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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Mechanistic studies on the catalytic cycle of rhodium-catalyzed asymmetric 1,4-addition of aryltitanate reagents to alpha,beta-unsaturated ketones
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Mechanistic studies on the catalytic cycle of rhodium-catalyzed asymmetric 1,4-addition of aryltitanate reagents to alpha,beta-unsaturated ketones

机译：铑催化芳基钛酸酯试剂向α，β-不饱和酮的不对称1,4-加成反应的催化机理

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摘要

Addition of lithium aryl(tetraisopropoxy)titanates [ArTi(OPr-i)4(-)Li(+)] to alpha,beta-unsaturated ketones proceeded with high enantioselectivity (up to 99% ee) in the presence of an excess amount of chlorotrimethylsilane and a rhodium catalyst (3 mol % Rh), generated from [RhCl(C2H4)(2)](2) and (S)-binap, in tetrahydrofuran at 20degreesC to give high yields of the corresponding silyl enolates as 1,4-addition products. The presence of chlorotrimethylsilane is essential for the 1,4-addition to take place. P-31 NMR spectroscopic studies revealed that the catalytic cycle consists of three transformations, that is, (i) insertion of an enone into arylrhodium species forming (oxa-pi-allyl)rhodium intermediate, (ii) silylation of the (oxa-pi-allyl)rhodium with chlorotrimethylsilane giving silyl enolate and a chloro-rhodium complex, and (iii) transmetalation of aryl group from aryltitanate to the chloro-rhodium regenerating the aryl-rhodium.
机译：在过量存在的芳族（四异丙氧基）钛酸锂[ArTi（OPr-i）4（-）Li（+）]向α，β-不饱和酮中进行高对映选择性（高达99％ee）的过程氯三甲基硅烷和铑催化剂（3摩尔％Rh），由[RhCl（C2H4）（2）]（2）和（S）-联苯胺在四氢呋喃中于20°C生成，以高产率得到相应的甲硅烷基烯醇酸酯，为1,4 -附加产品。氯三甲基硅烷的存在对于1，4-加成反应至关重要。 P-31 NMR光谱研究表明，催化循环包括三个转化，即（i）将烯酮插入形成（oxa-pi-烯丙基）铑中间体的芳基铑物种中；（ii）（oxa-pi）的甲硅烷基化-烯丙基）铑与氯代三甲基硅烷，得到甲硅烷基烯醇酸酯和氯铑配合物，以及（iii）芳基从芳基钛酸酯到氯铑的金属转移，再生了芳基铑。

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