INTRA-MOLECULAR DIPOLAR CYCLOADDITION REACTIONS WITH AZOMETHINE YLIDES

The intramolecular 1,3-dipolar cycloaddition reactions of several aziridine carboxylates containing π neighboring 7r bond were studied. The only reaction found to occur on thermolysis of cis- and trans-allyl 1-isopropyl-2-(p-bi-phenyl)-3-aziridinecarboxylate corresponds to isomerization about the three-membered ring. With this system, equilibration of the ring-opened azomethine ylides occurs at a faster rate than internal cycloaddition. Attachment of an electron-withdrawing carbomethoxy substituent to the double bond was found to significantly enhance the intramolecular dipolar cycloaddition rate. Isomerization of the less reactive cis-azomethine ylide to the trans form was still found to compete with the cycloaddition reaction. An additional system which was also studied involved the thermal chemistry of cis- and trans-methyl N-(4-carbomethoxy-3-butenyl)-2-(p-biphenyl)-3-aziridinecarbox-ylate. The azomethine ylides derived from these aziridines undergo regioselective cycloadditions which are compatible with the principles of frontier MO theory. Copyright © 1979, American Chemical Society. All rights reserved.