Single-Step Synthesis of Iodinated Oxazoles from N-Propargyl Amides Mediated by I2/Iodosylbenzene/Trimethylsilyl Trifluoromethanesulfonate Systems

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Are Terminal Alkynes Necessary for MAO-A/MAO-B Inhibition? A New Scaffold Is Revealed

A versatile family of quaternary propargylamines was synthesized employing the KA2 multicomponent reaction, through the single-step coupling of a number of amines, ketones, and terminal alkynes. Sustainable synthetic procedures using transition metal catalysts were employed in all cases. The inhibitory activity of these molecules was evaluated against human monoaminoxidase (hMAO)-A and hMAO-B enzymes and was found to be significant. The IC50 values for hMAO-B range from 152.1 to 164.7 nM while the IC50 values for hMAO-A range from 765.6 to 861.6 nM. Furthermore, these compounds comply with Lipinski's rule of five and exhibit no predicted toxicity. To understand their binding properties with the two target enzymes, key interactions were studied using molecular docking, all-atom molecular dynamics (MD) simulations, and MM/GBSA binding free energy calculations. Overall, herein, the reported family of propargylamines exhibits promise as potential treatments for neurodegenerative disorders, such as Parkinson's disease. Interestingly, this is the first time a propargylamine scaffold bearing an internal alkyne has been reported to show activity against monoaminoxidases.

Synthesis and Antiproliferative Evaluation of d-Glucuronamide-Based Nucleosides and (Triazolyl)methyl Amide-Linked Pseudodisaccharide Nucleosides

The synthesis and antiproliferative evaluation of novel d-glucopyranuronamide-containing nucleosides is described. Based on our previously reported anticancer d-glucuronamide-based nucleosides, new analogues comprising N/O-dodecyl or N-propargyl substituents at the glucuronamide unit and anomerically-N-linked 2-acetamido-6-chloropurine, 6-chloropurine or 4-(6-chloropurinyl)methyl triazole motifs were synthesized in 4-6 steps starting from acetonide-protected glucofuranurono-6,3-lactone. The methodologies were based on the access to N-substituted glycopyranuronamide precursors, namely 1,2-O-acetyl derivatives or glucuronoamidyl azides for further nucleobase N-glycosylation or 1,3-dipolar cycloaddition with N9 - and N7 -propargyl-6-chloropurines, respectively. N-Propargyl glucuronamide-based N9 -purine nucleosides were converted into (triazolyl)methyl amide-6,6-linked pseudodisaccharide nucleosides via cycloaddition with methyl 6-azido-glucopyranoside. A CuI/Amberlyst A-21 catalytic system employed in the cycloaddition reactions also effected conversion into 6-dimethylaminopurine nucleosides. Antiproliferative evaluation in chronic myeloid leukemia (K562) and breast cancer (MCF-7) cells revealed significant effects exhibited by the synthesized monododecylated purine-containing nucleosides. A N-propargyl 3-O-dodecyl glucuronamide derivative comprising a N9 -β-linked 6-chloropurine moiety was the most active compound against MCF-7 cells (GI50 =11.9 μM) while a related α-(purinyl)methyltriazole nucleoside comprising a N7 -linked 6-chloropurine moiety exhibited the highest activity against K562 cells (GI50 =8.0 μM). Flow cytometry and immunoblotting analysis of apoptosis-related proteins in K562 cells treated with the N-propargyl 3-O-dodecyl glucuronamide-based N9 -linked 6-chloropurine nucleoside indicated that it acts via apoptosis induction.

N-Iodosuccinimide-Mediated Synthesis of Benzo-Fused Bisimidazoles Enabled by a One-Pot Tandem Reaction of Fluorinated Propargyl Amidines

A N-iodosuccinimide (NIS)-mediated divergent and efficient tandem reaction between fluorinated propargyl amidines and aromatic o-diamines without any metal catalyst and additive under mild reaction conditions was developed for the synthesis of benzo-fused bisimidazoles in moderate to excellent yields. Preliminary mechanistic studies suggested that this reaction proceeded by an intermediate of secondary amine derived from 5-iodomethyl imidazole, and NIS played another role of oxidation reagent to promote the formation of a benzimidazole motif.

Iodine-Promoted Oxidative Cyclization of Methyl Azaarenes and α-Amino Ketones for One-Pot Synthesis of 2-Azaaryl-5-aryl Oxazoles

A high efficiency protocol was developed for the synthesis of 2,5-disubstituted oxazoles via iodine-promoted oxidative domino cyclization. These reactions were performed with readily available methyl azaarenes and α-amino ketones under metal-free conditions. This protocol is a simple method with high functional group compatibility, a wide range of substrates, and excellent yield, providing a new way to synthesize azaarene-attached oxazoles.

Zn(OTf)2-Promoted Isocyanide-Based Three-Component Reaction: Direct Access to 2-Oxazolines and β-Amino Amides

An efficient one-pot reaction of propargylamides, isocyanides, and water catalyzed by zinc was developed for the rapid construction of 2-oxazolines with a wide functional group tolerance. The methylene-3-oxazoline was proven to play a vitally important role to start the tandem cascade transformation through unfunctionalized alkynes with sequential nucleophilic addition approaches of isocyanide and water. Notably, with a slight alteration of the reaction temperature and the addition of one molecule of water, various β-amino amide derivatives were synthesized in good to excellent yields.

Iron-Catalyzed Cycloaddition of Amides and 2,3-Diaryl-2H-azirines To Access Oxazoles via C-N Bond Cleavage

A novel and efficient iron-catalyzed cycloaddition reaction using readily available 2,3-diaryl-2H-azirines and primary amides is reported. A wide range of trisubstituted oxazoles could be achieved in good yields with good functional group compatibility. In this transformation, two C-N bonds were cleaed and new C-N and C-O bonds were formed.

InCl3-catalyzed 5-exo-dig cyclization/1,6-conjugate addition of N-propargylamides with p-QMs to construct oxazole derivatives

An InCl₃-catalyzed tandem intramolecular 5-exo-dig cyclization/1,6-conjugate addition/aromatization of N-propargylamides with p-QMs to produce oxazoles tethering diarylmethane has been successfully developed.

Silyl Group-Directed 6-exo-dig Iodocyclization of Homopropargylic Carbamates and Amides

Iodocyclization of silyl group-substituted homopropargylic carbamates and amides proceeded via 6-exo-dig mode to afford 6-vinylene-4,5-dihydro-1,3-oxazines in moderate to quantitative yields. This is the first report for silyl group-solely directed iodocyclization of alkynes utilizing the β-silyl effect. Under these mild reaction conditions, various functionalities such as secondary alcohol, acetal, urea, and sulfide were tolerated.

Efficient Synthesis of the N-(buta-2,3-dienyl)carboxamide of Isopimaric Acid and the Potential of This Compound towards Heterocyclic Derivatives of Diterpenoids

The N‐(2,3‐butadienyl)carboxamide of isopimaric acid, that is, compound 3, was prepared through a two‐step synthetic procedure starting from the natural diterpene isopimaric acid. The Pd‐catalyzed cross‐coupling and subsequent cyclization of terpenoid allene 3 with several aryl iodides and aryl bromides gave access to optically active diterpenoid–oxazoline derivatives in good to excellent yields. The functional group tolerance in the aryl iodides was demonstrated by several examples, including substrates with additional N‐tert‐butoxycarbonyl‐protected amino, hydroxy, and carboxy substituents in the ortho position. The cross‐coupling–cyclization reaction of those compounds with allene 3 proceeded selectively with the formation of cyclization products on the substituent in the aromatic ring. This transformation opens a potential route to the synthesis of hybrid compounds containing a tricyclic diterpenoid and several heterocycles.

Preparation of oxazolines and oxazoles via a PhI(OAc)2-promoted cyclization of N-propargylamides

A metal-free cyclization of N-propargylamides for the synthesis of various oxazolines and oxazoles via a 5-exo-dig process is presented. Using (diacetoxyiodo)benzene (PIDA) as a reaction promoter and lithium iodide (LiI) as an iodine source, intramolecular iodooxygenation of N-propargylamides proceeded readily, leading to the corresponding (E)-5-iodomethylene-2-oxazolines in good to excellent isolated yields. In addition, using the PhI(OAc)2/LiI system, N-propargylamides can be converted to the corresponding oxazole-5-carbaldehydes in the presence of oxygen under visible light irradiation. The resulting products can be further converted into various oxazoline and oxazole derivatives after simple derivatizations, and this method ultimately offers an efficient route to a variety of biologically active structures.

Metal-free iodine(iii)-promoted synthesis of 2,5-diaryloxazoles

A nonmetal-catalyzed oxidative cyclization to achieve 2,5-disubstituted oxazoles from inexpensive and readily available substituted chalcone, (diacetoxyiodo)benzene (PIDA) and ammonium acetate (NH4OAc) at room temperature is described. The reaction forms a variety of 2,5-diaryloxazoles in good to excellent yields with broad substrate scope under mild conditions without the requirement of ligands and additional bases.

Elemental tellurium mediated synthesis of 2-(trifluoromethyl)oxazoles using trifluoroacetic anhydride as reagent

An elemental tellurium mediated synthesis of 2-(trifluoromethyl)oxazoles from the reaction of acetophenone oxime acetates with trifluoroacetic anhydride is described.

Synthesis of 2,5-disubstituted oxazoles via cobalt(iii)-catalyzed cross-coupling of N-pivaloyloxyamides and alkynes

An efficient synthesis of 2,5-disubstituted oxazoles via cobalt(iii)-catalyzed cross-coupling of N-pivaloyloxyamides and alkynes is described herein.