An experimental and computational study of new spiro-barbituric acid pyrazoline scaffolds: restricted rotation vs. annular tautomerism

A regioselective [3+2] cycloaddition (32CA) reaction to synthesize unsymmetric spiro-barbituric pyrazolines containing a chromone or phenolic pyrazole moiety was achieved, providing good to excellent yields.

Multimolecular Self-Organization of 1-Acetyl-1,3-bis(haloarylamines) in KOH/DMSO System: From Acetylene Gas and o-Halo Arylamines toward a Higher Molecular Complexity and Diversity

An unprecedented self-organization of three molecules of acetylene, two molecules of o-halo arylamine, and one molecule of water to 1-acetyl-1,3-bis(haloarylamines) in the KOH/DMSO system has been discovered. These high-value 1,3-bis(arylamines) are capable of acting as efficient "platform molecules" to provide one-pot access to hexahydropyrrolo[3,2-b]indoles, 3-haloarylamino-pyrrolidines, benzyliden piperidinols, and other functionalized diamines.

Synthetic strategies for pyrrolo[2,1-f][1,2,4]triazine: the parent moiety of antiviral drug remdesivir

This review summarizes diverse synthetic protocols for the preparation of pyrrolo[2,1-f][1,2,4]triazine derivatives, covering literature sources from the past two decades. For effective representation, the synthetic methods toward the title compound are classified into six distinct categories: 1) synthesis from pyrrole derivatives, 2) synthesis via bromohydrazone, 3) synthesis via formation of triazinium dicyanomethylide, 4) multistep synthesis, 5) transition metal mediated synthesis, and 6) rearrangement of pyrrolooxadiazines. A brief outline of all optimized schemes is provided with relevant examples.

Oxaazabicyclooctene Oxides, Another Type of Bridgehead Nitrones: Diastereoselective Assembly from Acetylene Gas, Ketones, and Hydroxyl Amine

Unique bridgehead nitrones, 8-oxa-6-azabicyclo[3.2.1]oct-6-ene 6-oxides, have been assembled diastereoselectively via acetyldihydropyrans, products of one-pot self-organization of two molecules of ketones and two molecules of acetylene, which after oximation undergo acid-catalyzed ring closure. The proposed mechanism includes the enol double-bond protonation, followed by intramolecular cyclization involving the interaction of the carbocation formed with a nitrogen atom. A broad range of substrates tolerate this facile transformation, in which the bridgehead nitrones were isolated in high yields.

Acetylene-based two-step diastereoselective synthesis of bridgehead dihydro-oxadiazines using ketones and hydrazine as the only reactants

Bridgehead dihydro-1,3,4-oxadiazines are synthesized by the acid-catalyzed diastereoselective reaction of hydrazine with 6,8-dioxabicyclo[3.2.1]octanes, the products of the superbase-promoted self-organization of acetylene with ketones.

A unified synthesis of topologically diverse Aspidosperma alkaloids through divergent iminium-trapping

Aspidospermidine, vincadifformine, 1,2-dehydroaspidospermidine, goniomitine, and quebrachamine, five Aspidosperma alkaloids distributed within three structurally diverse topologies, were synthesized from a single molecular scaffold, namely indole-valerolactam 6. This common intermediate can be divergently manipulated, through the incorporation of conformational and electronic constraints that influence the chemo-selectivity of the iminium ion derived therefrom, between three different reaction paths: N(1) vs. C(3) cyclization (indole numbering) vs. over-reduction. Moreover, a catalytic carbene insertion for direct C(3)-H indole functionalization is reported for the first time in an approach to goniomitine (4), and a following tandem ester reduction/iminium generation/cyclization secured its tetracyclic system. The development of a highly diastereoselective one-pot hemi-reduction/cyclization/deprotection process to obtain a cis-pyridocarbazole directly allowed the synthesis of pentacyclic Aspidosperma alkaloids 1, 2, and 3.

Visible-Light-Induced External Radical-Triggered Annulation To Access CF2-Containing Benzoxepine Derivatives

A facile and diversified synthesis of functionalized CF₂-containing benzoxepine derivatives via photoredox catalysis was achieved in this work. This novel protocol features broad substrate scope, mild reaction conditions, operational simplicity, easy scale-up, and versatile derivatization, which would facilitate its practical and broad applications in the construction of valuable and synthetically challenging heterocycles.

Michael addition at neutral pH: a facile synthesis of 1,3-dinitroalkanes

Base-catalyzed Michael addition of nitroalkane to conjugated nitroalkene suffers serious practical difficulties due to the formation of oligomeric byproduct. Given its importance for synthesis of pharmacologically relevant organic compounds, a scalable synthesis of 1,3-dinitroalkane is developed by addition of nitroalkane to nitroalkene in aqueous phosphate buffer at pH 7.0 with no added traditional base catalyst.

Decorated Cyclopentadienes from Acetylene and Ketones in Just Two Steps

The products of the one-pot assembly of acetylene and ketones in the KOH/DMSO system, 7-methylene-6,8-dioxabicyclo[3.2.1]octanes, undergo an acid-catalyzed (CF₃COOH, room temperature) rearrangement to rarely substituted cyclopentadienes in good-to-excellent yields. The mechanism of the rearrangement has been supported by the isolation and corresponding transformations of two intermediates.

Selective syntheses of diversely substituted 2-hydroxy-4′-hydroxybenzophenones through [4 + 2] or [3 + 3] annulation of penta-3,4-dien-2-ones with 3-formylchromones

A selective synthesis of 2-hydroxy-4′-hydroxybenzophenones or their 3′-acylated counterparts via the cascade reactions of 3-formylchromones with diversely substituted penta-3,4-dien-2-ones is presented.

One-pot transition-metal-free cascade synthesis of thieno[2,3-c]coumarins from chromones

A one-pot transition-metal-free, base-mediated synthesis of a novel series of functionalized thieno[2,3-c]coumarins has been developed through a cascade reaction from chromones.

PPL catalyzed four-component PASE synthesis of 5-monosubstituted barbiturates: Structure and pharmacological properties

Enzymatic four-component reactions are very rare although three-component enzymatic promiscuous reactions are widely reported. Herein, we report an efficient PASE protocol for the synthesis of potentially lipophilic zwitterionic 5-monosubstituted barbiturates by four component reaction of mixture of ethyl acetoacetate, hydrazine hydrate, aldehyde and barbituric acid in ethanol at room temperature. Seven different lipases were screened for their promiscuous activity towards the synthesis of 5-monosubstituted barbiturates and the lipase from porcine pancreas (PPL) found to give optimum efficiency. The zwitterionic 5-monosubstituted barbiturates with pyrazolyl ring showed promising pharmacological activity upon screening for antibacterial and apoptotic properties.

Rapid access to α-carbolines via a one-pot tandem reaction of α,β-unsaturated ketones with 2-nitrophenylacetonitrile and the anti-proliferative activities of the products

An effective and convenient method has been developed for the preparation of 2 or 2,4-substituted α-carbolines via a one-pot tandem reaction of α,β-unsaturated ketones with 2-nitrophenylacetonitrile in the presence of zinc dust, acetic acid and triethylamine. This protocol presents a simple, rapid and pot/step economical strategy for preparing biologically interesting α-carbolines with moderate anti-tumor activities.