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■ [N](3,5)Isoxazolophanes: Dynamic Behavior and Reaction with Electron-deficient Acetylene Leading to [N](2,6)Pyridinophanes

Hiroyuki Yamamoto and Makoto Nitta*

*Department of Chemistry, School of Science and Engineering, Materials Research Laboratory for Bioscience and Photonics, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan

Abstract

¹H NMR spectroscopy at various temperatures clarified the dynamic behavior of the oligomethylene chains for [8](3,5)isoxazolophane (1) and unsubstituted and 4-methyl-substituted [9](3,5)isoxazolophanes (2a,b). The energy barriers (ΔG_c^‡) for the bridge flipping are 18.6 kcalmol^-1 (T_c 100 °C) for 1 and 11.5 kcalmol^-1 (T_c-10 °C) for 2a. Compound (2b) does not undergo bridge flipping in temperatures ranging from 25 °C to 150 °C. The energy barriers for the pseudorotation are 11.1-11.2 kcalmol^-1 (Tc -10 °C), 9.1 kcalmol^-1 (T_c-70 °C), and 8.6 kcalmol^-1 (T_c-80 °C) for 1, 2a, and 2b, respectively. The Mo(CO)₆-induced reaction of 2a,b with dimethyl acetylenedicarboxylate afforded [9](2,6)pyridinophane derivatives, albeit in low yields.