Chirooptical 2,2′‐Dimethoxybiphenyl Crystals Generated From Suzuki–Miyaura Coupling Reaction Catalyzed by Pd‐Loaded Chiral Silica
Shunpei Yoshimori, Ren‐Hua JinABSTRACT
In this work, we report a one‐pot approach that combines crystal ripening with the Suzuki–Miyaura coupling reaction. We investigated the reaction between 2‐methoxyphenyl bromide and 2‐methoxyphenylboronic acid, catalyzed by a series of Pd‐loaded chiral optical (D‐ or L‐) and racemic (DL‐) silica/polyethyleneimine (PEI) systems, which produced crystalline 2,2′‐dimethoxybiphenyl (DMB). The silica used as a catalyst was prepared using our previously established method, in which chirality was imparted to the silica through catalytic templates composed of polyethyleneimine (PEI) and tartaric acid. Both enantiopure (D‐ or L‐; 100% ee) and racemic (DL‐; 0% ee) tartaric acid‐mediated silica, after tartaric acid removal and palladium (Pd) loading, exhibited similar catalytic activities, leading to the quantitative precipitation of 2,2′‐dimethoxybiphenyl in a water/ethanol (1:1 by volume) medium. Interestingly, the 2,2′‐dimethoxybiphenyl crystals formed and ripened in the presence of Pd‐loaded chiral D‐ and L‐silica/PEI exhibited octahedral morphology and displayed remarkable chiroptical activity with a mirror‐image relationship. This represents a novel example of using chiral Pd‐loaded silica to synthesize axially chiral biphenyl in crystalline form.