A One‐Pot Approach to Phenanthridine Derivatives through Two‐Step Rhodium(I) and Gold(I) Catalysis

Abstract

An effectiveo ne-pot procedure for the synthesis of phenanthridine derivatives containing N-or O-heterocycles has been developed through at wo-stepr hodium-catalyzed[ 2 + +2+ +2] cycloaddition and gold-catalyzedh eterocyclization under mild conditions.T he substrate scope has been investigated and ap lausible reactionm echanism has been proposed on the basis of control experiments and previousl iterature reports.Keywords: [2+ +2+ +2] cycloaddition;g old catalysis; heterocyclization;o ne-pot procedure;r hodium catalysis Polycyclicc ompounds containingN -a nd O-heterocycles are the core structures in av ariety of pharmacologicala gents and natural alkaloids.[1] Thus far, the development of new synthetic methodso rs trategies for heterocyclic compounds hasbeenavery important area in organic synthesis.[2] Recently,t he synthesiso f substituted or functionalized phenanthridines hasa ttracted much attention sincet hey are the core structural motifsi nm anyb iologically active molecules as shown in Figure 1, andn ew synthetic protocols for these compounds are stillh ighly desirable. [3] Over the past decades,s ynthesis of polycyclic compounds has made significant progress and al arge number of useful andpractical methodshavebeen explored, in which transition metal catalysish as been playing av ery important role.W ith the aid of transition metal catalysis, one can rapidly generate complex molecular structures from easily accessible starting materials under mild reaction conditions.F or example,t he transitionm etal-catalyzed [2+ +2+ +2] cycloaddition reactions of unsaturated compounds are very useful and straightforward methods for constructing polycyclic compounds.[4] Various highly regioselective [2+ +2+ +2] cycloadditions of diynes under Co,N i, Ir, Ru, Au or Rh catalysis have been reported by several groups.[5-10] Furthermore,heterocyclizations of alkynes under transitionm etal catalysis are also practical and straightforward methodst oc onstruct heterocyclic compounds. [11][12][13][14][15][16][17][18] Nowadays,o ne-pot synthesis is becoming an importants trategys incei tc an improve the efficiency of ac hemical reaction. Theo ne-pot reactions combiningt ransitionm etal catalysis ando rganocatalysis leadt om anye legant and effective synthetic protocols. [19,20] On the basis of this strategy,m ultistep chemical transformationsc an be performed sequentially to givec omplexm olecules in as ingle reaction vessel,s ubsequently reducing work-up and purification steps.Recently,t he reactions catalyzed by gold complexes have been exploreds ignificantly.M oreover, some examples about gold-catalyzed cascade reactions and dual-metal catalysisw ith gold ands econd metals have

Gold-Catalyzed Domino Synthesis of Functionalized Benzofurans and Tetracyclic Isochromans via Formal Carboalkoxylation

“…activates the alkyne π-bond to generate an (alkenyl)metal intermediate bearing an electrophilic migrating group, which then shifts to the most nucleophilic 3-position of heterocycles. As a migrating group, α-alkoxyalkyl, , allyl, , benzyl, , acyl, methyl, sulfonyl, boryl groups, and so on have been employed . Recently, Oh and co-workers reported an elegant synthesis of 2,3-disubstituted indoles via silver-catalyzed condensation of N -( o -alkynylaryl)­formimidates and active methylene compounds followed by the migratory cycloisomerization based on the carboamination of alkynes with 1,3-alkenyl shifts (eq 2).…”

Pd-Catalyzed Migratory Cycloisomerization of N-Allyl-o-allenylaniline Derivatives

“…Transition-metal-catalyzed migratory cycloisomerization provides a powerful approach in organic synthesis. , In particular, migratory cycloisomerizations of o -alkynylaryl ethers and amines having a migrating group on the heteroatom have been used to the synthesis of 2,3-disubstituted benzofurans and indoles (Scheme , eq 1). As migrating groups, α-alkoxyalkyl, allyl, , propargyl, benzyl, , acyl, , methyl, sulfonyl, , silyl, boryl groups, and so on have been employed.…”