Asymmetric decomposition of isoxazolidine derivatives under catalysis by optically active palladium(II) complexes was examined. When racemic ethyl cis-2,5-dimethyl-5-phenylisoxazolidine-3-carboxylate (cis-1a) was treated with a catalytic amount of [Pd(MeCN)2{(S)-TolBINAP}](BF4)2 in CH2Cl2 for 60 h, optically active substrate was recovered with 99% ee and in 48% yield. The highest selectivity was achieved on treatment of racemic ethyl trans-2,4-dimethyl-5,5-diphenylisoxazolidine-3-carboxylate, to give the optically active substrate in 74% yield with 35% ee. The kf/ks value of this reaction reaches as high as 732. For this decomposition, each substrate should have both a methyl group on the 2-position and an alkoxycarbonyl group on the 3-position of the isoxazolidine ring. The enantioselectivities of the recovered substrates were influenced not only by the other substituent groups on the 4- and 5-positions but also by the geometrical structures of the substrates. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)
Read full abstract