Total Synthesis of Iheyamine A via the Cyanide-Catalyzed Imino-Stetter Reaction

Copper-Catalyzed Cascade Cyclization of 2-Nitrochalcones with NH-Heterocycles

We developed a method for allowing cascade cyclization of 2-nitrochalcones with pyrazoles, imidazole, and indazole in the presence of CuI catalyst, DBU base, and THF solvent. The conditions were tolerant of an array of useful functionalities including ester, nitro, cyano, halogen groups. A mechanistic consideration was also provided, as H2O2 was presumably a byproduct. Our method appears to be a rare example to directly prepare C3-heterocyclic unprotected indoles.

Synthesis, structural modification, and biological activity of a novel bisindole alkaloid iheyamine A

Diseases caused by plant viruses and pathogens pose a serious threat to crop yield and quality. Traditional pesticides have gradually developed drug resistance and brought certain environmental safety issues during long-term overuse. There is an urgent need to discover new candidate compounds to address these issues. In this study, we achieved the efficient synthesis of iheyamine A and its derivatives, and discovered their excellent antiviral activities against tobacco mosaic virus (TMV). Most compounds displayed higher antiviral activities against TMV than commercial ribavirin at 500 μg/mL, with compounds 3a (Inactive effect IC50: 162 µg/mL), 3d (Inactive effect IC50: 249 µg/mL), 6p (Inactive effect IC50: 254 µg/mL), and 7a (Inactive effect IC50: 234 µg/mL) exhibiting better antiviral activities than ningnanmycin at 500 μg/mL (Inactive effect IC50: 269 µg/mL). Meanwhile, the structure-activity relationships of this type of compounds were systematically studied. We chose 3a for further antiviral mechanism research and found that it can directly act on viral coat protein (CP). The interaction of 3a and CP was further verified via molecular docking. These compounds also showed broad-spectrum fungicidal activities against 8 plant pathogenic fungi, especially for P. piricola. This study provides a reference for the role of iheyamine alkaloids in combating plant pathogenic diseases.

Seven-membered N-heterocycles as approved drugs and promising leads in medicinal chemistry as well as the metal-free domino access to their scaffolds

Azepanes or azepines are structural motifs of many drugs, drug candidates and evaluated lead compounds. Even though compounds having N-heterocyclic 7-membered rings are often found in nature (e.g. alkaloids), the natural compounds of this group are rather rare as approved therapeutics. Thus, recently studied and approved azepane or azepine-congeners predominantly consist of semi-synthetically or synthetically-obtained scaffolds. In this review a comparison of approved drugs and recently investigated leads was proposed taking into regard their structural aspects (stereochemistry), biological activities, pharmacokinetic properties and confirmed molecular targets. The 7-membered N-heterocycles reveal a wide range of biological activities, not only against CNS diseases, but also as e.g. antibacterial, anticancer, antiviral, antiparasitic and against allergy agents. As most of the approved or investigated potential drugs or lead structures, belonging to 7-membered N-heterocycles, are synthetic scaffolds, this report also reveals different and efficient metal-free cascade approaches useful to synthesize both simple azepane or azepine-containing congeners and those of oligocyclic structures. Stereochemistry of azepane/azepine fused systems, in view of biological data and binding with the targets, is discussed. Apart from the approved drugs, we compare advances in SAR studies of 7-membered N-heterocycles (mainly from 2018 to 2023), whereas the related synthetic part concerning various domino strategies is focused on the last ten years.

Efficient approach to 1,1'-bisindoles via copper(I)-catalyzed double domino reaction

A highly efficient copper(I)-catalyzed approach for the synthesis of 1,1'-bisindoles that is based on the formation of four bonds in one step has been developed. The unprecedented three component reaction between one molecule of a 1,2-bis(2-bromoaryl)hydrazine and two molecules of a 1,3-diketone employing 10 mol% CuI as a catalyst and Cs2CO3 as a base in DMSO at 100 °C for 24 h delivers substituted 1,1'-bisindoles with yields up to 92%. The new method proceeds as a double domino condensation/Ullmann type C-C coupling. It allows an efficient and practical access to substituted 1,1'-bisindoles in one step from easily available starting materials.

Synthesis of 2-(2-nitrophenyl)indoline-3-acetic acid derivatives via base-catalyzed cyclization of N-(2-nitrobenzyl)-2-aminocinnamic acid derivatives

A protocol for the synthesis of 2-(2-nitrophenyl)indoline-3-acetic acid derivatives was developed via base-catalyzed cyclization of N-(2-nitrobenzyl)-2-aminocinnamic acid derivatives. The synthetic utility of this methodology was illustrated by the concise synthesis of dihydropaullone, a partially saturated analog of paullone. Furthermore, the indoline scaffold could be further converted to the corresponding indoles and other indole-fused heterocycles.

Total Syntheses of Iheyamines A and B

An efficient synthetic route to iheyamine A and its analogues was discovered; the crucial one-pot transformation included a C-C migration to form the characteristic seven-membered ring. Subsequent addition of acetone to iheyamine A initiated a cascade process to complete the total synthesis of iheyamine B.

Asymmetric Total Synthesis of Iheyamine B

Herein, we report the first asymmetric total synthesis of iheyamine B from 2,2'-bisindoloazepinone using the stereoselective construction of the trans-vicinal 2-oxopropyl moiety in the azepine scaffold. The asymmetric decarboxylative allylic alkylation provided the α-allylated 2,2'-bisindoloazepinone intermediate. The subsequent conversion of the lactam moiety into another allyl group in a trans-selective manner followed by Wacker oxidation of each allyl unit to the corresponding 2-oxopropyl group completed the total synthesis of iheyamine B.

Direct, four-step synthetic pathway to iheyamine A and several analogues

A novel synthetic route toward the pentacyclic azepinobisindole alkaloid iheyamine A and its several analogues has been developed in four steps from commercially available isatins and tryptamines. This crucial transformation involves the Bischler-Napieralski cyclization to deliver the characteristic seven-membered framework. Then the ester intermediate undergoes a hydrolyzation-decarboxylation-dehydrogenation cascade to yield the final product.

Cyanide Anions as Nucleophilic Catalysts in Organic Synthesis

The nucleophilic addition of a cyanide anion to a carbonyl group is the basis for several cyanide-catalyzed organic reactions, which are summarized in this review. Since cyanide is also a good leaving group, it is an excellent catalyst for transacylation reactions. As an electron-withdrawing group, it also stabilizes a negative charge in its α-position, thus allowing the umpolung of aldehydes to formyl anion equivalents. The two leading examples are the benzoin condensation and the Michael–Stetter reaction furnishing α-hydroxy ketones and 1,4-dicarbonyl compounds, which are both catalyzed by cyanides. The review also covers variants like the silyl-benzoin coupling, the aldimine coupling and the imino-Stetter reaction. Moreover, some cyanide-catalyzed heterocyclic syntheses are reviewed.

1 Introduction

2 Nucleophilic Additions

2.1 Cyanohydrin Formation

2.2 Corey–Gilman–Ganem and Related Oxidation Reactions

2.3 Conjugate Addition

2.4 Intramolecular Carbocyanation

3 Transacylation Reactions

3.1 Ester Hydrolysis and Transesterification

3.2 Formation of Amides

3.3 Ketones from Esters

3.4 Esters from Ketones

4 Transformations Involving an Umpolung

4.1 Benzoin Condensation

4.2 Aldimine Coupling

4.3 Michael–Stetter Reaction

4.4 Imino-Stetter Reaction

5 Formation of Heterocycles

5.1 Oxazolines from Isocyanoacetates

5.2 Imidazoles from TosMIC via Oxazolines

5.3 Bargellini Reaction

6 Conclusion

Total Synthesis of Hinckdentine A

The total synthesis of (±)-hinckdentine A is described herein. A cyanide-catalyzed imino-Stetter reaction of the aldimine derived from ethyl 2-amino-3,5-dibromocinnamate and 5-bromo-2-nitrobenzaldehyde followed by oxidative rearrangement afforded a 2,2-disubstituted 3-indolinone derivative containing the carbon skeleton and all of the functional groups present in the natural product correctly positioned, including three bromine atoms. Subsequent D-ring formation and seven-membered C-ring construction completed the total synthesis of hinckdentine A.

A Stereodivergent Strategy for Total Syntheses of Antirhine Alkaloids

Total syntheses of the antirhine alkaloids are described. The cyanide-catalyzed imino-Stetter reaction of the aldimine derived from ethyl 2-aminocinnamate and 4-bromopyridine-2-carboxaldehyde provided a 2-pyridinyl substituted indole-3-acetate, which was further converted into the corresponding indoloquinolizidinium intermediate through C-ring formation. Subsequent trans-selective installation of the homoallylic alcohol side-chain at C-15 in the resulting indoloquinolizidinium allowed the total syntheses of antirhine and its known epimer.