phosphine–nickel complex and an axially chiral sodium dicarboxylate has been developed. The transformation features mild reaction conditions, a broad substrate scope, and excellent functional group tolerance, offering an efficient approach to an array of enantioenriched O-propargyl hydroxylamines. Mechanistic studies support the presumed role of the chiral carboxylate as a counterion for nickel catalysis enabling
已经开发了通过结合膦-镍络合物和轴向手性二羧酸钠催化的高度对映选择性的 O-炔丙基化。该转化具有温和的反应条件、广泛的底物范围和出色的官能团耐受性,为一系列富含对映体的O-炔丙基羟胺提供了一种有效的方法。机理研究支持手性羧酸盐作为镍催化的抗衡离子的假定作用,从而能够发现高度立体选择性的转化。该反应的威力通过其在强效萤火虫萤光素酶抑制剂和 ( S )-二氢yashabushiketol 的不对称全合成中的应用来说明。
Asymmetric palladium-catalyzed annulation of benzene-1,2-diol and racemic secondary propargylic carbonates bearing two different substituents
The palladium-catalyzed cyclization of benzene-1,2-diol with various racemic secondary propargyl carbonates having no acetylenic hydrogen in the presence of (R)-Binap as the chiral ligand afforded the two regioisomers of the corresponding 2,3-dihydro-1,4-dioxin derivatives in quite good yields, and also in enantioselectivities going from 40 to 97%. The cyclization of benzene-1,2-diol with methyl (R)-1-methyl-3-phenylpro-2-yn-1-yl carbonate in the presence of dppb as the achiral ligand afforded 2-benzylidene-3-methyl-2,3-dihydro-1,4-benzodioxine as the major product with 15% ee. The use of (R)-Binap as the chiral ligand afforded the (+) cyclized compound in 45% ee, when the (-) enantiomer was obtained with 77% ee in the presence of (S)-Binap. All the results suggest that in this case the enantioselective step is the diastereoselective protonation of the palladium-carbene intermediates. (C) 2005 Elsevier Ltd. All rights reserved.