Hypervalent Iodine Reagent-Promoted Hofmann-Type Rearrangement/Carboxylation of Primary Amides

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.

Reactivity, Pathways, and Iodinated Disinfection Byproduct Formation during Chlorination of Iodotyrosines Derived from Edible Seaweed

Iodine derived from edible seaweed significantly enhances the formation of iodinated disinfection byproducts (I-DBPs) during household cooking. Reactions of chlorine with monoiodotyrosine (MIT) and diiodotyrosine (DIT) derived from seaweed were investigated. Species-specific second-order rate constants (25 °C) for the reaction of hypochlorous acid with neutral and anionic MIT were calculated to be 23.87 ± 5.01 and 634.65 ± 75.70 M-1 s-1, respectively, while the corresponding rate constants for that with neutral and anionic DIT were determined to be 12.51 ± 19.67 and 199.12 ± 8.64 M-1 s-1, respectively. Increasing temperature facilitated the reaction of chlorine with MIT and DIT. Based on the identification of 59 transformation products/DBPs from iodotyrosines by HPLC/Q-Orbitrap HRMS, three dominant reaction pathways were proposed. Thermodynamic results of computational modeling using density functional theory revealed that halogen exchange reaction follows a stepwise addition-elimination pathway. Among these DBPs, 3,5-diiodo-4-hydroxy-benzaldehyde and 3,5-diiodo-4-hydroxy-benzacetonitrle exhibited high toxic risk. During chlorination of MIT and DIT, iodinated trihalomethanes and haloacetic acids became dominant species at common cooking temperature (80 °C). These results provide insight into the mechanisms of halogen exchange reaction and imply important implications for the toxic risk associated with the exposure of I-DBPs from household cooking with iodine-containing food.

Metal-Free Synthesis of Pharmaceutically Relevant Sulfonylureas via Direct Reaction of Sulfonamides with Amides

A metal-free process has been developed for the sustainable synthesis of medicinally important sulfonylureas in one pot via the direct reaction of sulfonamides with amides in green solvent (DMC). The reaction proceeded efficiently at room temperature, and the products were obtained in good to excellent yields. The use of readily accessible, inexpensive, and environmentally benign starting materials and reagents, metal-free mild reaction conditions, wide substrate scope, tolerance to air and moisture, operational simplicity, and good atom economy are the salient features of this reaction protocol. Gram-scale synthesis of antidiabetic drugs tolbutamide and chlorpropamide in excellent yields further revealed the practical utility of this procedure. Additionally, the synthetic value of this straightforward method is showcased by the late-stage modification of drug molecules, including drug-drug conjugation with good yields. Preliminary mechanistic studies indicated the in situ generation of an isocyanate intermediate, which further reacts with sulfonamide to form sulfonylurea. As compared to other related methods reported for sulfonylurea synthesis, the current method obviates the requirement of traditional multistep protocols involving isolation of hazardous isocyanates and avoids the use of toxic phosgene.

Electrooxidative Hofmann Rearrangement of Phthalimides to Access Anthranilate Derivatives

A simple and efficient electrooxidative Hofmann rearrangement reaction of phthalimides was developed. Anthranilate derivatives were synthesized in moderate to good yields under green and mild conditions using phthalimides as a rearrangement precursor. This approach not only provides a strategy for synthesizing anthranilates and deuterated anthranilate derivatives with high deuteration efficiency but also realizes efficient conversion at the gram scale. A possible reaction mechanism is proposed.

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.

PIFA-Mediated Tandem Hofmann-Type Rearrangement and Cyclization Reaction of α-Acyl-β-aminoacrylamides: Access to Polysubstituted Oxazol-2(3H)-ones

An efficient and straightforward synthesis of polysubstituted oxazol-2(3H)-ones has been developed via a tandem Hofmann-type rearrangement and cyclization reaction of various α-acyl-β-aminoacrylamides mediated by phenyl iodine(III) bis(trifluoroacetate) (PIFA) in the presence of trifloroacetic acid (TFA). This novel protocol features readily available starting materials, mild reaction conditions, simple execution, high chemoselectivity, good functional group tolerance, and a metal-free oxidation process.

Direct C-H aminocarbonylation of N-heteroarenes with isocyanides under transition metal-free conditions

A C-C bond forming amide synthesis through direct C-H aminocarbonylation of N-heteroarenes with isocyanides was developed. The reaction was mediated by an inorganic persulfate salt under transition metal-free conditions. Mechanistic studies suggested a radical pathway for this reaction without the participation of H₂O and O₂. This method also showed merits of substrate availability, easy operation and atom economy. It provided an efficient route for straightforward synthesis of N-heteroaryl amides.

Synthesis of unsymmetrical urea from aryl- or pyridyl carboxamides and aminopyridines using PhI(OAc)2via in situ formation of aryl- or pyridyl isocyanates

The synthesis of unsymmetrical ureas (N-aryl-N′-pyridylurea and N,N′-bipyridylurea) from aryl- or pyridyl carboxamides and aminopyridines in the presence of PhI(OAc)2 has been reported. The formation of pyridylisocyanates from their corresponding carboxamides via Hofmann rearrangement is confirmed.

Iodine-mediated 1,2-aryl migration of primary benzhydryl amines

This iodine-mediated 1,2-aryl migration reaction of primary amines is transition-metal-free and operationally simple, and can be conducted on a gram scale.