Chemoselective synthesis of ketones and ketimines by addition of organometallic reagents to secondary amides

Divergent Synthesis of Enynals and Dihydrobenzo[f]isoquinolines via Deoxyalkynylation of Enaminones Enabled by the Cooperative Action of Tf2O/Pd/Cu

A variety of enynals and dihydrobenzo[f]isoquinolines were effectively synthesized with favorable functional group compatibility via deoxyalkynylation of enaminones enabled by the cooperative action of Tf2O/Pd/Cu. The reaction system demonstrated the ability to be expanded to the deoxyarylation/deoxyaryloxylation of enaminones with arylboronic acids or phenols, facilitating the efficient formation of C-C/C-O bonds and showcasing the practicality and versatility of the methodology.

Direct synthesis of dialkyl ketones from deoxygenative cross-coupling of carboxylic acids and alcohols

Carboxylic acids and alcohols are widely commercially available, structurally diverse, benchtop stable, and ubiquitous in both natural products and pharmaceutical agents, making them ideal coupling partners for organic synthesis. Though various transformations have been developed by enabling the activation and subsequent cross-coupling of carboxylic acids and alcohols in separate contexts, the direct coupling of these two structural motifs to build value-added molecules is rare. Herein, we developed a direct deoxygenative cross-coupling between carboxylic acids and alcohols for dialkyl ketone synthesis via photoredox/nickel dual catalysis. This protocol provides a powerful platform to construct a wide range of structurally diverse ketone scaffolds with broad substrate scope, good functional group tolerance, step-economy and mild reaction conditions, using simple and readily available substrates. Moreover, the large-scale synthesis and late-stage functionalization of biological molecules also demonstrate the potential practicality.

A Proline-Based Artificial Enzyme That Favors Aldol Condensation Enables Facile Synthesis of Aliphatic Ketones via Tandem Catalysis

A proline-based artificial enzyme is prepared by grafting the l-proline moieties onto the surface of bovine serum albumin (BSA) protein through atom transfer radical polymerization (ATRP). The artificial enzyme, the BSA-PolyProline conjugate, prefers to catalyze the formation of unsaturated ketones rather than β-hydroxy ketones in the reaction between acetone and aldehydes, which is difficult to achieve in free-proline catalysis. The altered reaction selectivity is ascribed to the locally concentrated l-proline moieties surrounding the BSA molecule, indicating a microenvironmental effect-induced switching of the reaction mechanism. Taking advantage of this selectivity, we used this artificial enzyme in conjunction with a natural enzyme, old yellow enzyme 1 (OYE1), to demonstrate a simple synthesis of different aliphatic ketones from acetone and aldehydes via tandem catalysis.

Stable Amide Activation of N-Acetylated Glycosamines for the Synthesis of Fused Polycyclic Glycomimetics

N-Acetylation of carbohydrates is an underexplored target for chemoselective derivatization and generation of glycomimetic scaffolds. Through mild amide activation, we report that N-acetimidoyl heterocycles are stable in neutral or basic conditions yet are excellent leaving groups through acid catalysis. While this specific reactivity could prove broadly useful in amide activation strategies, stably activated N-acetylated sugars can also be diversified using libraries of hydrazides. We optimized an acid-catalyzed one-pot sequence that includes nucleophilic displacement, cyclodehydration, and intramolecular glycosylation to ultimately deliver pyranosides fused to morpholines or piperazines. This strategy of stable activation followed by acid-triggered reaction sequences exemplifies the efficient assembly of 3D-rich fused glycomimetic libraries.

Chemoselective α-Trifluoroacetylation of Amides Using Highly Electrophilic Trifluoroacetic Anhydrides and 2,4,6-Collidine

Chemoselective α-acylation of tertiary amides proceeded with highly electrophilic acid anhydrides and weak bases under mild conditions. β-Ketoamides containing trifluoroacetyl or perfluoroacyl groups were selectively obtained even in the presence of other functional groups such as ketone, ester, etc. Density functional theory calculations suggest that 1-acyloxyenamine is the key intermediate for the chemoselective α-acylation.

Amide Skeletal Elongation via Amino Acid Insertion

Amide derivatization is useful to access valuable organic compounds considering the ready availability of molecules containing amide functionality. Current methods to derivatize amide mainly focus on the synthesis of carbonyl-containing compounds and amines. Incorporating both parts of the initial amide into the new derivatives is rare. Herein, we describe a simple and practical amide derivatization through amino acid insertion to prepare more complex amides. This insertion is applicable to a wide range of amino acids and more importantly, the chiral information is completely conserved during the insertion. Comparison of this insertion strategy with conventional amide synthesis demonstrates the synthetic advantages of this new protocol.

Ketones from aldehydes via alkyl C(sp3)-H functionalization under photoredox cooperative NHC/palladium catalysis

Direct synthesis of ketones from aldehydes features high atom- and step-economy. Yet, the coupling of aldehydes with unactivated alkyl C(sp³)-H remains challenging. Herein, we develop the synthesis of ketones from aldehydes via alkyl C(sp³)-H functionalization under photoredox cooperative NHC/Pd catalysis. The two-component reaction of iodomethylsilyl alkyl ether with aldehydes gave a variety of β-, γ- and δ-silyloxylketones via 1,n-HAT (n = 5, 6, 7) of silylmethyl radicals to generate secondary or tertiary alkyl radicals and following coupling with ketyl radicals from aldehydes under photoredox NHC catalysis. The three-component reaction with the addition of styrenes gave the corresponding ε-hydroxylketones via the generation of benzylic radicals by the addition of alkyl radicals to styrenes and following coupling with ketyl radicals. This work demonstrates the generation of ketyl radical and alkyl radical under the photoredox cooperative NHC/Pd catalysis, and provides two and three component reactions for the synthesis of ketones from aldehydes with alkyl C(sp³)-H functionalization. The synthetic potential of this protocol was also further illustrated by the late-stage functionalization of natural products.

Ti-Catalyzed Modular Ketone Synthesis from Carboxylic Derivatives and gem-Dihaloalkanes

Ketones are ubiquitous in organic synthesis. However, the general method to convert widely available carboxylic acids, unactivated esters, and amides into ketones remains elusive. Herein, we describe the Ti-catalyzed modular ketone synthesis from carboxylic derivatives and easily accessed gem-dihaloalkanes. Notably, this protocol could achieve the direct catalytic olefination of carboxylic acids. This method features a sequence of olefination and electrophilic transformation and good functional group compatibility and allows rapid access to various functionalized ketones. Preliminary mechanistic studies provide insights into the reaction pathway and support the intermediacy of plausible alkylidene titanocene and gem-bimetallic complexes.

Palladium-Catalyzed Directed Aldehyde C-H Arylation of Quinoline-8-carbaldehydes: Exploring the Reactivity Differences between Aryl (Pseudo) Halides

We have developed a method for Pd-catalyzed direct C-H arylation of quinoline-8-carbaldehydes with either aryl iodides or aryl diazonium salts for the synthesis of aryl quinolinyl ketones. Aryl iodide substituted with an electron-donating group favors the reaction, whereas aryl diazonium salt substituted with an electron-withdrawing group showed excellent reactivity. A range of aryl quinolinyl ketones were synthesized in good-to-excellent yields, with very good functional group tolerance. Our methodology was successfully applied to synthesize highly potent tubulin polymerization inhibitors and can be easily scaled up to a gram scale.

Multicatalysis protocol enables direct and versatile enantioselective reductive transformations of secondary amides

The catalytic asymmetric geminal bis-nucleophilic addition to nonreactive functional groups is a type of highly desirable yet challenging transformation in organic chemistry. Here, we report the first catalytic asymmetric reductive/deoxygenative alkynylation of secondary amides. The method is based on a multicatalysis strategy that merges iridium/copper relay catalysis with organocatalysis. A further combination with the palladium-catalyzed alkyne hydrogenation allows the one-pot enantioselective reductive alkylation of secondary amides. This versatile protocol allows the efficient synthesis of four types of α-branched chiral amines, which are prevalent structural motifs of active pharmaceutical ingredients. The protocol also features excellent enantioselectivity, chemoselectivity, and functional group tolerance to be compatible with more reactive functional groups such as ketone and aldehyde. The synthetic utility of the method was further demonstrated by the late-stage functionalization of two drug derivatives and the concise, first catalytic asymmetric approach to the κ-opioid antagonist aticaprant.

Gram-Scale Enantioselective Synthesis of (+)-Lucidumone

The first enantioselective total synthesis of (+)-lucidumone is described through a 13-step synthetic pathway (longest linear sequence). The key steps involve the formation of a bridged bicyclic lactone by an enantioselective inverse-electron-demand Diels-Alder cycloaddition, C-O bond formation to assemble two fragments, and a one-pot retro-[4 + 2]/[4 + 2] cycloaddition cascade. The synthesis is scalable, and more than one gram of natural product was synthesized in one batch.

Ir-Catalyzed Chemoselective Reductive Condensation Reactions of Tertiary Amides with Active Methylene Compounds

The catalytic reductive condensation reactions of tertiary amides with active methylene compounds leading to multifunctionalized non-N-containing products is described. The reactions proceed through sequential iridium-catalyzed hydrosilylation of the amides followed by acid-mediated condensation with the active methylene compounds. This scalable method is broad in scope and shows remarkable chemoselectivity for the amide group in the presence of several sensitive or even more reactive functionalities such as ester, cyano, nitro, silyl dienol ether, and ketone.

Ni-Catalyzed Divergent Synthesis of 2-Benzazepine Derivatives via Tunable Cyclization and 1,4-Acyl Transfer Triggered by Amide N-C Bond Cleavage

Ligand-directed divergent synthesis can transform common starting materials into distinct molecular scaffolds by simple tuning different ligands. This strategy enables the rapid construction of structurally rich collection of small molecules for biological evaluation and reveals novel modes of catalytic transformation, representing one of the most sought-after challenges in synthetic chemistry. We herein report a Ni-catalyzed ligand-controlled tunable cyclization/cross-couplings for the divergent synthesis of pharmacologically important 2-benzazepine frameworks. The bidentate ligand facilitates the nucleophilic addition of the aryl halides to the amide carbonyl, followed by 1,4-acyl transfer and cross-coupling to obtain 2-benzazepin-5-ones and benzo[c]pyrano[2,3-e]azepines. The tridentate ligand promotes the selective 7-endo cyclization/cross-coupling to access to 2-benzazepin-3-ones. The protocol operates under mild reaction conditions with divergent cyclization patterns that can be easily modulated through the ligand backbone.

Electrophile-Dependent Reactivity of Lithiated N-Benzylpyrene-1-Carboxamide

In this paper, we describe the lithiation of N-benzylpyrene-1-carboxamide with RLi-TMEDA. We found that the reaction outcome strongly depends on the electrophile used in the quenching step. The electrophile can be introduced at either the benzylic position or at the C-2 position in the pyrene nucleus. Furthermore, when H⁺ was used as the quencher, the product of the intramolecular carbolithiation of the pyrene K-region was formed. Dehydrogenation of the obtained compound with DDQ allowed the synthesis of a novel nitrogen polycyclic compound with an aza-benzo[c,d]pyrene (azaolympicene) skeleton. Attempts to extend the reaction scope to the amides substituted in the phenyl ring 8a and 8b gave an unexpected result. The reaction of both compounds with BuLi gave 1-valerylpyrene (9) in good yield. Photophysical properties, including absorption spectra, emission spectra and quantum yields of the emission of selected products, were studied and discussed.

Total synthesis of (±)-vinoxine: construction of the bridged pyrido[1,2-a]indole skeleton via Tf2O-mediated Bischler-Napieralski reaction and stereoselective radical cyclization

The total synthesis of (±)-vinoxine was achieved featuring the assembly of a multi-substituted tetrahydropyrido[1,2-a]indole skeleton through the Tf₂O-mediated Bischler-Napieralski reaction. The characteristic diazabicyclo[3.3.1]nonane skeleton was stereoselectively constructed via radical cyclization based on the one stereochemistry of the C3 position. The established methodology provides new options for the synthesis of natural products and pharmaceuticals containing the multi-substituted pyrido[1,2-a]indole skeleton.

Triflic Anhydride (Tf2O)-Activated Transformations of Amides, Sulfoxides and Phosphorus Oxides via Nucleophilic Trapping

Trifluoromethanesulfonic anhydride (Tf2O) is utilized as a strong electrophilic activator in a wide range of applications in synthetic organic chemistry, leading to the transient generation of a triflate intermediate. This versatile triflate intermediate undergoes nucleophilic trapping with diverse nucleophiles to yield novel compounds. In this review, we describe the features and applications of triflic anhydride in organic synthesis reported in the past decade, especially in amide, sulfoxide, and phosphorus oxide chemistry through electrophilic activation. A plausible mechanistic pathway for each important reaction is also discussed.

1 Introduction

2 Amide Chemistry

2.1 Carbon Nucleophiles

2.2 Hydrogen Nucleophiles

2.3 Nitrogen Nucleophiles

2.4 Oxygen and Sulfur Nucleophiles

2.5 hosphorus Nucleophiles

2.6 A Vilsmeier-Type Reagent

2.7 Umpolung Reactivity in Amides

3 Sulfoxide Chemistry

3.1 Oxygen Nucleophiles

3.2 Carbon Nucleophiles

3.3 Nitrogen Nucleophiles

3.4 Thionium Reagents

4 Phosphorus Chemistry

4.1 Hendrickson’s Reagent

4.2 Diaryl Phosphine Oxides

4.3 Phosphonates, Phosphates and Phosphinates

5 Conclusion and Outlook

Transition-metal-catalyst-free reaction of amides and acetonitriles: synthesis of β-ketonitriles

The first example of the coupling reaction between amide and acetonitrile for the synthesis of β-ketonitriles was developed. Various amides provide the corresponding β-ketonitriles in good yields.

Remote C-H Pyridylation of Hydroxamates through Direct Photoexcitation of O-Aryl Oxime Pyridinium Intermediates

Herein, we report an efficient strategy for the remote C-H pyridylation of hydroxamates with excellent ortho-selectivity by designing a new class of photon-absorbing O-aryl oxime pyridinium salts generated in situ from the corresponding pyridines and hydroxamates. When irradiated by visible light, the photoexcitation of oxime pyridinium intermediates generates iminyl radicals via the photolytic N-O bond cleavage, which does not require an external photocatalyst. The efficiency of light absorption and N-O bond cleavage of the oxime pyridinium salts can be modulated through the electronic effect of substitution on the O-aryl ring. The resultant iminyl radicals enable the installation of pyridyl rings at the γ-CN position, which yields synthetically valuable C2-substituted pyridyl derivatives. This novel synthetic approach provides significant advantages in terms of both efficiency and simplicity and exhibits broad functional group tolerance in complex settings under mild and metal-free conditions.

Tf2O/TTBP (2,4,6-Tri-tert-butylpyrimidine): An Alternative Amide Activation System for the Direct Transformations of Both Tertiary and Secondary Amides

Ten types of Tf₂O/TTBP-mediated amide transformation reactions were investigated. The results showed that compared with pyridine derivatives 2,6-di-tert-butyl-4-methylpyridine (DTBMP) and 2-fluoropyridine (2-F-Pyr.), TTBP can serve as an alternative amide activation system for the direct transformation of both secondary and tertiary amides. For most surveyed examples, higher or comparable yields were generally obtained. In addition, Tf₂O/TTBP combination was used to promote the condensation reactions of 2-(tert-butyldimethylsilyloxy)furan (TBSOF) with both tertiary and secondary amides, the one-pot reductive Bischler-Napieralski-type reaction of tertiary lactams, and Movassaghi and Hill's modern version of the Bischler-Napieralski reaction. The value of the Tf₂O/TTBP-based methodology was further demonstrated by the concise and high-yielding syntheses of several natural products.

From Esters to Ketones via a Photoredox-Assisted Reductive Acyl Cross-Coupling Strategy

A method was developed for ketone synthesis via a photoredox-assisted reductive acyl cross-coupling (PARAC) using a nickel/photoredox dual-catalyzed cross-electrophile coupling of two different carboxylic acid esters. A variety of aryl, 1°, 2°, 3°-alkyl 2-pyridyl esters can act as acyl electrophiles while N-(acyloxy)phthalimides (NHPI esters) act as 1°, 2°, 3°-radical precursors. Our PARAC strategy provides an alternative and reliable way to synthesize various sterically congested 3°-3°, 3°-2°, and aryl-3° ketones under mild and highly unified conditions, which have been otherwise difficult to access. The combined experimental and computational studies identified a Ni⁰ /Ni^I /Ni^III pathway for ketone formation.

Functionalized Polyhydroquinolines from Amino Acids Using a Key One-Pot Cyclization Cascade and Application to the Synthesis of (±)-Δ7-Mesembrenone

Substituted polyhydroquinolines are ubiquitous skeletal cores found in drugs and bioactive natural products. As a new route to access this motif, we successfully developed a one-pot cyclization cascade with high chemocontrol and diastereoselectivity. The sequence generates two cycles, three carbon-carbon bonds, and an all-carbon quaternary center in a highly convergent process. Functionalized polyhydroquinolines and congeners can be accessed from commercially available amino acids. This versatile and robust strategy was applied to the synthesis of (±)-Δ7-mesembrenone.

Synthesis of 1-(1-Arylvinyl)pyridin-2(1H)-ones from Ketones and 2-Fluoropyridine

We describe a simple and efficient procedure for the synthesis of N-vinyl-substituted pyridones from ketones and 2-fluoropyridine in the presence of trifluoromethane sulfonic anhydride, followed by a base treatment. Various ketones with electron-donating or electron-withdrawing groups at the benzene rings can be used in this reaction. A preliminary mechanistic study indicates that it is not very likely that both vinyl triflates and vinyl cations play major roles as intermediates in this transformation.

Direct alkylation of N,N-dialkyl benzamides with methyl sulfides under transition metal-free conditions

Amides are a fundamental and widespread functional group, and are usually considered as poor electrophiles owing to resonance stabilization of the amide bond. Various approaches have been developed to address challenges in amide transformations. Nonetheless, most methods use activated amides, organometallic reagents or transition metal catalysts. Here, we report the direct alkylation of N,N-dialkyl benzamides with methyl sulfides promoted by the readily available base LDA (lithium diisopropylamide). This approach successfully achieves an efficient and selective synthesis of α-sulfenylated ketones without using transition-metal catalysts or organometallic reagents. Preliminary mechanism studies reveal that the deprotonative aroylation of methyl sulfides is promoted by the directed ortho-lithiation of the tertiary benzamide with LDA.

Uniting Amide Synthesis and Activation by PIII/PV-Catalyzed Serial Condensation: Three-Component Assembly of 2-Amidopyridines

An organophosphorus (P^III/P^V redox) catalyzed method for the three-component condensation of amines, carboxylic acids, and pyridine N-oxides to generate 2-amidopyridines via serial dehydration is reported. Whereas amide synthesis and functionalization usually occur under divergent reaction conditions, here a phosphetane catalyst (together with a mild bromenium oxidant and terminal hydrosilane reductant) is shown to drive both steps chemoselectively in an auto-tandem catalytic cascade. The ability to both prepare and functionalize amides under the action of a single organocatalytic reactive intermediate enables new possibilities for the efficient and modular preparation of medicinal targets.

Direct Synthesis of Ketones from Methyl Esters by Nickel-Catalyzed Suzuki-Miyaura Coupling

The direct conversion of alkyl esters to ketones has been hindered by the sluggish reactivity of the starting materials and the susceptibility of the product towards subsequent nucleophilic attack. We have now achieved a cross-coupling approach to this transformation using nickel, a bulky N-heterocyclic carbene ligand, and alkyl organoboron coupling partners. 65 alkyl ketones bearing diverse functional groups and heterocyclic scaffolds have been synthesized with this method. Catalyst-controlled chemoselectivity is observed for C(acyl)-O bond activation of multi-functional substrates bearing other bonds prone to cleavage by Ni, including aryl ether, aryl fluoride, and N-Ph amide functional groups. Density functional theory calculations provide mechanistic support for a Ni⁰ /Ni^II catalytic cycle and demonstrate how stabilizing non-covalent interactions between the bulky catalyst and substrate are critical for the reaction's success.

Continuous flow as an enabling technology: a fast and versatile entry to functionalized glyoxal derivatives

We herein report two complementary strategies employing organolithium chemistry for the synthesis of glyoxal derivatives. Micro-mixer technology allows for the generation of unstable organometallic intermediates and their instantaneous in-line quenching with esters as electrophiles. Selective mono-addition was observed via putative stabilized tetrahedral intermediates. Advantages offered by flow chemistry technologies facilitate direct and efficient access to masked 1,2-dicarbonyl compounds while mitigating undesired by-product formation. These two approaches enable the production of advanced and valuable synthetic building blocks for heterocyclic chemistry with throughputs of grams per minute.

Enantioselective Reductive Cyanation and Phosphonylation of Secondary Amides by Iridium and Chiral Thiourea Sequential Catalysis

The combination of transition-metal catalysis and organocatalysis increasingly offers chemists opportunities to realize diverse unprecedented chemical transformations. By combining iridium with chiral thiourea catalysis, direct enantioselective reductive cyanation and phosphonylation of secondary amides have been accomplished for the first time for the synthesis of enantioenriched chiral α-aminonitriles and α-aminophosphonates. The protocol is highly efficient and enantioselective, providing a novel route to the synthesis of optically active α-functionalized amines from the simple, readily available feedstocks. In addition, the reactions are scalable and the thiourea catalyst can be recycled and reused.

Synthesis of Ketones by C-H Functionalization of Aldehydes with Boronic Acids under Transition-Metal-Free Conditions

A method for the synthesis of ketones from aldehydes and boronic acids via a transition-metal-free C-H functionalization reaction is reported. The method employs nitrosobenzene as a reagent to drive the simultaneous activation of the boronic acid as a boronate and the activation of the C-H bond of the aldehyde as an iminium species that triggers the key C-C bond-forming step via an intramolecular migration from boron to carbon. These findings constitute a practical, scalable, and operationally straightforward method for the synthesis of ketones.

Formation of o-Allyl- and Allenyl-Modified Amides via Intermolecular Claisen Rearrangement

We developed a new transition-metal-free intermolecular Claisen rearrangement process to introduce allyl and allenyl groups into the α position of tertiary amides. In this transformation, amides were activated by trifluoromethanesulfonic anhydride to produce the keteniminium ion intermediates that exhibit strong electrophilic activity. This atom-economical process delivers α position-modified amides under mild conditions in moderate to good yields and showcases a broad substrate compatibility.

Synthesis of Spirocyclic Isoindolones Using an Alkynyl aza-Prins/Oxidative halo-Nazarov Cyclization Sequence

In this report, we describe an alkynyl halo-aza-Prins cyclization of 3-hydroxyisoindolones to prepare aza-Prins products. These Prins adducts undergo oxidation at the 3-isoindolone position after activation of the amide by triflic anhydride and 2-chloropyridine to form a pentadienyl cation capable of undergoing a halo-Nazarov cyclization. Using this methodology, angular-fused N-heterocyclic small molecules with two new rings, two new carbon-carbon bonds, a vinyl halide, and an aza-tertiary stereocenter can be obtained in good yields.

A Fast and General Route to Ketones from Amides and Organolithium Compounds under Aerobic Conditions: Synthetic and Mechanistic Aspects

We report that the nucleophilic acyl substitution reaction of aliphatic and (hetero)aromatic amides by organolithium reagents proceeds quickly (20 s reaction time), efficiently, and chemoselectively with a broad substrate scope in the environmentally responsible cyclopentyl methyl ether, at ambient temperature and under air, to provide ketones in up to 93 % yield with an effective suppression of the notorious over-addition reaction. Detailed DFT calculations and NMR investigations support the experimental results. The described methodology was proven to be amenable to scale-up and recyclability protocols. Contrasting classical procedures carried out under inert atmospheres, this work lays the foundation for a profound paradigm shift of the reactivity of carboxylic acid amides with organolithiums, with ketones being straightforwardly obtained by simply combining the reagents under aerobic conditions and with no need of using previously modified or pre-activated amides, as recommended.

Chemoselective α-Sulfidation of Amides Using Sulfoxide Reagents

The direct α-sulfidation of tertiary amides using sulfoxide reagents under electrophilic amide activation conditions is described. Employing convenient and readily available reagents, selective functionalization takes place to generate isolable sulfonium ions en route to α-sulfide amides. Mechanistic studies identified activated sulfoxides as promoters of the desired transformation and enabled the extension of the methodology from benzylic to aliphatic amide substrates.

α-Functionalisation of Ketones Through Metal-Free Electrophilic Activation

Triflic anhydride mediated activation of acetophenones leads to highly electrophilic intermediates that can undergo a variety of transformations when treated with nucleophiles. This electrophilic ketone activation gives access to α‐arylated and α‐oxyaminated acetophenones under metal‐free conditions in moderate to excellent yields and enables extension to the synthesis of arylated morpholines via generation of vinylsulfonium salts. Computational investigations confirmed the transient existence of intermediates derived from vinyl triflates and the role of the oxygen atoms at the para position of aromatic ring in facilitating their stabilisation.

A Novel Class of 7-Membered Heterocyclic Compounds

The work presented herein describes the synthesis of a formerly inaccessible class of heterocyclic compounds. The reaction relies on α‐phthalimido‐amides, which are readily prepared from amino acids in 2 simple reactions steps. Under amide activation conditions in which classical keteniminium ions are not formed, the nitrile solvent is incorporated into the new fused 7‐membered ring system. Due to the absence of a keteniminium intermediate, the stereogenic information in the α‐position is fully retained.