74 イソキノリンアルカロイドの合成研究

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Benz[d]indeno[1,2-b]azepines have received attention recently especially because of the important key-intermediates in the synthesis of isoquinoline alkaloids of rhoeadine, spirobenzyl, phthalide and protopine types. We now wish to report new methods for the synthesis of the phthalide isoquinoline and protopine alkaloids, in which the benzindenoazepines 1 and their 12-oxo derivatives 2 were efficiently prepared by the general method consisting of two kinds of intramolecular dehydrative cyclizations. Preparation of 1 and 2: Thermal cyclization of the amino acids derived from the benzyl cyanides 8 gave the benzazepinones 11, which were benzylated with the appropriate benzylbromides in the presence of sodium hydride. The products, benzylbenzazepinones 12, which were also obtained from the nitriles 9, were successively heated with phosphoryl chloride to afford the desired benzindenoazepines 1. Further, this enamines 1 underwent autoxidation to the corresponding 12-oxo derivatives 2, on exposure to oxygen in the presence of Triton B. Protopine alkaloid 5: 1h was converted to ten-membered amide ketone 13 by photooxygenative ring enlargement reaction. Subsequently, 13 was reduced with lithium aluminum hydride, and the resultant amino alcohol 14 was treated with activated manganese dioxide to afford preudo protopine 5 in good yield. Phthalide isoquinoline alkaloid 6: When 15 was heated in dilute hydrochloric acid, the conversion of the benzazepine ring system into the isoquinoline proceeded smoothly to led to formation of the yellow immonium salt 17. Reduction of this salt with sodium borohydride in methanol, followed by acid treatment with dilute hydrochloric acid, gave cordrastine I (6-αH) in good yield, accompanied by a trace of cardrastine II (6-βH). The latter was more efficiently prepared by similar reduction in methanol containing 5%-sodium bicarbonate solution.
天然有機化合物討論会の論文
1979-09-20

74 イソキノリンアルカロイドの合成研究

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