An effective new synthesis of 2-aminopyrrole-4-carboxylates

Efficient syntheses of 2-aminopyrroles are presented starting from β-dicarbonyl compounds, bromoacetonitrile, and amines. Alkylation of β-dicarbonyl compounds with bromoacetonitrile furnished α-cyanomethyl-β-dicarbonyl compounds. The condensation reaction of α-cyanomethyl-β-dicarbonyl compounds with amines catalyzed by p-TsOH affords the corresponding enamines in good yields. Base catalyzed cyclization via the addition of an amine moiety to the carbon-nitrogen triple bond of nitrile furnished 2-aminopyrroles in high yields.     

Zinc perchlorate catalyzed one-pot amination-annulation of α-cyanomethyl-β-ketoesters in water. Regioselective synthesis of 2-aminopyrrole-4-carboxylates

In this paper, we report the efficient and regioselective synthesis of 2-aminopyrrole-4-carboxylates as derivatives of conformationally restricted analogues of γ-amino butyrates (GABA) via a zinc perchlorate catalyzed amination-annulation of α-cyanomethyl-β-ketoesters under mild reaction conditions in water.     

Efficient one-pot synthesis of ethyl 2-substitued-4-methylthiazole-5-carboxylates

A new and practical one-pot procedure for the synthesis of several 2-sustituted-4-methylthiazole-5-carboxylates from commercially available starting materials is described. Under mild reaction conditions, some of the products with alkyl group on the 2-amino group or with various groups on 2-substituted phenyl ring were obtained in good yields from ethyl acetoacetate, N-bromosuccinimide, thiourea, or its N-substituted derivatives in an efficient way instead of the traditional two-step reaction.     

An improved Pfitzinger reaction: Eco-efficient synthesis of quinaldine-4-carboxylates by TMSCl-mediated

We report herein an improved Pfitzinger reaction for the synthesis of highly functionalized quinaldines from 1,3-dicarbonyl compounds, isatins and alcohols mediated by TMSCl. This synthesis involves cyclization and esterification in one-step cascade process for the formation of a carboxylate (CO₂R) at the 4-position of quinaldine ring. Moreover, this procedure shows highly efficient, good functional group tolerance, operational simplicity, environment-friendly and feasibility of scale up.     

Three-component synthesis of methyl 6-alkyl-3-cyano-2-halopyridine-4-carboxylates

A procedure has been developed for the synthesis of methyl 6-alkyl-3-cyano-2-halopyridine-4-carboxylate by three-component reaction of 4-oxoalkane-1,1,2,2-tetracarbonitriles with hydrogen halides in methanol.     

Palladium- or nickel-catalyzed reaction of alkynes with trimethylsilyl cyanide. A new synthesis of 5-aminopyrrole-2-carbonitriles

The reaction of alkynes with trimethylsilyl cyanide (1) in the presence of a palladium or nickel catalyst gave 5-aminopyrrole-2-carbonitriles in high yields with high regioselectivity.     

A new convenient synthesis of trisubstituted 1,3-dioxole-4-carboxylates from methyl 2-diazo-3-oxobutyrate and aldehydes

The interaction between methyl 2-diazo-3-oxobutyrate and the carbonyl group of aliphatic, aromatic, and α,β-unsaturated aldehydes under bis(hexafluoroacetoacetonato)copper(II) catalysis furnishes 1,3-dioxole-4-carboxylates in preparatively useful yields. The apparent 1,3-dipolar cycloaddition reaction of the metal carbene complex is remarkably free of competing processes.     

Asymmetric synthesis of 2H-azirine 3-carboxylates

[reaction: see text] Dehydrochlorination of methyl 2-chloroaziridine 2-carboxylates generates the first examples of enantiopure 2-substituted 2H-azirine 3-carboxylates which undergo the aza Diels-Alder reaction with dienes to give bicyclic and tricyclic aziridines in good yields.     

Solid-phase synthesis of 3-aminopyrrole-2,5-dicarboxylate analogues

An efficient strategy has been developed for the solid-phase parallel synthesis of 3-aminopyrrole-2,5-dicarboxylate analogues. A library of twenty-nine 2,3,5-trisubstituted pyrroles has been synthesized on Wang resin by a 5-6 step process. The attachment of (2S,4R)-4-hydroxy-N-(PhF)proline cesium salt (PhF = 9-(9-phenylfluorenyl)) to Wang bromide resin, followed by alcohol oxidation, produced the resin-bound 4-oxo-N-(PhF)prolinate as the pyrrole precursor. Resin-bound 3-aminopyrroles were synthesized by treatment of the oxo-N-(PhF)prolinate resin with different secondary amines and diversified at the 2-position by acylation with trichloroacetyl chloride and haloform reactions with primary amines. 3-Aminopyrrole-2,5-dicarboxylates were isolated in 81-99% purity and 51-99% yields after cleavage from the resin using TFA or sodium methoxide.     

An unusual dehalogenation in the Suzuki coupling of 4-bromopyrrole-2-carboxylates

An unusual dehalogenation of 4-bromopyrrole-2-carboxylates under Suzuki coupling conditions has been observed. This dehalogenation can be suppressed by protection of the pyrrole nitrogen. Using a BOC protecting group, not only is dehalogenation suppressed, but the protecting group is also removed under the reaction conditions.     

Organocatalyzed enantioselective synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylates

The organocatalyzed enantioselective synthesis of biologically active 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylate derivatives was achieved using bifunctional cinchona alkaloids as the catalysts. Using quinine thiourea as the catalyst, the tandem Michael addition-cyclization reaction between 1,3-cyclohexanediones and alkylidenecyanoacetate derivatives gives the desired products in high yields (up to 92%) and good ee values (up to 82%).     

ZnO nanoparticles-mediated regioselective synthesis of methyl-N-alkylated 1,2,3-triazole-4-carboxylates

The 1,2,3-triazoles are versatile synthetic intermediates of many biologically active compounds, and their N-1 substituted analogues are potential pharmaceutically important derivatives. In this study, an efficient regioselective N-alkylation reaction of methyl-1H-1,2 3-triazole-4-carboxylate 3 with alkyl halides 4 catalyzed by ZnO nanoparticles in the presence of potassium hydroxide as base and DMSO as solvent is reported which leads to methyl N ₁-alkylated 1,2,3-triazole-4-carboxylates 5 in good yields.     

A new methodology for the synthesis of 3-amino-1H-indole-2-carboxylates

A new methodology has been developed for the synthesis of 3-amino-1H-indole-2-carboxylates. 2-Aminobenzonitriles were protected as benzyl (2-cyanophenyl)carbamates and converted into corresponding glycinate esters using sodium hydride and bromoacetate esters. Sodium hydride efficiently promotes the addition of the glycinate α-carbon to the cyano group at low temperatures, resulting in the formation of the desired indole core with 3-amino and 2-carboxylate groups. This new methodology uses Pd–C mediated hydrogenolysis with molecular hydrogen, providing neutral conditions for removal of the N-carbamate protecting group. This methodology demonstrates good functional group tolerance towards a variety of substituents in the aromatic ring and ester groups. The overall yield of 3-amino-1H-indole-2-carboxylates obtained by this four-step methodology is at least 30% or higher with yields as high as 50% realised for three of the indoles investigated in this study.     

Wittig homologation of 2-(chloromethyl)-2H-chromen-2-ol derivatives: a new facile synthesis of substituted 2,3-dihydrobenzoxepine-4-carboxylates

Wittig homologation of 2-(chloromethyl)-2H-chromen-2-ol derivatives 2a–t with (ethoxycarbonylmethylene)triphenylphosphorane provided the 2-oxoethylidene-2,3-dihydrobenzoxepine-4-carboxy-lates 3a–t with Z (cis) selectivity. Various basic catalysts were studied for the reaction of 2-(chloromethyl)-2H-chromen-2-ol 2a with the combination of Wittig reagent to provide compound 3b. The reaction of 2-(chloromethyl)-2H-chromen-2-ol 2a with other Wittig reagents, such as methylene(triphenylene)phosphorane and (1-ethoxycarbonylethylidene)triphenylphosphorane provided ketone derivative 4a rather 2-oxoethylidene derivative 3b. The ketone derivative 4a was reacted with Wittig reagent (ethoxycarbonylmethylene)triphenylphosphorane to give 2,3-dihydrobenzoxepine-4-carboxylate 3b. The present approach is novel, straight forward and being reported for the first time.     

Ring closure and rearrangement reactions of 4-azido-2-oxoquinoline-3-carboxylates and 4-azidocoumarin-3-carboxylates

4-Azido-2-oxoquinoline-3-carboxylates and 4-azidocoumarin-3-carboxylates 6 , which were obtained from the corresponding 4-hydroxy derivatives 1 via 4-tosylates 2 or 4-chloro compounds 4 , cyclized upon thermolysis to 3-alkoxyisoxazolo[4,3-c]quinolin-4(5H)-ones or the corresponding coumarins 8 , whereas at slightly higher temperatures a 3-O, 4-O-rearrangement took place to give the 4-alkoxy-isoxazolo[4,3-c]-quinolin-3-ones and the corresponding coumarins 9. The necessary reaction conditions could be obtained easily with the help of differential scanning calorimetry.     

Diastereoselective synthesis of 2-fluoroaziridine-2-carboxylates by Reformatsky-type aza-Darzens reaction

The reaction of ethyl dibromofluoroacetate with imines using zinc metal gave 2-fluoroaziridine-2-carboxylates via aza-Darzens reaction of the primary product of the Reformatsky reaction with high diastereoselectivity in excellent yields (quantitative yield and Dr = 85:15). This chemoselective formation of 2-fluoroaziridines was achieved by using CH₃CN as a solvent. Interestingly, the reaction proceeded without activation of zinc metal, which was necessary for the Reformatsky reaction of bromodifluoroacetate. None of α-bromo-α-fluoro-β-lactams, four-membered cyclization products, and noncyclized 3-amino-2-bromo-2-fluorocarboxylic esters, usual Reformatsky adducts, were formed.     

A facile synthesis of 3,5-diaminopyrazole-4-carbothioamides and 3,5-diaminopyrazole-4-carboxylates

Simple and convenient synthesis of hitherto unknown 3,5-diaminopyrazole-4-carbothioamides 3 as well as new ethyl 3,5-diaminopyrazole-4-carboxylates 7 is reported. The key intermediates were 2-cyano-propenethioamides 2 and 2-(ethoxycarbonyl)propenethioamides 5 which were readily obtained by reaction of phenyl isothiocyanate with 3-(2-acylhydrazino)-3-aminopropenenitriles 1 and ethyl 3-(2-acylhydrazino)-3-aminopropenoates 4 respectively. Intramolecular cyclization of compounds 2 afforded pyrazole-4-carbothioamides 3 while propenethioamides 5 gave pyrazole-4-carboxylates 7 .     

Palladium-catalyzed N-arylation of 2-aminobenzothiazole-4-carboxylates/carboxamides: facile synthesis of PARP14 inhibitors

We have developed a palladium-catalyzed N-arylation of the biologically interesting, but synthetically rather challenging 2-arylaminobenzothiazoles bearing multiple functionalities. This protocol was successfully used to readily synthesize our initial PARP14 inhibitor followed by a limited structural optimization. A more potent PARP14 inhibitor with an IC₅₀ value of 1.69 μM was identified, and the interaction was ascertained by the X-ray co-crystal structure of the catalytic domain of PARP14 in complex with compound 8.