Experimental and Computational Evidence for Gold Vinylidenes: Generation from Terminal Alkynes via a Bifurcation Pathway and Facile C–H Insertions

Abstract

Facile cycloisomerization of (2-ethynylphenyl)alkynes is proposed to be promoted synergistically by two molecules of BrettPhosAuNTf2, affording tricyclic indenes in mostly good yields. A gold vinylidene is most likely generated as one of the reaction intermediates based on both mechanistic studies and theoretical calculations. Different from the well-known Rh, Ru and W counterparts, this novel gold species is highly reactive and undergoes facile intramolecular C(sp3)-H insertions as well as O-H and N-H insertions. The formation step for the gold vinylidene is predicted theoretically to be complex with a bifurcated reaction pathway. The pyridine N-oxide acts as a weak base to facilitate the formation of an alkynylgold intermediate, and the bulky BrettPhos ligand in the gold catalyst likely plays a role in sterically steering the reaction toward the gold vinylidene formation.

Gold‐Catalyzed Cascade Reactions of Alkynes for Construction of Polycyclic Compounds

“…Also in 2012, Zhang reported a gold‐catalyzed cascade cyclization of diynes 72 , in the presence of a pyridine oxide 73 , to produce 1,2‐dihydrocyclopenta[ a ]indene derivatives 74 (Scheme ) 21. Although the presence of the N ‐oxide 73 as an additive is not essential, the reaction became slower and less efficient as the amount of the N ‐oxide was decreased.…”

The preference for dual-gold(i) catalysis in the hydro(alkoxylation vs. phenoxylation) of alkynes

“…However, more recently the importance of dual gold catalysis, by means of cycloisomerization reactions first proposed by Toste and Houk, 11 and Gagosz, 12 and later established for many synthetic protocols. 13,14 Well-defined digold pre-catalysts are now used for a number of applications. [15][16][17][18][19][20][21][22][23] Dual gold catalysis might help to overcome the hurdle that Au I has only two coordination sites available, with a linear geometry.…”

Automated Quantum Mechanical Predictions of Enantioselectivity in a Rhodium‐Catalyzed Asymmetric Hydrogenation

“…[25] Thefinal free energies were based on M06 single-point energiesusing the SDD basis set with ECP for Rh and 6-311 ++G(d,p)for all other atoms. [25] Thefinal free energies were based on M06 single-point energiesusing the SDD basis set with ECP for Rh and 6-311 ++G(d,p)for all other atoms.…”