Synthesis of 7-(3-piperidyl)-[1,6]naphthyridine and 7-(4-pipe-ridyl)[1,6]naphthyridine

7-(3-Piperidyl)- and 7-(4-piperidyl)[1,6]naphthyridines have been synthesized from 2-methylpyridine-3-carbaldehyde cyclohexylimine and the methylmethoxycarboxamides (Weinreb amides) of N-Boc- substituted nipecotic and isonipecotic acids.     

One-pot synthesis of Weinreb amides employing 3,3-dichloro-1,2-diphenylcyclopropene (CPI-Cl) as a chlorinating agent

The synthesis of N^α-protected amino alkyl Weinreb amides starting from the corresponding α-amino acids as well as carboxylic acids has been delineated through the in situ generation of acid chlorides using CPI-Cl as a chlorinating agent. The protocol is simple; the reaction conditions employed were mild, and compatible with all the three commonly used urethane protecting groups namely, Boc, Cbz and Fmoc groups. The resulting Weinreb amides are obtained in good yields as optically pure products.     

A Photochemical Protocol for the Synthesis of Weinreb and Morpholine Amides from Carboxylic Acids

In recent years, the development of light-mediated methods for synthetic applications has attracted high interest, because such methods constitute alternative approaches for the production of valuable chemical products. We study herein a photochemical protocol for the synthesis of Weinreb amides and morpholine amides from carboxylic acids. Various carboxylic acids were directly coupled to N,O-dimethylhydroxylamine, upon irradiation with either LED 370 nm or sunlight in the presence of 4-dimethylaminopyridine and bromotrichloromethane, providing Weinreb amides in moderate to high yields. Similarly, morpholine amides were obtained in satisfactory to high yields under sunlight or LED 370 nm irradiation. Thus, the versatile building blocks Weinreb amides and morpholine amides may be efficiently synthesized directly from carboxylic acids by light-mediated approaches, without the need of coupling reagents or pre-activation of carboxylic acids.     

One-pot preparation of Oxazol-5(4H)-ones from amino acids in aqueous solvents

A method for one-pot synthesis of oxazol-5(4H)-ones has been developed using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM), which is available for the activation of carboxylic acids in an aqueous solvent. The oxazolones were prepared by the N-acylation of amino acids with carboxylic acids and the subsequent cyclodehydration of the resulting N-acylamino acids by the addition of N,N-diethylaniline. Since both these reactions proceed effectively with the same coupling reagent, DMT-MM, in aqueous solvents, the procedure is simplified and becomes easy to perform. In addition, 5-(triazinyloxy)oxazole derivatives have been synthesized by controlling the basicity of the reaction system.     

Synthesis of N(3-dimethylaminopropyl)-6-substituted naphtho[2,1-b]thiophene-4-carboxamides

A series of N-(3-dimethylaminopropyl)-6-substituted naphtho[2,1-b]thiophenes-4-carboxamides have been synthesized. 6-Substituted naphtho[2,1-b]thiophene-4-carboxylic acids were obtained upon oxidative-photo-cyclization of α-(2-thienyl)-β-arylacrylic acids. The naphtho[2,1-b]thiophene carboxylic acids were converted to the corresponding amides through their acid chlorides or, in one case, by use of 1,1-carbonyldiimidazole coupling of the amine and the acid.     

A one-flask synthesis of Weinreb amides from chiral and achiral carboxylic acids using the deoxo-fluor fluorinating reagent

[structure] The reagent [bis(2-methoxyethyl)amino]sulfur trifluoride (Deoxo-Fluor reagent) converts carboxylic acids to the corresponding acid fluorides, which then react with N,N-dimethylhydroxylamine to give the corresponding Weinreb amides in high yields. The reaction proceeds without racemization when optically active acids are used as the starting material. This method is operationally simple and provides the products in high purity.     

One-pot synthesis of aldehydes or ketones from carboxylic acids via in situ generation of Weinreb amides using the Deoxo-Fluor reagent

A one-pot, high yield conversion of carboxylic acids to the corresponding aldehydes and ketones is described. The highlight of this methodology is the in situ generation of Weinreb amides with the Deoxo-Fluor reagent, which undergo nucleophilic reaction with DIBAL-H and Grignard reagents.     

2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate as an efficient coupling reagent for the amidation and phenylhydrazation of carboxylic acids at room temperature

The synthesis of amides and phenylhydrazides from the reaction of corresponding carboxylic acids with primary aliphatic, aromatic amines or phenylhydrazine in the presence of triethylamine or diisopropylethyl amine as a base using 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU) proceeds smoothly under mild conditions to afford the corresponding amides or phenylhydrazides in good to high yields in ethyl acetate at room temperature.     

Synthesis of various acylating agents directly from carboxylic acids

Abstract

A straightforward synthesis of acylating reagents such as Weinreb and MAP amides from aromatic, aliphatic carboxylic acids, and amino acids using PPh₃/NBS combination is described. A chemo-selective modification of the carboxylic acid group into Weinreb amide in the presence of more reactive aldehydes and ketones is presented. All reactions were performed at ambient temperature under air using undried commercial grade solvent. Furthermore, the present methodology could be performed at a gram scale under inert-free reaction conditions. In addition, 7-azaindoline amide auxiliary (used for catalytic asymmetric aldol- and Mannich-type reactions), which behaves like Weinreb amide is also synthesized under similar reaction conditions.     

Microwave-assisted and continuous flow multistep synthesis of 4-(pyrazol-1-yl)carboxanilides

A series of 4-(pyrazol-1-yl)carboxanilides active as inhibitors of canonical transient receptor potential channels were synthesized in an efficient three-step protocol using controlled microwave heating. The general synthetic strategy involves condensation of 4-nitrophenylhydrazine with appropriate 1,3-dicarbonyl building blocks, followed by reduction of the nitro group to the amine, which is then amidated with carboxylic acids. Compared to the conventional protocol a dramatic reduction in overall processing time from ~2 days to a few minutes was achieved, accompanied by significantly improved product yields. In addition, the first two steps in the synthetic pathway were also performed under continuous flow conditions providing similar isolated product yields. As an alternative to the three-step protocol, a novel two-step route to the desired 4-(pyrazol-1-yl)carboxanilides was devised involving condensation of 4-bromophenylhydrazine with appropriate 1,3-dicarbonyl building blocks, followed by Pd-catalyzed Buchwald-Hartwig amidation with carboxylic acid amides.     

Rhodium/diene-catalyzed asymmetric 1,4-addition of arylboronic acids to alpha,beta-unsaturated Weinreb amides

Rhodium/chiral diene (S,S)- complex has been found to effectively catalyze the 1,4-addition of arylboronic acids to alpha,beta-unsaturated Weinreb amides, furnishing useful beta-chiral Weinreb amides in high enantioselectivity.     

In situ alcohol oxidation-Wittig reactions using N-methoxy-N-methyl-2-(triphenylphosphoranylidine)acetamide: application to the synthesis of a novel analogue of 5-oxo-eicosatetraenoic acid

Benzylic, allylic, propargylic and unactivated alcohols can be oxidised with activated manganese dioxide in the presence of N-methoxy-N-methyl-2-(triphenylphosphoranylidine)acetamide to generate directly the corresponding α,β-unsaturated Weinreb amides. Elaboration of the resulting Weinreb amides is also described, in particular as part of a new route to analogues of the arachidonic acid metabolite 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid.     

Solution-phase synthesis of a combinatorial library of 3-[4-(coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acid amides

The parallel solution-phase synthesis of a new combinatorial library of 3-[4-(R1-coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acid amides 9 has been developed. The synthesis involves two steps: 1) the synthesis of core building blocks - 3- [4-(coumarin-3-yl)-1,3-thiazol-2-ylcarbamoyl]propanoic acids, 6 - by the reaction of 3-(omega-bromacetyl)coumarins 1 with 3-amino(thioxo)methylcarbamoylpropanoic acid (5); 2) the synthesis of the corresponding 3-[4-(coumarin-3-yl)-1,3-thiazol-2-yl- carbamoyl]propanoic acids amides 9 using 1,1'-carbonyldimidazole as a coupling reagent. The advantages of the method compared to existing ones are discussed.     

Preparation of ferrocenyl imidazolines using bis(triphenyl)oxodiphosphonium trifluoromethanesulfonate

An efficient synthesis of ferrocenyl imidazolines starting from ferrocenyl carboxylic acids has been developed. Bis(triphenyl)oxodiphosphonium trifluoromethanesulfonate was used to convert smoothly ferrocenyl carboxylic amides bearing an amine side chain, derived from ferrocenyl carboxylic acids and 1,2-diamines, to their corresponding ferrocenyl imidazolines.     

Functionally Substituted 3-Heterylpyrazoles: XI. 3-[3-Aryl(heteryl)pyrazol-4-yl]propenoic and Propanoic acids

3-Aryl(heteryl)-4-formylpyrazoles by condensation with malonic acid furnish 3-[3-aryl(heteryl)- pyrazol-4-yl]propenoic acids that in the presence of Raney nickel are reduced by hydrazine hydrate to 3-[3-aryl(heteryl)pyrazol-4-yl]propanoic acids. The successive conversion of both type acids into the corresponding acyl chlorides, esters, and amides was performed.     

Asymmetric synthesis of anti-α-substituted β-amino ketones from sulfinimines

Previously unknown, enantiopure, β-amino ketones were prepared in modest yield by addition of lithium reagents to N-sulfinyl anti-α-substituted β-amino Weinreb amides. Grignard reagents failed to add to these Weinreb amides in contrast to the syn-α-substituted isomers which did. The anti-α-substituted β-amino Weinreb amides were prepared by addition of LiN(OMe)Me to the corresponding N-sulfinyl anti-α-substituted β-amino esters because α-alkylation of N-sulfinyl β-amino Weinreb amide enolates resulted in poor diastereoselectivities.     

DIC-Mediated Coupling of Carboxylic Acids to (4R, 5S)-4-Methyl-5-Phenyl-2-Oxazolidinone

The use of diisopropylcarbodiimide as an agent to effect the coupling of carboxylic acids to Evans' chiral auxiliary (4R, 5S)-4-methyl-5-phenyl-2-oxazolidinone provides the corresponding acyl derivatives in good yields.     

4-Functionally Substituted 3-Heterylpyrazoles: III. 3-Aryl(heteryl)pyrazole-4-carboxylic Acids and Their Derivatives

3-Aryl(heteryl)-4-formylpyrazoles were cleanly oxidized by potassium permanganate in water-pyridine medium to afford in high yield 3-aryl(heteryl)pyrazole-4-carboxylic acids, that were further converted into the corresponding chlorides and amides.     

ω-(2-benzimidazolyl)perfluorinated carboxylic acids and their derivatives

A convenient method is proposed for the preparation of -(2-benzimidazolyl) perfluorinated carboxylic acids and their amides by condensation of o-phenylenediamine with imides of perfluorinated dicarboxylic acids. The transformations of the o-aminoanilides of the amides of the perfluorinated dicarboxylic acids were studied by thermal analysis and mass spectroscopy.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1262–1265, September, 1976.     

Transformation of 3-(3-arylalkylcarbamoyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-1-yl)propanenitriles into amides and acids

A mixture of hydrochloric and acetic acids depleted in water was proposed to effect stepwise transformation of 3-(3-arylalkylcarbamoyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-1-yl)propanenitriles into the corresponding amides and then into the acids. The procedure turned out to be efficient with 3-[(2-phenylethyl)-carbamoyl] derivatives, whereas the reactions with benzylcarbamoyl analogs were accompanied by partial or complete debenzylation.