Pd-Catalyzed Cascade Intramolecular Heck Cyclization/Dearomatization of Indoles for the Construction of Two All-Carbon Quaternary Centers

Pd-Catalyzed cascade Heck cyclization/carbonylation of indoles with aryl formates: enantioselective construction of indolo[2,1-a]isoquinolines

An efficient palladium-catalyzed cascade cyclization/carbonylation of indoles with aryl formates to access ester-functionalized indolo[2,1-a]isoquinoline scaffolds has been developed. In addition, an asymmetric variant is also achieved using a chiral phosphine ligand, affording the indolo[2,1-a]isoquinoline products in good yields and enantioselectivities.

Photoredox-Catalyzed Tandem Cyclization of Enaminones with N-Sulfonylaminopyridinium Salts toward the Synthesis of 3-Sulfonaminated Chromones

A photoredox-catalyzed intermolecular tandem sulfonamination/cyclization of enaminones was realized by using N-aminopyridinium salts as the sulfonaminated reagents without transition-metal catalysts or bases. The reaction exhibits a broad scope and good functional group tolerance, good yields, and regioselectivity. Preliminary mechanistic studies support the radical property of the reaction and the involvement of N-centered radical intermediates.

Nickel-Catalyzed Enantioselective Dearomative Heck-Reductive Allylic Defluorination Reaction of Indoles

Herein, we describe a nickel-catalyzed asymmetric dearomative aryl-difluoroallylation reaction of indoles with α-trifluoromethyl alkenes as an electrophilic coupling partner. The reaction proceeds via a cascade sequence involving dearomative Heck cyclization and reductive allylic defluorination. A series of gem-difluoroallyl substituted indolines are obtained in moderate to good yields (36-77% yield) with excellent enantioselectivity (up to 99% ee). The reaction features broad functional group tolerance, scaled-up synthesis, and late-stage diversification.

Construction of Conjugated 1,3-Enynes via Pd-Catalyzed Cascade Alkynylation of Aryl Phenol-Tethered Alkynes with Alkynyl Bromides

An efficient Pd-catalyzed cascade alkynylation of aryl phenol-tethered alkynes with alkynyl bromides is described. This protocol could provide various conjugated 1,3-enynes possessing a polysubstituted spirocyclohexadienone, as well as an all-carbon tetrasubstituted alkene moiety. The products could also undergo ring-expansion and cyclization transformations under different conditions to convert to diverse fused cyclic scaffolds.

Iodine(III)-Mediated C-C Bond Coupling to Construct Spirocyclic Indolenines of Various Ring Sizes

Herein, we report a novel iodine(III)-mediated intramolecular dearomative spirocyclization of indole derivatives to generate highly strained spirocyclobutyl, spirocyclopentyl, and spirocyclohexyl indolenines in moderate to good yields. A set of structurally novel, densely functionalized spiroindolenines with broad functional group compatibility was efficiently constructed in this way under mild reaction conditions. Moreover, the β-enamine ester as a versatile functional group in the product provides great convenience for the synthesis of bioactive compounds and related natural products.