| The allyl moiety is an important group capable of undergoing various synthetic functional group conversions because it possesses a carbon-carbon double bond;as a result,reactions for the introduction of allyl moieties into organic molecules are highly desirable.[1]Among reactions,α-allylic alkylations of tertiary amines represent particularly useful and challenging reactions for preparing homoallylic amines,which are frequently employed as intermediates for the synthesis of pharmaceuticals and natural products.Although significant advances have been achieved,noble metal-based photocatalysts and transition metals are usually necessary in such approaches.The pursuit of a greener and more efficient method is of great interest.Here,we report a novel,visible light-induced,photocatalyst-and transition-metal-free,sp3 C-Hα-allylic alkylation of N-aryl tetrahydroisoquinolines.The reaction uses a 400 nm LED lamp as the light source,N,N,-dimethylformamide（DMF）as the solvent,cesium carbonate as the base,and allyl bromide as the allyl radical precursor.The utility and practicality of thisα-allylation of N-aryl tetrahydroisoquinolines were demonstrated by the gram-scale preparation of 1-（2-methylallyl）-2-phenyl-1,2,3,4-tetrahydroisoquinoline.The products can also be transformed to produce berberine analogs with anticancer and antibacterial activity.The mechanism involves a novel in situ-generated electron-donor-acceptor（EDA）complex between the N-aryl tetrahydroisoquinolines and an allyl or a benzyl bromide.Irradiation with purple light triggered single-electron transfer from the N-aryl tetrahydroisoquinolines to the allyl or benzyl bromide of the EDA complex,inducing the formation of the corresponding radical and the subsequent radical-radical coupling.This approach represents the first example of a photocatalyst-and transition-metal-freeα-allylic and benzylic functionalization of N-aryl tetrahydroisoquinolines. |
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