C3 -Symmetric Boron Lewis Acid with a Cage-Shape for Chiral Molecular Recognition and Asymmetric Catalysis

Akihito Konishi; Koichi Nakaoka; Hikaru Maruyama; Hideto Nakajima; Tomohiro Eguchi; Akio Baba; Makoto Yasuda

doi:10.1002/chem.201605712

C₃ -Symmetric Boron Lewis Acid with a Cage-Shape for Chiral Molecular Recognition and Asymmetric Catalysis

Chemistry. 2017 Jan 26;23(6):1273-1277. doi: 10.1002/chem.201605712. Epub 2016 Dec 22.

Authors

Akihito Konishi^{1

2}, Koichi Nakaoka¹, Hikaru Maruyama¹, Hideto Nakajima¹, Tomohiro Eguchi¹, Akio Baba¹, Makoto Yasuda¹

Affiliations

¹ Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.
² Center for Atomic and Molecular Technologies, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.

PMID: 27933675
DOI: 10.1002/chem.201605712

Abstract

Chiral Lewis acids play an important role in the precise construction of various types of chiral molecules. Here, a cage-shaped borate 2 was designed and synthesized as a chiral Lewis acid that possesses a unique C₃ -symmetric structure composed of three homochiral binaphthyl moieties. The highly symmetrical structure of 2 with homochirality was clearly elucidated by X-ray crystallographic analysis. The peculiar chiral environment of 2⋅THF exhibited chiral recognition of some simple amines and a sulfoxide. Moreover, the application of 2⋅THF to hetero-Diels-Alder reactions as a chiral Lewis-acid catalyst afforded the enantioselective products, which were obtained through an entropy-controlled pathway according to the analysis of the relationship between optical yield and reaction temperature. In particular, the robust chiral reaction field of 2⋅THF allowed the first example of an asymmetric hetero-Diels-Alder reaction with a simple diene despite the requirement of high temperature.

Keywords: binaphthyl; cage-shaped borate; chiral Lewis acid; chiral molecular recognition; hetero-Diels-Alder reaction.