How to Make Five Contiguous Stereocenters in One Reaction: Asymmetric Organocatalytic Synthesis of Pentasubstituted Cyclohexanes

Enantioselective Total Synthesis of [3]-Ladderanol through Late-Stage Organocatalytic Desymmetrization

Ladderane phospholipids, with their unusual ladder-like arrangement of concatenated cyclobutane rings, represent an architecturally unique class of natural products. However, despite their fascinating structure and other necessary impetus, only a few synthetic studies of these molecules have been reported so far. We have now devised a concise total synthesis of [3]-ladderanol, a component of natural ladderane phospholipids, using an organocatalytic enantioselective desymmetrizing formal C(sp² )-H alkylation. Our synthetic strategy rests on the late-stage introduction of chirality, thus allowing facile access to both enantiomers of [3]-ladderanol as well as an analogue. This is the first time a desymmetrization strategy is applied to the synthesis of [3]-ladderanol. The scope of this desymmetrizing C(sp² )-H alkylation of meso-cyclobutane-fused cyclohexenediones is also presented.

Parts-per-Million-Level, Catalytic [3+2]-Annulations for the Asymmetric Synthesis of Methanobenzo[7]annulenes

3-Alkyl-lawsones selectively reacted with α-alkyl-nitroethylenes under 500 parts-per-million (ppm) quinine-NH-thiourea-catalysis to furnish the chiral methanobenzo[7]annulenes in up to >99 % ee with >20 : 1 dr and TON up to 1820 through tandem Michael/Henry [3+2]-annulations. These asymmetric ppm-level, catalytic tandem [3+2]-annulations would be highly inspirational for the design of many more ppm-level organocatalytic reactions, and at the same time these final molecules are basic skeletons of antibiotics.

Enantio- and Diastereoselective, Complete Hydrogenation of Benzofurans by Cascade Catalysis

We report an enantio- and diastereoselective, complete hydrogenation of multiply substituted benzofurans in a one-pot cascade catalysis. The developed protocol facilitates the controlled installation of up to six new defined stereocenters and produces architecturally complex octahydrobenzofurans, prevalent in many bioactive molecules. A unique match of a chiral homogeneous ruthenium-N-heterocyclic carbene complex and an in situ activated rhodium catalyst from a complex precursor act in sequence to enable the presented process.

An Enamide-Based Domino Reaction for a Highly Stereoselective Synthesis of Tetrahydropyrans

A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ‐bonds and five continuous stereogenic centers are formed in this one‐pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E‐ or a Z‐configured enamide.

Catalytic Asymmetric Synthesis of 3,4-Disubstituted Cyclohexadiene Carbaldehydes: Formal Total Synthesis of Cyclobakuchiols A and C

The first catalytic approach for the asymmetric synthesis of 3,4-disubstituted cyclohexadiene carbaldehydes through an inverse-electron-demand Diels-Alder reaction is described. A variety of arylacetaldehydes and α,β,γ,δ-unsaturated aldehydes are tested under the mild reaction conditions catalyzed by l-proline to obtain the trans diastereomeric products with good yields and high enantioselectivities. The scope of this methodology is further extended to the asymmetric synthesis 3,4-disubstituted cyclohexane carbaldehydes and their derivatives. The practicality of this method is demonstrated by the gram-scale synthesis. This methodology is successfully applied for the formal total synthesis of cyclobakuchiol A, an antipyretic and anti-inflammatory agent, and cyclobakuchiol C.

Deeper Insight into the Six-Step Domino Reaction of Aldehydes with Malononitrile and Evaluation of Antiviral and Antimalarial Activities of the Obtained Bicyclic Products

The straightforward and efficient synthesis of complex aza‐ and carbobicyclic compounds, which are of importance for medicinal chemistry, is a challenge for modern chemical methodology. An unprecedented metal‐free six‐step domino reaction of aldehydes with malononitrile was presented in our previous study to provide, in a single operation, these bicyclic nitrogen‐containing molecules. Presented here is a deeper investigation of this atom‐economical domino process by extending the scope of aldehydes, performing post‐modifications of domino products, applying bifunctional organocatalysts and comprehensive NMR studies of selected domino products. The thermodynamic aspects of the overall reaction are also demonstrated using DFT methods in conjunction with a semi‐empirical treatment of van der Waals interactions. Furthermore, biological studies of seven highly functionalized and artemisinin‐containing domino products against human cytomegalovirus (HCMV) and Plasmodium falciparum 3D7 are presented. Remarkably, in vitro tests against HCMV revealed five domino products to be highly active compounds (EC₅₀ 0.071–1.8 μm), outperforming the clinical reference drug ganciclovir (EC₅₀ 2.6 μm). Against P. falciparum 3D7, three of the investigated artemisinin‐derived domino products (EC₅₀ 0.72–1.8 nm) were more potent than the clinical drug chloroquine (EC₅₀ 9.1 nm).

One-pot sequential organocatalysis: highly stereoselective synthesis of trisubstituted cyclohexanols

A highly diastereoselective (d.r. >99:1) and enantioselective (ee value up to 96%) synthesis of trisubstituted cyclohexanols was achieved by using a one-pot sequential organocatalysis that involved a quinidine thiourea-catalyzed tandem Henry-Michael reaction between nitromethane and 7-oxo-hept-5-en-1-als followed by a tetramethyl guanidine (TMG)-catalyzed tandem retro-Henry-Henry reaction on the reaction products of the tandem Henry-Michael reaction. Through a mechanistic study, it has also been demonstrated that similar results may also be achieved with this one-pot sequential organocatalysis by using the racemic Henry product as the substrate.

One-pot organocatalytic asymmetric synthesis of 3-nitro-1,2-dihydroquinolines by a dual-activation protocol

Generally, amine-catalyzed enantioselective transformations rely on chiral enamine or unsaturated iminium intermediates. Herein, we report a protocol involving dual activation by an aromatic iminium and hydrogen-bonding. An enantioselective aza-Michael-Henry domino reaction of 2-aminobenzaldehydes with nitroolefins has been developed through this protocol using primary amine thiourea catalysts to provide a variety of 3-nitro-1,2-dihydroquinolines in moderate yields and with up to 90% ee. The mechanism for the catalytic enantioselective reaction was confirmed by ESI mass spectrometric detection of the reaction intermediates. The products formed are substructures found in skeletons of important biological and pharmaceutical molecules.

Alpha,alpha-diarylprolinol ethers: new tools for functionalization of carbonyl compounds

Alpha,alpha-diaryl(dialkyl)prolinol ethers constitute a potent organocatalyst family which has been shown to be very general for a broad range of reactions involving enamine and iminium ion activation or a combination of both. The reactions are characterized by an efficient steric control approach and can lead to a variety of alpha-, beta-, gamma-, and alpha,beta-functionalized carbonyl compounds with excellent stereocontrol. As a full expression of their catalytic activity, these compounds are also excellent promoters of elegant cascade processes and valuable catalysts in water-compatible systems.

Asymmetric aminocatalysis--gold rush in organic chemistry

Catalysis with chiral secondary amines (asymmetric aminocatalysis) has become a well-established and powerful synthetic tool for the chemo- and enantioselective functionalization of carbonyl compounds. In the last eight years alone, this field has grown at such an extraordinary pace that it is now recognized as an independent area of synthetic chemistry, where the goal is the preparation of any chiral molecule in an efficient, rapid, and stereoselective manner. This has been made possible by the impressive level of scientific competition and high quality research generated in this area. This Review describes this "Asymmetric Aminocatalysis Gold Rush" and charts the milestones in its development. As in all areas of science, progress depends on human effort.