An efficient and practical synthesis of optically pure β‐pyrazole‐substituted alcohols was achieved by an asymmetric ring‐opening reaction of meso‐epoxides with pyrazole derivatives as the nucleophile. In the presence of 1 mol % of an N,N′‐dioxide–Sc(OTf)3 complex, excellent enantioselectivity and yields were obtained from meso‐epoxides. The process could also be used for a mixture of cis‐ and trans‐stilbene
Allenes in Asymmetric Catalysis: Asymmetric Ring Opening of <i>meso</i>-Epoxides Catalyzed by Allene-Containing Phosphine Oxides
作者:Xiaotao Pu、Xiangbing Qi、Joseph M. Ready
DOI:10.1021/ja9041127
日期:2009.8.5
Unsymmetrically substituted allenes (1,2-dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically
Epoxide desymmetrizations by bromide are very rare despite the large synthetic potential of chiral bromohydrins. Herein we present a new concept for epoxide desymmetrizations in which a bifunctional Lewis acid...
Asymmetric Azidation under Hydrogen Bonding Phase-Transfer Catalysis: A Combined Experimental and Computational Study
作者:Jimmy Wang、Matthew A. Horwitz、Alexander B. Dürr、Francesco Ibba、Gabriele Pupo、Yuan Gao、Paolo Ricci、Kirsten E. Christensen、Tejas P. Pathak、Timothy D. W. Claridge、Guy C. Lloyd-Jones、Robert S. Paton、Véronique Gouverneur
DOI:10.1021/jacs.1c13434
日期:2022.3.16
encouraged us to undertake a detailed study on the application of hydrogen bonding phase-transfer catalysis (HB-PTC) to enantioselective azidation with sodium azide. So far, this phase-transfer manifold has been applied exclusively to insoluble metal alkali fluorides for carbon–fluorine bond formation. Herein, we disclose the asymmetric ringopening of meso aziridinium electrophiles derived from β-chloroamines
不对称催化叠氮化对于获得对映体富集的含氮分子的重要性增加,但使用廉价叠氮化钠的方法仍然很少。这鼓励我们对氢键相转移催化(HB-PTC)在叠氮化钠对映选择性叠氮化中的应用进行详细研究。到目前为止,这种相转移歧管仅应用于不溶性金属碱金属氟化物以形成碳-氟键。在此,我们公开了在手性双脲催化剂存在下,由 β-氯胺与叠氮化钠衍生的内消旋氮丙啶鎓亲电子试剂的不对称开环。对新型氢键叠氮化物配合物的结构进行了计算分析,在固态通过 X 射线衍射,在溶液相通过1 H 和14 N/ 15 N NMR 光谱。与N-异丙基化的 BINAM 衍生的双脲,叠氮化物以三足方式与所有三个 NH 键末端结合在能量上是有利的,这种排列让人想起相应的动态更刚性的三叉氢键合氟化物络合物。计算分析表明,导致主要对映异构体的最稳定过渡态显示来自叠氮化物阴离子的氢键末端的攻击。所有三个氢键都保持在过渡态;然而,如在不对称 HB-PTC 氟化中所见,亲核试剂和单齿脲之间的
Hydrogen Bonding Phase-Transfer Catalysis with Potassium Fluoride: Enantioselective Synthesis of β-Fluoroamines
作者:Gabriele Pupo、Anna Chiara Vicini、David M. H. Ascough、Francesco Ibba、Kirsten E. Christensen、Amber L. Thompson、John M. Brown、Robert S. Paton、Véronique Gouverneur
DOI:10.1021/jacs.8b12568
日期:2019.2.20
Potassium fluoride (KF) is an ideal reagent for fluorination because it is safe, easy to handle and low-cost. However, poor solubility in organic solvents coupled with limited strategies to control its reactivity has discouraged its use for asymmetric C-F bond formation. Here, we demonstrate that hydrogenbonding phase-transfer catalysis with KF provides access to valuable β-fluoroamines in high yields