Au-Catalyzed Hexannulation and Pt-Catalyzed Pentannulation of Propargylic Ester Bearing a 2-Alkynyl-phenyl Substituent: A Comparative DFT Study.

The mechanistic pathways of metal-catalyzed pentannulation and hexannulation of aromatic enediyne were studied quantum mechanically with Pt and Au salts. In agreement with the experimental facts, our result shows that the pentannulation favors over the hexannulation under Pt-catalyzed conditions and the reverse possibility favors when the Pt salt is replaced with an Au one. The Pt-catalyzed reaction involves a long-range acyl migration that follows the cyclization step.

Ligand-assisted acyl migration in Au-catalyzed isomerization of propargylic ester to diketone: a DFT study.

Gold-catalyzed isomerization of propargylic ester to a diketone derivative is a fascinating example for the generation of the C-C bond in organoaurate chemistry as it is one of the few reactions that exploit the nucleophilicity of organoaurates to a migrating acyl group. The proposed mechanistic pathway, involving the formation of a four-membered intermediate, has never been substantiated by any theoretical or experimental evidence. Detailed theoretical calculation suggests that the formation of an alkylideneoxoniumcyclobutene intermediate is highly unlikely.

Mechanism of the gold(III)-catalyzed isomerization of substituted allenes to conjugated dienes: a DFT study.

The mechanism of gold(III) [Au(III)]-catalyzed isomerization of alkyl-substituted allenes to conjugated dienes in the presence of a nitroso compound (additive) was studied quantum mechanically using hybrid density functional PBE0 with 6-31G** basis set for lighter atoms and (aug)-ccpVDZ basis set and LANL2 electron core potential for Au atom. Several pathways, involving the nitroso compound in a free or bound state to the gold-allene (GA) complex, were investigated. Calculated results reveal that the unbound nitroso compound acts as a better proton transferring agent in the isomerization process and utilizes its own nitrogen atom to carry the proton.