Organophotoredox 1,6-Addition of 3,4-Dihydroquinoxalin-2-ones to para-Quinone Methides Using Visible Light

Abstract

An organophotoredox 1,6-radical addition of 3,4dihidroquinoxalin-2-ones to para-quinone methides catalyzed by Fukuzumi's photocatalyst is described under the irradiation of a HP Single LED (455 nm). The corresponding 1,1-diaryl compounds bearing a dihydroquinoxalin-2-one moiety (20 examples) are obtained with good to excellent yields under mild reaction conditions. Several experiments have been carried out in order to propose a reaction mechanism.

Catalytic Nucleophilic and Electrophilic Functionalization of Dihydroquinoxalin‐2‐ones

“…Using these conditions, we could synthesize 20 products ( 42 ) bearing a 1,1‐diaryl moiety in 44–99 % yield (Scheme 17). [27] Regarding the reaction mechanism, the interaction of the excited state form of [Mes‐Acr‐Me][BF 4 ] with 4‐benzyl‐3,4‐dihydroquinoxalin‐2‐one 1 was proven by luminescence quenching experiments, suggesting that the first SET may occur between these two species (Scheme 17). Then, the resulting nitrogen‐centered radical cation 8 experiments a deprotonation to generate α‐amino radical 9 , which is able to react with p ‐quinone methide ( 41 ) in a 1,6‐fashion to form the expected oxygen‐centered radical 43 .…”