NIS-Catalyzed Reactions: Amidation of Acetophenones and Oxidative Amination of Propiophenones

Oxidative Amination of Aldehydes with Amines into α-Amino Ketones

Oxidative amination for the installation of nitrogen functional molecules from nitrogen nucleophiles has always been a very challenging topic in organic synthesis. Here we report a novel conversion of different aldehydes with secondary amines for the synthesis of diversified α-amino ketones. This method can be achieved through oxidative rearrangement of an in situ-generated enamine intermediate promoted by commercially available sodium percarbonate. Furthermore, this one-pot process is also suitable for the functional modification of complex molecules.

The electrochemically enabled α-C(sp3)-H azolation of ketones

C-H/N-H cross-coupling has become a key technology for the selective conjugation of azole drug molecules. However, the development of new synthetic models and green chemical methods is imperative to enhance the construction of multi-functional compounds and compounds with unique functional groups. We herein reported an electrochemical synthesis of α-tetrazolyl ketones with excellent yields and broad substrate scope, encompassing electron-donating and electron-withdrawing groups of aryl ketones, heterocycles, and alkyl and various ketone drugs. It was further proved that α-iodoketone was involved in this transformation of the reaction as a critical intermediate.

Selective Synthesis of N-[1,3,5]Triazinyl-α-Ketoamides and N-[1,3,5]Triazinyl-Amides from the Reactions of 2-Amine-[1,3,5]Triazines with Ketones

In this study, we report a selective approach for synthesizing N-([1,3,5]triazine-2-yl) α-ketoamides and N-([1,3,5]triazine-2-yl) amides from ketones with 2-amino[1,3,5]triazines through oxidation and oxidative C-C bond cleavage reaction, respectively. The transformation proceeds under mild conditions, provides good functional group tolerance and chemoselectivity, and will serve as a valuable tool for the synthesis of bioactive products.

Iron-Catalyzed Oxidative α-Amination of Ketones with Primary and Secondary Sulfonamides

We report the iron-catalyzed α-amination of ketones with sulfonamides. Using an oxidative coupling approach, ketones can be directly coupled with free sulfonamides, without the need for prefunctionalization of either substrate. Primary and secondary sulfonamides are both competent coupling partners, with yields from 55% to 88% for deoxybenzoin-derived substrates.

α-Amination of Carbonyl Compounds by Using Hypervalent Iodine-Based Aminating Reagents Containing a Transferable (Diarylmethylene)amino Group

Hypervalent iodine-based aminating reagents containing a transferable (diarylmethylene)amino group can be used for the α-amination of simple carbonyl compounds such as esters, amides, and ketones in the presence of a lithium base. The (diarylmethylene)amino groups of the products can be readily modified, thus providing access to primary amines and diarylmethylamines. The developed method features transition-metal-free conditions and a simple one-pot procedure without the need to prepare enolate equivalents separately, thus offering a general and practical approach to the synthesis of a wide variety of α-amino carbonyl compounds. Experimental mechanistic investigations indicate that this amination proceeds through a unique radical coupling of an α-carbonyl radical with an iminyl radical; they are generated through a single-electron transfer between a lithium enolate and the hypervalent iodine reagent.

Mg(OtBu)2-catalyzed C–H oxidation of α-azido arylethanones using TBHP as the oxidant and carbonyl oxygen source: facile access to primary α-ketoamides

A Mg(OtBu)2-catalyzed C(sp3)–H oxidation of α-azido arylethanones to straightforwardly produce primary α-ketoamides is presented.

Palladium-catalyzed benzylic C(sp3)-H carbonylative arylation of azaarylmethyl amines with aryl bromides

A highly selective palladium-catalyzed carbonylative arylation of weakly acidic benzylic C(sp3)-H bonds of azaarylmethylamines with aryl bromides under 1 atm of CO gas has been achieved. This work represents the first examples of use of such weakly acidic pronucleophiles in this class of transformations. In the presence of a NIXANTPHOS-based palladium catalyst, this one-pot cascade process allows a range of azaarylmethylamines containing pyridyl, quinolinyl and pyrimidyl moieties and acyclic and cyclic amines to undergo efficient reactions with aryl bromides and CO to provide α-amino aryl-azaarylmethyl ketones in moderate to high yields with a broad substrate scope and good tolerance of functional groups. This reaction proceeds via in situ reversible deprotonation of the benzylic C-H bonds to give the active carbanions, thereby avoiding prefunctionalized organometallic reagents and generation of additional waste. Importantly, the operational simplicity, scalability and diversity of the products highlight the potential applicability of this protocol.

NHC-Catalyzed Aza-Benzoin Condensation of N,N'-Dipyridin-2-yl Aminals with Aldehydes

α-Amino ketones are useful compounds because of their synthetic utility and bioactivities. After observing the ability of N,N'-dipyridin-2-yl aminals to form imines in situ, the synthesis of α-amino ketones using N,N'-dipyridin-2-yl aminals was proposed. Through the NHC-catalyzed aza-benzoin reaction between aromatic/aliphatic aldehydes and N,N'-dipyridin-2-yl aminals, α-amino ketones, including aromatic, heterocyclic, and aliphatic versions, were synthesized with yields up to 99%. A direct route toward N-Boc-protected α-amino ketones from N,N,N'-tris-Boc aminals was also discovered, yielding the desired N-Boc-protected α-amino ketones in yields up to 73%.

Electrochemical Oxidative Coupling Between Benzylic C(sp3)-H and N-H of Secondary Amines: Rapid Synthesis of α-Amino α-Aryl Esters

An intermolecular electrochemical coupling between the benzylic C(sp³)-H bond and various secondary amines is reported. The electronic behavior of two electronically rich units viz the α-position of α-aryl acetates and amines was engineered electrochemically, thus facilitating their reactivity for the direct access of α-amino esters. A series of acyclic/cyclic secondary amines and α-aryl acetates were tested to furnish the corresponding α-amino esters with high yields (up to 92%) under mild conditions.

Amidation-Ketonization-Selenation of Terminal Alkynes Using TEMPO and Elemental Selenium

Herein, we present a novel silver- or copper-mediated direct amidation-ketonization-selenation of terminal alkynes for the synthesis of α-oxo-selenoamides. The reaction utilized easily accessible elemental selenium as the source of selenium. In addition, the ¹⁸O labeling experiment revealed that TEMPO is the oxygen source of the carbonyl group. The reaction takes advantage of an unsaturated C≡C bond to construct new C═O, C═Se, and C-N bonds in one step.

Recent advances in the synthesis of α-amino ketones

Due to the importance of the amino ketone motif in synthetic and medicinal chemistry, the number of protocols developed in recent years has considerably increased. This review serves to collate and critically evaluate novel methodologies published since 2011 towards this high value synthon. The chapters are divided by the requisite functionality in the starting material, and an emphasis is placed on discussing functional group compatibility and resultant product substitution patterns. Throughout, applications to medicinal targets are highlighted and mechanistic details are presented, and we further provide a short outlook for future development and emerging potential within this area.

Biogenic synthesis of Pd-nanoparticles using Areca Nut Husk Extract: a greener approach to access α-keto imides and stilbenes

An eco-friendly green method for a one-step synthesis of palladium nanoparticles and their synthetic utility are reported.

Unveiling the reaction process of the amine in direct amidation of aromatic ketones in H2O

In the classical amidation between aromatic ketones and amines, 2.0 equivalents of amines are necessarily required to gain satisfying yields. The specific role of the amine in the direct amidation already puzzled us for a long time. In this work, we disclosed that the amine acts as both reactant and catalyst. Specifically, the determination of reaction intermediates revealed the full mechanism, based on which, the introduction of one equivalent base in the amidation is showcased here that a high yield (∼95 %) can be afforded using only 1.1 equiv. of amine.

C-H/C-C Functionalization Approach to N-Fused Heterocycles from Saturated Azacycles

Herein we report the synthesis of substituted indolizidines and related N-fused bicycles from simple saturated cyclic amines through sequential C-H and C-C bond functionalizations. Inspired by the Norrish-Yang Type II reaction, C-H functionalization of azacycles is achieved by forming α-hydroxy-β-lactams from precursor α-ketoamide derivatives under mild, visible light conditions. Selective cleavage of the distal C(sp2)-C(sp3) bond in α-hydroxy-β-lactams using a Rh-complex leads to α-acyl intermediates which undergo sequential Rh-catalyzed decarbonylation, 1,4-addition to an electrophile, and aldol cyclization, to afford N-fused bicycles including indolizidines. Computational studies provide mechanistic insight into the observed positional selectivity of C-C cleavage, which depends strongly on the groups bound to Rh trans to the phosphine ligand.

Oxidative Deconstruction of Azetidinols to α-Amino Ketones

A silver-mediated synthesis of α-amino ketones via the oxidative deconstruction of azetidinols has been developed using a readily scalable protocol with isolated yields up to 80%. The azetidinols are easily synthesized in one step and can act as protecting groups for these pharmaceutically relevant synthons. Furthermore, mechanistic insights are presented and these data have revealed that the transformation is likely to proceed through the β-scission of an alkoxy radical, followed by oxidation and C-N cleavage of the resulting α-amido radical.

I2-catalyzed intramolecular oxidative amination of C(sp3)–H bond: efficient access to 3-acylimidazo[1,2-a]pyridines under neat condition

An efficient and “green” protocol for the synthesis of 3-acylimidazo[1,2-a]pyridines through intramolecular oxidative α-amination of carbonyl compounds has been developed. The reaction proceeds smoothly utilizing I₂ as a catalyst and H₂O₂ as an oxidant under neat condition with broad substrate scope. Several complex nitrogen-containing fused rings are conveniently constructed, which are not easy to access by traditional methods.

An efficient and green protocol for the synthesis of 3-acylimidazo[1,2-a]pyridines utilizing I₂ as a catalyst and H₂O₂ as an oxidant under neat condition or in water was developed.

Recent advances in iodine mediated electrochemical oxidative cross-coupling

This review article gives an overview of the recent development of iodine mediated electrochemical oxidative coupling reactions.

Recent developments in functionalization of acyclic α-keto amides

This review describes the synthetic utility of α-keto amides to synthesize various important molecules via mono, dual and triple functionalization reactions.

iEDDA Reaction of the Molecular Iodine-Catalyzed Synthesis of 1,3,5-Triazines via Functionalization of the sp3 C-H Bond of Acetophenones with Amidines: An Experimental Investigation and DFT Study

The present work reports an inverse electron demand Diels-Alder (iEDDA)-type reaction to synthesize 1,3,5-trizines from acetophenones and amidines. The use of molecular iodine in a catalytic amount facilitates the functionalization of the sp³ C-H bond of acetophenones. This is a simple and efficient methodology for the synthesis of 1,3,5-triazines in good to excellent yields under transition-metal-free and peroxide-free conditions. The reaction is believed to take place via an in situ iodination-based oxidative elimination of formaldehyde. DFT calculations at the M062X/6-31+G(d,p) level were employed to investigate the reaction mechanism. Reaction barriers for the cycloaddition as well as a formaldehyde expulsion steps were computed, and a multistep mechanism starting with the nucleophilic attack by benzamidine on an in situ generated imine intermediate has been proposed. Both local and global reactivity descriptors were used to study the regioselectivity of the addition steps.

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 one-pot oxidation of ethylarenes for the preparation of α-ketoamides under mild conditions

Here we developed a highly efficient solvent-free, one-pot procedure for synthesizing α-ketoamides from ethylarenes and amines, by oxidizing a C–H bond sp³ center.

One pot synthesis of α-ketoamides from ethylarenes and amines: a metal free difunctionalization strategy

One-pot and metal free synthesis of α-ketoamides has been described through in situ generation of aryl ketones from easily available ethylarenes followed by amidation with various amines. This multiple oxidation protocol involves catalytic I₂-pyridine-TBHP (t-butyl hydroperoxide) mediated oxidative benzylic carbonylation and sequential NaI-TBHP mediated oxidative amidation without using any solvent.

Lewis Acid and (Hypo)iodite Relay Catalysis Allows a Strategy for the Synthesis of Polysubstituted Azetidines and Tetrahydroquinolines

A catalytic [3 + 1]-annulation reaction between cyclopropane 1,1-diester and aromatic amine is developed based on the relay catalysis strategy. Lewis acid-catalyzed nucleophilic ring opening of cyclopropane 1,1-diester with aromatic amine and (hypo)iodite-catalyzed C-N bond formation are combined successfully in one reaction. Using this reaction, biologically important azetidines and tetrahydroquinolines can be prepared directly.