A Highly Stereoselective Hydrogen‐Bond‐Mediated Michael–Michael Cascade Process through Dynamic Kinetic Resolution
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Michael macht's möglich: Die Titelreaktion, die direkt zu Thiochromanen führt, wird effizient durch ein Thioharnstoffderivat eines China-Alkaloids katalysiert. Das organokatalytische Verfahren umfasst eine neuartige dynamische Racematspaltung durch eine Kaskade aus Michael- und Retro-Michael-Reaktionen.Keywords:
Michael reaction
Kinetic resolution
Abstract Ausgehend vom Lacton (I) erhält man über (II) ein Gemisch der Furanderivate (IV), das zum Keton (V) oxidiert wird.
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Component (thermodynamics)
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Highly Asymmetric Michael Addition to α,β‐Unsaturated Ketones Catalyzed by 9‐Amino‐9‐deoxyepiquinine
Michael–Michael–retro-Michael cascade reactions are promoted by the highly efficient organocatalyst 9-amino-9-deoxyepiquinine (1). The asymmetric direct vinylogous Michael addition of α,α-dicyanoalkenes to α,β-unsaturated ketones may be followed by an intramolecular Michael addition and a retro-Michael reaction to afford polysubstituted 2-cyclohexen-1-one derivatives with high enantioselectivity (see example).
Michael reaction
Addition reaction
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A remarkably stereoselective reduction of a γ-hydroxyketone with two equiv. of lithium triethylborohydride has been observed and this effect has been suggested to originate from 'chelation control'; the reaction has been utilised in a short stereoselective synthesis of ancistrofuran.
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A linear turbine cascade experimental apparatus often consists of only a few cascade blades. Advantages to this arrangement are increased from using larger cascade blades and easier optical access. However, fewer cascade blades in the cascade row make it difficult to establish periodic flow conditions between blades. In this study, a 160% pitch passage for cascade experiments with a single blade is designed to satisfy infinite cascade flow conditions without any flow control or tailboards. Fourteen geometric design variables are applied to the design of a 160% pitch passage by using a gradient-based optimization method and a genetic algorithm. Flow structures within a passage designed with a genetic algorithm are closer to the infinite cascade flow conditions than those obtained with a gradient-based method. The results show that infinite cascade flow conditions can be obtained by modifying only the passage walls of the cascade experimental apparatus.
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Michael reaction
Tandem
One-pot synthesis
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A one-pot, two-step aza-Michael/Michael/Michael process was developed to diastereospecifically construct C6a,C10a-cis-hydrophenanthridines in a highly enantioselective manner (83-99% ee). The tricyclic products were provided in 50-99% isolated yields, sequentially promoted by bifunctional squaramide and diamine in a one-pot operation. This doubly annulative protocol indicated that the complicated polycyclic structures could be easily constructed via full employment of the available reaction sites of readily prepared precursors.
Michael reaction
Squaramide
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Adaptive IIR filters implemented in cascade-form are attractive due to the ease with which their stability may be monitored. Four cascade-form structures are compared for use in adaptive filtering with respect to complexity of implementation, error surface geometry, and adaptation speed. The four structures include a cascade of second order pole/zero sections, a cascade of second order all-pole sections followed by a tapped delay line, and two new structures. The latter pair includes a tapped cascade, which is a cascade of second order all-pole sections whose output is constructed as a weighted combination of signals tapped from the cascade. The second new structure is a modification of the tapped cascade that yields orthogonal signals at the taps of the cascade. It is shown that the tapped cascade provides the best overall performance in the respects noted above.
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Abstract In the presence of a catalytic amount of several trityl salts, 2,3,5-tri-O-benzyl-d-ribofuranose smoothly reacted with alcohols to give various β-ribofuranosides in high yields with high stereoselectivity while reversed stereoselectivity was observed in the coexistence of lithium perchlolate.
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