Intramolekulare Cycloadditionen Mit Azomethin‐Yliden: Synthese und NMR‐Untersuchungen einiger Paracyclophan‐Derivate vom Makrolid‐Typ

Abstract

Intramolecular Cycloaddition Reactions with Azomethine Ylides: Synthesis and NMR Investigations of Some Macrolide‐Type Paracyclophanes Several aziridine derivatives bearing a para ‐substituted phenyl group have been prepared as precursors of azomethine ylides for intramolecular 1,3‐dipolar cycloadditions. Upon heating in refluxing toluene, the expected reactions take place resulting in the regioselective formations of the pairs of diastereoisomers 14 / 15 and 16 / 17 , respectively. As indicated by the sharply decreasing yield in the a ‐series (< 5%), a useful application of this method for preparing paracyclophane compounds is restricted to derivatives with more than 11 bridging atoms. The results of detailed 1 H‐ and 13 C‐NMR investigations with the pyrrolidino‐annulated cyclophanes are discussed with respect to the configuration at the five‐membered heterocycles and to the conformational flexibility of the bridges.