Synthesis and Conformational Analysis of Trioxatricornan-Based Macrocyclophanes

Abstract

The synthesis of macrocyclophanes 7 and 8 is described. The constructions are composed of one phloroglucinol and one 2,6,10-triaminotrioxatricornan subunit. The subunits are linked by tri-and hexamethylene (7 and 8, respectively) chains. Conformational analysis by empirical force field calculations and 1H NMR techniques demonstrates that 7 has adopted a collapsed conformation, leaving no space between the two aromatic subunits. Macrocyclophane 1, in which the phloroglucinol oxygens have been replaced by methylenes, has instead adopted an open conformation, leaving a void in the macrocyclophane interior. The conformational preference of the side chains is shown to be the dominant factor in determining the overall conformation of 7 and its a-methylene analog 1. With the use of low-temperature 1H NMR, the barrier for the process of equivalencing all exchangeable sites in 7 is estimated at 8.6 kcal/mol. © 1995, American Chemical Society. All rights reserved.