Our novel synthetic route to isoellipticine featured palladium‐catalyzed intramolecular reactions for the construction of the B ring of the pyridocarbazole nucleus. The adequate palladium‐catalyzed reaction depended upon the oxidation conditions that were applied in order to prepare the immediate synthetic precursor. When CAN was used to make the quinone intermediate, an oxidative cyclization through a double C−H bond activation was applied. Conversely, when the oxidation condition involved TCCA as oxidant, a direct C−H arylation was employed. Both approaches showed similar efficiencies in order to construct the pyridocarbazole nucleus. Isoellipticine was prepared in only 5 steps with a 21%–23% overall yield.
Marine alkaloids caulibugulones A-D were synthesized in six steps starting from the readily available 2,5-dimethoxybenzaldehyde. Pomeranz-Fritsch reaction of N-(2,5-dimethoxybenzyl)-N-(2,2-dimethoxyethyl)-2-nitrobenzenesulfonamide proceeded smoothly to give 5,8-dimethoxyisoquinoline, which was oxidized to isoquinolinediones by a tunable oxidation reaction with N-haloimides. Therefore, NBS furnished direct conversion to the isoquinoline-5,8-dione; alternatively, N-haloimides of cyanuric acid provided both oxidation and halogenation generating 6,7-dihaloisoquinoline-5,8-diones. Aminolyses of these isoquinolinediones with methylamine or ethanolamine produced the isoquinolinedione alkaloids caulibugulones A-D in 24-57% overall yield.
Recebido em 5/8/09; aceito em 16/11/09; publicado na web em 24/3/10 FATTY ESTER CONTENT DETERMINATION IN SOYBEAN METHYL BIODIESEL BY GAS CHROMATOGRAPHY USING ETHYL OLEATE AS INTERNAL STANDARD. A method for ester content determination in soybean methyl biodiesel was studied, using ethyl oleate as internal standard. A biodiesel sample was analyzed and had its purity estimated as 92.8%. Method accuracy was evaluated by comparison with the result obtained via EN14103, with a relative difference of 0.1%. Repetitivity and intermediate precision were estimated as 2 and 1.5%, respectively.
Ellipticine was synthesized in six steps and 20% global yield starting from the readily available 2,5-dimethoxy isoquinoline. Unprecedented regioselective control of the nucleophilic attack on the isoquinoline-5,8-dione is first described. Investigation of the possible pathways of this transformation through density functional theory calculations reveals unexpected N-oxide assistance in cascade tautomerizations, which was crucial for directing the nucleophilic attack and hastening the overall process. Using this strategy, we prepared the aniline-isoquinolinedione adduct and submitted it to an intramolecular double C−H cross-coupling activation to furnish ellipticinequinone, which gave ellipticine after a MeLi addition/BH 3 reduction sequence.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.