Stereochemistry of nitrogen heterocycles. 69. 13C NMR spectra of stereoisomeric 10-methyl-5-oxygen-substituted trans-decahydroquinolines

Abstract

The 13C NMR spectra of 5-keto- and 5a- and 5e-hydroxy-10-methyl- and 1,10-dimethyltrans-decahydroquinolines have been recorded and interpreted. The increments of the oxo and hydroxy groups in the 10-methyldecahydroquinoline and the isostructural 10-methyldecaline systems were compared. The difference between the increments of azacyclic and the carbocyclic systems appears- at the γ-positions relative to the electronegative substituents (C(7) and C(9)) and at the antiperiplanar γ-positions relative to nitrogen (C(5) and C(7)). The increments of the oxo and the equatorial hydroxy groups in the aza ring are more shielded than in the carbon ring (at C(7), 2 ppm; at C(g), 1 ppm), while the increments of the axial hydroxy group are more deshielded (at C(5), 1.5–2.0 ppm; at C(9), 1.0–1.5 ppm). The more the respective carbon atoms of the heterocycle are hydrogenated, the stronger are the deshielding Β-effect and the shielding γ-effect of the methyl group on nitrogen.