Asymmetric Michael additions catalysed by Ni(II) and Co(II) complexes with homochiral ligands

Catalysts’ evolution in the asymmetric conjugate addition of nitroalkanes to electron-poor alkenes

This review provides a journey of the catalyst usage for the enantioselective conjugate addition of nitroalkanes to electron-poor olefins from the early attempts to the latest achievements. Selected applications are also reported.

Enantioselective Access to Robinson Annulation Products and Michael Adducts as Precursors

The Robinson annulation is a reaction that has been useful for numerous syntheses since its discovery in 1935, especially in the field of steroid synthesis. The products are usually obtained after three consecutive steps: the formation of an enolate (or derivative), a conjugate addition, and an aldol reaction. Over the years, several methodological improvements have been made for each individual step or alternative routes have been devised to access the Robinson annulation products. The first part of this Review outlines the most relevant developments towards the formation of monocarbonyl-derived Robinson annulation products (MRA products, MRAPs) and activated monocarbonyl-derived Robinson annulation products (AMRA products, AMRAPs). The following sections are then devoted to the diastereoselective and enantioselective synthesis of these products, while the last section describes the enantiomeric resolution of racemic mixtures.

Asymmetric synthesis of substituted NH-piperidines from chiral amines

Previously, we reported an efficient asymmetric synthesis of substituted piperidines through an exocyclic chirality induced nitroalkene/amine/enone (NAE) condensation reaction. An effective protecting group strategy was developed herein to achieve enantiopure piperidines (yields up to 92%) with complete chirality retention (ee > 95%). A simple derivatization of the obtained piperidines gave thiourea catalysts, indicating the strong potential of this method for producing new amine-based dual functional organocatalysts for future development.

Highly Enantioselective Conjugate Addition of Nitromethane to Chalcones Using Bifunctional Cinchona Organocatalysts

Cinchona alkaloid-derived chiral bifunctional thiourea organocatalysts were synthesized and applied in the Michael addition between nitromethane and chalcones with high ee and chemical yields.

Ionic and Covalent Copper(II)-Based Catalysts for Michael Additions. The Mechanism

Cu(SbF6)2-AdamBox and copper(II) bis-(5-tert-butylsalicylaldehydate) catalyze the Michael addition in neutral media. Mechanistic studies, based on UV-vis, IR, and electrospray ionization mass spectrometry (ESI-MS), suggest that copper enolates of the beta-dicarbonyl formed in situ are the active nucleophilic species.

Catalytic asymmetric conjugate addition of nitroalkanes to cycloalkenones

Nitroalkanes add to cyclic and acyclic enones in an enantioselective manner in the presence of catalytic quantities of L-proline and trans-2,5-dimethylpiperazine as excess additive.