| Abstract
| - For the synthesis of protopine alkaloids, we studied a reaction sequence based on a ring enlargement ofindeno[2,1-a][3]benzazepines by a singlet oxygen oxygenation, followed by conversion of an amidecarbonyl group of the resultant 10-membered keto-lactam to a methylene group, which is the last stepfor completion of the synthesis. The key substances, indeno[2,1-a][3]benzazepines, were prepared byBischler−Napieralski cyclization of alkoxy-substituted 1-(2-bromobenzyl)-3-benzazepin-2-ones. Stericeffects of the substituents in this synthesis were examined.
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