Efficient three-component reactions of α-thiocyanato ketones stereoselectively forming E-3-aroylidene-2-oxindole derivatives

A new three-component reaction of α-thiocyanato ketones under microwave irradiation for the stereoselective synthesis of 25 examples of E-3-aroylidene-2-oxindole derivatives has been described. The domino reaction simultaneously installs C–S and C–C bonds through continuous [3+2] cycloaddition/ring opening of in situ generated 1,3-oxathiolanes/S_N2-type reaction sequence.     

Friedländer reaction/quinoxalinone–benzimidazole rearrangement sequence: expeditious entry to diverse quinoline derivatives with the benzimidazole moieties

A protocol has been developed for the efficient synthesis of structurally diverse 4-(benzimidazol-2-yl)quinolines via reactions of 3-(2-aminophenyl)quinoxalin-2(1H)-ones and ketones, including acetone, acetophenones, 1,3-pentanedione and ethyl acetoacetate. The selective formation of the very different quinoline derivatives depends on the structure of ketones. The key steps are proposed to involve the new acid-catalyzed rearrangement of the spiro-quinoxalinone derivatives formed in situ from the reaction of 3-(2-aminophenyl)quinoxalin-2(1H)-ones and ketones under the modified Friedländer reaction. This transformation would facilitate the synthesis by short reaction times, large-scale synthesis, simple and prompt isolation of the products, which are the main advantages of this procedure.     

Efficient access to novel hexahydro-chromene and tetrahydro-pyrano[2,3-d]pyrimidine-annulated benzo-δ-sultones via a domino Knöevenagel-hetero-Diels-Alder reaction in water

An efficient catalyst-free, diastereosective synthesis of novel hexahydro-chromene and tetrahydro-pyrano[2,3-d]pyrimidine-annulated benzo-δ-sultones is described. A number of 2-formyl-4-phenyl (E)-2-phenylethenesulfonates were synthesized and underwent a one-pot domino Knöevenagel-hetero-Diels-Alder reaction, respectively, with dimedone and N,N-dimethylbarbituric acid in water, affording the desired products in moderate to excellent yields.     

New regio-selective method of combinatorial synthesis of substituted thiophenes,thieno[3,2-b]pyridines and other heterocycles via combination of ‘domino’-type reactions

We present a novel combinatorial multicomponent regio-selective approach towards the synthesis of thieno[3,2-b]pyridines and pyridine pyrans. The methodology is based on the ‘domino’-type reaction. The high regio-selectivity in this reaction is gained by the in situ generation of the mono-potassium salt of 2-cyano-1-mercaptoethenethiolate. We also demonstrate that the use of ethyl 2-cyanoacetate in this reaction as a CH-acid leads to the termination of the domino sequence at the Dieckmann condensation step and yields novel ethyl 3-(4-cyano-3-hydroxy-5-(alkylthio)thiophen-2-yl)-3-oxopropanoate.     

Domino reaction of 3-nitro-2-(trifluoromethyl)-2H-chromenes with 2-(1-phenylalkylidene)malononitriles: synthesis of functionalized 6-(trifluoromethyl)-6H-dibenzo[b,d]pyrans and a rare case of [1,5] sigmatropic shift of the nitro group

A variety of functionalized 6-(trifluoromethyl)-6H-dibenzo[b,d]pyrans were easily synthesized in good yields under mild conditions by a domino reaction of 3-nitro-2-(trifluoromethyl)-2H-chromenes with 2-(1-phenylethylidene)- and 2-(1-phenylpropylidene)malononitriles. In the latter case, intermediate 7-amino-10-methyl-10-nitro-9-phenyl-6-(trifluoromethyl)-10,10a-dihydro-6H-benzo[c]chromene-8-carbonitriles were isolated as a result of a rare [1,5] sigmatropic shift of the nitro group.     

Novel thiophosphonodiamides as efficient hydrogen bond donor catalysts in tandem Michael addition–cyclization of malononitrile and 2-(E)-2-nitrovinylphenols

From l-amino acid, three chiral thiophosphonodiamides were prepared as new hydrogen bond donor organocatalysts. Under the mediation of the catalyst derived from l-valine, a tandem Michael addition/cyclization reaction between (E)-2-(2-nitrovinyl)phenols and malononitrile proceeds smoothly, giving pharmaceutically valuable 2-amino-4H-chromene-3-carbonitriles in high yields with 66–95% ee within 2 h.     

Syntheses and structures of iron carbonyl complexes derived from N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine and N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine

The reaction of N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine (1) with Fe₂(CO)₉ in refluxing acetonitrile yielded di-(μ₃-thia)nonacarbonyltriiron (2), μ-[N-(5-methyl-2-thienylmethyl)-η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido]hexacarbonyldiiron (3), and N-(5-methyl-2-thienylmethylidene)amine (4). If the reaction was carried out at 45 °C, di-μ-[N-(5-methyl-2-thienylmethylidene)-η¹(N);η¹(S)-2-thiolethylamino]-μ-carbonyl-tetracarbonyldiiron (5) and trace amount of 4 were obtained. Stirring 5 in refluxing acetonitrile led to the thermal decomposition of 5, and ligand 1 was recovered quantitatively. However, in the presence of excess amount of Fe₂(CO)₉ in refluxing acetonitrile, complex 5 was converted into 2-4. On the other hand, the reaction of N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine (6) with Fe₂(CO)₉ in refluxing acetonitrile produced 2, μ-[N-(6-methyl-2-pyridylmethyl)-η¹ (N_py);η¹:η¹(N); η¹:η¹(S)-2-thiolatoethylamido]pentacarbonyldiiron (7), and μ-[N-(6-methyl-2-pyridylmethylidene)-η²(C,N);η¹:η¹(S)-2- thiolethylamino]hexacarbonyldiiron (8). Reactions of both complex 7 and 8 with NOBF₄ gave μ-[(6-methyl-2-pyridylmethyl)-η¹(N_py);η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido](acetonitrile)tricarbonylnitrosyldiiron (9). These reaction products were well characterized spectrally. The molecular structures of complexes 3, 7-9 have been determined by means of X-ray diffraction. Intramolecular 1,5-hydrogen shift from the thiol to the methine carbon was observed in complexes 3, 7, and 9.     

A facile route to the pentacyclic lamellarin skeleton via Grob reaction between 3-nitro-2-(trifluoromethyl)-2H-chromenes and 1,3,3-trimethyl-3,4-dihydroisoquinolines

The basic structural framework of lamellarin alkaloids, 8,9-dihydro-6H-chromeno[4′,3′:4,5]pyrrolo[2,1-a]isoquinoline derivatives, has been obtained in good yields via Grob reaction between 3-nitro-2-(trifluoromethyl)-2H-chromenes and 1,3,3-trimethyl-3,4-dihydroisoquinolines in refluxing isobutanol. When the reaction was carried out in toluene at room temperature, only Michael adducts, as a mixture of two diastereomers, were isolated.     

Palladium-catalyzed stereoselective synthesis of (E)-β,γ-unsaturated amides

A facile Suzuki type cross-coupling reaction of alkenylborane with 2-bromo-N,N-dimethylacetamide in the presence of a catalytic amount of tricyclohexylphosphine as the ligand has been demonstrated to be a convenient way for the synthesis of (E)-β,γ-unsaturated amides.     

Facile stereoselective synthesis of cis- and trans-3-alkoxyazetidin-2-ones

A highly stereoselective synthesis of cis- and trans-3-alkoxy-3-phenyl/benzylthioazetidin-2-ones is described. The reaction of α-chlorosulfide-β-lactams with various alcohols catalyzed by a Lewis acid such as ZnCl₂ in the presence of molecular sieves (3-4 Å) leads to cis-3-alkoxy-3-phenyl/benzylthio-β-lactams whereas treatment of potassium 2-alkoxy-2-phenylthioethanoate with appropriate Schiff's base using POCl₃ in the presence of triethylamine leads to the formation of trans-3-alkoxy-3-phenylthioazetidin-2-ones as major products.     

A one-pot synthesis and mild cleavage of 2-[2- or 5-(alkylsulfanyl)pyrrol-1-yl]ethyl vinyl ethers by t-BuOK/DMSO: a novel and facile approach to N-vinylpyrroles

Substituted N-[2-(vinyloxy)ethyl]pyrroles, prepared in good yield through an allenic or acetylenic carbanion/isothiocyanate one-pot methodology from 2-(vinyloxy)ethyl isothiocyanate and allyloxyallene, methoxyallene, N,N-dimethyl-2-propyn-1-amine, and 3-methoxy-1-(methylsulfanyl)-1-propyne, are smoothly converted into the corresponding N-vinylpyrroles using t-BuOK/DMSO (room temperature). The reaction proceeds via elimination of vinyl alcohol from the N-[2-(vinyloxy)ethyl] substituent and represents a novel approach to N-vinylpyrroles.     

Convenient synthesis of 3-fluoro-4,5-diphenylfuran-2(5H)-one from benzoin ethers : Novel and efficient Z-E isomerisation and cyclisation of 2-fluoroalkenoate precursors, substitution of vinylic fluorine

Mixtures of ethyl (E)- and (Z)-4-alkoxy-2-fluoro-3,4-diphenylbut-2-enoates (6-8) prepared from benzoin ethers and ethyl 2-(diethoxyphosphoryl)-2-fluoroacetate were transformed in high yields to the target 3-fluoro-4,5-diphenylfuran-2(5H)-one (14) using bromine in tetrachloromethane at room temperature. The non-cyclisable Z-isomers 6b-8b were gradually isomerised to the cyclisable E-isomers 6a-8a during the process. The reaction of the (E)-butenoates 6a-8a with boron trifluoride led to furanone 14, while in Z-isomers 6b-8b both alkoxy group and vinylic fluorine were substituted with bromine during the reaction. Mechanisms for both complex reactions have been proposed. Furanone 14 was transformed to 2-[tert-butyl(dimethyl)silyloxy]-3-fluoro-4,5-diphenylfuran (18) as a novel building block.     

Diels-Alder reaction of optically active (E)-γ-keto-α,β-unsaturated p-tolylsulfoxides with cyclopentadiene

The Diels-Alder reaction of enantiomerically pure (E)-γ-keto-α,β-unsaturated p-tolylsulphoxides 3 with cyclopentadiene give four easily separable diastereomers. The effect of several Lewis acids on the reaction was studied, finding a high endo selectivity with respect to the carbonyl group and moderate π-diastereoselectivity using BF₃·Et₂O as catalyst. The reactivity of compounds 3 as well as their endo selectivity are both higher than those observed for the corresponding (E)-3-sulfinylacrylates.     

Synthesis of 2-diphenylphosphinoyl-3,5-diaryl-3,4-dihydro-2H-telluropyrans by reaction of chalcones with bis[(diphenylphosphinoyl)methyl]telluride

The NaH-promoted tandem Michael addition/intramolecular Wittig-Horner reaction of bis[(diphenylphosphinoyl) methyl]telluride with chalcones stereoselectively afforded trans-2-diphenylphosphinoyl-3,5-diaryl-3,4-dihydro-2H-telluropyran derivatives in 51-72% yield, under mild conditions.     

A new three-step domino Knoevenagel-hetero-Diels-Alder oxidation reaction

A new catalyst-free domino Knoevenagel-hetero-Diels-Alder oxidation reaction is reported. 6H-Chromeno[4′,3′:4,5]thiopyrano[2,3-d][1,3]thiazol-4-ium-2-olates are formed in good yields via reaction of 2-(2-propynyloxy)benzaldehydes with 4-thioxo-1,3-thiazolidin-2-one.     

The substrate specificity of the heat-stable stereospecific amidase from Klebsiella oxytoca

The substrate specificity of the heat-stable stereospecific amidase from Klebsiella oxytoca was investigated. In addition to the original substrate, 3,3,3-trifluoro-2-hydroxy-2-methylpropanamide, the amidase accepted 2-hydroxy-2-(trifluoromethyl)-butanamide and 3,3,3-trifluoro-2-amino-2-methylpropanamide as substrates. Compounds with larger side chains and compounds where the hydroxyl group was substituted with a methoxy group, or in which the CF₃ group was substituted by CCl₃, were not accepted. The biotransformation is a new synthetic route to (R)-(+)-3,3,3-trifluoro-2-amino-2-methylpropanoic acid, and its related (S)-(−)-amide, and to (R)-(+)-2-hydroxy-2-(trifluoromethyl)-butanoic acid and its related (S)-(−)-amide.     

Rapid access to 3-(N-substituted)-aminoquinolin-2(1H)-ones using palladium-catalyzed C-N bond coupling reaction

A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs₂CO₃ as a base.     

A simple synthesis of the pentacyclic lamellarin skeleton from 3-nitro-2-(trifluoromethyl)-2H-chromenes and 1-methyl(benzyl)-3,4-dihydroisoquinolines

The basic structural framework of lamellarin alkaloids, 8,9-dihydro-6H-chromeno[4′,3′:4,5]pyrrolo[2,1-a]isoquinoline derivatives, has been obtained in good yields via Grob synthesis between 3-nitro-2-(trifluoromethyl)-2H-chromenes and 1-methyl-3,4-dihydroisoquinolines in refluxing isobutanol. In the case of 1-benzyl-3,4-dihydroisoquinolines, a dynamic NMR effect was observed in the ¹H and ¹⁹F NMR spectra of the products as a result of restricted rotation about the single bond linking the benzene ring and the heterocyclic system. When the reaction was carried out with 3-nitro-2-(trichloromethyl)-2H-chromenes in toluene at room temperature, only Michael adducts, as a mixture of two diastereomers, were isolated.     

A new and efficient one-pot synthesis of 2-hydroxy-1,4-dihydrobenzoxazines via a three-component Petasis reaction

The secondary amines synthesized by the reaction between 2-aminophenols and aromatic aldehydes, via the reduction of the corresponding imines, were employed in the synthesis of new 2-hydroxy-2H-1,4-benzoxazine derivatives through a one-pot Petasis multicomponent reaction in good to excellent yields.     

Synthesis of tetrahydro-5-azaindoles and 5-azaindoles using Pictet-Spengler reaction—appreciable difference in products using different acid catalysts

Pictet-Spengler condensation of 2-(aryl)-2-(1H-pyrrol-2-yl)ethanamines using conventional acid catalysts like TMSCl or TFA resulted in the formation of substituted 5-azaindoles involving a tandem one pot four steps reaction sequence. By contrast use of glacial acetic acid furnished the targeted tetrahydro-5-azaindoles in diastereoselective manner. These were readily dehydrogenated to 5-azaindoles.