C(2)-symmetric 2,6-diallylpiperidine 1-carboxylic acid methyl ester (5) was examined via the double asymmetric allylboration of glutaraldehyde followed by aminocyclization and carbamation as a promising chiral building block for piperidine-related alkaloids, which were synthesized by the desymmetrization of 5 using intramolecular iodocarbamation as a key step. [reaction: see text]
A novel C2-symmetric 2,6-diallylpiperidine carboxylic acid methyl ester 1 was prepared by the double asymmetric allylboration of glutaldehyde followed by an aminocyclization and carbamation. On the basis of desymmetrization of 1 using iodocarbamation, one allyl group of 1 was protected and monofunctionalizations of the resulting oxazolidinone 11 were performed. The reaction of the N-methoxycarbonyl piperidine 25 employing decarbamation reagent (n-PrSLi or TMSI) as a key step gave oxazolidinone 26 or 17 including an intramolecular ring formation, which was transformed in a few steps into (-)-porantheridine (2) and (-)-2-epi-porantheridine (3), respectively. In addition, the expedient synthesis of (+)-epi-dihydropinidine (4), (2R,6R)-trans-solenopsin A (5), and precoccinelline (6), starting from 11 is described.
Rings with 7 or more members Q 0050Fragmentation of Tertiary Cyclopropanol Compounds Catalyzed by Vanadyl Acetylacetonate. -In the presence of a catalytic amount of vanadyl acetylacetonate and oxygen, tertiary cyclopropanol compounds afford β-hydroxyketones and β-diketones. When 3-substituted bicycloalkanols are treated with a catalytic amount of VO(acac)2 under oxygen the corresponding peroxides are obtained. Bicycloalkanes bearing an ethoxycarbonyl group at the 2-position produce γ-oxocarboxylate derivatives using the same reaction conditions. In these cases VO(acac)2 acts as a Lewis acid. -(KIRIHARA*, M.; KAKUDA, H.; ICHINOSE, M.; OCHIAI, Y.; TAKIZAWA, S.; MOKUYA, A.; OKUBO, K.; HATANO, A.; SHIRO, M.; Tetrahedron 61 (2005) 20, 4831-4839; Dep. Mater. Sci., Shizuoka Inst. Sci. Technol., Fukuroi, Shizuoka 437, Japan; Eng.) -Bartels 36-059
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