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Stereochemistry and 13 C NMR investigation of 9‐halotetrahydro‐4 H ‐pyrido[1,2‐ a ]pyrimidin‐4‐ones
Author(s) -
Tóth Gábor,
Hermecz István,
Breining Tibor,
Mészáros Zoltán,
Bitter István
Publication year - 1983
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570200322
Subject(s) - chemistry , substituent , conformational isomerism , halogen , ring (chemistry) , chemical shift , stereochemistry , additive function , crystallography , molecule , organic chemistry , mathematical analysis , alkyl , mathematics
It was shown that the halogen atom occupies the quasi‐axial position in the predominant conformer of the 9‐halo derivatives of tetrahydro‐4 H ‐pyrido[1,2‐ a ]pyrimidin‐4‐ones. When R 3 = Me, the conformational equilibrium is determined by the latter substituent which is always quasi‐axial. The effects of the methyl group and the halogen atoms on the 13 C chemical shifts (SCS values) were used for the identification of cis and trans isomers. Interesting non additivity of substituent effects was found in derivatives bearing quasi‐axial substituents at C‐6 and C‐9: and this was caused by the ring flattening.