Catalytic Synthesis of 1H-2-Benzoxocins: Cobalt(III)-Carbene Radical Approach to 8-Membered Heterocyclic Enol Ethers

A catalytic synthesis of cyclic guanidines, which are found in many biologically active compounds and natu-ral products, was developed, wherein transition-metal hydrogen atom transfer and radical-polar crossover were employed. This mild and functional-group tolerant process enabled the cyclization of alkenyl guanidines bearing common protective groups, such as Cbz and Boc. This powerful method not only provided the common 5- and 6-membered rings but also an unusual 7-membered ring. The derivatization of the products afforded various heterocycles. We also investigated the se-lective cyclization of mono-protected or hetero-protected (TFA and Boc) alkenyl guanidines and their further derivatiza-tions.

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Pyrone-derived Marine Natural Products: A Review on Isolation, Bio-activities and Synthesis

Current Organic Chemistry ◽

10.2174/1385272824666200217101400 ◽

2020 ◽

Vol 24 (4) ◽

pp. 354-401 ◽

Cited By ~ 2

Author(s):

Keisham S. Singh

Keyword(s):

Natural Products ◽

Marine Natural Products ◽

Marine Fungi ◽

Kojic Acid ◽

Biological Activities ◽

Biological Significance ◽

Pyrone Ring ◽

Enol Ethers ◽

Bioactive Natural Products ◽

Marine Metabolites

Marine natural products (MNPs) containing pyrone rings have been isolated from numerous marine organisms, and also produced by marine fungi and bacteria, particularly, actinomycetes. They constitute a versatile structure unit of bioactive natural products that exhibit various biological activities such as antibiotic, antifungal, cytotoxic, neurotoxic, phytotoxic and anti-tyrosinase. The two structure isomers of pyrone ring are γ- pyrone and α-pyrone. In terms of chemical motif, γ-pyrone is the vinologous form of α- pyrone which possesses a lactone ring. Actinomycete bacteria are responsible for the production of several α-pyrone compounds such as elijopyrones A-D, salinipyrones and violapyrones etc. to name a few. A class of pyrone metabolites, polypropionates which have fascinating carbon skeleton, is primarily produced by marine molluscs. Interestingly, some of the pyrone polytketides which are found in cone snails are actually synthesized by actinomycete bacteria. Several pyrone derivatives have been obtained from marine fungi such as Aspergillums flavus, Altenaria sp., etc. The γ-pyrone derivative namely, kojic acid obtained from Aspergillus fungus has high commercial demand and finds various applications. Kojic acid and its derivative displayed inhibition of tyrosinase activity and, it is also extensively used as a ligand in coordination chemistry. Owing to their commercial and biological significance, the synthesis of pyrone containing compounds has been given attention over the past years. Few reviews on the total synthesis of pyrone containing natural products namely, polypropionate metabolites have been reported. However, these reviews skipped other marine pyrone metabolites and also omitted discussion on isolation and detailed biological activities. This review presents a brief account of the isolation of marine metabolites containing a pyrone ring and their reported bio-activities. Further, the review covers the synthesis of marine pyrone metabolites such as cyercene-A, placidenes, onchitriol-I, onchitriol-II, crispatene, photodeoxytrichidione, (-) membrenone-C, lihualide-B, macrocyclic enol ethers and auripyrones-A & B.

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Addition of Allylsilanes and Silyl Enol Ethers to Small Oxygenated Rings: New Tools for Organic Synthesis

Current Organic Chemistry ◽

10.2174/1385272819666140201002221 ◽

2014 ◽

Vol 18 (5) ◽

pp. 525-546 ◽

Cited By ~ 4

Author(s):

Carmen Hernandez-Cervantes ◽

Miriam Alvarez-Corral ◽

Manuel Munoz-Dorado ◽

Ignacio Rodriguez-Garcia

Keyword(s):

Organic Synthesis ◽

Enol Ethers ◽

Silyl Enol Ethers

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α-Alkoxyalkyl Triphenylphosphonium Salts: Synthesis and Reactions

Current Organic Chemistry ◽

10.2174/1385272823666190926092242 ◽

2019 ◽

Vol 23 (16) ◽

pp. 1738-1755

Author(s):

Humaira Y. Gondal ◽

Zain M. Cheema ◽

Abdul R. Raza ◽

Ahmed Abbaskhan ◽

M. I. Chaudhary

Keyword(s):

Carbonyl Compounds ◽

Claisen Rearrangement ◽

Alder Reaction ◽

Coupling Reactions ◽

Phosphonium Salts ◽

Organic Transformations ◽

Enol Ethers ◽

Wide Range ◽

Synthetic Methodologies ◽

Alkoxy Groups

Following numerous applications of Wittig reaction now functionalized phosphonium salts are gaining attention due to their characteristic properties and diverse reactivity. This review is focused on α-alkoxyalkyl triphenylphosphonium salts: an important class of functionalized phosphonium salts. Alkoxymethyltriphenylphosphonium salts are majorly employed in the carbon homologation of carbonyl compounds and preparation of enol ethers. Their methylene insertion strategy is extensively demonstrated in the total synthesis of a wide range of natural products and other important organic molecules. Similarly enol ethers prepared thereof are important precursors for different organic transformations like Diels-Alder reaction, Claisen rearrangement, Coupling reactions, Olefin metathesis and Nazarov cyclization. Reactivity of these α-alkoxyalkylphosphonium salts have also been studied in the nucleophilic substitution reactions. A distinctive application of this class of phosphonium salts was recently reported in the phenylation of carbonyl compounds under very mild conditions. Synthesis of structurally diverse alkoxymethyltriphenylphosphonium salts with variation in alkoxy groups as well as counter anions are reported in literature. Here we present a detailed account of different synthetic methodologies for the preparation of this unique class of quaternary phosphonium salts and their applications in organic synthesis.

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Recent Developments in the Catalytic Synthesis of 2-Substituted Benzoxazoles

Current Organic Chemistry ◽

10.2174/1385272821666170623080714 ◽

2017 ◽

Vol 21 (19) ◽

Cited By ~ 6

Author(s):

Jian He

Keyword(s):

Catalytic Synthesis ◽

Recent Developments

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Synthesis of 3,4-Dihydropyrimidin-2(1H)-one Derivatives Using Activated Montmorillonite as Catalyst

Letters in Organic Chemistry ◽

10.2174/1570178615666180627113617 ◽

2018 ◽

Vol 16 (1) ◽

pp. 59-65

Author(s):

Sofiane Mekki ◽

Lahcen Krabia ◽

Saleh Mahmoud Saleh Mohamed ◽

Salima Saidi-Besbes

Keyword(s):

Catalytic Synthesis ◽

Montmorillonite Clays

An efficient catalytic synthesis of 4-aryl-3,4-dihydropyrimidine-2(1H)-one derivatives using copper (II), iron (III) and zinc (II) exchanged montmorillonite clays as a catalyst is described. The desired products were obtained in good yields.

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