“Chiral Perturbation Factor” Approach Reveals Importance of Entropy Term in Stereocontrol of the 2,4-Pentanediol-Tethered Reaction
摘要:
The stereocontrol mechanism of the 2, 4-pentanediol (PD)-tethered reaction was studied in detail using a reaction system consisting of phenyl and rhodium carbenoid moieties. Different tethers were examined to analyze the effects of the methyl groups on the PD tether. Among the reactions with these tethers, the PD tether achieves an unmeasurably high stereoselectivity in a diastereomeric ratio of > 500. Another tether showing a high but measurable stereoselectivity in a ratio of 41 is mostly controlled by the entropy term. To clarify the role of the methyl groups on the chiral tethers, which are the origin of the stereocontrol, the "chiral perturbation factor" is introduced. This parameter is defined as the rate of a chiral reaction relative to that of an achiral reference reaction. By analyzing the temperature dependence of the chiral perturbation factors for different chiral-tethered reactions, high potentials of the PD-tethered reaction in its stereocontrol are concluded to be due to the entropy term.
Di-2-methoxyethyl Azodicarboxylate (DMEAD): An Inexpensive and Separation-friendly Alternative Reagent for the Mitsunobu Reaction
作者:Takashi Sugimura、Kazutake Hagiya
DOI:10.1246/cl.2007.566
日期:2007.4.5
Di-2-methoxyethyl azodicarboxylate (DMEAD) was prepared as an alternative of DEAD or DIAD for the Mitsunobureaction. Removal of the hydrazinedicarboxylate generated from DMEAD becomes much easier owing to the polar and water-soluble property.
AZODICARBOXYLIC ACID BIS(2-ALKOXYETHYL) ESTER COMPOUND, AND PRODUCTION INTERMEDIATE THEREOF
申请人:Hagiya Kazutake
公开号:US20100048881A1
公开(公告)日:2010-02-25
Provided is an industrially safe and useful azodicarboxylic acid bis(2-alkoxyethyl) ester compound that is useful for the Mitsunobu reaction in which it is used in combination with a phosphorus compound to carry out a dehydration condensation reaction, and also useful as an oxidizing agent, and a starting material for various synthetic processes. Also provided are a production intermediate of the above-described compound, and methods for producing these compounds. An azodicarboxylic acid bis(2-alkoxyethyl) ester compound represented by formula (1);
wherein A represents an alkyl group having 1 to 10 carbon atoms.
Remote stereocontrol of intramolecular rhodium carbene addition driven by a small and flexible chiral 2,4-pentanediol tether
作者:Chun Young Im、Takashi Sugimura
DOI:10.1016/j.tet.2012.03.009
日期:2012.5
Intramolecular rhodium carbenoid additions were studied using 2,4-pentanidiol as a chiral tether between a diazo group, a precursor of the carbene, and an aromatic group to be reacted with the carbene. The reaction was designed to perform the addition at a remote position, conserving the original high stereoselectivity appeared at additions near the tether, in addition to high regioselectivity and sufficient reaction efficiency. Substitution on the near reaction sites, the carbene carbon and aromatic group, in the reactant was effective to relegate the reaction site to a remote position. In the present study, two remote reactions, one dealing with C-H insertion and the other classified in Buchner reaction, were found to give sole products in high yields. (C) 2012 Elsevier Ltd. All rights reserved.
BIS(2-ALKOXYETHYL) AZODICARBOXYLATE ESTER COMPOUND AND INTERMEDIATE FOR PRODUCTION OF THE SAME
申请人:Toyo Boseki Kabushiki Kaisha
公开号:EP2112136B1
公开(公告)日:2012-05-23
Entropy-Controlled Asymmetric Synthesis. How Differential Activation Entropy Is Induced in Chiral Tethered Reactions
[GRAPHICS]Kinetic measurements to determine effective molarities of intramolecular reactions using 2,4-pentanediol and related tethers showed that methyl groups on the tether accelerate the major diastereomeric process but decelerate the minor process. The efficient promotion of stereocontrol is suggested to be due to chiral perturbation of the reaction rate through the entropy term, The conformation of the encounter complex of the reagent and reactant moieties was deduced by stereochemical analysis of the intramolecular adducts.