Fast construction of isoquinolin-1(2H)-ones by direct intramolecular C-H/N-H functionalization under metal-free conditions

Alkynyl hydroxylamines: key precursors for 1,2-N/O heterocycles

1,2-N/O Heterocycles are privileged scaffolds found in numerous natural products and have been shown to exhibit diverse pharmacological properties. Additionally, these compounds have emerged as important synthons in organic chemistry. Recent years have witnessed immense interest in these heterocycles from both the medicinal and the synthetic chemistry community. In light of the ever-increasing demand for isoxazolidine, isoxazoline, isoxazole, 1,2-oxazinane, 1,2-oxazine and 1,2-oxazepine in drug discovery, this review highlights an overview of recent methods (up to 2024) for the synthesis of these heterocycles starting from alkynyl hydroxylamines. The mechanistic pathways and stereo-electronic factors affecting yield and selectivity of the products are briefly explained to generate the understanding needed for future developments in this domain.

Iodine(III)-Mediated Keto-oximation of O-Alkynyl Hydroxylamines: A Route to 3-Acyl Isoxazolines and 1,2-Oxazines

An intramolecular iodine(III)-mediated keto-oximation of O-alkynyl hydroxylamines offers rapid and straightforward access to 3-acyl Δ2-isoxazolines and 1,2-oxazines. This approach features mild, metal-free, and aerobic reaction conditions with good functional group tolerance. Moreover, the synthetic utility of this method is demonstrated by the synthesis of unique structural motifs such as isoxazolidine, 3-vinyl isoxazoline, and 2,5-diphenylpyrazine derivatives by the conversion of 3-acyl Δ2-isoxazolines, thereby showcasing its efficiency and applicability in synthetic chemistry.

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.

Solvent-dependent chemoselective synthesis of different isoquinolinones mediated by the hypervalent iodine(III) reagent PISA

Isoquinolinone is an important heterocyclic framework in natural products and biologically active molecules, and the efficient synthesis of this structural motif has received much attention in recent years. Herein, we report a (phenyliodonio)sulfamate (PISA)-mediated, solvent-dependent synthesis of different isoquinolinone derivatives. The method provides highly chemoselective access to 3- or 4-substituted isoquinolinone derivatives by reacting o-alkenylbenzamide derivatives with PISA in either acetonitrile or wet hexafluoro-2-isopropanol.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Synthesis of acyloxy-2H-azirine and sulfonyloxy-2H-azirine derivatives via a one-pot reaction of β-enamino esters, PIDA and carboxylic acid or sulfonic acid

PIDA mediated oxidative acyloxylation/azirination and sulfonyloxylation/azirination of β-enamino esters were investigated. A series of functionalized acyloxy-2H-azirine and sulfonyloxy-2H-azirine derivatives was synthesized in moderate to good yields. This represents the first oxidative sulfonyloxylation/azirination of β-enamino esters with PIDA and sulfonic acid for access to sulfonyloxy-2H-azirine. Hypervalent iodine reagents enable cascade C-O/C-N bond formation. Furthermore, a possible reaction pathway was proposed based on the experimental results.