Multi-Component Coupling Reactions Involving Carbon Dioxide Via Visible Light-Induced Energy Transfer

Carbamate is an important organic motif with biological and medical activity.The traditional synthetic methods of carbamate mainly apply phosgene and its derivatives as starting material.Additionally,some synthetic methods without phosgene were developed,such as the reductive carbonylation of aromatic nitrocompounds,the oxidative carbonylation of amines,oxidative coupling,and the classic Curtius rearrangement and Hofmann rearrangement.Even so,the existing synthetic methods of carbamte mainly focused on the synthesis of alkyl carbamate,while the synthetic research of aryl carbamate is still very rare.During the previous decades,carbon dioxide（CO₂）has been widely used in carbamate synthesis as an easily available,non-toxic and renewable carbon resource,yet so far,no general method has been developed to synthesize O-aryl carbamate directly from carbon dioxide through a one-step process under relatively mild conditions.On the other hand,the visible-light-promoted energy transfer process has been developed rapidly in recent years.Among them,the visible-light-promoted energy transfer via the synergistic catalysis of transition metal/photocatalyst has become an attractive research direction,which has realized the construction of various kinds of C–C,C–O and C–N bonds.Therefore,this synergistic catalytic approach could provide an efficient access to nitrogen-containing organic molecules with diverse structural features.Based on the above research background,this paper applied the synergistic catalytic system of photoredox catalyst（fac-Ir（ppy）₃）and nickel catalyst（Ni Br₂·diglyme）,realized the visible-light-promoted three-component coupling reaction of amine,CO₂,and halogenated aromatic hydrocarbons through energy transfer.This method utilizes readily available feedstock chemicals,and reaction proceeds under mild process conditions with good functional group tolerance.Various secondary amines and substituted aromatic halides and heteroaromatic halides could participate in the reaction well,and aryl carbamates with diverse structures were obtained by 20–97%yields.Preliminary studies on the reaction mechanism were conducted.Through control experiments,on-off switching light experiments,and zero-valent nickel direct catalysis experiments,it is confirmed that the process may proceeds via the energy transfer pathway,that is,the excited state photocatalyst and the carbamate-Ni complex undergo energy transfer to generate excited state Ni species,then the excited state Ni species performs reductive elimination to genetate target product.This process provides a mild,efficient and green access for the synthesis of aryl carbamates.The development of this reaction is of great significance to the synthesis of biomedicines and pesticides with aryl carbamate structure.It can also be used to synthesize key organic intermediates with carbamates as protecting groups and guiding groups.