β-(2-Aminophenyl)-α,β-ynones afforded 3-unsubstituted 2-acylindoles in good yields in the presence of 20 mol % AgOTf under (microwave) MW heating. The use CuOTf as a catalyst resulted in a similar reaction outcome, generally with a lower efficiency. This transformation represents the first example of 5- endo-dig cyclization of 2-alkynylanilines bearing an acyl group linked to the triple bond. By contrast with the previously reported gold-catalyzed reaction of β-(2-aminophenyl)-α,β-ynones, which resulted in the formation of dibenzo[1,5]diazocines through a sequential process triggered by an intermolecular hydroamination, a selective intramolecular anti-Michael hydroamination was observed in the present study by silver/copper catalysis. Density functional theory calculations on the Ag-catalyzed reaction revealed that the catalyst induces an electrostatic arrangement in the TS coherent with the experimentally observed cyclization.
Sequential addition/annulation reactions of sulfinate and nitrite anions to β-(2-aminophenyl)-α,β-ynones led to valuable 4-sulfonylquinolines and 4-nitroquinolines. The latter proved to be versatile precursors of N-unsubstituted 4-aminoquinolines and 4-quinolones. Reaction of β-(2-aminophenyl)-α,β-ynones with DMF/NaOH resulted in the formation of 4-(dimethylamino)quinolines. The use of an alternative CO-free procedure for the preparation of substrates β-(2-aminophenyl)-α,β-ynones allowed extension of the methodology to the synthesis of 4-substituted 2-alkylquinolines
A novel, efficient, and mild synthetic route for the preparation of 2-aminoquinolines via a gold-catalyzed cascade reaction of β-(2-aminophenyl)-α,β-ynones with ynamides has been developed. This process tolerates a wide range of functionalities such as halogen, alkyl, aryl, and heteroaryl groups, leading to original heterocycles in fair to very good yields.
beta-(2-Aminophenyl)-alpha,beta-ynones afforded exclusively challenging dibenzo[1,5]diazocines by means of (JonPhosAuNCMe)SbF6 catalysis. In contrast with the known gold-catalyzed reaction path of 2-alkynylanilines that leads to indoles, ynones underwent an auto intermolecular hydroamination. This process resulted finally in the formation of an eight-membered ring, likely through a selective 8-exo-dig intramolecular hydroamination that prevailed over the possible cyclocondensation reaction (that would result in the formation of 4-aminoquinoline derivatives). The easy availability of beta-(2-aminophenyl)-alpha,beta-ynones and the simple cyclization procedure make this approach suitable for the preparation of a wide range of useful dibenzodiazocines. The methodology can be extended to the use of beta-(2-aminophenyl)-alpha,beta-ynoates as substrates
b-(2-Alkynylphenyl)-a,b-ynones undergo a gold-catalyzed oxidative two-fold cyclization in the presence of N-oxides to give 1,3-disubstituted-8H-indeno[1,2-c]furan-8-ones in good yields. This cascade process is triggered by a selective oxygen transfer from an N-oxide onto the gold-activated alkynone to generate a a-dioxocarbene intermediate which, via carbene transfer across the remaining alkyne moiety and subsequent cyclization through nucleophilic attack by a carbonyl oxygen, achieves the construction of 1,3disubstituted fused polycyclic furans.
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