Visible Light Induced Hydrophosphinylation Of Unactivated Alkenes Catalyzed By Salicylaldehyde

Phosphorus-containing organic compounds are of great significance due to their unique functional activities,and they have a wide range of applications in medicine,agriculture,materials science,and catalysis.Strategies for the construction of organophosphorus compounds include the formation of carbon-phosphorus bonds through transition metal-mediated coupling,nucleophilic substitution,addition reactions,and the like.Among them,the hydrophosphorylation of unsaturated bonds,especially carbon-carbon double bonds,is a simple,efficient and atom-economical method for the synthesis of novel tertiary phosphine oxides.For unactivated alkenes,due to the lack of activation by electron withdrawing groups,the electrophilicity is weak and the reactivity is greatly reduced.Traditional methods often require activation by free radical initiators,microwaves,UV light and high temperature(> 120 °C),and the substrate scope is often limited.In recent years,with the development of the field of visible light-induced reaction,it has attracted a lot of attention for its advantages of green energy source,mild reaction conditions and high efficiency.The currently reported visible-light-induced hydrophosphorylation of non-activated olefins undergoes a photoredox mechanism and requires the use of noble metal-based complexes or organic molecules with larger ?-conjugated systems as photocatalysts.Aldehydes can be used as photoorganocatalysts in organic synthesis.Due to the ?-?conjugation of carbonyl functional groups and aryl groups,aromatic aldehydes can be excited under visible light irradiation,thereby playing a catalytic role.We selected salicylaldehyde as a photocatalyst from the screening of many aromatic aldehydes,and successfully realized the visible light-induced hydrophosphorylation of non-activated alkenes.This reaction has two advantages: low-energy excitation(visible light: blue LED,30 W)and an inexpensive catalyst source.The reaction is carried out with water as solvent under air atmosphere,and the product yield is usually high.And successful gram-scale experiments were performed.Based on experimental results,computational studies and previous studies,photoredox and energy transfer processes are excluded,and a hydrogen atom transfer activation mechanism is proposed.