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[摘要]：Ethyl 1-oxo-indane-2-carboxylate with a 1,4-diketone motif gave a benzo[c]azocane-1-one derivative - an eight-membered ring lactam - in a bismuth-mediated ring-expansion reaction with methylamine (40% yield). Yields with other primary amines were significantly lower. The ester function in the heterocyclic product could be saponified to give the free carboxylic acid, which was further amidated with para-bromoaniline. The molecular structure of the latter was established by X-ray single-crystal analysis. Benzo[c]azo-canones exist in two diastereoisomeric conformations, causing double signal sets in the NMR spectra. Slow interconversion between these conformers was proved by EXSY NMR spectroscopy. Moreover, a conformational analysis by DFT calculations revealed the two diastereoisomers to be boat conformers that interconvert through a twist conformer. The maximum barrier for this process was calculated to be approximately 70 kJ/mol. Reaction of the corresponding methyl 1-oxoindane-2-carboxylate with methylamine gave the benzo[c]azocanone in lower yield. A spirolactam and an indeno[1,2-b]pyrrole were formed as further products. When using an indanone-derived 1,4-diketone without an ester function, several primary amines could be used in a bismuth-catalyzed Paal-Knorr reaction to give indeno[1,2-b]pyrrole derivatives with up to quantitative yields in several cases. Attempts to synthesize a caprolactam derivative from a cyclobutanone derived beta-oxo ester with 1,4-diketone motif were unsuccessful. |
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