Carbon-13 magnetic resonance. XXIII. Methyldecalins

Toxic Furanoeremophilanes from Senecio bonariensis

“…Trans A/B ring stereochemistry was supported by reported data for cis-and trans-decalin (Dalling et al, 1973;Gough et al, 1972), comparison with cis-and trans-decalones (Birnbaum et al, 1974) and 3-substituted 9-oxo-10␣H-furanoeremophilane data (Chalmers et al, 1980). Chemical shifts of A-ring carbons were calculated taking into account methyl substituent parameters for substituted cyclohexanes (Dalling and Grant, 1972) adding deshielding ␤-effect of a carbonyl group.…”

13C magnetic resonance spectra of some isoquinoline alkaloids and related model compounds

“…The following compounds were prepared by standard procedures and gave satisfactory spectral and physical date: B,7-dimefho~y-I.2~3~4-fefr~I1ydroisoq~~i~10line (8) (213 22), 6,7-dimeii1oxy-2-methyi-I,2,3,4-tetra!z~riroisoqui1ioIine (2) (23), 6,7-din1ea/~ox~~-3,4-diIzydroisoq~iinoline (3) (Zl), 6,7-dimethox~~-2-rrzeihyl-3,4-dih~droisoquinolit1ium iodide (4) (2113 9,8-dir~1ethoxy-I~2~3~4-ie~1'al1ydroisoq~inoIine (7) (24), (+)-(a)-l)-izyrdrastine (10) (251, 6,7-riimeethoxyphthali& (14) (26), 6,7-methylenedioxyp/it/aaIide (Ida) (27), 6-nitrophthalide (15a) (281, 6-ur?zii~ophtlialide (156) (28,29), and (i)-nandirzine (17) (30).…”

“…4) are dtastereomeric 13-methyltetrahydroprotoberberines. It is known from pmr studies (15) that corydaline is a trcms-quinolizidine and mesocorydaline a cis-quinolizidine, in which the methyl groups are axial and equatorial, respectively, in ring C. The change from a trans to a cis configuration in going from 19 to 20 is evident in the upfield shift of carbons, 5,6, 8, and 13 and is attributed to y-gauche interactions (12,16,17) in the c u compound. On the other hand C-14 moves slightly downfield, a trend also observed in the quinolizidine systems of the Nrl~har and Lycopodium alkaloids (3,4).…”

β-Carbon Shielding Effects in Carbon-13 Nuclear Magnetic Resonance Spectroscopy

“…There have been a number of attempts to correlate carbon-13 chemical shifts in saturated hydrocarbons with molecular structural features (1)(2)(3)(4)(5)(6). The additivity parameters reported recently by Grant and co-workers (5, 6) appeared to be the best to date, since they were based on conformationally well defined model systems.…”