Chiral Tethered Reaction and Entropy-Driven Asymmetric Synthesis

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  • キラル架橋反応とエントロピー駆動不斉合成
  • キラル カキョウ ハンノウ ト エントロピー クドウ フセイ ゴウセイ

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Abstract

The 2, 4-pentanediol (PD) -tethered reaction is a stereocontrolled reaction having versatile applicability. When reactant and reagent elements are connected through a PD tether prior to their reaction, stereochemical purity of the product is very high for nine different types of reactions so far studied. Selectivity of one of the reactions shows temperature independency in a wide range from -78 to 150°C, which indicates that the selectivity is governed by the entropy term. The strict stereocontrol at the high reaction temperature can be extended to vapor phase reaction performed above 250 °C. To understand how the two methyl groups on the PD tether stereocontrol the reaction, a new parameter, chiral perturbation factor, is introduced. By this analysis, it is disclosed that the methyl groups do not promote large activation enthalpy change for both diastereomeric processes. In contrast, change in the activation entropy is large and in opposite sing, which should be an origin of the strict stereocontrol by the PD tether.

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