Intermolecular and Intramolecular Azomethine Ylide Dipolar Cycloadditions for the Synthesis of Highly Functionalized Pyrroles and Pyrrolidines

Article abstract of DOI:10.1021/jo00213a022

N-Alkyl- and N-arylaziridines carrying a single carboxy ester function undergo thermally induced electrocyclic ring opening to produce azomethine ylides which subsequently react with acetylenes or olefins to yield substituted pyrroles or pyrrolidines, respectively.The <3 + 2> dipolar cycloaddition reaction can be performed in either an intermolecular or intramolecular mode and displays high regioselectivity and stereoselectivity with a variety of dipolarophiles.The yield of cycloadducts depends upon the electronic characteristics and the substitution pattern of the dipolarophile and upon the mode of cycloaddition employed.In the intermolecular reaction, the yield of adducts is poor unless the dipolarophile is activated.Intramolecular cycloadditions with monosubstituted olefins or acetylenes give adducts in yields of 45-70percent.Although the yields of adducts in these instances are moderate, the starting materials are readily prepared and the method is an effective means for the assembly of a structurally complex heterocyclic system with high regiochemical and stereochemical control of peripheral substituents.In those instances in which the dipolarophilic component is disubstituted, the cycloaddition gives synthetically useful yields when the dipolarophile carries an electron-withdrawing functionality.