Reductive cascade transformations of heteroatom-containing unsaturated molecules by Lewis acid catalysis

Abstract

The Lewis acid catalysts have played a significant role in organic synthesis. Tris(penetafluorophenyl)borane $B(C_6F_5)_3$ is one of those Lewis acid catalysts, which has received much attention due to its high reactivity and selectivity. Although a diverse range of organic transformations using Lewis acidic boron have been established, the development of new C-X (X = Si, B, etc.) bond formation is still in infancy. In this regard, this thesis describes the development of the reductive cascade transformations of unsaturated molecules to give new $sp^3$ C-Si or C-B bonds via the Lewis acidic boron catalysis as follows.

First, the silylative reductive amination of conjugated aldehydes via a Lewis acidic boron catalysis has been developed for the first time. Unsaturated imines generated through a condensation reaction of a broad range of aldehydes with amines, underwent a new C-Si bond formation under the boron catalyst. The NMR study revealed that the bulkiness of amine has an influence on the catalytic reactivity and selectivity.

Second, the boron-catalyzed double hydroboration of quinolines was investigated. This study includes a direct formation of C-B bond at the $\beta$-position to the nitrogen atom via the consecutive borylative reduction of a range of quinolines. This borylated tetrahydroquinolines could be converted to 3-hydroxytetrahydroquinolines upon simple oxidation in one-pot. This study revealed that the stereochemistry of the products was determined by the position of the substituents in quinolines.