What is it about?
The formation of 3,1-benzoxazin derivatives could easily be suppressed by a hydrolytic workup. Alternatively, by increasing the reaction temperature and/or time, 3,1-benzoxazin derivatives can be obtained exclusively. Optimisations of the reaction conditions as well as the scope and the course of the transformations were investigated. The products were characterized by 1H, 13C and 15N NMR spectroscopy. The corresponding resonances were assigned on the basis of the standard 1D and gradient selected 2D NMR experiments (1H–1H gs-COSY, 1H–13C gs-HSQC, 1H–13C gs-HMBC) with 1H–15N gs-HMBC as a practical tool to determine 15N NMR chemical shifts at the natural abundance level of 15N isotope.
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Why is it important?
We have demonstrated that Fischer indolisation of N-(α-ketoacyl) anthranilic acids can serve as a mild and highly efficient alternative for the preparation of 2-(indol-2-carboxamido) benzoic acids. By simple changes in the reaction conditions, this protocol offers a potential to access 2-indolyl-3,1-benzoxazin-4-ones.
Perspectives
The anthranilic acid, indol-2-carboxamide and 3,1-benzoxazin-4-one structural motifs discussed herein were fully characterized by 1H, 13C and 15N NMR spectroscopy. The data presented will help in unequivocal identification of these classes of compounds.
Stanislav Kafka
Univerzita Tomase Bati ve Zline
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This page is a summary of: Fischer indolisation ofN-(α-ketoacyl)anthranilic acids into 2-(indol-2-carboxamido)benzoic acids and 2-indolyl-3,1-benzoxazin-4-ones and their NMR study, Organic & Biomolecular Chemistry, January 2014, Royal Society of Chemistry,
DOI: 10.1039/c4ob01714e.
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