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Communication | Special issue | Vol 13, No. 1, 1979, pp.187-190
Published online, 1st January, 1970
DOI: 10.3987/S-1979-01-0187
Boron Trifluoride-promoted Transformation of 3,5-Bis(methoxycarbonyl)-4-phenylisoxazoline N-Oxide into 3H-Indole N-Oxide Derivative

Eisuke Kaji* and Shonosuke Zen

*School of Pharmaceutical Sciences, Kitasato University, Shirokane, Minato-ku, Tokyo 108-8641, Japan


3,5-Bis(methoxycarbonyl)-4-phenylisoxazoline N-oxide (1a) was readily transformed into 3H-indole N-oxide derivative (2a) by the reaction with boron trifluoride etherate in reasonable yield. Mechanism of the transformation was found to involve an ionic intermediate (5), generated by rupture of the nitrogen-oxygen bond, which cyclizes to 3H-indole N-oxide through an intramolecular aromatic substitution. Evidence for the proposed mechanism was obtained by the reaction of 4-phenylisoxazoline-4-d N-oxide (1b) with boron trifluoride to form the expected 3H-indole-3-d N-oxide (2b), as well as by stereochemical consideration.