Zirconium-Catalyzed Enantioselective [3+2] Cycloaddition of Hydrazones to Olefins Leading to Optically Active Pyrazolidine, Pyrazoline, and 1,3-Diamine Derivatives
作者:Yasuhiro Yamashita、Shū Kobayashi
DOI:10.1021/ja049498l
日期:2004.9.1
conducted in high yields with high enantioselectivities using a chiral zirconium catalyst. These reactions open ways to synthetically and biologically important pyrazoline, pyrazolidine, and 1,3-diamine derivatives. Further, several experiments suggested that the reactions proceeded via concerted pathways.
Allyltrimethoxysilane Addition to<i>N</i>-Acylhydrazones: Two Catalytic Methods Employing CuCl and Fluoride
作者:Gregory K. Friestad、Hui Ding
DOI:10.1055/s-2004-829190
日期:——
Two alternative reaction conditions developed for allyltrimethoxysilane addition to N-benzoylhydrazones enable efficient and versatile access to homoallylic α-branched amines. Aldehyde hydrazones, both aromatic and aliphatic, and ketone hydrazones all give good yields. One set of conditions employs catalytic amounts of CuCl and tetrabutylammonium triphenyldifluorosilicate (TBAT); improved yields and reaction times are obtained at 80 °C in the presence of bis(diphenylphosphino)ethane (dppe) and t-BuOH as additives. The second set of conditions employs 20 mol% TBAT as a fluoride source in a metal-free catalytic system; here t-BuOH offers only modest improvement, and ambient temperatures are optimal. For example, under this second set of conditions, the N-benzoylhydrazone from ethyl pyruvate affords the homoallylic tert-alkyl amine adduct in 78% yield.
Allyltrichlorosilanes reacted with benzoylhydrazones in DMF without the use of any catalyst to afford the corresponding homoallylic benzoylhydrazines in good to high yields. The reactions proceeded at 0 degrees C to room temperature under mild conditions. In addition, it was found that the reactions tolerated well the steric hindrance of hydrazones and allyltrichlorosilanes. Indeed, ketone-derived