title: Intramolecular cycloaddition of O-tert-butyldimethylsilyloximes in the presence of BF3 x OEt2.
abstract: [reaction: see text] Intramolecular cycloaddition of novel 1,3-dipoles, N-boranonitrones, was examined. Treatment of O-tert-butyldimethylsilyloximes 9-12 having olefin moieties with 2 equiv of BF3 x OEt2 generated N-boranonitrones, which underwent intramolecular cycloaddition to afford N-nonsubstituted cycloadducts 16 (and/or 18) after extractive workup. Despite the Lewis-acidic conditions, the olefin geometry of the substrates was retained in the cycloadducts in the present cycloaddition. The electronic nature of the N-boranonitrones appeared to be electrophilic. In the case of substrate 11c, having an electron-donating methyl group at an internal position of the olefin moiety, the cycloaddition gave the bridged cycloadduct 18b. The cycloaddition proceeded at relatively low temperature, and the diastereoselectivity was high.
authors.affiliation: Showa Pharmaceutical University, Higashi-tamagawagakuen, Machida, Tokyo 194-8543, Japan. tamura@ac.shoyaku.ac.jp
authors.forename: Osamu
authors.initials: O
authors.lastname: Tamura
authors.forename: Takahiro
authors.initials: T
authors.lastname: Mitsuya
authors.forename: Xin
authors.initials: X
authors.lastname: Huang
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tsutsumi
authors.forename: Sanae
authors.initials: S
authors.lastname: Hattori
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ishibashi