74640-77-0Relevant academic research and scientific papers
A Novel Ring Transformation of 3,5-Bis(methoxycarbonyl)-4-phenyl-2-isoxazoline-2-oxides into 2-Methoxycarbonyl-1-oxido-3H-indole-3-acetates
Takahashi, Kiyobumi,Kaji, Eisuke,Zen, Shonosuke
, p. 8 - 15 (2007/10/02)
3,5-Bis(methoxycarbonyl)-4-phenyl-2-isoxazoline-2-oxides (1) were readily transformed into 2-methoxycarbonyl-1-oxido-3H-indole-3-acetates (2) in the presence of Lewis acids such as titanium tetrachloride in dichloromethane.The reaction may occur via initial N-O bond fission to form an ionic intermediate (B), which cyclizes to 3H-indole-1-oxide (2) through an intramolecular aromatic substitution, on the basis of deuterium incorporation experiments as well as stereochemical considerations.With regard to the substituent effect, the reaction of meta-substituted phenylisoxazolines (1f-h) having an o,p-orientating group such as halogen was facilitated to provide 5-substituted 3H-indole-1-oxides (2f-h) in good yield.In contrast, the reaction of para-substituted compounds (1b-e) having the same substituents gave benzofuro-isoxazoles(7b-e) preferentially, rather than 6-substituted 3H-indole-1-oxides (2b-e). Keywords -- 2-isoxazoline-2-oxide; 1-oxido-3H-indole-3-acetate; titanium tetrachloride; ring transformation; intramolecular aromatic substitution
