Bifunctional Biphenyl-2-ylphosphine Ligand Enables Tandem Gold-Catalyzed Propargylation of Aldehyde and Unexpected Cycloisomerization

Abstract

Despite extensive studies in gold catalysis, σ-allenylgold species have not been invoked as catalytic intermediates and their reactivities not studied. This work reports for the first time they are generated in situ and undergo nucleophilic addition to activated aldehydes in a bifunctional phosphine ligand-enabled gold catalysis. This development reveals a broad range of opportunities to achieve propargylic C–H functionalization for the first time under catalytic and mild conditions. The homopropargylic alcohols generated undergo ligand-enabled cycloisomerizations involving an unexpected silyl migration.

Buchwald‐Type Ligands on Gold(I) Catalysis

“…[110] This allowed the reaction with electrophiles such as aldehydes 99 via 1,2-addition, followed by cyclization with concomitant 1,2-silyl migration yielding silylated dihydrofuranes 101 (Scheme 18). [111]…”

Propargylsilanes as Reagents for Synergistic Gold(I)‐Catalyzed Propargylation of Carbonyl Compounds: Isolation and Characterization of σ‐Gold(I) Allenyl Intermediates

“…In this sense, Zhang et al. very recently published an excellent and very carefully designed gold(I)‐catalyzed propargylation reaction of aldehydes (Figure ).…”

“…However, although several π‐gold allenyl and gold allenylidene complexes have been isolated and characterized, σ‐gold allenyl complexes remained unknown until characterization by Gimeno and co‐workers, and very recently by Hashmi et al., although in both cases, without catalytic relevance. These species have also received little attention as intermediates in gold catalytic reactions, with the exception of the very recent work by Zhang and co‐workers and Pyne, Hyland, and co‐workers …”

Bifunctional Phosphine Ligand Enabled Gold‐Catalyzed Alkynamide Cycloisomerization: Access to Electron‐Rich 2‐Aminofurans and Their Diels–Alder Adducts

“…[8b] Lately,w ed emonstrated that the initial isomerization of alkynes into allenes can become asymmetric when ac hiral version of L4 is employed as the gold ligand, [9] and the allenylgold intermediate can be trapped by activated aldehydes. [10] We envisioned that the isomerization of an acetylenic amide into an allenylic amide can likewise be realized by agold catalyst featuring our designed bifunctional ligands.As such, asequence related to that in Scheme 1A should permit, for the first time,a ccess to highly the electron-rich 2aminofuran in as traightforward and expedient manner.…”