A Telescoped Route to 2,6-Disubstituted 2,3,4,5-Tetrahydropyridines and 2,6-syn-Disubstituted Piperidines: Total Synthesis of (−)-Grandisine G

Crystal structure and Hirshfeld surface analysis of (E)-1-(2,4-di-methyl-furan-3-yl)-3-phenyl-prop-2-en-1-one

The title compound, C15H14O2, adopts an E configuration about the C=C double bond. The furan ring is inclined to the phenyl ring by 12.03 (9)°. In the crystal, pairs of mol-ecules are linked by C-H⋯O hydrogen bonds, forming dimers with R 2 2(14) ring motifs. The mol-ecules are connected via C-H⋯π inter-actions, forming a three dimensional network. No π-π inter-actions are observed.

Formal Fluorinative Ring Opening of 2-Benzoylpyrrolidines Utilizing [1,2]-Phospha-Brook Rearrangement for Synthesis of 2-Aryl-3-fluoropiperidines

A ring expansion of 2-benzoylpyrrolidines, which involves the formal fluorinative ring opening utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis and a subsequent intramolecular reductive amination, was developed. The operationally simple three-step protocol provides an efficient access to 2-aryl-3-fluoropiperidines. The methodology was further applied to the syntheses of azepanes and tetrahydroquinolines.

Diversity-Oriented Synthesis of Thiazolidine-2-imines via Microwave-Assisted One-Pot, Telescopic Approach and Its Interaction with Biomacromolecules

In this work, a one-pot, telescopic approach is described for the combinatorial library of thiazolidine-2-imines. The synthetic manipulation proceeds smoothly via the reaction of 2-aminopyridine/pyrazine/pyrimidine with substituted isothiocyanates followed by base catalyzed ring closure with 1,2-dibromoethane to obtain thiazolidine-2-imines with broad substrate scope and high functional group tolerance. The synthetic strategy merges well with the thiourea formation followed by base catalyzed ring closure reaction for the thiazolidine-2-imine synthesis in a more modular and straightforward approach. The synthetic procedure reported herein represents a cleaner route toward thiazolidine-2-imines as compared to traditional methodologies. Moreover, the biological significance of combinatorially synthesized thiazolidin-2-imines has been investigated for their use as possible inhibitors for acetyl cholinesterase through molecular docking studies.

Stereoselective synthesis of 2,6-disubstituted piperidine alkaloids

Among the large number of structurally diverse alkaloids, 2,6-disubstituted piperidine and its analogs have often been targeted when exploiting new synthetic techniques perhaps because of their strong pharmacological properties. This review outlines synthetic strategies to build the 2,6-disubstituted piperidine structural motif with a focus on stereochemical control of two substituents at C2 and C6. The key reactions in this process are then classified on the basis of how the piperidine rings were built with specific examples of natural products that control the stereochemical outcomes and their transition states.

Crystal structure and Hirshfeld surface analysis of 6-benzoyl-3,5-di-phenyl-cyclo-hex-2-en-1-one

In the title compound, C25H20O2, the central cyclo-hexenone ring adopts an envelope conformation. The mean plane of the cyclo-hexenone ring makes dihedral angles of 87.66 (11) and 23.76 (12)°, respectively, with the two attached phenyl rings, while it is inclined by 69.55 (11)° to the phenyl ring of the benzoyl group. In the crystal, the mol-ecules are linked by C-H⋯O and C-H⋯π inter-actions, forming a three-dimensional network.

Physically mixed catalytic system of amino and sulfo-functional porous organic polymers as efficiently synergistic co-catalysts for one-pot cascade reactions

Acid/base bi-functional polymeric materials were prepared using physically mixed porous polymers P(DVB-VBS) with sulfonic acid and P(DVB-VBA) with amino groups for various cascade reactions.

Regio- and Diastereoselective Cross-Dehydrogenative Coupling of Tetrahydropyridines with 1,3-Dicarbonyl Compounds

A regio- and diastereoselective cross-dehydrogenative coupling of N-carbamoyl tetrahydropyridines with a variety of 1,3-dicarbonyl compounds is described. The method exhibits good functional group tolerance, diastereoselectively generating cis-2,6- or cis-2,4-substituted tetrahydropyridines by using different types of 1,3-dicarbonyls. Moreover, a two-step sequence involving diastereoselective cross-dehydrogenative coupling followed by epimerization was also developed, allowing facile access to trans-2,6-substituted tetrahydropyridines as single isomers. Applications in natural product synthesis and divergent analogue preparation were further demonstrated.

Stereoselective strategies for the construction of polysubstituted piperidinic compounds and their applications in natural products’ synthesis

An abridged and far-reaching review communication on the construction of the polysubstituted piperidinic core using diverse methodologies for the benefit of organic chemists interested in the total synthesis of biologically active compounds.

Diastereoselectively Complementary C-H Functionalization Enables Access to Structurally and Stereochemically Diverse 2,6-Substituted Piperidines

The preparation of 2,6-substituted piperidine derivatives through diastereoselective C-H functionalization of corresponding nitrogen heterocycles represents an appealing protocol and yet remains a formidable challenge. Here, we describe a stereochemically complementary oxidative C-H functionalization of N-carbamoyl tetrahydropyridines with a wide variety of building blocks, providing either the cis- or trans-2,6-substituted piperidines with diverse patterns of functionalities. The mild metal-free process exhibits excellent regio- and diastereoselectivities as well as functional group tolerance. The synthetic utilities in natural product and analogue syntheses are also described.

Telescoped Synthesis of 2-Acyl-1-aryl-1,2-dihydroisoquinolines and Their Inhibition of the Transcription Factor NF-κB

A sequential single-flask multicomponent reactions is highly effective for the synthesis of 1,2-dihydroisoquinolines through amidealkylation from intermediate N-acylisoquinolinium salts under mild conditions. N-Acylisoquinolinium ions and trichloromethyl-1-(1H-indol-3-yl)isoquinoline-2(1H)-carboxylate have demonstrated their reactivity toward aromatic and aliphatic π-nucleophiles. One of the 1,2-dihydroisoquinoline derivatives was found to be a potent inhibitor for transcription factor NF-κB by blocking IκBα degradation, p65 nuclear translocation, and NF-κB DNA binding in TNF-α-induced NIH 3T3 cells.

Synthesis of Enantiopure 3-Hydroxypiperidines from Sulfinyl Dienyl Amines by Diastereoselective Intramolecular Cyclization and [2,3]-Sigmatropic Rearrangement

The highly diastereoselective base-promoted intramolecular cyclization of a variety of enantiopure sulfinyl dienyl amines provides novel sulfinyl tetrahydropyridines that are readily converted to 3-hydroxy tetrahydropyridines via sigmatropic rearrangement. The influence of N- and C- substituents on the process has been studied. Procedures to shorten the sequence such as the tandem cyclization followed by [2,3]-sigmatropic rearrangement, as well as cyclization of the free amine, under Boc- or ArSO- deprotection conditions have been examined. Good to excellent levels of selectivity are generally observed for the reported transformations (dr: 75/25 to >98/2). A novel protocol to access substituted amino dienyl sulfoxides is also reported.

Simple Indolizidine and Quinolizidine Alkaloids

This review of simple indolizidine and quinolizidine alkaloids (i.e., those in which the parent bicyclic systems are in general not embedded in polycyclic arrays) is an update of the previous coverage in Volume 55 of this series (2001). The present survey covers the literature from mid-1999 to the end of 2013; and in addition to aspects of the isolation, characterization, and biological activity of the alkaloids, much emphasis is placed on their total synthesis. A brief introduction to the topic is followed by an overview of relevant alkaloids from fungal and microbial sources, among them slaframine, cyclizidine, Steptomyces metabolites, and the pantocins. The important iminosugar alkaloids lentiginosine, steviamine, swainsonine, castanospermine, and related hydroxyindolizidines are dealt with in the subsequent section. The fourth and fifth sections cover metabolites from terrestrial plants. Pertinent plant alkaloids bearing alkyl, functionalized alkyl or alkenyl substituents include dendroprimine, anibamine, simple alkaloids belonging to the genera Prosopis, Elaeocarpus, Lycopodium, and Poranthera, and bicyclic alkaloids of the lupin family. Plant alkaloids bearing aryl or heteroaryl substituents include ipalbidine and analogs, secophenanthroindolizidine and secophenanthroquinolizidine alkaloids (among them septicine, julandine, and analogs), ficuseptine, lasubines, and other simple quinolizidines of the Lythraceae, the simple furyl-substituted Nuphar alkaloids, and a mixed quinolizidine-quinazoline alkaloid. The penultimate section of the review deals with the sizable group of simple indolizidine and quinolizidine alkaloids isolated from, or detected in, ants, mites, and terrestrial amphibians, and includes an overview of the "dietary hypothesis" for the origin of the amphibian metabolites. The final section surveys relevant alkaloids from marine sources, and includes clathryimines and analogs, stellettamides, the clavepictines and pictamine, and bis(quinolizidine) alkaloids.

One-pot, two-step synthesis of imidazo[1,2-a]benzimidazoles via a multicomponent [4 + 1] cycloaddition reaction

A one-pot, two-step synthesis of imidazo[1,2-a]benzimidazoles has been achieved by a three-component reaction of 2-aminobenzimidazoles with an aromatic aldehyde and an isocyanide. The reaction involving condensation of 2-aminobenzimidazole with an aldehyde is run under microwave activation to generate an imine intermediate under basic conditions which then undergoes [4 + 1] cycloaddition with an isocyanide.