Direct Deoxygenative Intramolecular Acylation of Biarylcarboxylic Acids

Abstract

A photocatalyzed intramolecular cyclization is developed for the synthesis of fluorenones. In this photoredox reaction, triphenylphosphine is used as an inexpensive and effective deoxygenative reagent for biarylcarboxylic acids to give acyl radicals, which quickly undergo intramolecular radical cyclization. Reactions in the presence of air and continuous flow photoredox technology demonstrate the generality and practicality of this process.

Dual-role catalysis of iridium in photo-irradiation synthesis of 9-fluorenone through intramolecular cyclization via hydrogen evolution

“…The resulting acyl radical on A˙ then attacked the ortho -C–H component of the aryl, forming intramolecular ring-closed radical B˙. 11,12 Since there is no additional oxidant in the system, B˙ cannot afford fluorenone directly. We thus proposed that radical B˙ was reduced by [Ir II ] to anionic C − , which is only one step away from the production of 9-fluorenone and hydrogen.…”

Electricity-Promoted Friedel–Crafts Acylation of Biarylcarboxylic Acids

“…The fluorenone architecture and its derivatives are common motifs in natural products, biological active, and optoelectronic compounds (Scheme ). Accordingly, many synthetic strategies, such as the oxidation of fluorenes, transition-metal-catalyzed C–H activation, radical cyclization, have been devised to access fluorenones, and the development of novel strategies remains a valuable undertaking. One of the most convenient and practical approaches to fluorenones is the Friedel–Crafts acylation of biarylcarboxylic acids and their acyl chlorides .…”