Photocatalytic C-I Bond Borylation and Phosphorylation of Diaryliodonium Salts with Excellent Atom-Economy

Abstract

Highly atom-economic conversion of diaryliodonium salts represents an underdeveloped but highly desirable domain. Most reactions involving these species only utilize single aryl group of the diaryliodonium and produce an equivalent of aryl iodide as waste. Herein, by further transforming the side-product aryl iodide, we report an overall new two-step one-pot strategy that allows photocatalytic C−I bond borylation and phosphorylation of diaryliodonium salts and ensures effective conversion of both aryl groups of the diaryliodonium into the relevant arylboronic esters or arylphosphonic esters. Mechanistic investigations suggest that electron-donor-acceptor (EDA) complex is formed between the photocatalyst phenothiazine (PTH) and diaryliodonium salt substrate. Upon visible light irradiation, this complex produces aryl radical and aryl iodide. With addition of a base in the second step, the reducing ability of the photocatalyst is enhanced via proton-coupled electron transfer (PCET) process, thereby aryl iodide produced in the first step is reduced to yield aryl radical again. Both aryl radicals generated in the two steps react with B2(OR)4 or P(OR)3 to produce the corresponding monoarylation product in a quantitative yield.