Diamination/Oxidative Cross-Coupling/Bicyclization of Anilines and Methyl Ketones: Direct I2-Promoted Synthesis of 1,2-Fused Oxindoles

One Stone, Three Birds: One-Pot Synthesis of Pyrido[3,2-a]phenoxazin-5-one Derivatives from o-Aminophenols with Triple Roles, Paraformaldehyde, and Enaminones via the Povarov Reaction

A novel multicomponent cascade cyclization reaction in one pot for the preparation of pyrido[3,2-a]phenoxazin-5-ones from simple o-aminophenols, paraformaldehyde, and enaminones has been established. It is noteworthy that o-aminophenol plays multiple roles serving as both a bis-nucleophile and an iminoquinone precursor, which can in situ generate aminophenoxazinones to undergo the Povarov reaction for the first time to yield pyrido[3,2-a]phenoxazin-5-ones with a high efficiency. Moreover, the photoluminescence of pyrido[3,2-a]phenoxazin-5-ones has polarity sensitivity and features aggregation-induced emission (AIE) characteristics, which is promising for bioimaging and theranostic applications.

Iodine-Mediated Oxidative Annulation of β,γ-Unsaturated Hydrazones in Dimethyl Sulfoxide: A Strategy to Build 1,6-Dihydropyridazines and Pyrroles

Simple, commercially available iodine was successfully employed as a highly efficient and chemoselective catalyst for the oxidative annulation of β,γ-unsaturated hydrazones to produce 1,6-dihydropyridazines under mild conditions for the first time. Interestingly, when active β,γ-unsaturated hydrazone compounds containing electron-donating groups, such as furyl, thienyl, and cycloalkyl, were used, pyrroles were obtained. A gram-scale preparation experiment and further derivatization of pyridazines demonstrated the potential applicability of our synthesis method. Experimental studies and density functional theory calculations unveiled the origin of the chemoselectivity determining the formation of different products.

Recent Advances of Green Catalytic System I2/DMSO in C–C and C–Heteroatom Bonds Formation

Developing a green, practical and efficient method for the formation of C–C and C–Heteroatom bonds is an important topic in modern organic synthetic chemistry. In recent years, the I2/DMSO catalytic system has attracted wide attention because of its green, high efficiency, atomic economy, low cost, mild reaction conditions and it is environment-friendly, which is more in line with the requirements of sustainable chemistry. Heteroatom-containing compounds have shown lots of important applications in pharmaceutical synthesis, agrochemicals, material chemistry and organic dyes. At present, the I2/DMSO catalytic system has been successfully applied to the synthesis of various heteroatom-containing compounds. The C–C and C–Heteroatom bonds have been formed efficiently, which has been proved to be a green and mild catalytic system. In this review, the research achievements of the I2/DMSO catalytic system in the formation of C–C and C–Heteroatom bonds from 2015 to date are described, and the research area is prospected. This review attempts to reveal the general law of iodine catalysis and lay a foundation for the design of new reactions.

2,4-Diamino-5-(nitromethyl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile

Dimethyl sulfoxide (DMSO) is a cheap polar aprotic solvent used in organic synthesis and in pharmacology because of its low cost, high stability, and non-toxicity. Multicomponent reactions (MCRs) are highly convergent processes and have good atom, step, and pot economies. In this communication, the multicomponent transformation of salicylaldehyde, malononitrile dimer, and nitromethane in DMSO at room temperature was investigated to give 2,4-diamino-5-(nitromethyl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile in good yield. The structure of the earlier unknown compound was confirmed by means of elemental analysis, mass-, nuclear magnetic resonance, and infrared spectroscopy.

Iodine-DMSO mediated conversion of N-arylcyanothioformamides to N-arylcyanoformamides and the unexpected formation of 2-cyanobenzothiazoles

Cyanoformamides are ubiquitous as useful components for assembling key intermediates and bioactive molecules. The development of an efficient and simple approach to this motif is a challenge. Herein, we demonstrate the effectiveness of the I₂-DMSO oxidative system in the preparation of N-arylcyanoformamides from N-arylcyanothioformamides. The synthetic method features mild conditions, broad substrate scope, and high reaction efficiency. Furthermore, this method provides an excellent entry to exclusively afford 2-cyanobenzothiazoles which are useful substrates to access new luciferin analogs. The structures of all new products were elucidated by multinuclear NMR spectroscopy and high accuracy mass spectral analysis. Crystal-structure determination by means of single-crystal X-ray diffraction was carried out on (4-bromophenyl)carbamoyl cyanide, 5,6-dimethoxybenzo[d]thiazole-2-carbonitrile, 5-(benzyloxy)benzo[d]oxazole-2-carbonitrile, 4,7-dimethoxybenzo[d]thiazole-2-carbonitrile, and (5-iodo-2,4-dimethoxyphenyl)carbamoyl cyanide, a key intermediate with mechanistic implications.

Conversion of N-arylcyanothioformamides to N-arylcyanoformamides and 2-cyanobenzothiazoles has been achieved with I₂-DMSO oxidative system.

Oxidative C–H Acyloxylation of Acetone with Carboxylic Acids under Iodine Catalysis

Iodine-catalyzed oxidative C(sp3)–H acyloxylation of acetone with carboxylic acids has been developed. The method employs iodide­ as catalyst and sodium chlorite as oxidant. Substituted benzoic acids, naphthoic acids and heteroaromatic carboxylic acids can be used, and 2-oxopropyl carboxylates are obtained with good to excellent yields.

Reactions involving aryl methyl ketone and molecular iodine: a powerful tool in the one-pot synthesis of heterocycles

The preparation of heterocyclic compounds has attracted great attention in organic chemistry because of their extensive application in the field of bioactive molecules, materials science, and natural products.

One-Pot Tandem Assembly of Amides, Amines, and Ketones: Synthesis of C4-Quaternary 3,4- and 1,4-Dihydroquinazolines

A multicomponent tandem assembly procedure for the synthesis of diverse C4-quaternary 3,4-dihydroquinazolines from amides, amines, and ketones has been developed. The one-pot reaction involves successive triflic anhydride mediated amide dehydration, ketimine addition, and Pictet-Spengler-like cyclization processes and affords products in up to 92% yield. Conversion of 3,4-dihydroquinazolines to the corresponding 1,4-dihydroquinazolines via a two-step N1 dealkylation and regioselective N3 functionalization protocol, including computational rationale for the observed regioselectivity, is also described.

Sulfoxide Reduction/C(sp3)-S Metathesis Cascade in Ionic Liquid

A sulfoxide reduction/C-S bond metathesis cascade between sulfoxides and alkyl bromides has been developed to access high-value sulfides without the use of any catalysts or bases. In this cascade, classical Kornblum oxidation is employed to reduce sulfoxides with alkyl bromides in ionic liquid. This protocol features high functional tolerance, mild conditions, promising scalability, and sustainable solvents.

I2/DMSO mediated multicomponent reaction for the synthesis of 2-arylbenzo[d]imidazo[2,1-b] thiazole derivatives

Synthesis of a series of 2-arylbenzo[d]imidazo[2,1-b] thiazoles tethered with barbituric acid moiety has been reported from the three component reaction of 2-aminobenzothiazoles, barbituric acids and terminal aryl acetylenes or aryl methyl ketones in the presence of I2 in DMSO medium. Both conventional and microwave heating conditions can be used for this multicomponent reaction. The salient features of this methodology are: (i) formation of one C-C and two C-N bonds in one-pot under metal-free oxidation followed by cyclization, (ii) selective formation of the fused imidazole ring, (iii) wide substrate scope, (iv) easy purification of the products, (v) products having more than one pharmaceutically important motifs and (vi) gram scale synthesis possible.

Iodine-Promoted Domino Oxidative Cyclization for the One-Pot Synthesis of Novel Fused Four-Ring Quinoxaline Fluorophores by sp3 C-H Functionalization

A method for the synthesis of novel fused four-ring quinoxaline skeleton has been described by an I₂ promoted sp³ C-H functionalization between 1,2,3,3-tetramethyl-3H-indolium iodides and 1,2-diamines. This transformation proceeds smoothly under metal- and peroxide-free conditions through a sequential iodination, oxidation, annulation and rearrangement. Moreover, 8,9-dichloro-5,12,12-trimethyl-2-(trifluoromethyl)-5,12-dihydroquinolino[2,3-b]quinoxaline showed good photophysical properties and was used in live cell imaging, indicating the potential value of this skeleton as a fluorophore in probes.

I2-Promoted Multicomponent Dicyclization and Ring-Opening Sequences: Direct Synthesis of Benzo[e][1,4]diazepin-3-ones via Dual C-O Bond Cleavage

A novel and efficient formal [4 + 2+1] annulation of aryl methyl ketones and 2-aminobenzyl alcohols for the synthesis of benzo[e][1,4]diazepin-3-ones is reported. This reaction successfully affords diverse seven-membered ring lactams via dual C-O bond cleavage. A preliminary mechanistic study showed that a multicomponent dicyclization and ring-opening sequence might occur, with the introduction of methyl sulfide proposed as the last step. This efficient strategy with mild reaction conditions and a broad substrate scope has potential applications in chemistry and medicine.

An iodine-promoted one-pot and metal-free access to indolin-2-ones

A new method for the synthesis of indolin-2-ones has been realized by an I2-promoted oxidative reaction from 1,2,3,3-tetramethyl-3 H-indolium iodides. This transformation proceeded smoothly under metal-free and peroxide-free conditions in a cascade manner.

I2-Catalyzed oxidative synthesis of N,4-disubstituted quinazolines and quinazoline oxides

An easy and efficient approach to the synthesis of N,4-disubstituted quinazoline-2-amine and oxides is described. This transformation proceeds smoothly in the presence of molecular iodine. The metal-free protocol presented here is insensitive to air moisture and operationally simple. This versatile and synthetic methodology is broadly applicable to a variety of N,4-disubstituted quinazoline-2-amines and oxides, which are synthesized in good to excellent yields starting from readily available inexpensive precursors.

Direct synthesis of 2-oxo-acetamidines from methyl ketones, aromatic amines and DMF via copper-catalyzed C(sp3)-H amidination

A convenient method for the synthesis of 2-oxo-acetamidines from methyl ketones using aromatic amines and DMF as nitrogen sources is reported via copper-catalyzed C(sp3)-H amidination. Various methyl ketones react readily with aromatic amines and DMF, producing 2-oxo-acetamidines in yields of 47 to 92%. This protocol features the simultaneous formation of C-N and C[double bond, length as m-dash]N bonds using DMF and aromatic amines as two different nitrogen sources. It thus provides an efficient approach to construct acyclic amidines via three C(sp3)-H bond amidination. Based on the preliminary experiments, a plausible mechanism of this transformation is disclosed.

Direct oxidative dearomatization of indoles: access to structurally diverse 2,2-disubstituted indolin-3-ones

Described is an efficient oxidative dearomatization of indoles with TEMPO oxoammonium salt and a broad range of nucleophiles.

I2/DMSO-mediated multicomponent reaction of o-hydroxyaryl methyl ketones, rongalite, and DMSO: access to C3-sulfenylated chromones

An efficient I₂–DMSO reagent system-mediated multicomponent reaction strategy for the synthesis of C3-sulfenylated chromones from o-hydroxyaryl methyl ketones, rongalite, and dimethyl sulfoxide has been developed.

A concise synthesis and biological study of evodiamine and its analogues

Efficient access to evodiamine and its analogues is presented via Lewis acid catalysis. In this reaction, three chemical bonds and two heterocyclic-fused rings are constructed in one step.

Synthesis of 1 H-Pyrrol-3(2 H)-ones via Three-Component Reactions of 2,3-Diketo Esters, Amines, and Ketones

An efficient one-pot, three-component reaction of 2,3-diketo esters with amines and ketones has been developed for the synthesis of 1 H-pyrrol-3(2 H)-ones. By using trifluoroacetic acid (TFA) as the additive and acetonitrile (MeCN) as the solvent, this convenient method provides a library of 1 H-pyrrol-3(2 H)-ones in moderate to good yields. The simple protocol features readily available starting materials, a straightforward process, good functional group tolerance, and broad substrate scope.

Asymmetric Synthesis of Chiral 1,2-Amino Alcohols and Morpholin-2-ones from Arylglyoxals

Chiral 1,2-amino alcohols are privileged scaffolds with important applications as drug candidates and chiral ligands. Although various methods for the preparation of this structural motif have been reported, these methods are limited because of the use of precious metals and ligands. Here, we report a practical and high yielding synthesis of chiral 1,2-amino alcohols using arylglyoxals and pseudoephedrine auxiliary. This reaction is catalyzed by a Brønsted acid and provides morpholinone products in high yields and selectivities. The morpholine ring was converted into 1,2-amino alcohols in a two-step protocol.

NaHS·nH2O-induced umpolung: the synthesis of 2-acyl-3-aminoindoles from aryl methyl ketones and 2-aminobenzonitriles

An efficient method for constructing 2-acyl-3-aminoindoles from methyl ketones and 2-aminobenzonitriles is described, in which NaHS·nH₂O is used as a novel umpolung reagent for the first time in organic synthesis.

Iodine-catalyzed cross-coupling of isocyanides and thiols for the synthesis of S-thiocarbamates

Synthesis of S-thiocarbamates by employing simple and readily available precursors under mild reaction conditions with good to excellent yields.

Iodine/DMSO oxidations: a contemporary paradigm in C–N bond chemistry

A new era in the organic synthetic world is demanding greener protocols for the execution of reactions.

Synthesis of disulfides tethered pyrroles from β-ketothioamides via a bicyclization/ring-opening/oxidative coupling reaction

A DABCO-promoted three-component reaction of β-ketothioamides, arylglyoxals and 2-cyanoacetate to construct disulfides tethered pyrroles has been developed.

Microfluidic synthesis of α-ketoesters via oxidative coupling of acetophenones with alcohols under metal-free conditions

An efficient and novel method for the synthesis of α-ketoesters has been developed via oxidative coupling of acetophenones with alcohols under TBHP/I₂/DBU conditions in a microfluidic chip reactor, which has a wide substrate scope, uses a lower dosage of iodine and affords higher product yields in only a few seconds.

Solvent-free iodine-promoted synthesis of 3,2′-pyrrolinyl spirooxindoles from alkylidene oxindoles and enamino esters under ball-milling conditions

A solvent-free mechanochemical reaction of alkylidene oxindoles with enamino esters via an iodine-promoted tandem Michael/cyclization sequence has been developed to provide a variety of spirocyclic oxindoles in moderate to good yields with excellent diastereoselectivities.