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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

✍ Scribed by Trevor A. Crabb; Philip A. Jupp

Publisher
John Wiley and Sons
Year
1980
Tongue
English
Weight
478 KB
Volume
13
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

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.

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