Palladium(II)-Catalyzed Redox-Neutral Cyclizations of Alkynes Containing Alkenyl or Electrophilic Functional Groups: A Convenient Synthesis of Carbocycles and Heterocycles

Abstract

The palladium(II)-catalyzed redox-neutral cyclizations of alkynes bearing alkenyl or electrophilic functional groups, such as carbonyl, imino, or cyano groups, were developed to provide convenient approaches to various carbocycles and heterocycles. These tandem reactions are initiated by nucleopalladation of alkynes, transmetalation of arylboron reagents with palladium, or hydropalladation of alkynes, and they are quenched by β-heteroatom elimination, addition to electron-deficient alkenes, or addition to carbon–heteroatom multiple bonds. This account reviews these types of reaction, with a focus on our contributions to the field.1 Introduction2 Tandem Reactions of Functionalized Alkynes Initiated by Nucleo­palladation3 Tandem Reactions Of Functionalized Alkynes Initiated by Transmetalation of Palladium(Ii) with Arylboron Reagents4 Tandem Reactions of Functionalized Alkynes Initiated by Hydro­palladation5 Conclusion

Palladium-catalyzed cascade cyclization/intramolecular redox-relay Heck arylation of alkenols: access to tetrahydro-β-carbolines from 2-(hydroxyalkenynyl)sulfonanilides

“…Over the past decade, significant advances have been made in the development of palladium-catalyzed redox-relay Heck-type processes by Sigman's group and others, in which the double bond migrates along the alkyl chain by iterative β-hydride elimination/migratory insertion steps until captured by the alcohol moiety. 7 Inspired by the success of these achievements, we envisaged that the combination of Pd( ii )-catalyzed cyclization of alkynes 8 and the redox-relay Heck arylation of alkenols might offer a novel convergent cascade reaction to access tetrahydro-β-carbolines and their analogs. We surmised that 2-(hydroxyenynyl)sulfonanilides could engage in sequential electrophilic cyclization and redox-relay Heck cyclization.…”

“…Removing LiCl (entry 13) or the phosphine ligand (entry 14) reduced the yield of 2a , which indicated that the potential chelation of chloride might stabilize the indolyl palladium intermediate. 8 In the absence of the palladium catalyst, no reaction was observed (entry 15).…”

LiCl-Mediated and Palladium-Catalyzed Oxidative Cyclization of Furan–Ynes via Dearomatizing Alkoxyalkenylation of Furan

“…Palladium-catalyzed enyne cyclization initiated by nucleopalladation of alkynes represents a synthetically appealing approach for the synthesis of structurally diverse carbocycles or heterocycles in a high step-economy fashion . During this process, alkynes could react with various nucleophiles and generate diverse vinylpalladium species, which are prone to Heck-type insertion with alkenes (Scheme a) .…”

Enantioselective Synthesis of Fused Isocoumarins via Palladium-Catalyzed Annulation of Alkyne-Tethered Malononitriles

“…Intramolecular oxypalladation of alkynoic acid derivatives and sequential addition to electrophiles (e.g., carbonyls, α, β-unsaturated compounds) have been established as a powerful tool to construct condensed oxygen-containing heterocycles . Palladium-catalyzed annulations of ortho -alkynylbenzoates to afford isocoumarin scaffolds were reported by Lu, Li, Jiang, Sridharan, and others .…”