trans-Selective Synthesis of Substituted 1,2,4-Triazolidines

Significance

In the presence of a Ru(II)-porphyrin catalyst, α-diazoesters decompose to a Ru carbenoid species, which upon reaction with an aromatic imine generates an azomethine ylide, which undergoes a 1,3-dipolar cycloaddition with alkylazo­dicarboxylates to stereoselectively afford 1,2,4-triazolidines in good to very good yields. Catalyst loadings are generally low (0.5 mol%), and the reaction is tolerant of several alkyl azodicarboxylates and both electron-rich and electron-poor aromatic imines; although an imine derived from an aliphatic amine afforded no product. Using a phenylmenthol-derived diazoester, the product was obtained with moderate diastereoselectivity.