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886棋牌游戏平台

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从中医角度来看,几乎任何一个传统节日的设立都有其养生意义。腊八节自然也不例外。正因如此,腊八节的不少传统习俗都有养生保健价值,值得当代人效仿。

时间:05-19
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腊八粥里的赤豆是主力

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【磁力

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The development of a Pd(II)-catalysed enantioselective fluorination of C(sp3)?H bonds would offer a new approach to making chiral organofluorines. However, such a strategy is particularly challenging because of the difficulty in differentiating prochiral C(sp3)?H bonds through Pd(II)-insertion, as well as the sluggish reductive elimination involving Pd?F bonds. Here, we report the development of a Pd(II)-catalysed enantioselective C(sp3)?H fluorination using a chiral transient directing group strategy. In this work, a bulky, amino amide transient directing group was developed to control the stereochemistry of the C?H insertion step and selectively promote the C(sp3)?F reductive elimination pathway from the Pd(IV)–F intermediate. Stereochemical analysis revealed that while the desired C(sp3)?F formation proceeds via an inner-sphere pathway with retention of configuration, the undesired C(sp3)?O formation occurs through an SN2-type mechanism. Elucidation of the dual mechanism allows us to rationalize the profound ligand effect on controlling reductive elimination selectivity from high-valent Pd species.

时间:05-19
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中间挖个小洞以盐填之

时间:05-19
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