AuI Iminophosphorane Complexes as Efficient Catalysts for the Cycloisomerization of Alkynyl Amides under Air, at Room Temperature, and in Aqueous or Eutectic-Mixture Solutions.

New iminophosphorane-phosphine AuI complexes [AuCl(κ1 -P-Ph2 PCH2 P{=NP(=S)(OR)2 }Ph2 )] (3 a,b) and [Au2 Cl2 (µ2 -P,S-Ph2 PCH2 P{=NP(=S)(OR)2 }Ph2 )] (4 a,b) proved to be general, very efficient, and recyclable (up to four consecutive runs) catalysts for the cycloisomerization of alkynyl amides in water or choline chloride-based eutectic mixtures as green solvents. Remarkably, this cycloisomerization reaction took place under mild conditions (low catalyst loading, at room temperature, and in the absence of cocatalysts or protecting atmosphere) to give the corresponding alkylidene lactams by employing an efficient and sustainable methodology.

Mechanistic Insights into the Post-Cyclization Isomerization in Gold-Catalyzed 7-exo-dig-Hydroarylations.

The subsequent double-bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron-rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold-catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species.