Gold(I)-Catalyzed Cascade Cyclization of Alkynyl Indoles for the Stereoselective Construction of the Quaternary Carbon Center of Akuammiline Alkaloids

Syntheses of Tetracyclic Indoline Derivatives Via Gold(I)-Catalyzed Hydroamination/Cycloisomerization Cascade of 2-Ethynyltryptamides

“…In the context of activation of alkynes, such as cycloisomerization of 1, n -enynes and carbon–heteroatom bond formation reactions, the nucleophilic attack to activated alkynes was often involved to form trans -alkenyl-gold complexes in mechanism . Thus, in recent years, many homogeneous gold­(I)-catalyzed reactions have been developed and applied in synthesizing scaffolds of many natural products and heterocyclic compounds …”

Construction of the Akuammiline Alkaloid Core Structure via Stereoselective E-Ring Formation

“…Our group recently reported a method for construction of the quaternary carbon center in the akuammiline-type fused indoline moiety via gold­(I)-catalyzed cyclization (Scheme ). By this methodology, linear alkynyl indole-type substrates 10 (R = H, halogen, alkyl, and methoxy) bearing a carboxylic acid moiety at the indole C3-position, prepared from protected 2-iodoaniline ( 7 ), glycidol ( 8 ), propargyl alcohol ( 9 ), and several C1 units, were stereoselectively converted to tetracyclic indolines 11 by treatment with BrettPhosAu­(MeCN)­SbF 6 (5 mol %). Of these indolines, 11a (R = H) was converted to 12 in several steps including reductive cleavage of the N , O -acetal moiety using sufficient reactivity of the lactone ring, providing a potential precursor for diversity-oriented synthesis of akuammiline alkaloids with different C-rings.…”