Photoredox Catalyzed Radical Cascade Reactions For The Synthesis Of Cyclic Compounds

Visible-light photocatalysis is a novel and green catalytic mode.The radical cascade reaction which can simply and efficiently construct C-C bonds and C-X bonds via photoredox catalysis,plays an important role in synthesis of complex cyclic compounds.In this thesis,a series of indene-containing polycyclic compounds and tetralone derivatives are synthesized by the radical-mediated tandem cyclization strategy by photoredox catalysis under mild conditions,which are mainly divided into two parts:（1）Photocatalytic[2+2+1]annulation of 1,6-enynes and N-hydroxyphthalimide estersThe synthesis of indene-containing polycyclic compounds has certain challenges due to its complex structure.Herein,a photoredox catalytic cascade cyclization of 1,6-enynes and N-hydroxyphthalimide esters is reported to efficiently synthesize a series of cyclopenta[a]indene derivatives,in which N-hydroxyphthalimide esters act as suitable carbon radical sources after reduction decarboxylation process.This reaction has the characteristics of mild conditions and good functional group compatibility.It is worth noting that the conversion can also be carried out in the PPh₃/Na I catalytic system without precious metal photocatalysts in moderate yields.（2）Photocatalytic radical cascade cyclization of vinyl azides andα-carbonyl alkyl bromidesWe have also developed the radical cyclization of vinyl azides andα-carbonyl alkyl bromides by using highly reducing organic photocatalyst,and successfully prepared a series of tetralones derivatives.In this reaction,vinyl azides is used as radical acceptor and anitrogen radical precursor,andα-carbonyl alkyl bromides is used as 1,2-diradical synthons.According to the results of control experiments and radical trapping experiments,the reaction may proceed by a radical pathway,so we propose a iminyl radical-triggered hydrogen atom transfer（HAT）mechanism.This method without the requirement of precious metal complexes as photocatalysts,can realizes C-Br bond and remote Csp³-H bond activation,and has the advantages of good atom economy and mild reaction conditions.