吉田 泰志

A method for accessing pyrazole-containing helicene-like molecules from easily accessible NOBIN derivatives was developed. The reaction proceeded efficiently via diazonium salt intermediates, which provided a series of helicene-like molecular products in yields of 77%-89% regardless of their steric and electronic natures. The photophysical properties of the products were investigated. The 3,3′-disubstituted molecules showed a characteristic blue shift in their emission spectra. Product derivatizations were conducted, and interesting reactivities toward nucleophiles were observed.

Asymmetric construction of chiral N,S-acetal skeletons is important because they are widely present in natural products and pharmaceuticals. Halogen-bonding is a unique interaction that has been an organic synthesis focus, although research into chiral variants is limited. Halonium salts have been found to act as halogen-bonding catalysts and asymmetric catalysis using chiral bromonium salts under basic conditions was recently discovered by our group. Herein, we report the asymmetric syntheses of chiral N,S-acetals in good-to-excellent yields and enantioselectivities (82–97% ee) through bulky thiol additions to imines catalysed by a chiral iodonium salt under neutral conditions. The reaction mechanism was studied using NMR experiments and DFT calculations of a plausible intermediate, which revealed that the imine substrate is activated by the catalyst in a bidentate manner. The abnormal counteranion effect observed for the tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion in the present system was examined by 1H NMR spectroscopy. (Figure presented.).

Bromonium salts, which are hypervalent bromine reagents, have been explored as being strong electrophiles owing to their extremely high nucleofugalities. Only one example of their catalytic application has been reported by our group; however, their chiral versions have not yet been researched. Halogen-bonding (XB) has been widely applied in chemistry; however, its successful application to highly enantioselective Lewis acid catalysis has not yet been achieved. Herein, we report the design and development of chiral cyclic diarylbromonium salts. These catalysts enabled a highly enantioselective Lewis acid XB catalysis, giving products with up to 96% ee.

Bromonium salts have been typically but infrequently used in various reactions as good leaving groups or as aryl or vinyl transfer reagents owing to their extremely high nucleofugality. Herein, we report the synthesis of novel, stable bromonium salts and their first catalytic application to the Michael reaction, with excellent product yield (up to 96%).

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Chiral α-amino-δ-keto esters are important precursors of organocatalysts, pharmaceuticals, and biochemically interesting molecules. The organocatalytic asymmetric umpolung reaction of imines has been developed to obtain chiral amines in a highly enantioselective manner. Herein, we report the organocatalytic asymmetric umpolung synthesis of α-amino-δ-keto esters in high yield (up to 95% ee, >20/1 r.r.). (Figure presented.).