Trienamine Catalysis with 2,4-Dienones: Development and Application in Asymmetric Diels-Alder Reactions

Enantioselective [4 + 2] Cycloaddition Reaction of Vinylquinolines with Dienals Enabled by Synergistic Organocatalysis

An unprecedented organocatalytic enantioselective [4 + 2] cycloaddition reaction of vinyl quinolines with dienals is achieved with the synergistic activation of CH₃SO₃H and a chiral aminocatalyst. The power of the process is demonstrated by its high efficiency of the production of new synthetically and biologically valued chiral quinoline architectures in high yields and with excellent enantioselectivities.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Synthesis of (E,E)-Dienones and (E,E)-Dienals via Palladium-Catalyzed γ,δ-Dehydrogenation of Enones and Enals

A new strategy for the synthesis of conjugated (E,E)-dienones and (E,E)-dienals via a palladium-catalyzed aerobic γ,δ-dehydrogenation of enones and enals has been developed. The method can be employed in the direct and efficient synthesis of various (E,E)-dienones and (E,E)-dienals, including non-substituted α-, β-, and γ- and/or δ-substituted (E,E)-dienones and (E,E)-dienals. The protocol is featured by the ready accessibility and elaboration of the starting materials, good functional group compatibility, and mild reaction conditions. Furthermore, the reaction is of complete E,E-stereoselectivity and uses molecular oxygen as the sole clean oxidant.

Enantioselective Construction of Octahydroquinolines via Trienamine-Mediated Diels-Alder Reactions

A trienamine-mediated asymmetric Diels-Alder reaction using a 5-nitro-2,3-dihydro-4-pyridone derivative as a dienophile in the presence of a secondary amine organocatalyst derived from cis-hydroxyproline was discovered. The reaction provides optically active octahydroquinolines through an endo-selective [4 + 2] cyclization pathway. The following stereoselective denitration, isomerization, and/or hydrogenation generated divergent stereoisomers of decahydroquinolines, which are useful synthons for the total synthesis of Lycopodium alkaloids.

Organocatalysis: A Brief Overview on Its Evolution and Applications

The use of small organic molecules as catalysts has gained increasing importance recently. These substances, the so-called organocatalysts, present a lot of advantages, like being less toxic, less polluting, and more economically viable than the organometallic catalysts that dominate asymmetric synthesis. This work intends to briefly show some classic works and recent publications, explaining the advantages of organocatalysis and the different types of compounds used in this field, as well as their course of action.

Asymmetric vinylogous aldol addition of alkylidene oxindoles on trifluoromethyl-α,β-unsaturated ketones

A novel vinylogous aldol addition of alkylidene oxindole with 1-trifluoromethyl-3-alkylidene-propan-2-ones is presented. The reaction, catalyzed by a bifunctional tertiary amine, provides an efficient application of the vinylogous reactivity of oxindoles for the preparation of enantioenriched trifluoromethylated allylic alcohols.

Trienamine catalyzed asymmetric synthesis and biological investigation of a cytochalasin B-inspired compound collection

Due to their enhanced metabolic needs many cancers need a sufficient supply of glucose, and novel inhibitors of glucose import are in high demand. Cytochalasin B (CB) is a potent natural glucose import inhibitor which also impairs the actin cytoskeleton leading to undesired toxicity. With a view to identifying selective glucose import inhibitors we have developed an enantioselective trienamine catalyzed synthesis of a CB-inspired compound collection. Biological analysis revealed that indeed actin impairment can be distinguished from glucose import inhibition and led to the identification of the first selective glucose import inhibitor based on the basic structural architecture of cytochalasin B.

Combining cycloisomerization with trienamine catalysis: a regiochemically flexible enantio- and diastereoselective synthesis of hexahydroindoles

The synthesis of polysubstituted hexahydroindoles through trienamine-organocatalyzed cycloadditions of pyrrolidinyl dienals, prepared by palladium-catalyzed cycloisomerization, is reported.

Catalytic asymmetric hetero-Diels–Alder reactions of enones with isatins to access functionalized spirooxindole tetrahydropyrans: scope, derivatization, and discovery of bioactives

Concise hetero-Diels–Alder reactions were developed to provide various functionalized spirooxindole tetrahydropyrans useful for the discovery of bioactive molecules.

1,3-Dienones and 2H-Pyran-2-ones from Soft α-Vinyl Enolization of β-Chlorovinyl Ketones: Defined Roles of Brönsted and Lewis Base

The eliminative reaction pathways of (E)-β-chlorovinyl ketones were investigated in the presence of both Brönsted and Lewis bases. The Brönsted base, Et3N, effected the soft α-vinyl enolization of (E)-β-chlorovinyl ketones to [3]cumulenol intermediates; in turn, a catalytic amount of Lewis base, PPh3, initiated isomerization to provide 1,3-dienones in high yields. The introduction of a carbon-based nucleophile into the reaction mixture provided the highly efficient synthetic route to 2H-pyran-2-ones in one pot, where the carbon-based nucleophile generated by an extra equivalent of Brönsted base, Et3N, attacked the electrophilic [3]cumulenol intermediates to initiate cyclization to give 2H-pyran-2-ones.

Direct Catalytic Asymmetric Doubly Vinylogous Michael Addition of α,β-Unsaturated γ-Butyrolactams to Dienones

An asymmetric doubly vinylogous Michael addition (DVMA) of α,β-unsaturated γ-butyrolactams to sterically congested β-substituted cyclic dienones with high site-, diastereo-, and enantioselectivity has been achieved. An unprecedented DVMA/vinylogous Michael addition/isomerization cascade reaction affords chiral fused tricyclic γ-lactams with four newly formed stereocenters.

The ever-expanding role of asymmetric covalent organocatalysis in scalable, natural product synthesis

Following the turn of the millennium, the role of asymmetric covalent organocatalysis has developed into a scalable, synthetic paradigm galvanizing the synthetic community toward utilization of these methods toward more practical, metal-free syntheses of natural products. A myriad of reports on asymmetric organocatalytic modes of substrate activation relying on small, exclusively organic molecules are delineating what has now become the multifaceted field of organocatalysis. In covalent catalysis, the catalyst and substrate combine to first form a covalent, activated intermediate that enters the catalytic cycle. Following asymmetric bond formation, the chiral catalyst is recycled through hydrolysis or displacement by a pendant group on the newly formed product. Amine- and phosphine-based organocatalysts are the most common examples that have led to a vast array of reaction types. This Highlight provides a brief overview of covalent modes of organocatalysis and applications of scalable versions of these methods applied to the total synthesis of natural products including examples from our own laboratory.

Copper–dienamine catalysis: γ-oxyamination of α,β-unsaturated aldehydes

A multicatalytic system composed of copper complexes and sec-amine compounds is proposed for γ-oxyamination of α,β-unsaturated aldehydes.

Trienamine catalysis with linear deconjugated 3,5-dienones

Deconjugated linear 3,5-dienones with substantial substitutions were used in β,ε-regioselective Diels–Alder cycloadditions with 3-olefinic oxindoles via trienamine catalysis of cinchona-based primary amines.