Pyridone annulation via tandem Curtius rearrangement/6π-electrocyclization: total synthesis of (-)-lyconadin C

Synthesis of Substituted 2-Pyridones via 6π-Electrocyclization of Dienyl Isocyanates

A one-pot Curtius rearrangement of dienyl carboxylic acids followed by a 6π-electrocyclization process to form substituted 2-pyridone products has been developed. Dienyl isocyanates generated from aliphatic acids were more reactive than their aromatic counterparts. Additionally, substitution patterns of the carboxylic acids had an impact on the efficiency of the cyclization.

Nanocrystalline ZnO: A Competent and Reusable Catalyst for the Preparation of Pharmacology Relevant Heterocycles in the Aqueous Medium

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Nanoparticle catalyzed synthesis is a green and convenient method to achieve most of the chemical transformations in water or other green solvents. Nanoparticle ensures an easy isolation process of catalyst as well as products from the reaction mixture avoiding the hectic work up procedure. Zinc oxide is a biocompatible, environmentally benign and economically viable nanocatalyst with effectivity comparable to the other metal nanocatalyst employed in several reaction strategies. This review mainly focuses on the recent applications of zinc oxide in the synthesis of biologically important heterocyclic molecules under sustainable reaction conditions.

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Application of zinc oxide in organic synthesis: Considering the achievable advantages of this nanocatalyst, presently several research groups are paying attention in anchoring zincoxide or its modified structure in several types of organic conversions e.g. multicomponent reactions, ligand-free coupling reactions, cycloaddition reaction, etc. The advantages and limitations of this nanocatalyst are also demonstrated. The present study aims to highlight the recent multifaceted applications of ZnO towards the synthesis of diverse heterocyclic motifs. Being a promising biocompatible nanoparticle, this catalyst has an important contribution in the fields of synthetic chemistry and medicinal chemistry.

The 6π-azaelectrocyclization of azatrienes. Synthetic applications in natural products, bioactive heterocycles, and related fields

Covering: 2006 to 2018 The application of the 6π-azaelectrocyclization of azatrienes as a key strategy for the synthesis of natural products, their analogs and related bioactive or biomedically-relevant compounds (from 2006 to date) is comprehensively reviewed. Details about reaction optimization studies, relevant reaction mechanisms and conditions are also discussed.

Recent applications of the 1,2-carbon atom migration strategy in complex natural product total synthesis

1,2-Carbon atom rearrangement has been broadly applied as a guiding strategy in complex molecule assembly. As it entails the carbon-carbon or carbon-heteroatom bond migration between two vicinal atoms, this type of reaction is capable of generating structural complexity through a molecular skeletal reorganization. This review will focus on recent employment of this strategy in the total synthesis of natural products, highlighting the exceptional utility of such synthetic methodologies in the construction of intricate carbocycles, heterocycles or structurally complex motifs from synthetically more accessible precursors.

Second-Generation Synthesis of (+)-Fastigiatine Inspired by Conformational Studies

(+)-Fastigiatine is a complex alkaloid isolated from the alpine club moss Lycopodium fastigatum, most commonly found in New Zealand. It has been the subject of two successful synthetic campaigns. A second-generation route toward fastigiatine was developed to resolve two problematic steps from our initial synthesis. Selective reduction and protection of the C13 ketone improved the yield and reliability of the dibromocarbene ring expansion step. In the prior synthesis, cuprate addition to the C10 enone generated a 1:1 mixture of isomers in an advanced intermediate. Protection of the C13 alcohol with a large silyl group changed the conformational preference of the enone and led to a more selective conjugate addition to produce the desired β-epimer at C10. MacMillan's decarboxylative photoredox addition method proved to be more practical than the prior aminomethyl cuprate addition chemistry. The second-generation synthesis is longer than the original but improves the selectivity and reproducibility of the overall route.

The Curtius rearrangement: mechanistic insight and recent applications in natural product syntheses

The Curtius rearrangement is a versatile reaction in which a carboxylic acid can be converted to an isocyanate through an acyl azide intermediate under mild conditions. The resulting stable isocyanate can then be readily transformed into a variety of amines and amine derivatives including urethanes and ureas. There have been wide-ranging applications of the Curtius rearrangement in the synthesis of natural products and their derivatives. Also, this reaction has been extensively utilized in the synthesis and application of a variety of biomolecules. In this review, we present mechanistic studies, chemical methodologies and reagents for the synthesis of isocyanates from carboxylic acids, the conversion of isocyanates to amines and amine derivatives, and their applications in the synthesis of bioactive natural products and their congeners.

Application of the Curtius rearrangement to the synthesis of 1′-aminoferrocene-1-carboxylic acid derivatives

The shortest synthesis of N-protected 1′-aminoferrocene-1-carboxylic acid from readily available ferrocene-1,1′-dicarboxylic acid is reported.

Serralongamines B-D, three new Lycopodium alkaloids from Lycopodium serratum var. longipetiolatum, and their inhibitory effects on foam cell formation in macrophages

Three new Lycopodium alkaloids, serralongamines B-D (1-3), have been isolated from the club moss Lycopodium serratum var. longipetiolatum, and the structures were elucidated on the basis of spectroscopic data and chemical transformation. 1 and 3 significantly exhibited the inhibitory activity against foam cell formation in human macrophages, one of characteristic features of early atherosclerotic lesions.

The first asymmetric total synthesis of lycoposerramine-R

The first asymmetric total synthesis of lycoposerramine-R was accomplished by a strategy featuring the stereoselective intramolecular aldol cyclization giving a cis-fused 5/6 bicyclic skeleton and a new method for the construction of the pyridone ring via the aza-Wittig reaction, thereby establishing the absolute configuration of the natural product.

Total Syntheses of Lyconadins: Finding Efficiency and Diversity

Lyconadins A-C are important members of the Lycopodium alkaloid family with challenging structural features and interesting biological profile. Herein, various synthetic strategies and methods for their preparation are summarized with the focus on constructive bond formation and our efficient and divergent synthesis based on functional group pairing (FGP) strategy.

Cooperative activation of cyclobutanones and olefins leads to bridged ring systems by a catalytic [4 + 2] coupling

Bridged-ring systems are widely found in natural products and successful syntheses of them frequently feature intramolecular Diels-Alder (IMDA) reactions. These reactions are subclassified as either type I or type II IMDAs depending on how the diene motif is tethered to the rest of the substrate - type I are tethered at the 1-position of the diene and type II at the 2-position. While the type I IMDA has been used to great success, the molecular scaffolds accessible by type II IMDAs are limited by the strain inherent in the formation of a sp²-carbon at a bridgehead position. Here, we describe a complementary approach that provides access to these structures through the C−C activation of cyclobutanones and their coupling with olefins. Various alkenes have been coupled with cyclobutanones to provide a range of bridged skeletons. The ketone group of the products serves as a convenient handle for downstream functionalization.

Divergent total syntheses of lyconadins A and C

Divergent and concise total syntheses of two lycopodium alkaloids, lyconadins A and C have been developed. The synthesis of lyconadin A, having potent neurotrophic activity, features an efficient one-pot ketal removal and formal aza-[4+2] cyclization to form the cagelike core structure. A tandem ketal removal/Mannich reaction was developed to build the tricyclic structure of lyconadin C. Both lyconadins A and C were synthesized from a pivotal intermediate.