A modular approach to α,β-unsaturated N-aryl ketonitrones

A modular approach to α,β-unsaturated N-aryl ketonitrones has been developed. Specifically, condensation of anilines and enals followed by alkylation of the resulting α,β-unsaturated imines provided N-allyl anilines, which were subjected to oxidation with Oxone® to form α,β-unsaturated N-aryl ketonitrones. This modular approach is general and provides rapid access to diversely substituted α,β-unsaturated N-aryl ketonitrones with a single purification step in good yields.     

A convenient synthesis of tetrazolo[1,5-a]-α-cycloalkanones

A convenient synthesis of a series of tetrazolo[1,5-a]-α-cycloalkanones 4a-d with the carbonyl group attached at the tetrazole carbon is described. The sequence entails the formation of an exocyclic olefin at the α-methylene position and subsequent ozonolysis. The reactions proceed under mild conditions, and the tetrazole moiety is well tolerated.     

Carbonyl olefination with a-stannyl ester enolates: A new synthesis of α,β-unsaturated esters

The reaction of α-stannyl ester enolates with carbonyl compounds is described. α,β-Unsaturated esters are obtained in good yields. A reaction mec     

A facile access to thieno[2,3-b]indoles via sulfur-mediated decarboxylative cyclization of α, β-unsaturated carboxylic acids with indoles

An efficient synthesis of thieno[2,3-b]indoles via a one-pot three-component reaction was well established. By using inexpensive and commercial available indoles and α, β-unsaturated carboxylic acids in the presence of elemental sulfur, various functional groups were achieved in moderate to good yields.     

Enantioselective synthesis of indolo[2,3-b]-dihydrothiopyranones via [3+3] cycloaddition of chiral α,β-unsaturated acylammonium salts

A nucleophile-catalyzed Michael addition/proton transfer/lactonization (NCMPL) organocascade process of chiral α,β-unsaturated acylammonium salts and indoline-2-thiones is described, which delivers the indolo[2,3-b]dihydrothiopyranone motifs in high yields (up to 97%) with good to excellent enantioselectivities (up to 98% ee).     

Enantioselective rhodium-catalyzed [4+2] cycloaddition of α,β-unsaturated imines and isocyanates

A [4+2] cycloaddition of α,β-unsaturated imines and isocyanates catalyzed by a phosphoramidite-rhodium complex provides pyrimidinones in good yields and high enantioselectivities.     

Synthesis of the substituted spiro segment of halichlorine--use of radical cyclization and stereospecific cuprate addition to an α,β-unsaturated lactam

Radical cyclization (26a,b → 27a,b+28) and cuprate addition (28 → 31) were used as key steps to construct the spiro core 4 of halichlorine.     

Synthesis of novel spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones via three component reaction

A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a]chromeno[2,3-d]pyrimidine-14,3′-indoline]-1,2′,13(2H)-triones was developed via the Domino Knoevenagel condensation–Michael addition–intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H₃PW₁₂O₄₀) as an effective and inexpensive catalyst.     

Regio- and diastereoselective synthesis of new functionalized indolo[2,3-b]indole-pyrimidine based on C–N bond formation via a four-component reaction

A facile and diastereoselective synthetic procedure has been designed for the preparation of new substituted indolo[2,3-b]indole (IDID) moiety at position-5 of the pyrimidine ring by a one-pot four-component reaction of dimedone, aniline and substituted derivatives, barbituric acid/thiobarbituric acid and isatin under mild conditions. This method proceeds rely on a CsbndN bond formation under catalyst-free conditions affording a range of skeletally diversity 5-indolo[3,2-b]indole-pyrimidine-based heterocycles. 5-Indolo[2,3-b]indol-pyrimidine-2,4,6-trione and 5-indolo[2,3-b]indol-2-thioxo-pyrimidine-4,6-dione were obtained in EtOH solvent in high yield, short reaction time and diastereoselectivity. The structural diversities of the synthesized compounds have been confirmed spectroscopically, by IR ¹H- and ¹³C NMR, EI-MS spectra and elemental analyses which agree with the proposed structures.     

Reaction of 1-substituted 3,5-diamino-1,2,4-triazoles with β-keto esters: synthesis and new rearrangement of mesoionic 3-amino-2H-[1,2,4]triazolo-[4,3-a]pyrimidin-5-ones

Reaction of 3,5-diamino-1-R-1,2,4-triazoles (R=Ph, Bn) with β-keto esters results in the reversible formation of N-(5-amino-1-R-1,2,4-triazol-3-yl)-substituted enaminoesters (8). Subsequent transformations depended on the reaction conditions. Compounds 8 undergo intermolecular reactions of condensation and amidation in the absence of solvent. However, in the presence of acetic acid they form 3-amino-5-oxo-2-R-2,5-dihydro-[1,2,4]triazolo[4,3-a]pyrimidin-4-ium-8-ides (10) followed by rearrangement to 3-amino-1-R-[1,2,4]triazolo[4,3-a]pyrimidin-5-ones (11). The transformation of 10 into 11 represents a new type of rearrangement in the azolopyrimidine series. Heating of enaminoesters 8 in ethanol with sodium ethoxide present, proved to be a suitable method for the preparation of the mesoionic compounds 10.     

Phosphine-catalyzed highly diastereoselective [3+2] cyclization of isatin derived electron-deficient alkenes with α-allenic esters

A novel phosphine-catalyzed highly diastereoselective [3+2] cycloaddition of isatin derived α,β-unsaturated ketones with α-allenic ester has been developed.     

Photoinduced cyclization of 3-acyl-2-halo-1-[(ω-phenylethynyl)alkyl]indoles to azaheterocyclo[1,2,3-lm]-fused benzo[c]carbazoles

A one-pot synthesis of azaheterocyclo[1,2,3-lm]-fused benzo[c]carbazoles (2 and 3) has been developed by photocyclization of 3-acyl-2-halo-1-[(ω-phenylethynyl)alkyl] indoles (1) in good to excellent yields. All products are formed from 1 via two sequential photocyclization reactions. Two products, 9-chloro-7,8-dihydro-6H-benzo[c]pyrido[1,2,3-lm]carbazole (2a-h) and 7,8-dihydro-6H-benzo[c]pyrido[1,2,3-lm]carbazole (3a-h), are produced in the photocyclization of 2-halo-1-[(ω-phenylethynyl)alkyl]indole-3-carbaldehydes (1a-h). In contrast, only products 2a-h are produced in the photocyclization of 3-acetyl-2-chloro-1-[(ω-phenylethynyl)alkyl]indole-3-carbaldehydes (1o-t). The 9-H in 3a-h (n = 2) does originate from the formyl group in 1a-h via 1,5-hydrogen shift. The structures of three new products, 9-bromo-7,8-dihydro-6H-benzo[c]pyrido[1,2,3-lm]carbazole (2b), 9-chloro-10-methyl-7,8-dihydro-6H-benzo[c]pyrido[1,2,3-lm]carbazole (3h) and 12-chloro-7,8-dihydro-6H-benzo[c]pyrido[1,2,3-lm]carbazole (2w), have been corroborated by single-crystal X-ray structural analyses.     

Transition-metal-free,visible-light-mediated regioselective C–H trifluoromethylation of imidazo[1,2-a]pyridines

A transition-metal-free, visible-light-induced trifluoromethylation of imidazo[1,2-a]pyridines has been developed at mild conditions by employing cheap and commercially available anthraquinone-2-carboxylic acid (AQN-2-CO₂H) as the photo-organocatalyst, and Langlois reagent as the trifluoromethylating reagent. A series of 3-(trifluoromethyl)imidazo[1,2-a]pyridine derivatives with broad functionalities could be conveniently and efficiently obtained by direct regioselective functionalization.     

A general route to α-alkyl (E)-α,β-unsaturated aldehydes

Bis(trimethylsilyl)-tert-butylaldimines 3 react with aldehydes in the presence of zinc bromide at room temperature to give, after hydrolysis, the desired α-alkyl α,β-ethylenic aldehydes in good yield and with very high E stereoselectivity. The reaction was believed to proceed via the α-silyl β-siloxyimines 4.     

CuI catalyzed domino coupling–cyclization of 2-iodo-phenols and 1-alkynes to the synthesis of 2-substituted benzo[b]furans/furo-pyridines

CuI/proline-catalyzed coupling reaction of 2-iodo-phenols with terminal alkynes and the following cyclization process is carried out successively in DMSO at 80?°C. Under this tandem process, 2-substituted benzo[b]furans/furo-pyridines were synthesized in good to excellent yields with a great diversity.     

Mechanism and selectivity of nickel-catalyzed [3 + 2] cycloaddition of cyclopropenones and α,β-unsaturated ketones: A computational study

Density functional theory calculations have been performed to investigate the nickel-catalyzed [3 + 2] cycloaddition of cyclopropenones and α,β-unsaturated ketones. The computations show that the overall catalytic cycle consists of four major steps, including: (1) C-C oxidative addition of the cyclopropenone to afford the four-membered nickelacycle, (2) isomerization, (3) migratory insertion via a 4,1-insertion fashion, and (4) C-C reductive elimination to deliver the [3 + 2] cycloaddition product. The enantioselectivity is mainly attributed to the π-π interaction between the diphenylcyclopropenone moiety and the phenyl substituent of the oxazoline ring of the ligand. The chemoselectivity of the C = O versus C = C insertion was rationalized in terms of the steric effect.     

Oxone®-mediated direct arylselenylation of imidazo[2,1-b]thiazoles,imidazo[1,2-a]pyridines and 1H-pyrazoles

Oxone mediated reaction of imidazo[2,1-b]thiazole, imidazo[1,2-a]pyridine and 1H-pyrazole derivatives with diaryl diselenides is presented here. The methodology represents an efficient and simple protocol for carrying out the selective synthesis of 5-arylselanyl-imidazo[2,1-b]thiazoles, 3-arylselanyl-imidazo[1,2-a]pyridines and 4-arylselanyl-1H-pyrazoles in high yields using a stable, nontoxic and cheap oxidant. The reactions were conducted at 60?°C in air using acetonitrile as solvent. Alternatively, the use of ultrasound irradiation is presented as a tool for fast and efficient energy transfer that significantly reduced the reaction time.     

Chemoselective one-pot access to benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones via copper-catalyzed oxidative [3 + 2] annulation of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols

An operationally simple and efficient one-pot method for the synthesis of 1-aroyl (or alkanoyl)-2-thioalkyl-3-aryl (or alkyl)-3H-benzo[e]indole-4,5-diones and naphtho[2,1-b]thiophene-4,5-diones has been devised by copper-catalyzed cross-coupling of α-oxoketene N,S-acetals/β-ketothioamides with α-/β-naphthols in open air for the first time. The key to the success of this transformation is the room temperature oxidation of α-/β-naphthol to 1,2-naphthoquinone as a reactive species, which undergoes formal [3 + 2] annulation with α-oxoketene N,S-acetals/β-ketothioamides via cascade sequence of Michael addition/tautomerization/oxidation/cyclization/aromatization reactions, enabling addition of a pyrrole/thiophene ring onto naphthoquinone moiety. Further, benzo[e]indole-4,5-diones were transformed to pentacyclic fused phenazine derivatives under solvent-free conditions. Based on our experimental outcomes, a tentative mechanistic rationale for this chemoselective protocol is proposed, which is well validated and supported by the control experiments.     

Palladium-catalyzed selective alkoxycarbonylation of α,β-unsaturated amides: a novel approach toward new ω-amido esters and N-substituted cyclic succinimides

The alkoxycarbonylation of α,β-unsaturated amides proceeded efficiently and regioselectivity to give ω-amido esters with complete conversion in the presence of the catalyst system: Pd(PPh₃)₂Cl₂/MeOH/CO/H₂O. The reaction was successfully applied to the alkoxycarbonylation of bis-acrylamides yielding, selectively, the corresponding di-ω-amido esters. These mono and di-ω-amido esters have been used as precursors for the synthesis of N-substituted cyclic succinimides in moderate to high yields.