Copper-Catalyzed Asymmetric Coupling of Allenyl Radicals with Terminal Alkynes to Access Tetrasubstituted Allenes.

In contrast to the wealth of asymmetric transformations for generating central chirality from alkyl radicals, the enantiocontrol over the allenyl radicals for forging axial chirality represents an uncharted domain. The challenge arises from the unique elongated linear configuration of the allenyl radicals that necessitates the stereo-differentiation of remote motifs away from the radical reaction site. We herein describe a copper-catalyzed asymmetric radical 1,4-carboalkynylation of 1,3-enynes via the coupling of allenyl radicals with terminal alkynes, providing diverse synthetically challenging tetrasubstituted chiral allenes. A chiral N,N,P-ligand is crucial for both the reaction initiation and the enantiocontrol over the highly reactive allenyl radicals. The reaction features a broad substrate scope, covering a variety of (hetero)aryl and alkyl alkynes and 1,3-enynes as well as radical precursors with excellent functional group tolerance.

Rhodium(III)-Catalyzed Synthesis of Skipped Enynes via C(sp3 )-H Alkynylation of Terminal Alkenes.

The RhIII -catalyzed allylic C-H alkynylation of non-activated terminal alkenes leads selectively to linear 1,4-enynes at room-temperature. The catalytic system tolerates a wide range of functional groups without competing functionalization at other positions. Similarly, the vinylic C-H alkynylation of α,ß- and ß,γ- unsaturated amides gives conjugated Z-1,3-enynes and E-enediynes.

Regioselective and Redox-Neutral Cp*IrIII -Catalyzed Allylic C-H Alkynylation.

Herein, we report a Cp*IrIII -catalyzed highly regioselective and redox-neutral protocol for the construction of 1,4-enynes from unactivated olefins and bromoalkynes via intermolecular allylic C-H alkynylation. The developed mild reaction conditions tolerate a broad range of common functional groups, even enabling selective alkynylation of allylic C-H bonds in the presence of other prominent directing groups. Mechanistic experiments including the isolation of a catalytically active IrIII -allyl species support an intermolecular allylic C-H activation followed by an electrophilic alkynylation.

Synthesis of Substituted Tropones by Sequential Rh-Catalyzed [5+2] Cycloaddition and Elimination.

Highly substituted tropones are prepared from cycloheptatrienes derived from Rh-catalyzed intermolecular [5+2] cycloaddition of 3-acyloxy-1,4-enynes and propargylic alcohols. The intermolecular [5+2] cycloaddition is highly regioselective for a variety of propargylic alcohols. Elimination of the cycloaddition products afforded various substituted tropones.