Stereodivergent Total Syntheses Of Chaetominine-Type Alkaloids And Radical Cascade Cyclization For The Synthesis Of Imidazo-Fused Heteroaromatics And The Synthesis Of 2-Carboxyl-6-Hydroxy-Octahydro-Indole(CHOI) Unit

The nitrogen-containing compounds are important as natural products and pharmaceuticals and the development of efficient methods for their preparation is highly desriable.First,a stereodivergent and enatioseleetive method has been developed for the total syntheses of chaetominine-type alkaloids including the proposed structures of(-)-pseudofischerine,(-)-aniquinazoline D and(-)-isochaetominine,(-)-isochaetominines A-C,(+)-14-epi-isochaetominine C,as well as the four hitherto unkown stereoisomers of isochaetominine C.The structures of natural(-)-pseudofischerine and(-)-aniquinazoline D have been revised as(-)-isochaetominine C and the structure of the natural(-)-isochaetominine have been revised tQ(-)-11-epi-chaetominine based on our synthetic efforts.(-)-chaetominine(-)-pseudofischerine(-)-aniquinazoline D(proposed structure,)(proposed structure)(-)-isochaetominine A(R=Me)(-)-isochaetominine B(R=Et)(+)-isochaetomine(-)-isochaetominine C(R=i-Pr)Next,an azaphilic radical cascade cyclization reaction has been devleoped leading to the efficient synthesis of imidazo-fused heteroaromatics from easily avaialble N-heteroaryl-O-propargyl carbamate.The organocatalyzed electrochemical synthesis is broad in scope,tolerates many common functional groups,proceeds under mild conditions without the need for any transition-metal catalyst or chemical oxidant.=-COOMe,37 examples,X=CH,N41%-92%yield R=H,40 examples,40%-94%yield solvent,Et4NBF4,80?7 examples,48%-81%yieldIn addition,two approaches toward analogs of the CHOI unit have been developed.The key steps of the synthetic route were based on Pd-catalyzed C-allylation and N-allylation,which converted a cyclic bis-allylic substrate into a hexahydroindole scaffold.Depending on the strategy applied,the position of alkene moiety of the hexahydroindole can be obtained at different positions.One-carbon homologation followed by epoxidation orsyn-dihydroxylation of the resulting bicyclic intermediates afforded CHOI analogues.