Quinolizidines, 4-phenyl

Conformational effects appear to be important in determining which tertiary a-hydrogen is removed. For example, 4-phenyl-, 4-p-nitrophenyl-, and 4-/)-methoxyphenylquinolizidine (83) all are oxidized to the corresponding /j < -iminium salts (84) and not to the conjugated zJ -iminium salts (85) (86). The authors Judged that steric hindrance was responsible or that the conformation of the 4-sabstituted quinolizidines did not contain ideal... 

The 2-hydroxy-2-(p-chlorophenyl)-9,10-dimethoxybenzo[a]quinolizidines both prefer the trans-fused conformations 198 and 199222 because the favored cis conformation 193 will carry an axial substituent at C-2, which undergoes considerable destabilization as a result of interaction with the phenyl group. 

Demethoxyabresoline (67) was obtained as a noncrystalline solid. Spectroscopic investigation revealed the presence of a phenolic OH, a 1-phenyl-quinolizidine system, and a trans-cinnamyl group. The stereochemistry at C-l, C-3, and C-5 was the same as in abresoline. The molecular formula C25H29N05 was established by mass spectrometry. The presence of fragment ions at m/e 259 (M —164) and 258 was characteristic of p-hydroxy-cinnamyl esters of the phenylquinolizidol (63a). The assigned structure 68 was confirmed by basic hydrolysis to 63a and p-hydroxycinnamic acid as well as by catalytic hydrogenation to a known dihydro derivative (52). 

Many quinolizidine alkaloids have been obtained by way of substituted perhydro-isoxazolo[2,3- ]pyridines. Reaction between 3,4-dimethoxy-benzaldehyde and the phosphorane derived from allyltriphenylphos-phonium bromide gave an - and Z-isomer mixture of l-(3,4-dimethoxy-phenyl)butadiene, which reacted with 2,3,4,5-tetrahydropyridine 1-oxide in boiling toluene to give the corresponding isomers of the isoxazolidines (43-46). The formation of the trans- (H-2, H-3a) isomers was favored in... 

There is no uniform classification for the A. In the literature divisions according to origin (examples Aconitum, Amaryllidaceae, Aspidosperma, cactus, Catharanthus, Cephalotaxus, Cinchona, coca, Corydalis, curare, Dendrobates, ergot, Erythrina, Iboga, Lycopodium, Maytenus, opium, Rauvol-fia, Senecio, Strychnos, tobacco, Vinca alkaloids, salamander, Solanum, Veratrum steroid alkaloids) in addition to divisions according to chemical structure (examples aporphine, benzylisoquinoline, bis-benzylisoquinoline, berberine, carboline, diterpene, inudazole, indole, indolizidine, isoquinoline, lupinane, macrocyclic, morphine, peptide, / -phenyl-ethylamine, piperidine, purine, pyridine, pyrrolidine, pyrrolizidine, quinoline, quinolizidine, quinucli-dine, spermine, spermidine, steroid, terpene, tro-pane, tropolone alkaloids) are used. 

There are surprisingly few common approaches to the lupin indolizidines and their quinolizidine homologs despite their structural similarity. One such approach was recently reported by Cutter et al., who used imino—aldol reactions of phenyl 5-chlorovalerate (992) as the starting point for the synthesis of both (—)-tashiromine (ent-929) and (—)-epilupinine (ent-921) (Scheme 123). " The addition of the hthium enolate of 992 to the (S)-N-sulfinylimine (- -)-993 proved to be highly diastereoselective, giving a 78% yield of the adduct (- -)-994 and its (S,S)-isomer (+)-995 in a ratio of 16 1. The stereochemistry of 994 was confirmed by X-ray diffraction. 

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