Dendritic Chiral Phosphine Lewis Bases-Catalyzed Asymmetric Aza-Morita–Baylis–Hillman Reaction ofN-Sulfonated Imines with Activated Olefins

Insights into the Morita–Baylis–Hillman reaction of isomeric dibenzofuran carbaldehydes: a theoretical and mass spectral study

Systematic theoretical and mass spectral investigations on the faster Morita–Baylis–Hillman (MBH) reaction of dibenzofuran-4-carbaldehyde (2) compared to its isomer, dibenzofuran-2-carbaldehyde (1) are described.

The highly enantioselective catalytic aza-Morita–Baylis–Hillman reaction

Chiral phosphine, amine or metal catalyzed asymmetric aza-MBH reactions of various imines with different Michael acceptors in recent decades have been discussed and the perspectives offered by these new developments have also been demonstrated.

Organocatalysis with dendrimers

This review gives an overview of the use of dendrimers and dendrons as organocatalysts, i.e. as catalysts in the absence of any metal. A large variety of dendrimeric structures have already been used for such a purpose, varying in size (generation), type and location (core or surface) of the organocatalytic entities, and overall chemical composition. The main types of reactions catalyzed concern bond formation (in particular C-C bonds), bond cleavage (in particular of esters), reductions and oxidations. In many cases, good to excellent enantioselectivities have been observed, in some cases associated with a positive dendritic effect (better properties when the generation of the dendrimer increases). Due to their large size compared to products, the dendrimeric organocatalysts can be often recovered and reused several times.

The aza-Morita-Baylis-Hillman reaction of electronically and sterically deactivated substrates

The aza-Morita-Baylis-Hillman (azaMBH) reaction has been studied for electronically and sterically deactivated Michael acceptors. It is found that electronically deactivated systems can be converted with electron-rich phosphanes and pyridines as catalysts equally well. For sterically deactivated systems clearly better catalytic turnover can be achieved with pyridine catalysts. This is in accordance with the calculated affinities of the catalysts towards different Michael-acceptors.

Asymmetric organocatalyzed Morita-Baylis-Hillman reactions

The use of organocatalyst to promote the Morita-Baylis-Hillman (MBH) and aza-MBH reaction is an asymmetric and atom-economic way to obtain functionalized allylic alcohols or amines respectively, which have recently been well exploited, providing access to chiral densely functionalized products, which are valuable building blocks that can be further applied in the synthesis of complex natural products.

Multifunctional chiral phosphine organocatalysts in catalytic asymmetric Morita-Baylis-Hillman and related reactions

Catalytic asymmetric synthesis has received considerable attention over the past few decades, becoming a highly dynamic area of chemical research with significant contributions to the field of organic synthesis. In the development of new catalysts, the concept of multifunctional catalysis described by Shibasaki and co-workers, namely, the combination of more than one functional group within a single molecule to activate the transformation, has proved a powerful strategy in the design of efficient transition metal-containing catalysts. A variety of reactions have since been addressed with multifunctional organocatalysts. One example is the Morita-Baylis-Hillman (MBH) reaction, in which a carbon-carbon bond is created between the alpha-position of an activated double-bond compound and a carbon electrophile. The seminal report on this reaction in 1972 described the prototypical couplings of (i) ethyl acrylate with acetaldehyde and (ii) acrylonitrile with acetaldehyde; the reaction is promoted by the conjugate addition of a nucleophilic catalyst to the alpha,beta-unsaturated aldehyde. Many variations of the MBH reaction have been reported, such as the aza-MBH reaction, in which an N-tosyl imine stands in for acetaldehyde. Recent innovations include the development of chiral molecules that catalyze the production of asymmetric products. In this Account, we describe the refinement of catalysts for the MBH and related reactions, highlighting a series of multifunctional chiral phosphines that we have developed and synthesized over the past decade. We also review similar catalysts developed by other groups. These multifunctional chiral phosphines, which contain Lewis basic and Brønsted acidic sites within one molecule, provide good-to-excellent reactivities and stereoselectivities in the asymmetric aza-MBH reaction, the MBH reaction, and other related reactions. We demonstrate that the reactivities and enantioselectivies of these multifunctional chiral phosphines can be adjusted by enhancing the reactive center's nucleophilicity, which can be finely tuned by varying nearby hydrogen-bonding donors. Artificial catalysts now provide highly economic access to many desirable compounds, but the general adaptability and reactivity of these platforms remain problematic, particularly in comparison to nature's catalysts, enzymes. The multifunctional organocatalysts described in this Account represent another positive step in the synthetic chemist's efforts to profitably mimic nature's catalytic platform, helping develop small-molecule catalysts with enzyme-like reactivities and selectivities.