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Proton magnetic resonance studies of compounds with bridgehead nitrogen. 37 –a comparison of the positions of conformational equilibria in 1‐methylperhydro‐oxazolo[3,4‐ a ]pyridines and in 1‐methylperhydrothiazolo [3,4‐ a ]pyridines
Author(s) -
Crabb Trevor A.,
Jupp Philip A.
Publication year - 1980
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270130113
Subject(s) - pyridine , chemistry , ring (chemistry) , proton magnetic resonance , carbon tetrachloride , stereochemistry , cis–trans isomerism , crystallography , nuclear magnetic resonance , medicinal chemistry , organic chemistry , physics
cis (1‐H, 8a‐H)‐1‐Methylperhydro‐oxazolo[3,4‐ a ]pyridine and cis (1‐H, 8a‐H)‐1‐methylperhydrothiazolo[3,4‐ a ]pyridine both adopt exclusively the trans ‐fused conformation in carbon tetrachloride solution at room temperature. Both parent unsubstituted systems exist under similar conditions as equilibria containing c. 67% (oxazolo compound) and 64% (thiazolo compound) of the trans ‐fused conformation. In marked contrast to these similar positions of conformational equilibria in both systems the trans (1‐H,8a‐H)‐1‐methylperhydrooxazolo[3,4‐ a ]pyridine exists as c. 73% trans ‐fused in equilibrium with a cis ‐fused conformation whereas the trans (1‐H, 8a‐H)‐1‐methylperhydrothiazolo[3,4‐ a ]pyridine exists almost exclusively in a cis ‐fused ring conformation. These differences in conformational equilibria are explained in terms of changes in non‐bonded interactions.