Studies with enaminones and enaminonitriles: synthesis of 3-aroyl and 3-heteroaroyl-pyrazolo-[1,5-a]pyrimidines

The reaction of electron rich aromatics with cyanoacetic acid and acetic anhydride afforded 3-oxoalkanenitriles. Indium trichloride was used as a Lewis acid catalyst when the aromatic ring was not sufficiently reactive. The synthesized 3-oxoalkanenitriles were subsequently condensed with dimethylformamide dimethylacetal (DMFDMA) to yield enaminones that reacted readily with hydrazine hydrate to yield 4-aroylpyrazole-3-amines. The 4-aroylpyrazole-3-amines were condensed with enaminones to yield 3-aroylpyrazolo[1,5-a]pyrimidines.     

<Emphasis Type="Italic">N,N,N′,N′</Emphasis>-tetramethylmethanediamine—A new reagent for aminomethylation of acetylenes

A new procedure has been developed for aminomethylation of terminal acetylenes with N,N,N′,N′-tetramethylmethanediamine in the presence of transition metals and lanthanide complexes and salts. The procedure ensures formation of the corresponding N,N-dimethylprop-2-yn-1-amines with high yield and selectivity.     

Novel syntheses of 3-anilino-pyrazin-2(1H)-ones and 3-anilino-quinoxalin-2-(1H)-ones via microwave-mediated Smiles rearrangement

In this Letter, we report a novel approach to the preparation of 3-anilino-pyrazin-2(1H)-ones and 3-anilino-quinoxalin-2(1H)-ones from the corresponding 3-halo pyrazin-2-amines and 3-haloquinoxalin-2-amines, using a microwave-mediated Smiles rearrangement.     

Synthesis of dimethyl substituted benzimidazoles containing cyclopropane fused onto five to eight membered [1,2-a]alicyclic rings and influence of methyl group substituents on cytotoxicity of benzimidazolequinones

Upon thermolysis 5,6-dimethyl-N-[(allyl, but-3-enyl, pent-4-enyl and hex-5-enyl-benzimidazol-2-yl)methylene]-(trans)-2,3-diphenylaziridin-1-amines (Eschenmoser hydrazones) form cyclopropane fused onto pyrrolo-, pyrido-, azepino- and azocino[1,2-a]benzimidazoles in 70, 50, 77 and 11% yield, respectively. The latter reaction also gave carbene insertion products. Dimethyl group substituents were found to significantly reduce the cytotoxicity of benzimidazolequinone towards human skin fibroblast cells.     

Mild synthesis of 5-(9-ethyl-9H-carbazol-3-yl)-N-aryl-1,3,4-thiadiazol-2-amines

An efficient synthetic method for heterocycles containing both carbazole and 1,3,4-thiadiazole moieties is described. 9-Ethyl-9H-carbazol-3-carbaldehyde reacted with 4-arylthiosemicarbazides, with acetic acid as catalyst, to give 1-(9-ethyl-9H-carbazol-3-yl)methylene-4-arylthiosemicarbazides, which were further treated with manganese dioxide at room temperature in acetone to give 5-(9-ethyl-9H-carbazol-3-yl)-N-aryl-1,3,4-thiadiazol-2-amines in good to high yield. This procedure has the advantages of mild conditions, easy separation, and simple manipulation.     

Nucleophilic reactivity of amines with an α-formylglycyl enol-tosylate fragment

The E-enol-tosylate of S-3-benzyl-6-formylpiperazine-2,5-dione reacts with 1°- and 2°-amines to yield its respective 3S-benzyl-6E-endiamine products while a 3°-amine, DABCO, exclusively yields a bis-3,6-ylidenepiperazine-2,5-dione product. These competitive reaction pathways with amine electron donors are shown to arise mechanistically via the same intermediate, or its tautomers, with an H-bond assisted nucleophilic substitution process being operative in the former case and an elimination reaction pathway in the latter instance.     

Two-pot synthesis of N,N-disubstituted 4H-3,1-benzothiazin-2-amines from aryl(2-isothiocyanatophenyl)methanones and secondary amines

A convenient synthesis of N,N-disubstituted 4H-3,1-benzothiazin-2-amines from aryl(2-isothiocyanatophenyl)methanones using a two-pot procedure has been developed. Thus, treatment of these isothiocyanato ketones with secondary amines gave the corresponding keto thioureas, which were allowed to react with sodium borohydride or methylmagnesium bromide to afford 1,1-dialkyl-3-{2-[aryl(hydroxy)methyl]phenyl}thioureas or 1,1-dialkyl-3-[2-(1-aryl-1-hydroxyethyl)phenyl]thioureas, respectively, in one pot. Hydrobromic acid-mediated cyclization of these hydroxy thiourea precursors provided the desired 4H-3,1-benzothiazin-2-amines.     

l-Proline-catalyzed three-component domino reactions for the synthesis of highly functionalized pyrazolo[3,4-b]pyridines

A series of novel N,3-dimethyl-5-nitro-1-aryl-1H-pyrazolo[3,4-b]pyridin-6-amines was obtained in good yields from the domino reactions of N-methyl-1-(methylthio)-2-nitroprop-1-en-1-amine, aromatic aldehydes, and 3-methyl-1-aryl-1H-pyrazol-5-amines in ethanol in the presence of green catalyst, l-proline. This transformation involves the formation of two C–C and one C–N bonds leading to the creation of a six-membered ring in a one-pot operation.     

Enantioenriched 1-aryl-2-fluoroethylamines. Efficient lipase-catalysed resolution and limitations to the Mitsunobu inversion protocol

Both enantiomers of eight 1-aryl-2-fluoroethylamines have been synthesised starting with 1-aryl-2-fluoroethanones. Kinetic resolution of the amines using lipase B from Candida antarctica with ethyl methoxyacetate as the acyl donor gave the (R)-amines in 96-99% ee and the (S)-methoxyacetamides in >99.5% ee. The resolution was robust with respect to variation in reaction temperature, acyl donor concentration, water activity and substrate structure. Nine other lipase preparations failed to catalyse the reaction or gave a low enantioselectivity. Secondly, a Mitsunobu inversion protocol starting with enantioenriched 1-aryl-2-fluoroethanols using phthalimide as nucleophile was employed in the synthesis of the (S)-1-aryl-2-fluoroethylamines. Both the inversion efficiency and yield depended on the aromatic substituents. For six of the substrates, clean inversion of the stereochemistry was observed. However, racemisation and low yields were the result when electron-donating substituents were present at the aromatic ring. When substituted with a cyano or a nitro group, an unexpected fluorine elimination occurred, limiting the yield for these transformations. The absolute configuration of the 1-aryl-2-fluoroethylamines was determined using circular dichroism.     

Eco-efficient one-pot tandem synthesis of 1-aryl-1H-tetrazol-5-amine by CAN via in situ generated 1-phenylthiourea and heterocumulene

A simple, cost-effective, environmentally benign, and efficient one-pot tandem approach to the synthesis of pharmaceutically important 1-aryl-1H-tetrazole-5-amines 3a-k and 4a-k has been described. The reaction utilized 1-phenyl thiourea, which was generated in situ from aqueous ammonia and isocyanates 1a-k, for the formation of heterocumenes using sodium azide, triethylamine, and ceric ammonium nitrate (CAN) to obtain various aryl-substituted 1H-tetrazole-5-amines (3a-k) in good to excellent yields.     

Sodium dithionite initiated reaction of pent-4-en-1-amines with fluoroalkyl iodides for the synthesis of 2-fluoroalkyl pyrrolidine derivatives

Pent-4-en-1-amines are reactive to fluoroalkyl iodides with respect to sodium dithionite initiated free radical addition reactions. We report here the development of a novel and efficient synthesis of 2-fluoroalkyl pyrrolidine derivatives by sodium dithionite initiated one-pot reaction of pent-4-en-1-amines bearing various protecting groups with fluoroalkyl iodides. Among which, the N-benzyl-pent-4-en-1-amine exhibited the best tolerance toward the reaction condition in the present study, affording the desired adducts 3 in moderate to good yields of 65-85%.     

One-pot,microwave-assisted synthesis of polymethylene-bridged bis(1H-1,2,4-triazol-5(3)-amines) and their tautomerism

A highly selective and efficient method for the synthesis of 3,3′(5,5′)-polymethylene-bis(1H-1,2,4-triazol-5(3)-amines) was developed using the reaction of dicarboxylic acids and aminoguanidine in an aqueous medium. This one-pot, microwave-promoted method was proved to be scalable affording the desired products in good yields and purity. The scope of the method was successfully explored by the preparation of a small library of polymethylene-bis(1H-1,2,4-triazol-5(3)-amines) with different alkyl chain linkers. The annular prototropic tautomerism in the prepared compounds was studied using NMR spectroscopy and X-ray crystallography.     

An efficient synthesis of fully substituted pyrazolo[3,4-b]pyridin-5-amines from α-azidochalcones

A facile, mild and efficient procedure for the synthesis of fully substituted pyrazolo[3,4-b]pyridin-5-amines is reported. A mixture of an α-azidochalcone, a 5-aminopyrazole and t-BuOK was stirred in DMF at ambient temperature for 5?min to afford the corresponding pyrazolo[3,4-b]pyridin-5-amines in good to excellent yields.     

Condensation of Vilsmeier salts,derived from tetraalkylureas,with amidoximes: a novel approach to access N,N-dialkyl-1,2,4-oxadiazol-5-amines

A novel approach, condensation of Vilsmeier salts and amidoximes, to access N,N-dialkyl-1,2,4-oxadiazol-5-amines has been developed. By this approach, a broad range of N,N-dialkyl-1,2,4-oxadiazol-5-amines, including aromatic, heteroaromatic, and aliphatic substituents, can be synthesized in good to high yields (up to 82%) under mild reaction conditions.     

Synthesis of enantiopure (S)-(E)-1-haloalk-1-ene-3-amines with total or very high diastereoselectivity by halomethylenation of α-amino aldehydes promoted by CrCl2

Highly diastereoselective synthesis of enantiopure (S)-(E)-1-haloalk-1-ene-3-amines was achieved by reaction of α-amino aldehydes with trihalomethane promoted by chromium dichloride. The absence of racemization in the halomethylenation reaction was checked by chiral HPLC. A mechanism to explain this transformation is proposed.     

One-pot synthesis of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines via palladium-catalyzed heteroannulation in water

The reaction of N-alkyl-3-chloroquinoxaline-2-amines with 1-alkynes, catalyzed by Pd-Cu, in the presence of sodium lauryl sulfate as the surfactant in water, leads to the one-pot formation of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines in good-to-high yields.     

Stereoselective synthesis of allylamines by iron-catalyzed cross-coupling of 3-chloroprop-2-en-1-amines with grignard reagents. Synthesis of naftifine

A general procedure for the synthesis of trans- and cis-allylamines has been developed on the basis of iron-catalyzed cross-coupling of Grignard reagents with stereochemically pure 3-chloroprop-2-en-1-amines prepared by allylation of amines with commercially available 1,3-dichloropropene isomers.     

Synthesis of 8,9-dihydro[1,2,4]triazolo[1,5-a]-quinazolin-6(7H)-one derivatives

Regioselectivity of the reactions of 1H-1,2,4-triazol-3-amines with 2-acyl-5,5-dimethylcyclohexane-1,3-diones and 2-dimethylaminomethylidene-5,5-dimethylcyclohexane-1,3-dione was studied. In all cases, the products were substituted 8,9-dihydro[1,2,4]triazolo[1,5-a]quinazolin-6(7H)-ones whose structure was determined by ¹H and ¹³C NMR spectroscopy.     

Stirring-controlled mono or double aminocarbonylation of 1,3-bis(2-iodoaryl)propan-2-amines

A palladium-catalyzed highly selective mono or double aminocarbonylation of 1,3-bis(2-iodoaryl)propan-2-amines under balloon pressure of CO has been developed. Tetracyclic isoquinolino[2,3-b]isoquinolinones were obtained through double aminocarbonylation when the reaction was stirred overnight, as most of organic reactions being operated. We accidentally found that monocarbonylated isoquinolinone products could be formed in good selectivity and chemical yield just without stirring the reaction mixture. The low concentration of CO in the still solution may account for the selectivity.     

AlCl3 induced C-N bond formation followed by Pd/C-Cu mediated coupling-cyclization strategy: synthesis of pyrrolo[2,3-b]quinoxalines as anticancer agents

AlCl₃ facilitated C-N bond forming reaction between 2,3-dichloroquinoxaline and anilines affording a convenient method for the preparation of N-aryl substituted 3-chloroquinoxalin-2-amines. A related N-benzyl derivative, however, was prepared via a conventional method. These N-alkyl/aryl substituted 3-chloroquinoxalin-2-amines on coupling with terminal alkynes in toluene under Pd/C-Cu catalysis afforded a range of 1,2-disubstituted pyrrolo[2,3-b]quinoxalines within 3-5 h in good to excellent yields. Some of the compounds synthesized showed promising anti-proliferative properties when tested in vitro against two cancer cell lines. Docking studies indicated that these molecules interact well with human Akt in silico.