Application Research On Allylation Of Aldehyde And Imine Via Umpolung

The homoallylic acohols and homoallylic amines are vital intermediates into numerous natural medicinal synthesis.The metal-catalyzed direct allylation of aldehydes,ketones and imines which is a hot spot in organic reaction research has been recognized as an important method for the preparation of homoallylic acohols and homoallylic amines.In the process of reactions,metals combine with allylated reagents to form allylmetal complexs.The allylpalladium complexs can exchang ligands with them to realize umpolung when there are metal reagents in the reaction system.However,the umpolung of allylcobalt complexs can be achieved via photocatalysis without metal reagents.We envisaged to achieve the allylation of aldehydes by dual photoderox and cobalt catalysis.We investigated the optimal conditions,the sensitivity of reaction and the substrate scope.The fluorescence quenching experiment,the color change experiment of reaction solution,and the UV-vis were used to speculate and verify the reaction mechanism.Then we got the conclusion based on the results of experiments: the electrophilic allylcobalt(III)complex can not add to aldehydes,however,its reduction product which is nucleophilic allylcobalt(II)complex can do it.Besides reversing the polarity of allylmetal complexs,the allylation of electrophiles can be also achieved by reversing the polarity of electrophiles.Imines can undergo umpolung in the alkaloid catalytic system,the copper catalytic system and the photocatalytic system.Among them,the photocatalysts and the nitrogen-containing electronic sacrificial agents can synergistically reduce imines into N-α radicals,but this process requires the participation of metals in the existing researches.Therefore,we envisaged to use the synergistic effect of metal-free organic photocatalysts and nitrogen-containing electronic electron donors to reduce the electrophilic imines into the nucleophilic N-α radicals coupling with the allyl or alkyl radicals.We investigated the optimal conditions and the applicable scope of imines and iodoalkanes and verified that the reaction is dominated by racidal coupling mechanism.