HIGHLY CHEMOSELECTIVE PALLADIUM-CATALYZED CONJUGATE REDUCTION OF ALPHA,BETA-UNSATURATED CARBONYL-COMPOUNDS WITH SILICON HYDRIDES AND ZINC-CHLORIDE COCATALYST
HIGHLY CHEMOSELECTIVE PALLADIUM-CATALYZED CONJUGATE REDUCTION OF ALPHA,BETA-UNSATURATED CARBONYL-COMPOUNDS WITH SILICON HYDRIDES AND ZINC-CHLORIDE COCATALYST
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DOI：
10.1021/ja00283a029
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发表时间：
1986-11-12
影响因子：
15
通讯作者：
GREENSPOON, N
中科院分区：
文献类型：
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作者：
KEINAN, E;GREENSPOON, N
由可溶性钯催化剂、钯硅烷和氯化锌组成的三组分体系能够有效地共辄还原n，n-不饱和酮和醛。最佳的一组条件包括二苯基硅烷作为最有效的氢化物供体，任何可溶性钯络合物在0或II氧化态，当它是稳定的膦配体，和ZnCl 2作为最好的刘易斯酸助催化剂。该反应对于宽范围的不饱和酮和醛是非常普遍的，并且它对于这些迈克尔受体是高度选择性的，因为在这些条件下，n，n-不饱和羧酸衍生物的还原非常缓慢。当使用二氘二苯基硅烷还原不饱和酮时，氘在底物的较少受阻面处立体选择性地引入，并且在β-位处区域选择性地引入。相反，当在痕量D2 O存在下进行还原时，氘掺入发生在n-位。氘掺入实验和NMR研究的基础上，催化循环被假定，其中第一步涉及可逆的配位的钯络合物的缺电子烯烃和氧化加成的硅氢化物，形成一个dopodopalladium烯烃络合物。氢化物迁移插入到配位烯烃中产生中间体烯醇化钯，其通过还原消除，塌缩回到Pd（0）络合物和甲硅烷基烯醇醚，其然后水解成饱和酮。除了催化水解之外，ZnCl 2还促进硅氢化过程。
A three-component system comprised of a soluble palladium catalyst, hydridosilane, and zinc chloride is capable of efficient conjugate reduction of «,/3-unsaturated ketones and aldehydes. The optimal set of conditions includes diphenylsilane as the most effective hydride donor, any soluble palladium complex in either the 0 or II oxidation state, when it is stabilized by phosphine ligands, and ZnCl2 as the best Lewis acid cocatalyst. The reaction is very general with respect to a broad range of unsaturated ketones and aldehydes, and it is highly selective for these Michael acceptors, as reduction of «,/3-unsaturated carboxylic acid derivatives is very sluggish under these conditions. When dideuteriodiphenylsilane is used to reduce unsaturated ketones, deuterium is stereoselectively introduced at the less-hindered face of the substrate and regioselectively at the/3-position. Conversely, when reductions are carried out in the presence of traces of D20, deuterium incorporation occurs at the «-position. On the basis of deuterium-incorporation experiments and NMR studies, a catalytic cycle is postulated in which the first step involves reversible coordination of the palladium complex to the electron-deficient olefin and oxidative addition of silicon hydride to form a hydridopalladium olefin complex. Migratory insertion of hydride into the coordinated olefin produces an intermediate palladium enolate which, via reductive elimination, collapses back to the Pd (0) complex and a silyl enol ether, which is then hydrolyzed to the saturated ketone. In addition to catalyzing that hydrolysis, ZnCl2 facilitates the hydrosilation process.