NMR Spectra and Stereochemistry of Perhydrooxazolopyridines

Article abstract of DOI:10.1002/mrc.1260260413

Low-temperature 13C and 1H NMR spectra show perhydrooxazolo<3,4-a>pyridine to exist in CDCl3-CFCl3 solution at 183 K as an equilibrium between 73percent trans-fused and 27percent O-inside cis-fused conformers. cis-(H-1, H-8a)-1-Alkylperhydrooxazolo<3,4-a>pyridines (alkyl=methyl, ethyl, isopropyl) adopt equilibria heavily biased towards the trans-fused conformers, whereas the epimers adopt 18percent O-inside cis-fused -->/<-- trans-fused conformational equilibria at 183 K in CDCl3-CFCl3.At 190 K in CDCl3 cis-(H-6, H-8a)-6-ethylperhydrooxazolo<3,4-a>pyridine adopts an equilibrium containing ca 3percent trans-fused conformer in equilibrium with 97percent O-inside cis-fused conformer.