Michihiko Noguchi, Hirofumi Okada, Shigeki Nishimura, Yoko Yamagata, Shinji Takamura, Masayuki Tanaka, Akikazu Kakehi and Hidetoshi Yamamoto
3-(Alk-2-enylamino)-2,2-dimethylpropionaldehyde oximes 3 underwent thermally induced 1,3-dipolar cycloaddition under mild conditions leading to isoxazolo[4,3-c]pyridine derivatives 4. The methyl groups at the 2-position and the alkenylamino nitrogen in oximes 3 should facilitate the cycloaddition due to restriction of the conformational flexibility of the reaction sites and promotion of the isomerisation to NH-nitrone intermediate, respectively.
N 7.56 for (E)-isomer and 7.36 for (Z)-isomer, respectively] according, to those of the related systems I. Pejkovic-Tadic, M. Haranisavljevic, S. Nesic, C. Pascual and W. Simon, Helv. Chim. Acta, 1965, 48, 1157 Search PubMed; A. Padwa, D. C. Dean, M. H. Osterhout, L. Precedo and M. A. Semones, J. Org. Chem., 1994, 59, 5347 CrossRef CAS Also, see refs. 3f and 4b.