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A modular flow platform for natural product synthesis was designed. To access different reaction setups with a maximum of flexibility, interchangeable 3D-printed components serve as backbone. By switching from liquid- to gas-driven flow, reagent and solvent waste is minimized, which translates into an advantageous sustainability profile. To enable inert conditions, Schlenk-in-flow techniques for the safe handling of oxygen- and moisture sensitive reagents were developed. Adopting these techniques, reproducible transformations in natural product synthesis were achieved.

A facile method for the amidation of aldehydes by a cascade approach was developed. This methodology, reported for the first time, uses a N-heterocyclic carbene (NHC) as the catalyst, and N-hydroxysuccinimide (NHS) mediated synthesis of amides utilising TBHP as the oxidant. Various substituted aldehydes reacted smoothly with NHS giving the corresponding active esters in moderate to good yields, which facilely converted into amides in one pot. In addition, the drug moclobemide was synthesized to represent the practical utility of the developed methodology. This journal is

Dehydrogenative amide bond formation from alcohols and amines has been regarded as an atom-economic and sustainable process. Among various catalytic systems, N-heterocyclic carbene (NHC)-based Ru catalytic systems have attracted growing interest due to the outstanding properties of NHCs as ligands. Herein, an NHC/Ru complex (1) was prepared and its structure was further confirmed with X-ray crystallography. In the presence of Cs2CO3, two NHC/Ru-based catalytic systems were disclosed to be active for this amide synthesis. System A, which did not contain any added ligand, required a catalyst loading of 1.00 mol%. Interestingly, improved catalytic performance was realized by the addition of an NHC precursor (L). Optimization of the amounts of L and other conditions gave rise to system B, a much more potent system with the Ru loading as low as 0.25 mol%. Moreover, an NHC-Ru-carbonate complex 6 was identified from the refluxing toluene of 1 and Cs2CO3, and further investigations revealed that 6 was an important intermediate for this catalytic reaction. Based on the above results, we claimed that the role of Cs2CO3 was to facilitate the formation of key intermediate 6. On the other hand, it provided the optimized basicity for the selective amide formation.

An efficient heterogeneous amidation catalyst has been prepared by co-polymerisation of styrene, DVB with 4-styreneboronic acid, which shows wide substrate applicability and higher reactivity than the equivalent homogeneous phenylboronic acid, suggesting potential cooperative catalytic effects. The catalyst can be easily recovered and reused; suitable for use in packed bed flow reactors.

An environmentally friendly, inexpensive, carbocatalyst, graphene oxide (GO) promoted efficient, metal-free transamidation of various carboxamides with aliphatic, cyclic, and aromatic amines is demonstrated. The protocol is equally applicable to phthalimide, urea, and thioamide determining its adaptability. The oxygenated functionalities such as carbonyl (?C=O), epoxy (?O?), carboxyl (?COOH) and hydroxyl (?OH), present on graphene oxide surface impart acidic properties to the catalyst. The graphene oxide being heterogeneous in nature, work efficiently under solvent-free reaction conditions providing desired products in good to excellent yields. The one-pot synthesis of 2,3-Dihydro-5H-benzo[b]-1,4-thiazepin-4-one moiety by GO catalyzed Aza Michael addition followed by intramolecular transamidation is also described. A plausible reaction mechanistic pathway involving H-bonding is discussed. The graphene oxide can be recycled and reused up to five cycles without much loss in catalytic activity. (Figure presented.).

Reactions of secondary thioamides with diaryliodonium salts under basic, transition metal-free conditions resulted in chemoselective S-arylation to provide aryl thioimidates in good to excellent yields. Equimolar amounts of thioamide, base and diaryliodonium salt were sufficient to obtain a diverse selection of products within short reaction times. Reactions with thiolactams delivered N-arylated thioamides in good yield at room temperature.

Transition-metal-catalyzed amide-bond formation from alcohols and amines is an atom-economic and eco-friendly route. Herein, we identified a highly active in situ N-heterocyclic carbene (NHC)/ruthenium (Ru) catalytic system for this amide synthesis. Various substrates, including sterically hindered ones, could be directly transformed into the corresponding amides with the catalyst loading as low as 0.25 mol.%. In this system, we replaced the p-cymene ligand of the Ru source with a relatively labile cyclooctadiene (cod) ligand so as to more efficiently obtain the corresponding poly-carbene Ru species. Expectedly, the weaker cod ligand could be more easily substituted with multiple mono-NHC ligands. Further high-resolution mass spectrometry (HRMS) analyses revealed that two tetra-carbene complexes were probably generated from the in situ catalytic system.

The atom-economic direct amidation of alcohols with amines has been recently highlighted as an attractive and promising transformation. Among the versatile reported catalytic systems, in situ generated N-heterocyclic carbene (NHC)/ruthenium (Ru) catalytic systems have demonstrated their advantages such as easy operation and use of commercial Ru compounds. However, the existing catalyst loadings are relatively high, and additional insights for the in situ catalyst generation are still not well-documented. In this work, a variety of benzimidazole-based NHC precursors were initially synthesized. Through the screening of various NHC precursors and other reaction conditions, active in situ catalytic systems were discovered for the efficient amide synthesis. Notably, the catalyst loading is as low as 0.5 mol %. Furthermore, additional experiments were performed to validate the rationale for the superiority of the current catalytic systems over our previous system. It was observed that the ligand structure is one of the reasons for the higher activity. In addition, the higher ratio of the NHC precursor/[Ru] is another important factor for the improvement. Further HR-MS analysis identified the formation of two mono-NHC-Ru species as major species and two Ru species bearing multiple NHC ligands as minor species. Hopefully, the efficient and readily-accessible catalytic systems reported herein could demonstrate great potential for further practical applications.

The addition of carbon nucleophiles to isocyanates represents a conceptually flexible and efficient approach to the preparation of amides. This general synthetic strategy has, however, been relatively underutilized owing to narrow substrate tolerance and the requirement for less favourable reaction conditions. Herein, we disclose a high-yielding, mass-efficient, and scalable method with appreciable functional group tolerance for the formation of amides by reaction of Grignard reagents with isocyanates. Through the application of flow chemistry and the use of substoichiometric amounts of CuBr2, this process has been developed to encompass a broad range of substrates, including reactants found to be incompatible with previously published procedures.

A general and efficient protocol for iso-selective aminocarbonylation of olefins with aliphatic amines has been developed for the first time. Key to the success for this process is the use of a specific 2-phosphino-substituted pyrrole ligand in the presence of PdX2(X=halide) as a pre-catalyst. Bulk industrial and functionalized olefins react with various aliphatic amines, including amino-acid derivatives, to give the corresponding branched amides generally in good yields (up to 99 %) and regioselectivities (b/l up to 99:1).

A method for the one-pot synthesis of substituted amides from aldehydes and amides is presented. Namely, condensation of aldehydes with N-tosylhydrazide generated the N-tosylhydrazones which were then reductively cross-coupled in situ with primary or secondary amides in the presence of a copper catalyst to afford secondary or tertiary amides, respectively. The reaction proceeded efficiently for a wide range of aldehydes and amides under the optimized conditions, i.e., 10 mol% of tetrakis(acetonitrile)copper(I) tetrafluoroborate [Cu(CH3CN)4BF4], 1 mol% of tetra-n-butylammonium iodide [(n-Bu)4NI], and sodium hydroxide [NaOH] as base in tetrahydrofuran (THF) at 80 C. As a result, the method provides a straightforward route for the synthesis of substituted amides from readily available aldehydes via a transition metal-catalyzed C(sp3)- N amide bond forming reaction.

Monocarbonyl activation of 2,2-disubstituted malonic acids with benzotriazole leads to decarboxylation of one of the carboxy groups and formation of a C-H bond. Intermediate carbonyl benzotriazoles then readily acylate nucleophilic reagents and peptides resulting in libraries of conjugates and peptidomimetics.

Beside showing that thermal radical reactions (reduction, Giese reaction) are efficient if bromo-/iodosugars are treated with NaBH3CN and 2,2″-azobisisobutyronitrile, we explored new initiation conditions on the basis of CuI salts (≤0.5 equiv.) supposed to produce radicals from organobromides through a set. This was confirmed, as at about 50 C under an inert atmosphere acetobromoglucose was reduced to the rearranged 2-deoxyglucose and as N-allyl α-bromoamides reacted, depending on the conditions, either by reductive cyclization or atom-transfer radical cyclization. A related cyclization occurred upon using Cu(OAc)2. This and other assays showed the reduction by NaBH3CN of CuII salts, either added or formed in situ. Having both ionic and radical reactivity, NaBH 3CN appears as a Janus reagent that may be useful for tin-free radical chemistry under mild and very simple conditions. Copyright

We present a simple method for direct and solvent-free formation of amides from carboxylic acids and amines using radiofrequency heating. The direct energy coupling of the AC magnetic field via nickel ferrite magnetic nanoparticles enables fast and controllable heating, as well as enabling facile work-up via magnetic separation.

We report a highly diastereoselective synthesis of vicinal diamines by the treatment of nitroepoxides with primary amines and then a reducing agent. When using a chiral primary amine, racemic nitroepoxides are transformed into chiral diamines as a single enantiomers (>95:5 er) through a dynamic kinetic asymmetric transformation (DYKAT). The overall process is a one-pot procedure combining the exposure of nitroepoxides to chiral amines to afford diastereomeric mixtures of aminoimines and subsequent stereoselective imine reduction.

A novel method of transamidation of carboxamides with amines using catalytic amounts of readily available boric acid under solvent-free conditions has been developed. The scope of the methodology has been demonstrated with (i) primary, secondary, and tertiary amides and phthalimide and (ii) aliphatic, aromatic, cyclic, acyclic, primary, and secondary amines.

The ruthenium catalyzed selective sp3 C-O cleavage with amide formation was reported in reactions of 3-alkoxy-1-propanol derivatives and amines. The cleavage only occurs at the C3-O position even with 3-benzyloxy-1-propanol. Based on the experimental results, O-bound and C-bound Ru enolate complexes were proposed as key intermediates for the unique selective sp3 C-O bond cleavage in 3-alkoxy-1-propanols.

The first example of aromatic cation-activated nucleophilic acyl substitution has been achieved. The conversion of carboxylic acids to their corresponding acid chlorides occurs rapidly in the presence of 3,3-dichlorocyclopropenes via the intermediacy of cyclopropenium carboxylate complexes. The effect of cyclopropene substituents on the rate of conversion is examined. The addition of tertiary amine base is found to dramatically accelerate reaction, and conditions were developed for the preparation of acid sensitive acid chlorides. Preparative scale peptide couplings of two N-Boc amino acids were achieved with this method.

The presented results and the available literature data convincingly suggest that there Is a new sterlcally driven mechanism for the formation of supramolecular hellclty In the solid state. This mechanism requires the presence of sterlcally bulky groups, such as tert-butyl, for which the spiral arrangement In uninterrupted hydrogen-bonding chains, serving as an axis for helical structure and maximizing the repulsive stereochemical Interactions, provide for the most efficient, spatially economical accommodation of these groups In a crystallographlc unit cell.

1,2,4-Triazole anion has been identified as an active acyl transfer catalyst suitable for the aminolysis and transesterification of esters.

2,2 -Dipyridyl diselenide (PySeSePy) is the catalyst or activator of choice for the direct reaction of carboxylic acids with azides and trimethylphosphine at room temperature. The mechanism of the process, which is not an aza-Wittig reaction, has been elucidated.

(Chemical Equation Presented) Pyrido- and pyrrolo[2,3-d]oxazoles can be conveniently prepared in high yield from the Ritter reaction of nitriles and in situ generated chiral cyclic N-acyliminium ions, cis-4-Hydroxy-5- acylaminopyrrolidines and cis-5-hydroxy-6-acylaminopiperidines can be readily obtained by acid hydrolysis of these bicyclic heterocyclic compounds, respectively.

A novel copper-catalyzed oxidative desulfurization reaction of thiocarbonyl compounds, using molecular oxygen as an oxidant and leading to formation of carbonyl compounds, has been developed, and the utility of the process is demonstrated by its application to the preparation of a carbonyl-18O labeled sialic acid derivative. The Royal Society of Chemistry.

The radical reactions of N-(2-halogenoalkanoyl)-substituted anilines (anilides) of type 1 have been investigated under various conditions. Treatment of compounds 1a-1o with Bu3SnH in the presence of (2,2′-azobis(isobutyronitrile) (AIBN) afforded a mixture of the indolones (oxindoles) 2a-2o and the reduction products 5a-5o (Table 1). In contrast, the N-unsubstituted anilides 1p-1s, 1u, and 1v gave the corresponding reduction products exclusively (Table 1). Similar results were obtained by treatment of 1 with Ni powder (Table 2) or wth Et3B (Table 3). Anilides with longer N-(phenylalkyl) chains such as 6 and 7 were inert towards radical cyclization, with the exception of N-benzyl-2-bromo-N,2-dimethylpropanamide (6b), which, upon treatment with Ni powder in i-PrOH, afforded the cyclized product 9b in low yield (Table 4). Upon irradiation, the extended anilides 6, 7, 10, and 11 yielded the corresponding dehydrobromination products exclusively (Table 5).

(Chemical equation presented) The Ritter reaction of enantiopure 2-(1-aminoalkyl)aziridines 1 with different nitriles afford enantiopure tetrasubstituted imidazolines 2. The opening of the aziridine ring takes place with total regio- and stereoselectivity. A mechanism to explain the described addition reaction is proposed.

A three-step synthesis of cyclohexane-1,3-dione (CHD) resin 6 on polystyrene resin is described. Resin 6 was used to prepare an amide library of high purity by microwave-assisted serial "capture and release" and can be recycled for this purpose. High-loading CHD resin 10 was also shown to scavenge allyl cations in solution.

Benzyl amides are obtained from benzyl chlorides with excellent yields in mild conditions by using hydrated ferric chloride, FeCl3·6H2O, as Lewis acid catalyst and common nitriles as both solvents and reagents.

N-Alkyl-N-nitrosoamides undergo competitive reactions whose rates are dependent upon the interplay of a number of factors. There already exists a significant body of work delineating the effects of pH on the partitioning of the nitrosoamides along their deaminative (-N2) and denitrosative (- NO+ ) pathways. In this paper, the issue of pH dependence is discussed with particular attention to nitrosoamide decompositions in nonaqueous media. The role of the acidity of the medium in the partitioning of the nitrosoamide between deamination and denitrosation and in the choice of deaminative pathways is revisited. In nonaqueous media under near-neutral conditions, the partitioning's pH dependence is evidently accompanied by a sensitivity to structural features in the nitrosoamide. Thus, diminution of steric crowding around the N-nitroso moiety as well as the presence of strongly electron-withdrawing acyl units (i.e., those derived from strong acids, e.g., tosyl and trifyl) increase the relative yield of amides by encouraging the denitrosative pathway. A mechanism for thermal denitrosation of nitrosoamides under near-neutral conditions is proposed in which rapid protonation at the acyl O rather than slow protonation at the amidic N is the first step in the reaction profile. A rate-limiting, bimolecular reaction between the O-conjugate acid and adventitious nucleophiles at the nitrosyl group then occurs followed by rapid tautomerization to amide.

The photolysis of naphtho[1,8-de]-1,3-dichalcogeninylidene 1-oxide derivatives (4 and 5) at >290 nm generates ketenes together with naphtho[1,8- cd]-1,2-dichalcogenole, which were confirmed by the trapping experiments and the direct observation using IR spectroscopy. The generation of ketenes from the selenium compounds 5 is more effective than that from the sulfur analogs 4.

The reaction of different protected alcohols, amines and amides with lithium and a catalytic amount of naphthalene (4 mol %) in THF at low temperature leads to their deprotection under very mild reaction conditions, the process being in many cases chemoselective.

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Various amides, including some with bulky substituents, are prepared in good yields from free carboxylic acids and amines under mild conditions by a one-step method using new condensing agents 2-halo-2,3-dihydro-1,3,4,2-oxadiazaphospholes, especially 5-methyl-2-chloro-3-phenyl-2,3-dihydro-1,3,4,2-oxadiazaphosphole.

ω-Azido acids, after activation of the carboxyl groups as mixed anhydrides, N3(CH2)nCOOCOAr (Ar = 3,5-dinitrophenyl or 2,4,6-trichlorophenyl), can be converted to macrolactams in good yields by treatment with Bu3P under high-dilution conditions; the prese

Facile nucleophilic attack on coordinated carboxylate ligaods is reported: complexes of tantalum(V) react rapidly with amines and amino acid esters to give the corresponding amides. Cyclopentadienyltantalum(V) amino acid carboxylate complexes have been pr

The electroreduction of NH-protic α-bromo amides in DMF generates an enolate-type base which undergoes a fast proton transfer from the parent compound (self-protonation), affording the corresponding reduced amide together with the conjugate base of the br

The hydroformylation of methyl methacrylate (1) or t-butyl methacrylate (2) takes place with fair to good chemoselectivity, the regioselectivity depending on the catalyst precursor used.By contrast, methacrylonitrile (3), methacrylamide (4), and N-benzyl-methacrylamide (5) undergo hydroformylation followed by subsequent reactions.The formyl product formed is reduced to the corresponding 2-cyano-2-methylpropan-1-ol in the case of 3, and undergoes cyclization to 2-methyl-2,3-dehydrobutyrolactames for 4 and 5.Under conditions of hydrocarbalkoxylation in the presence of palladium catalysts, 4 gives 3-methylsuccinimide.In the enantioselective reactions, extents of asymmetric induction of about 20-50percent have been obtained.

The formation of amide bonds from the reaction of metal carboxylates with amines was observed for the first time; complexes for titanium(IV), zirconium(IV) and tantalum(V) were investigated.

The electroreduction of protic 2-bromoisobutyramides was studied in acetonitrile in the presence of carbon dioxide by means of cyclic voltammetry and controlled-potential electrolysis.The electrogeneration of the α-carbanion is followed by a fast and quan

The electrochemical reduction of series of secondary and tertiary α-bromoisobutyramides has been studied in dipolar aprotic solvents.A carbanion is formed at the mercury electrode as a consequence of two-electron C-Br bond cleavage.Voltammetry and macroelectrolysis point to a self-protonation mechanism, the carbanion undergoing protonation by a parent molecule to yield the isobutyramide.Concurrently, tertiary 2-bromoamides undergo 1,2-elimination to yield an αβ-unsaturated amide, while secondary 2-bromoamides are deprotonated at the nitrogen atom, affording a bromo-containing anion.The decay of the latter is strongly dependent on the solvent and the substituent at nitrogen.In acetonitrile, elimination and fragmentation products are identified in the electrolysed solution.On the other hand, in N,N-dimethylformamide or N,N-dimethylacetamide, the bromo-containing anion is eventually cyclocondensed onto the carbonyl group of the amide solvent, to yield an oxazolidin-4-one derivative.Preliminary data suggest that an analogous cyclocoupling reaction takes place when the reduction is carried out in 1-methyl-2-pyrrolidone.

Electrochemical reduction of 2-bromo-carboxamides involves self-protonation of the electrogenerated bases and affords, among other products, cyclo-adducts incorporating a dimethylformamide unit.

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