Synthesis of Heterocycles by Utilizing Characteristic Features of Imines and Amides bearing the Alkoxy Group

摘要

Functional group having two adjacent heteroatoms exhibits unique characteristic features such as relatively higher nucleophilicity. In this account, transition metal-catalyzed intramolecular nucleophilic addition reaction of imines and amides bearing the alkoxy group on the nitrogen atom onto alkyne for the synthesis of a variety of heterocycles was described. The cyclization of N-alkoxyalkynylimines and subsequent rearrangement of the substituent on the oxygen atom provided trisubstituted isoxazoles in a highly atom-economical manner. In addition, gold catalyzed cascade reaction of N-allyoxyalkynylimines involving cyclization and subsequent [3+2]/retro-[3+2]/[3+2] cycloaddition reactions via generation of N-allyloxyazomethine ylide gave fused and bridged isoxazolidines. Reagent-controlled regiodivergent cyclization of Weireb amide, prepared from o-alkynyl benzoic acid, furnished isobenzofuranone and isoquinolinoes. Sequential reaction involving cyclization and rearrangement of N-allyloxypropiolamide for the preparation of 3-hydroxyisoxazoles also described.