A new synthon in heterocycle synthesis

A tetraehlorobenzodioxinone, prepared from 2-phenyl-4-benzyl-2-oxazolin-5-one and o-chloranil was found to react with clhanol to give the ester 6 . This compound reacted readily with various bis-nucleophiles to form five- and six-membered helerocyclic compounds.     

Biocatalyst CAL-B catalyzed synthesis of modified nucleosides: An overview

Nucleosides are valuable biologically active compounds, which display antitumour and antiviral activities. Various types of bioactive nucleosides are designed to improve their therapeutic efficacy, However this strategy faces the difficult selectivity issues of nucleoside chemistry. Therefore, the goal of this review is to give an idea of the opportunities provided by biocatalyst CAL-B procedures in the preparation of different types of bioactive nucleoside compounds. The function of Candida Antarctica lipase-B (CAL-B) in organic synthesis is reviewed. This enzyme has been found to be a principally efficient and robust lipase catalyzing an unexpected variety of reactions including many different regio- chemo, and diastereo-selective synthesis. Moreover, the structure of Candida Antarctica lipase-B is an example of an enzyme for which its specificity has been predicted based on acylation and deacylation mechanism on substrates.     

Highly efficient one-pot synthesis of dihydropyran heterocycle

Diammonium hydrogen phosphate and potassium carbonate-catalyzed one-pot synthesis of 1,4- phenylene-bis（2-amino-4H-pyran-3-carbonitrile and 2-amino-4-aryl-4H-pyran-3-carbonitrile deriva- tives has been achieved by a three-component cyclocondensation of aldehydes, malononitrile, and different nucleophiles in aqueous medium in high yields.     

Diastereoselectivity in the solid-phase synthesis of peptide heterocycle hybrids

Sixteen compounds containing the bicyclic moiety (3,8,10-trisubstituted 2,9-dioxo-5-thia-1,8-diazabicyclo[4.4.0]decane) were produced via solid-phase synthesis. Differing substitution at the 3- and 10-positions was used. These were analyzed using 2-D NMR techniques (ROESY) to determine the stereoselectivity of ring formation in the core heterocycle. Conformational analysis of the proposed transition state structure using Sybyl 6.8^® was used to rationalize the stereochemical outcome of ring formation.     

An overview of palladium-catalyzed synthesis of seven-membered heterocycles

Heterocyclic compounds are the ones that have always remained in the limelight owing to their superior contributions toward various disciplines such as biology, medicine, material science, pharmaceutical science, industry and so on. They form the building blocks of DNA and RNA macromolecules. Suitable tuning of these heterocyclic compounds can result in chemotherapeutic moieties with superlative efficiency. Seven-membered heterocyclic compounds are an important class of heterocyclic chemistry. Some of them are azepine, oxepine, thiepine, diazepine, thiazepine and so on. Transition metal-catalyzed synthesis of heterocycles has been the most explored in the recent past. Palladium is known as the best suitable catalyst for the same and that is the result of its excellent functional group tolerance and catalytic potency. Here, we intend to summarize the various investigations made on the palladium-catalyzed synthesis of seven-membered heterocycles. To the best of our knowledge, this is the first review in this topic and covers literature up to 2020.     

Recent advances in synthesis of 2-pyridones: a key heterocycle is revisited

Owing to the versatile applications in different areas including biology, natural compounds, dyes, and fluorescent materials, the synthesis of 2-pyridone compounds is an important research field and has attracted a great deal of attention. In this review, 2-pyridones new synthetic methods are classified to tree classes including reactions based on pyridine rings, cyclization, and cycloaddition reactions.     

Copper-catalysed benzofuran synthesis: developing aryl bromide-alkenyl triflates as general heterocycle precursors

A range of conjugated aryl bromide-alkenyl triflates, previously described as indole precursors, are efficiently converted to the corresponding benzofurans when treated with CuI/TMEDA and potassium hydroxide.     

An improved synthesis of alpha-carbolines under microwave irradiation

[reaction: see text]. Alpha-carbolines are interesting core structures for designing DNA-interacting small molecules. However, these compounds are not commercially available and their synthetic methods are low yielding or time consuming. The shortest synthetic route, the modified Graebe-Ullmann reaction, has been optimized by using microwave heating in four different types of apparatus to give shorter reaction times and enhanced yields. Optimized conditions enabled the preparation of a small library of alpha-carbolines.     

An overview of the total synthesis of africane-type sesquiterpenoids

Africane-type sesquiterpenoids consist of a bicyclo[5.3.0]decane structure and have been isolated from various natural environments. Their characteristic CC bond motifs, including a seven-membered ring core, fascinate many synthetic organic chemists. Thirteen total syntheses have been reported over the past four decades. The purpose of this digest is to provide an overview of these total syntheses of africane-type sesquiterpenoids, with an emphasis on methods for constructing the seven-membered ring structure.     

Gold-catalyzed heterocycle synthesis using homopropargylic ethers as latent electrophiles

[reaction: see text] Homopropargylic ethers with pendent nucleophiles, when subjected to Au catalysts in aqueous solvent, provide heterocyclic ketones. The reactions are efficient, tolerant of functionality and ambient atmosphere, and operationally simple. Diastereoselectivity can be predicted on the basis of product thermodynamics. This process demonstrates the viability of homopropargylic ethers to serve as latent electrophiles that can be unraveled under highly selective conditions to promote heterocycle formation through nucleophilic additions to alpha,beta-unsaturated ketones.     

Phosphorus heterocycle synthesis using phosphenium ions and 1,4-dienes

The stabilized phosphenium ion, [Prⁱ₂NPCl]⁺, reacts readily with 1,4-dienes to afford high yields of bicyclic phosphonium salts, the structure of one of which has been determined by X-ray crystallography.     

G--C quartet--a DNA-inspired Janus-GC heterocycle: synthesis, structural analysis, and self-organization

In this communication we disclose the synthesis and characterization of a DNA-inspired self-complementary heterocycle that contains AAD-DAA H-bond acceptor/donor patterns. Whereas in the past such AAD-DAA self-complementarity has given rise to trimeric and hexameric rosettes, we now demonstrate that the same H-bonding scheme, when properly arrayed, can be used to program a tetrameric rosette, which unlike a G-quartet requires no metal binding or peripheral components for preorganization. Of note, we exploit both 2D-NOESY and DOSY 1H NMR to substantiate the tetrameric stoichiometry in this noncovalent rosette comprising 12 H-bonds.     

An efficient synthesis of dithiocarbamates under ultrasound irradiation in water

Abstract  

Multicomponent reactions with ultrasonic activation have been used as a simple, rapid, atom economic, and green method for the synthesis of dithiocarbamate derivatives in water. The one-pot, three-component condensation of primary and secondary amines with carbon disulfide and unsaturated carbonyl compounds or alkyl halides under ultrasonic irradiation was developed as a green and fast protocol for the rapid high-yielding preparation of dithiocarbamates in water.     

Tandem reactions initiated by copper-catalyzed cross-coupling: a new strategy towards heterocycle synthesis

Copper-catalyzed cross-coupling reactions which lead to the formation of C-N, C-O, C-S and C-C bonds have been recognized as one of the most useful strategies in synthetic organic chemistry. During past decades, important breakthroughs in the study of Cu-catalyzed coupling processes demonstrated that Cu-catalyzed reactions are broadly applicable to a variety of research fields related to organic synthesis. Representatively, employing these coupling transformations as key steps, a large number of tandem reactions have been developed for the construction of various heterocyclic compounds. These tactics share the advantages of high atom economics of tandem reactions as well as the broad tolerance of Cu-catalyst systems. Therefore, Cu-catalyzed C-X (X = N, O, S, C) coupling transformation-initiated tandem reactions were quickly recognized as a strategy with great potential for synthesizing heterocyclic compounds and gained worldwide attention. In this review, recent research progress in heterocycle syntheses using tandem reactions initiated by copper-catalyzed coupling transformations, including C-N, C-O, C-S as well as C-C coupling processes are summarized.     

A cyclopropane fragmentation approach to heterocycle assembly: a convergent synthesis of oxepanes

[reaction: see text] A cyclopropanol fragmentation approach to the synthesis of oxepanes has been developed. This convergent strategy condenses cyclopropyl diols with aldehydes to form an acetal, which is subsequently rearranged to furnish a keto-oxepane. The reaction has been developed as a one-pot procedure, utilizing sequential addition of Al(OTf)3 and TiCl4. Yields range from 50 to 70% for the sequence. A Zimmerman-Traxler transition state disposing substituents in equatorial positions is consistent with the observed formation of strictly cis products.     

An overview on the copper-promoted synthesis of five-membered heterocyclic systems

The development of novel approaches for the preparation of small-sized heterocyclic products has remained an extremely attractive but challenging proposition. Copper has been known as one of the most applicable and significant transition metals utilized in the synthesis of organic products. A couple of factors such as high earth abundance and versatile catalysis resulted in the growth of copper-promoted synthesis of five-membered heterocyclic products. Utilizations such as making coins and electrical equipment express the importance of copper, as well. Here, a comprehensive overview of the copper-catalyzed synthesis of five-membered heterocyclic products is presented, focusing on the developments over the past 4 years.