Regio- and stereoselective copper-catalyzed α,β-protoboration of allenoates: access to Z-β,γ-unsaturated β-boryl esters

Electrophilic Halogenation of Allenoates and 3-Alkynoates: Synthesis of 1,4-Dicarbonyl (E)-3-Haloalkenes and Mechanistic Investigations

Allenoates traditionally provide halobutenolides upon reaction with halonium ions via electrophile-assisted halolactonization. Herein, an unusual electrophilic halogenation of di- and trisubstituted allenoates and 3-alkynoates is demonstrated with N-halosuccinimides under DABCO promotion. The protocol affords densely functionalized 1,4-dicarbonyl 3-haloalkenes in good yields with excellent (E)-stereoselectivity (up to 83% yield, >20:1 dr). The allenoates are presumed to form γ-haloallenoate intermediates, which further react with halonium ions and provide the desired scaffolds. The role of the nucleophilic base in the unusual transformation is demystified through control experiments and computational studies. The deliverables are identified as good synthons for various synthetic group transformations and valuable targets for biologically active pyridazine scaffolds.

Copper-Catalyzed Regio- and Enantioselective Protoboration of Allenyl Sulfones to Access Chiral Allylic Sulfones

An efficient method for copper-catalyzed asymmetric protoboration of allenyl sulfones with bis(pinacolato)diboron was developed, providing chiral allylic sulfones with high efficiency and excellent enantioselectivity. Notably, the directing effect of the sulfone group plays a pivotal role in achieving both high regioselectivity and enantioselectivity.

Copper catalysed protoboration of allenyl-Bdans: efficient synthesis of β-boryl allyl-Bdans

A novel strategy for the selective synthesis of β-boryl allyl-Bdan derivatives by employing Cu-catalyzed protoboration of allenyl-Bdan derivatives was developed.