Chloro-arylation of Alkenes via Cooperative Photoredox and Atom-transfer Catalysis

Abstract

Alkyl chlorides represent one of the most widely applicable synthetic intermediates in organic chemistry due to their multi-dimensional reactivities. This thesis primarily focused on the development of a photocatalytic, aryl radical mediated chloro-arylation reaction of alkenes. The goal was to obtain alkyl chlorides with high structural diversity from readily available alkenes and diaryliodonium salts. The developed transformation benefits from a high degree of modularity through the independent functionalization of diaryliodonium salts and alkenes. In addition, broad functional group tolerance is observed under the mild photochemical conditions.

The first part of this thesis specifically focused on the chloro-arylation of vinyl boronic esters, which provided a flexible strategy for the streamlined synthesis of complex β-aryl α-chloroboronic esters. Structurally diversified and readily available diaryliodonium triflate and vinyl boronic esters were tolerated. The obtained α-chloroboronic esters were further subjected to a series of downstream transformations showcasing versatile synthetic application of α-chloroboronic esters. We have also gained mechanistic insights into the mechanism of the reaction.

Following the success of chloro-arylation of vinyl boronic esters, we further applied such dual catalysed strategy on to a broader pool of alkenes. An extensive scope study demonstrated broad-spectrum tolerance to electron-deficient alkenes, styrene derivatives, and unactivated alkenes. Elucidation of the key mechanistic steps and intermediates revealed a unique inner-sphere single electron transfer (iSET) mechanism when [CuI(dpp)2]+ and [BPA.CuI]+ were used as photocatalyst and chlorine transfer catalyst, respectively.