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Effect of allylic strain on the conformations of diphenyl‐substituted tetrahydro‐1,3‐oxazin‐2‐ones and hexahydropyrimidin‐2‐ones
Author(s) -
Kurtev Bogdan J.,
Lyapova Maria J.,
Mishev Stoyan M.,
Nakova Olga G.,
Orahovatz Alexander S.,
Pojarlieff Ivan G.
Publication year - 1983
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/omr.1270210510
Subject(s) - conformational isomerism , allylic rearrangement , chemistry , ring (chemistry) , stereochemistry , strain (injury) , vicinal , cyclohexane conformation , cis–trans isomerism , molecule , hydrogen bond , biology , organic chemistry , anatomy , catalysis
The conformations of the cis and trans isomers of 4,6‐diphenyl‐, 4,5‐diphenyl‐ and 5,6‐diphenyltetrahydro‐1,3‐oxazin‐2‐one and 4,5‐diphenylhexahydropyrimidin‐2‐one, and of some of their N ‐substituted derivatives, have been studied by 1 H NMR. Conformers with 4a, 6e‐, 4a, 5e‐ and 5a, 6e‐phenyl groups are preferred in the respective isomers of the N‐H oxazinones, confirming a half‐chair conformation of the ring. Allylic strain caused by N ‐substituents shifts strongly the a,e⇌e, a equilibria in trans ‐4,6‐diphenyl‐ and cis ‐4,5‐diphenyl‐oxazinones, but only moderately the e,e⇌a,a equilibria in the compounds with trans ‐vicinal phenyl groups. In the latter, the diaxial conformation is preferred only in the case of bulky N ‐substituents. The diaxial conformation is more favoured in the trans ‐4,5‐diphenylpyrimidones.