Synthesis of Highly Functionalized Pyridines: A Metal-Free Cascade Process

Flexible Synthesis of Highly Substituted Pyridines Bearing 2-Fluoroalkyl Groups

Herein, we report a flexible process for the synthesis of highly functionalized pyridines containing 2-fluoroalkyl groups. Starting from easily accessible tert-butanesulfinamide derivatives, this new synthesis provides pyridine derivatives in good yields. The tandem process leading to pyridines includes a Pummerer-type rearrangement, an amide formation, a Mannich-type cyclization, and an elimination induced aromatization. In this Letter, we also demonstrate the modification of natural products using this protocol.

Cascade Rearrangement: Nitro Group-Participating Syntheses of 1,2,5-Thiadiazoles and 1,2,4-Thiadiazolones

A trifluoroacetic anhydride-mediated cascade process for the synthesis of thiadiazole derivatives is described. 1,2,5-Thiadiazoles and 1,2,4-thiadiazolones could be obtained by variation of the reaction conditions. A group of functionalized thiadiazole derivatives were synthesized in moderate to good yields from nitro-group-containing N-tert-butanesulfinamides. The reactions involved in this tandem process are a Pummerer-like rearrangement of the tert-butanesulfinamide unit, a nitrile oxide formation via nitro group rearrangement, addition of oxygenated nucleophiles, and an N-S bond forming cyclization followed by concomitant elimination.

Synthesis and biological activities of bicyclic pyridines integrated steroid hybrid

Reports on structural modification of heterosteroids through various reactions, and developed synthetic routes have considerably increased over the last decade. The present review encompasses the applicable approaches dealing with the utility of reactive moieties in various steroids for the synthesis of fused bicyclic pyridines, and binary bicyclic pyridines all over the years. The different sections include the synthesis of steroids-fused, and binary quinolines, pyridopyrimidines, imidazopyridines, spirocyclic imidazopyridines, pyrazolopyridines, thienopyridines, pyridinyl-thiazoles, and tetrazolopyridine hybrids, as well as, the diverse biological applications of these heterocyclic steroids. The researchers' interest was principally focused on investigating the flexibility of synthetic strategies for various derivatives of natural steroids and building proposals based on heterocyclic steroids for drug discovery, biological assessments, and synthetic applications.

Pummerer-like Rearrangement Induced Cascade Reactions: Synthesis of Highly Functionalized Imidazoles

Imidazoles are among the most important pharmacophores in medicinal chemistry. Herein we report a tandem protocol for the synthesis of highly substituted imidazoles through Pummerer-like rearrangement induced cascade reactions including two carbon-nitrogen bond formations, and concomitant aromatization under mild reaction conditions. This procedure gives imidazole derivatives bearing numerous functional groups and could be used for modifying natural products as well as pharmaceuticals.

Total synthesis of justicidin B, justicidin E, and taiwanin C: A general and flexible approach toward the synthesis of natural arylnaphthalene lactone lignans

Lignans are widely present in traditional medicinal plants. Many natural arylnaphthalene lactone lignans (NALLs) isolated from the genera Justicia, Haplophyllum, and Phyllanthus possess interesting biological activities. Herein, we report a general strategy for the total synthesis of this kind of lignans. Features of this new approach are an aryl-alkyl Suzuki cross-coupling to introduce the dioxinone unit, a cation-induced cyclization to construct the aryl dihydronaphthalene, and base-mediated oxidative aromatization to furnish the arylnaphthalene core. By incorporating these key transformations, the total syntheses of justicidins B and E and taiwanin C covered type I and type II NALLs were accomplished.

Carbon-Sulfur Bond Formation: Tandem Process for the Synthesis of Functionalized Isothiazoles

In this paper, we report a new process for the construction of 3,4,5-substituted isothiazoles via reaction cascades including Pummerer-like rearrangement, nucleophilic condensation, and sulfenamide cyclization followed by concomitant elimination and dehydration under mild reaction conditions. This process provides isothiazoles bearing fluorine and other functional groups in good to excellent yields from readily available starting materials.

Synthesis of pyrimido[2,1-a]isoindolone and isoindolo[2,1-a]quinazolinone via intramolecular aza-Prins type reaction

A novel aza-Prins type cyclization reaction involving N-acyliminium ions and amides is reported for the synthesis of tetrahydropyrimido[2,1-a]isoindole-2,6-dione and 6,6a-dihydroisoindolo[2,1-a]quinazoline-5,11-dione derivatives in excellent yields. The strategy features inexpensive reagents, mild reaction conditions, and metal-free synthesis of N-heterocyclic frameworks. Further, post-synthetic modification results in the unprecedented formation of its triazole, tetracyclic diazacyclopenta[def]phenanthrene-1,4(9a1H)-dione and carbonyl derivatives.