In Situ Catalyst Improvement in the Proline-Mediated α-Amination of Aldehydes
作者:Hiroshi Iwamura、Suju P. Mathew、Donna G. Blackmond
DOI:10.1021/ja046258x
日期:2004.9.1
proline-mediated α-amination of aldehydes exhibits autoinductive rate behavior and amplification of product enantiomericexcess. Further experiments highlight the role of product, offering suggestions for the design of catalysts of improved efficiency for such transformations. The unusual characteristics exhibited by these reactions implicate amino acid catalysis in rationalizations of the origin of biological
The enantioselectiveaddition of aldehydes to diethylazodicarboxylate in ionicliquids in the presence of chiralorganocatalysts has been investigated. Of seven differentorganocatalysts tested, L-proline and L-thiazoline-2-carboxylic acid gave the highest enantioselectivities (up to 94 % ee). The best results were obtained by using [bmim]PF6 and [hmim]BF4 as ionicliquids. The scope of the methodology
This article describes the thermally accelerated organocatalyticα-amination of disubstitutedaldehydes with azodicarboxylates under microwave conditions. Compared to the results previously obtained at room temperature, both yield and enantioselectivity could be significantly increased. Employing microwave irradiation resulted in a considerably reduced reaction time. Therefore, this improved protocol
A Coherent Mechanistic Rationale for Additive Effects and Autoinductive Behaviour in Proline-Mediated Reactions
作者:Natalia Zotova、Antonio Moran、Alan Armstrong、Donnaâ G. Blackmond
DOI:10.1002/adsc.200900665
日期:2009.11
Differences in the kinetic behaviour of aldol reactions compared to aminoxylation and amination reactions are rationalized by consideration of the rate-determining step in each case. Both autoinductivebehaviour and the rate-enhancing effect of additives are attributed to an effect on the enamine formation step.
Propylene carbonate is shown to be an environmentally friendly and sustainable replacement for dichloromethane and acetonitrile in proline-catalysed a-hydrazinations of aldehydes and ketones. Enantioselectivities comparable to those obtained in conventional solvents or ionic liquids can be obtained, even when using a lower catalyst loading.