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A Conformational Study of [3.3](2,6)Pyridinophane by the Dynamic NMR Method and X-ray Structural Analysis

✍ Scribed by Sako, Katsuya ;Tatemitsu, Hitoshi ;Onaka, Satoru ;Takemura, Hiroyuki ;Osada, Satoshi ;Wen, Gang ;Shinmyozu, Teruo ;Rudziński, Jerzy M.

Publisher
John Wiley and Sons
Year
1996
Tongue
English
Weight
518 KB
Volume
1996
Category
Article
ISSN
0947-3440

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✦ Synopsis

Abstract

A variable‐temperature ^1^H‐NMR study and X‐ray structural analysis show that the most stable conformational isomer of 3.3pyridinophane 2 is the syn(boat‐boat) conformer, and the relative stability order of the three stable conformers is syn(boat‐boat) > syn(chair‐boat) > syn(chair‐chair). This is in sharp contrast to the relative stability order of the parent [3.3]metacyclophane 1: syn(chair‐chair) > syn(chair‐boat) > syn(boat‐boat). The high stability of the syn(boat‐boat) conformer 2c is primarily attributed to weak attractive interactions via intramolecular hydrogen bonds between nitrogen lone pairs (N‐1, N‐2) and the axial hydrogen atoms (2A‐H, 11A‐H) on the central carbon atoms of the bridges, as suggested by their short transannular distances (2.50 Å).

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