Investigation Of Photoredox O-α-sp~3 C-H Cleavage Reactions

The research on functionalization of N-?-sp3 C-H has attracted interest from many organic chemists in recent years. However, the functionalization of O-?-sp3 C-H bonds is still less reported. The lone pair electrons of oxygen are too stable to be oxidized by the excited photosensitizer. It is very difficult to achieve functionalization of O-?-sp3 C-H bonds through single electron transfer process. We successfully realized O-?-sp3 C-H bonds cleavage by utilizing the ·CCl3 radical generated under visible-light photoredox conditions to abstract the hydrogen of the benzyl position, through the hydrogen atom transfer. Several practical organic reactions were developed based on the finding.This paper is divided into four parts:The first chapter is a summary of the O-?-sp3 C-H functionalization reactions and the visible-light-mediated O-?-sp3 C-H functionalization reactions.The second chapter is about visible light catalytic O-?-sp3 C-H functionalization reaction of benzyl alkyl ethers to form esters. We investigated the reaction between alkyl benzyl ethers and ethyl acetate. Transesterification reaction occurred to generate the corresponding esters under visible light photoredox conditions. Ir(dtb-bpy)(ppy)2PF6 was the catalyst and Br CCl3 was the oxidant. The reaction has never been reported in the literatures.The third chapter is about visible-light-promoted direct formation of aromatic aldehydes or ketones from alkyl benzyl ethers. In this reaction, alkyl benzyl ethers act as a masked carbonyl compounds. The reaction generate carbonyl compounds through the oxidative cleavage of alkyl benzyl ethers.The fourth chapter is about visible-light-promoted difunctionalization of diols. The reaction achieved the conversion of the two hydroxyl groups in diol to different functional groups in one step through ?-bromoacetals intermidiate.