Gold‐Catalyzed [3+2]/Retro‐[3+2]/[3+2] Cycloaddition Cascade Reaction of N‐Alkoxyazomethine Ylides

A novel cascade reaction has been developed for the synthesis of 2,6‐methanopyrrolo[1,2‐b]isoxazoles based on the gold‐catalyzed generation of an N‐allyloxyazomethine ylide. This reaction involves sequential [3+2]/retro‐[3+2]/[3+2] cycloaddition reactions, thus providing facile access to fused and bridged heterocycles which would be otherwise difficult to prepare using existing synthetic methods. Notably, this reaction allows the efficient construction of three C−C bonds, one C−O bond, one C−N bond and one C−H bond, as well as the cleavage of one C−C bond, one C−O bond and one C−H bond in a single operation. The intermolecular cycloaddition of an N‐allyloxyazomethine ylide and the subsequent application of the product to the synthesis of tropenol is also described. Going retro: A novel cascade reaction has been developed involving the gold‐catalyzed generation of an N‐allyloxyazomethine ylide and a subsequent [3+2]/retro‐[3+2]/[3+2] cycloaddition cascade to give bridged isoxazolidines. This cascade reaction allows efficient construction of three C−C bonds, one C−O bond, one C−N bond, and one C−H bond, as well as the cleavage of one C−C bond, one C−O bond, and one C−H bond in a single operation.