Asymmetric Synthesis of Substituted Homotropinones from N-Sulfinyl β-Amino Ketone Ketals. (−)-Euphococcinine and (−)-Adaline

Stereoselective Synthesis of 1-Substituted Homotropanones, including Natural Alkaloid (-)-Adaline

The stereocontrolled synthesis of 1-substituted homotropanones, using chiral N-tert-butanesulfinyl imines as reaction intermediates, is described. The reaction of organolithium and Grignard reagents with hydroxy Weinreb amides, chemoselective N-tert-butanesulfinyl aldimine formation from keto aldehydes, decarboxylative Mannich reaction with β-keto acids of these aldimines, and organocatalyzed L-proline intramolecular Mannich cyclization are key steps of this methodology. The utility of the method was demonstrated with a synthesis of the natural product (-)-adaline, and its enantiomer, (+)-adaline.

Four-Step Total Synthesis of (+)-Euphococcinine and (±)-Adaline

A four-step enantiospecific total synthesis of bicyclic homotropinone alkaloid euphococcinine and a racemic synthesis of adaline were reported. Key reactions in the synthesis are the diastereoselective addition of a Wittig phosphorene to the ketimines derived from Davis-Ellman sulfinamides, ring-closing metathesis, and intramolecular Michael reactions.

Multicomponent Cascade Reaction of 3-Formylchromones: Highly Selective Synthesis of Functionalized 9-Azabicyclo[3.3.1]nonane Derivatives

A novel protocol for the preparation of functionalized 9-azabicyclo[3.3.1]nonane (ABCN) derivatives from 3-formylchromones, enaminones, and heterocyclic ketene aminals (HKAs) through an unprecedented cascade reaction has been developed by simply refluxing the mixture of the substrates 1-3. As a result, a series of ABCNs were produced through a very complex cascade reaction. This protocol can be used in the synthesis of ABCNs that are suitable for combinatorial and parallel syntheses of ABCN natural-like products in a one-pot reaction.

Applications of aryl-sulfinamides in the synthesis of N-heterocycles

Enantiopure aryl-sulfinamides are important chiral auxiliaries in the asymmetric synthesis of amines and their derivatives. Here, we provide an overview of arylsulfinamide mediated asymmetric methods towards N-heterocycle synthesis. This methodology through sulfinylimines offers general access to structurally diverse piperidines, pyrrolidines, aziridines and their derivatives which represent the structural motif of many natural products and therapeutically important compounds. The review covers articles from 2006–2020 and we have categorized the review based on the ring size as 3-, 5-, and 6- membered heterocycles and their derivatives.

The review comprehends the usage of arylsulfinamides for the construction of diverse N-heterocycles like piperidines, pyrrolidines, aziridines, and their fused derivatives.

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

The 9-azabicyclo[3.3.1]nonane ring system is present in several insect- and plant-derived alkaloids. (-)-Adaline (1) and (+)-euphococcinine (2), found in secretions of Coccinelid beetles, and (+)-N-methyleuphococcinine (3), isolated from the Colorado blue spruce Picea pungens, are members of this alkaloid family. Their unique bicyclic system with a quaternary stereocenter, and the potent biological activity exerted by these homotropane alkaloids, make them attractive synthetic targets. This work aims briefly to review the chemical ecology of Adalia bipunctata and the recent methodologies to obtain adaline (1), euphococcinine (2), and N-methyleuphococcinine (3).

Discovery of 2-(1H-imidazo-2-yl)piperazines as a new class of potent and non-cytotoxic inhibitors of Trypanosoma brucei growth in vitro

The identification of a new series of growth inhibitors of Trypanosoma brucei rhodesiense, causative agent of Human African Trypanosomiasis (HAT), is described. A selection of compounds from our in-house compound collection was screened in vitro against the parasite leading to the identification of compounds with nanomolar inhibition of T. brucei growth. Preliminary SAR on the hit compound led to the identification of compound 34 that shows low nanomolar parasite growth inhibition (T. brucei EC₅₀ 5 nM), is not cytotoxic (HeLa CC₅₀ > 25,000 nM) and is selective over other parasites, such as Trypanosoma cruzi and Plasmodium falciparum (T. cruzi EC₅₀ 8120 nM, P. falciparum EC₅₀ 3624 nM).

Synthetic approaches towards alkaloids bearing α-tertiary amines

Alkaloids account for some of the most beautiful and biologically active natural products. Although they are usually classified along biosynthetic criteria, they can also be categorized according to certain structural motifs. Amongst these, the α-tertiary amine (ATA), i.e. a tetrasubstituted carbon atom surrounded by three carbons and one nitrogen, is particularly interesting. A limited number of methods have been described to access this functional group and fewer still are commonly used in synthesis. Herein, we review some approaches to asymmetrically access ATAs and provide an overview of alkaloid total syntheses where those have been employed.

Direct asymmetric syntheses of chiral aldehydes and ketones via N-acyl chiral auxiliary derivatives including chiral Weinreb amide equivalents

This article covers N-acyl chiral auxiliary-based approaches to the asymmetric synthesis of enantiopure aldehydes and ketones. The use of diastereoisomerically pure N-acyl derivatives of chiral auxiliaries (including chiral Weinreb amide equivalents) and their conversion to the corresponding enantiopure aldehydes and ketones in a single synthetic operation by treatment with a hydride reducing agent or an organometallic reagent, respectively, are highlighted.

Synthesis and applications of masked oxo-sulfinamides in asymmetric synthesis

This short perspective reports on the synthesis and applications of a class of chiral amino carbonyl compounds, masked oxo-sulfinamides where the amine is protected with an N-sulfinyl moiety and the carbonyl group is protected as the ketal or 1,3-dithiane. These polyfunctionalized chiral building blocks are prepared by addition of organometallic reagents to masked oxo-sulfinimines (N-sulfinyl imines) or the addition of oxo-organometallic reagents and lithio-1,3-dithianes to sulfinimines. Because unmasking of the amino and carbonyl groups results in cyclic imines, these chiral building blocks are particularly useful for the asymmetric synthesis of functionalized nitrogen heterocycles, including prolines, pipecolic acids, pyrrolidines, homotropinones, tropinones, and tropane alkaloids such as cocaine and C-1 cocaine analogues.

Enantioselective synthesis of cocaine C-1 analogues using sulfinimines (N-sulfinyl imines)

The first examples of cocaine analogues having substituents (methyl, ethyl, n-propyl, n-pentyl, and phenyl) at the C-1 position of the cocaine tropane skeleton were prepared by heating sulfinimine-derived α,β-unsaturated pyrrolidine nitrones. In the presence of the Lewis acid Al(O(t)Bu)(3) the nitrones undergo an intramolecular [3 + 2] cycloaddition to give tricyclic isoxazolidines that were transformed in three steps to the cocaine analogues. In the absence of the Lewis acid, lactams were formed resulting from rearrangement of the nitrone to an oxaziridine. A novel Pd- and base-promoted rearrangement of methanesulfonate salts of isoxazolidine to bridge bicyclic[4.2.1]isoxazolidines was discovered.

Asymmetric synthesis of anti-α-substituted β-amino ketones from sulfinimines

Previously unknown, enantiopure, β-amino ketones were prepared in modest yield by addition of lithium reagents to N-sulfinyl anti-α-substituted β-amino Weinreb amides. Grignard reagents failed to add to these Weinreb amides in contrast to the syn-α-substituted isomers which did. The anti-α-substituted β-amino Weinreb amides were prepared by addition of LiN(OMe)Me to the corresponding N-sulfinyl anti-α-substituted β-amino esters because α-alkylation of N-sulfinyl β-amino Weinreb amide enolates resulted in poor diastereoselectivities.

A facile process for the asymmetric synthesis of β-trifluoromethylated β-amino ketones via addition of ketone enolates to sulfinylimine

An efficient method for the asymmetric synthesis of β-trifluoromethylated β-amino ketones via addition of ketone-derivative enolates to trifluoromethylated sulfinylimine has been developed, with good chemical yields and excellent diastereoselectivities. This practical method was also proved to be suitable for large-scale preparation.

Asymmetric synthesis of cyclic cis-beta-amino acid derivatives using sulfinimines and prochiral Weinreb amide enolates

Cyclic cis-beta-amino Weinreb amides, valuable building blocks for the asymmetric synthesis of cyclic beta-amino acids derivatives, are readily prepared via ring-closing metathesis of sulfinimine-derived N-sulfinyl beta-amino diene Weinreb amides. These unsaturated cyclic cis-beta-amino Weinreb amides are valuable building blocks for the asymmetric synthesis of cyclic beta-amino acid derivatives.