Iron(III)-Catalyzed (4 + 2)-Cycloannulation of 2-Hydroxy Ketoxime Ethers with Indol-2-ylamides: Synthesis of Indole-Fused 2-Piperidinones.

A highly regio- and diastereoselective (4 + 2)-cycloannulation process of indanone-derived 2-hydroxy ketoxime ethers with 1,4-bisnucleophilic indol-2-ylamides has been developed. In the presence of 5 mol % FeCl3, densely functionalized 2-piperidinones containing two new σ-bonds and two vicinal quaternary stereogenic centers were formed under mild reaction conditions in a one-pot operation. Moreover, most of the products directly precipitated out of the solution and were isolated by simple filtration without purification by column chromatography.