Oxyanion Steering and CH−π Interactions as Key Elements in an N-Heterocyclic Carbene-Catalyzed [4 + 2] Cycloaddition
摘要:
The N-heterocyclic carbene catalyzed [4 + 2] cycloaddition has been shown to give gamma,delta-unsaturated delta-lactones in excellent enantio- and diastereoselectivity. However, preliminary computational studies of the geometry of the intermediate enolate rendered ambiguous both the origins of selectivity and the reaction pathway. Here, we show that a concerted, but highly asynchronous, Diels-Alder reaction occurs rather than the stepwise Michael-type or Claisen-type pathways. In addition, two crucial interactions are identified that enable high selectivity an oxyanion-steering mechanism and a CH-pi interaction. The calculations accurately predict the enantioselectivity of a number of N-heterocyclic carbene catalysts in the hetero-Diels-Alder reaction.
Catalytic Kinetic Resolution of Cyclic Secondary Amines
作者:Michael Binanzer、Sheng-Ying Hsieh、Jeffrey W. Bode
DOI:10.1021/ja209472h
日期:2011.12.14
The catalytic resolution of racemic cyclic amines has been achieved by an enantioselective amidation reaction featuring an achiral N-heterocyclic carbene catalyst and a new chiral hydroxamic acid cocatalyst working in concert. The reactions proceed at room temperature, do not generate nonvolatile byproducts, and provide enantioenriched amines by aqueous extraction.
Cooperative <i>N</i>-Heterocyclic Carbene/Lewis Acid Catalysis for Highly Stereoselective Annulation Reactions with Homoenolates
作者:Benoit Cardinal-David、Dustin E. A. Raup、Karl A. Scheidt
DOI:10.1021/ja910666n
日期:2010.4.21
A new approach that takes advantage of N-heterocyclic carbene/Lewis acidcooperativecatalysis provides access to cis-1,3,4-trisubstituted cyclopentenes from enals and chalcone derivatives with high levels of diastereoselectivity and enantioselectivity. The presence of Ti(OiPr)(4) as the Lewis acid allows for efficient substrate preorganization, which translates into high levels of diastereoselectivity
Catalytic Asymmetric Cross-Aza-Benzoin Reactions of Aliphatic Aldehydes with<i>N</i>-Boc-Protected Imines
作者:Daniel A. DiRocco、Tomislav Rovis
DOI:10.1002/anie.201202442
日期:2012.6.11
Crossed: A catalyst system has been developed that allows the direct asymmetric coupling of aliphaticaldehydes and N‐Boc‐protected imines in a cross‐aza‐benzoin reaction (see scheme; Boc=tert‐butoxycarbonyl). The active catalyst is shown to react rapidly with the imine, however, the presence of an acid as co‐catalyst renders this process reversible and allows the regeneration of the catalyst.
Highly Enantioselective [5 + 2] Annulations through Cooperative N-Heterocyclic Carbene (NHC) Organocatalysis and Palladium Catalysis
作者:Santanu Singha、Tuhin Patra、Constantin G. Daniliuc、Frank Glorius
DOI:10.1021/jacs.8b00868
日期:2018.3.14
The highly enantioselective [5 + 2] annulation of enals with vinylethylene carbonates through a cooperative N-heterocyclic carbene (NHC)/Pd catalytic system is reported. The use of a bidentate phosphine ligand was crucial to prevent coordination of the NHC organocatalyst to the active Pd catalyst. The complementary and matched combination of the chiral NHC catalyst and chiral phosphine ligand promotes
Catalytic Asymmetric α-Acylation of Tertiary Amines Mediated by a Dual Catalysis Mode: N-Heterocyclic Carbene and Photoredox Catalysis
作者:Daniel A. DiRocco、Tomislav Rovis
DOI:10.1021/ja3030164
日期:2012.5.16
the formation of the desired C-C bond with loss of H(2) as the only byproduct. Herein we report the catalytic asymmetric α-acylation of tertiaryamines with aldehydes facilitated by the combination of chiral N-heterocyclic carbene catalysis and photoredox catalysis.
交叉偶联反应是最广泛使用的 CC 键形成方法之一;然而,预活化起始材料的需求仍然是一个主要限制。直接利用 CH 键固有反应性的方法为这些方法提供了有效的替代方案,无需底物预激活。在此过程中,两个化学上不同的活化事件最终形成所需的 CC 键,并损失 H(2) 作为唯一的副产物。在此,我们报道了手性N-杂环卡宾催化和光氧化还原催化相结合促进叔胺与醛的催化不对称α-酰化反应。