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

Abstract

N-(α-ketoacyl)anthranilic acids reacted with phenylhydrazinium chloride in boiling acetic acid to afford 2-(indol-2-carboxamido)benzoic acids in good to excellent yields and 2-indolyl-3,1-benzoxazin-4-ones as by-products. The formation of the latter products could easily be suppressed by a hydrolytic workup. Alternatively, by increasing the reaction temperature and/or time, 2-indolyl-3,1-benzoxazin-4-ones 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 (1)H, (13)C and (15)N NMR spectroscopy. The corresponding resonances were assigned on the basis of the standard 1D and gradient selected 2D NMR experiments ((1)H-(1)H gs-COSY, (1)H-(13)C gs-HSQC, (1)H-(13)C gs-HMBC) with (1)H-(15)N gs-HMBC as a practical tool to determine (15)N NMR chemical shifts at the natural abundance level of (15)N isotope.

Regioselective Hydrolysis and Transesterification of Dimethyl 3-Benzamidophthalates Assisted by a Neighboring Amide Group

“…5%) level throughout the course of the reaction. The general lack of detecting 3,1-benzoxazin-4-one intermediates in other experiments from Tables and is reasonable owing to their highly reactive nature . 3,1-Benzoxazin-4-ones 11a , b were also prepared independently and 11a was exposed to the above-described reaction conditions, affording the expected products, i.e., monoester 6a and mixed esters 8a and 9a , respectively (Scheme ).…”

Synthesis of 1,4-Benzodiazepine-2,5-diones by Base Promoted Ring Expansion of 3-Aminoquinoline-2,4-diones

“…Due to the remarkable synthetic and biological relevance of 1,4-benzodiazepine-2,5-diones and related compounds, there is an urge to discover new strategies for their preparation. As a part of our interest in the chemistry of quinoline-2,4­(1 H ,3 H )-diones, − herein we report a novel approach to this scaffold that is based on a rearrangement of 3-aminoquinoline-2,4­(1 H ,3 H )-diones (Figure c). In a simple four-step protocol, this method employs anilines as starting substrates.…”