduction results from a highly ordered transition state, which allows this system to outperform the corresponding monofunctional ligands.…”