Synthesis of Enantiomerically Enriched Triarylmethanes by Enantiospecific Suzuki–Miyaura Cross-Coupling Reactions
摘要:
The Suzuki-Miyaura cross-coupling of chiral, enantiomerically enriched dibenzylic boronic esters is described. The reaction proceeds with almost complete retention of stereochemistry, providing access to triaryl-methanes, compounds that have high biological activity and are difficult to prepare in enantiomerically pure form using other methods.
Different primary benzyl-type carbamates were deprotonated by sec-butyllithium in the presence of a tert-leucinol-derived bis(oxazoline) ligand. The resulting configurationally labile epimeric complexes equilibrated and one diastereomer was strongly favored in the equilibria. After dynamic thermodynamic resolution, the complexes could be trapped with different classes of electrophiles to yield highly enantioenriched secondary benzyl carbamates. The stereochemical course of the substitution reactions was elucidated. High-level quantum chemical investigations were performed and allowed a prediction of both the favored complex and the enantiomeric excess that could be expected within the reactions.
Enantiospecific, Regioselective Cross-Coupling Reactions of Secondary Allylic Boronic Esters
作者:Laetitia Chausset-Boissarie、Kazem Ghozati、Emily LaBine、Jack L.-Y. Chen、Varinder K. Aggarwal、Cathleen M. Crudden
DOI:10.1002/chem.201303683
日期:2013.12.23
enantioselective Suzuki–Miyaura cross‐coupling of chiral, enantioenriched secondaryallylic boronic esters is described (see scheme; DME=dimethoxyethane, Bpin = pinacolboryl, dba = dibenzylideneacetone). Mechanistic studies show that the reactions proceed via γ‐selective transmetalation followed by reductive elimination. The reaction provides the first independent confirmation that the transmetalation of
A Relative Organolithium Stability Scale Derived from Tin−Lithium Exchange Equilibria. Substituent Effects on the Stability of α-Oxy- and α-Aminoorganolithium Compounds
作者:Paula Graña、M. Rita Paleo、F. Javier Sardina
DOI:10.1021/ja025552r
日期:2002.10.1
Quantitative thermodynamic stability scales of organolithiumcompounds can be derived from measurements of tin−lithium exchange equilibria. A ΔGeq scale of α-oxy- and α-aminoorganolithium compounds was established, and quantitative stabilization effects of O-alkyl, O-alkoxyalkyl, O-carbamoyl, N-carbamoyl, and O-carbonyl groups of the α-carbanion are presented. It has been found that an α-oxycarbanion
有机锂化合物的定量热力学稳定性标度可以从锡-锂交换平衡的测量中推导出来。建立了α-氧基-和α-氨基有机锂化合物的ΔGeq标度,并给出了α-碳负离子的O-烷基、O-烷氧基烷基、O-氨基甲酰基、N-氨基甲酰基和O-羰基的定量稳定作用。已经发现,α-氧碳负离子通过作为 O-取代基的羰基比通过烷基或烷氧基烷基更好地稳定,而不同的 O-羰基取代基的阴离子稳定效果是可比的。发现 N-氨基甲酰基比其 O-氨基甲酰基对应物具有更高的稳定作用。提供的 NMR 数据表明,苄基 N 或 O 取代的碳负离子具有高度平面化的结构,其中负电荷高度离域。从锡-锂交换中获得的稳定性数据可以轻松转换为“有效 pK”数据,这些数据可用于预测酸...
An unexpected transformation of benzyl carbamates into α-azidobenzeneacetamides
作者:Christoph Strässler、Heinz Heimgartner
DOI:10.1002/hlca.19970800706
日期:1997.11.3
treatment of benzyl carbamates 5 (Z-protected secondary amines) with lithium diisopropylamide (LDA), diphenyl phosphorochloridate (DPPC1), and NaN3 yielded the corresponding ã-azidobenzeneacetamides 6 in 45–50% yield (Schemes 2 and 3). In the case of Z-protected diisopropylamine 5b, the phosphate 7 was isolated as a minor product. A reaction mechanism for this unexpected transformation is proposed in
A novel nucleophilicsubstitutionreaction at the nitrogen of arylsulfonamides by means of phosphide anions has been described. This reaction allows for the efficient transformation of arylsulfonamides into synthetically valuable phosphamides, amines, and a variety of protected amines.