A new strategy for the synthesis of benzylic sulfonamides: palladium-catalyzed arylation and sulfonamide metathesis

An efficient two-step strategy has been developed to access diversely functionalized benzylic sulfonamides. Execution of this strategy required the development of two reaction methods: the palladium-catalyzed cross-coupling of aryl halides with CH-acidic methanesulfonamides and a metathesis reaction between the resulting alpha-arylated sulfonamides and diverse amines. The broad scope of the cross-coupling process combined with a versatile sulfonamide metathesis constitutes an efficient strategy for the synthesis of various benzylic sulfonamides.     

Straightforward synthesis of indolizidine alkaloid 167B

The synthetic access to indolizidines, substituted in C-5 position, was reported with good diastereoselectivity. The strategy developed was based on a key step of Michael addition associated with a Clauson-Kaas condensation.     

A rapid synthesis of 2-aryl-5-substituted-2,3-dihydrobenzofurans

[reaction: see text] An effective strategy has been developed for the rapid and efficient one-pot synthesis of 2-aryl-5-substituted-2,3-dihydrobenzofurans from readily available o-nitrotoluenes and aromatic aldehydes. This strategy allows access to a structurally diverse array of products for further manipulation.     

A modular procedure for the synthesis of functionalised β-substituted terthiophene monomers for conducting polymer applications

An efficient modular strategy has been developed for the synthesis of β-functionalised terthiophene monomers using Suzuki-Miyaura and Wittig/Horner-Emmons chemistries. This paper discusses the problems encountered with converting the β-terthiophene aldehyde building block to the β-terthiophene phosphonium salt and the use of this material in a Wittig condensation. An improved strategy using the β-terthiophene phosphonate building block constructed via Suzuki-Miyaura coupling protocols was developed. We have synthesised and characterised a broad range of functionalised terthiophene materials that have been designed for specific end-use applications. The availability of these building blocks has dramatically increased access to a range of key monomers.     

Exploration of the interrupted Fischer indolization reaction

A convergent method to access the fused indoline ring system present in a multitude of bioactive molecules has been developed. The strategy involves the condensation of hydrazines with latent aldehydes to ultimately deliver indoline-containing products by way of an interrupted Fischer indolization sequence. The method is convergent, mild, operationally simple, broad in scope, and can be used to access enantioenriched products. In addition, our approach is amenable to the synthesis of furoindoline and pyrrolidinoindoline natural products as demonstrated by the concise formal total syntheses of physovenine and debromoflustramine B. The strategy will likely enable the synthesis of more complex targets such as the communesin alkaloids.     

Regioselective Palladium-Catalyzed Cross-Coupling Reactions of 2,4,7-Trichloroquinazoline

The regioselective palladium-catalyzed cross-coupling reactions of 2,4,7-trichloroquinazoline with various aryl- and heteroarylboronic acids are reported. An efficient, sequential strategy was developed that provides access to novel, functionalized heterocycles.     

Stereodefined N,O-acetals: Pd-catalyzed synthesis from homopropargylic amines and utility in the flexible synthesis of 2,6-substituted piperidines

We developed a conceptually new synthetic strategy which exploits the stereochemical information of labile acyclic N,O-acetals. The key to this strategy, chemo- and stereoselective synthesis of N,O-acetals, was achieved by the Pd-catalyzed addition of sulfonyl-protected homopropargylic amines to alkoxyallene. The N,O-acetals generated in this way were combined with Au-catalyzed cycloisomerization to give an access to 2,6-disubstituted piperidines with stereochemical flexibility.     

One‐Pot Three‐Component Synthesis of Spirooxindoles Catalyzed by Hexamethylenetetramine in Water

A simple, convenient, and multicomponent strategy for synthesis of spirooxindole derivatives has been developed. This strategy provides a rapid access to construct a diversity‐oriented library of spirooxindoles by using three simple and readily available isatin, malononitrile or cyanoacetic ester, and 1,3‐dicarbonyl compound catalyzed by hexamethylenetetramine in water.     

Synthesis of Ugi-4CR boronate analogues via microwave irradiation

The synthetic condition for the synthesis of boronate ester Ugi-4CR analogs under mild conditions was developed. The reported reactions were carried out in methanol and promoted by microwave heating. This synthetic strategy could provide unique access to a broad range of boron-containing chemical libraries.     

An entry to a chiral dihydropyrazole scaffold: enantioselective [3 + 2] cycloaddition of nitrile imines

We have developed a versatile strategy to access dihydropyrazoles in highly enantioenriched form. Dipolar cycloaddition of electron-deficient acceptors and in situ-generated nitrile imines proceeds with high regio- and enantioselectivity using 10 mol % chiral Lewis acid catalyst. A variety of dihydropyrazoles that incorporate functionality for further manipulation have been prepared.     

Palladium catalyzed ring opening of azabicyclic olefins with organoindium and gallium reagents: a facile access towards benzylated cyclopentanoids

Palladium catalyzed desymmetrization of diazabicyclic olefins with organoindium and gallium reagents were examined. These reactions provided an easy access to trans-3,4-disubstituted cyclopentenes in good to excellent yields. Indium reagents exhibited better reactivity compared to gallium reagents. The developed methodology demonstrates a simple, clean and efficient route towards substituted cyclopentenes. The present strategy provides access to benzylated cyclopentene derivatives in one pot, which forms the skeleton of a number of biologically important molecules.     

Synthesis of sulfonyloxy furoxans via hydroxyfuroxan ammonium salts

Furoxans are distinctive heteroaromatic compounds in that they are potentially capable of releasing nitric oxide under physiological conditions. In order to utilize the furoxan scaffold for the development of functional molecules, synthetically relevant functional groups are required for access to diverse furoxans. In this report, a facile route to furoxans with sulfonyloxy groups, which are halide surrogates, has been developed. The key features of this strategy include the synthesis and utilization of bench-stable hydroxyfuroxan salts, the use of sulfonyl anhydrides in the sulfonylation step instead of sulfonyl chlorides, and the photochemical isomerization of one regioisomer to another in order to gain access to both.     

New Synthesis of A‐Ring Aromatic Strigolactone Analogues and Their Evaluation as Plant Hormones in Pea (Pisum sativum)

A new general access to A‐ring aromatic strigolactones, a new class of plant hormones, has been developed. The key transformations include in sequence ring‐closing metathesis, enzymatic kinetic resolution and a radical cyclization with atom transfer to install the tricyclic ABC‐ring system. The activity as plant hormones for the inhibition of shoot branching in pea of various analogues synthesized by this strategy is reported.     

Metal-free and base-free decarboxylation of substituted cinnamic acids in a deep eutectic solvent

Abstract

A metal-free and base-free strategy was developed in DES to synthesize styrenes for the first time by decarboxylation of cinnamic acid derivatives, which provided a renewable and cost efficiently protocol to access various styrenes including those with functional groups such as 4-vinylphenol and 1-chloro-4-vinylbenzene.     

A Local‐Desymmetrization‐Based Divergent Synthesis of Quinine and Quinidine

Herein we report a novel synthetic entry to the legendary quinuclidine natural products quinine and quinidine. The developed strategy is based on the use of a symmetrical and nonstereogenic precursor to access quinine and quinidine through a “local‐desymmetrization” approach, in stark contrast conceptually to the preparation of stereodefined disubstituted piperidines (or their acyclic precursors) as featured in all past syntheses. The developed strategy also provided quinine and quinidine derivatives that could not be readily obtained through previous total syntheses or by modification of the naturally occurring substances.     

An efficient large-scale synthesis of alkyl 5-hydroxy-pyridin- and pyrimidin-2-yl acetate

The synthesis of methyl 2-(5-hydroxy-3-methoxypyridin-2-yl)acetate and alkyl 2-(5-hydroxypyrimidin-2-yl)acetate is described. Methodology for an efficient access to 5-hydroxy-pyridin- and pyrimidin-2-yl acetate cores has been developed. Based on the difference in halogen reactivity, 5-bromo-2-chloropyridine and its pyrimidine analogue were functionalized judiciously by S_NAr and palladium-catalyzed reactions. The outlined strategy provides a high-yielding route suitable for large-scale synthesis of these compounds as well as paves the way for a potential rapid access to other heterocyclic analogues.     

Rapid and efficient access to secondary arylmethylamines

Ammoniomethyl trifluoroborates are very powerful reagents that can be used to access biologically relevant aryl- and heteroaryl-methylamine motifs via Suzuki-Miyaura cross-couplings. Until now, this method was limited to the production of tertiary and primary amines. The synthesis of a large array of secondary ammoniomethyltrifluoroborates has been achieved through a one step nucleophilic substitution reaction on the potassium bromomethyltrifluoroborate. Smooth cross-coupling conditions have been designed, based on the use of an aminobiphenyl palladium precatalyst, to couple these trifluoroborates efficiently with aryl bromides. This strategy offers a new way to access biologically relevant motifs and allows, with the previously developed methods, access to all three classes of aminomethylarenes.     

Palladium catalyzed domino C-H activation strategy: An access to 9- fluorenones

Palladium catalyzed domino C-H functionalization reaction of arylaldehyde with dihaloarene has been developed to access 9-flourenone molecules. Bidentate ligand assisted strategy, single step reaction, high yield and excellent functional group tolerance make this method concise and effective for the synthesis of 9-flourenone. In addition, proposed method has been successfully employed to synthesise Tilorone in gram scale.     

Using second-order calibration method based on trilinear decomposition algorithms coupled with high performance liquid chromatography with diode array detector for determination of quinolones in honey samples

A novel strategy that combines the second-order calibration method based on the trilinear decomposition algorithms with high performance liquid chromatography with diode array detector (HPLC-DAD) was developed to mathematically separate the overlapped peaks and to quantify quinolones in honey samples. The HPLC-DAD data were obtained within a short time in isocratic mode. The developed method could be applied to determine 12 quinolones at the same time even in the presence of uncalibrated interfering components in complex background. To access the performance of the proposed strategy for the determination of quinolones in honey samples, the figures of merit were employed. The limits of quantitation for all analytes were within the range 1.2-56.7 μg kg⁻¹. The work presented in this paper illustrated the suitability and interesting potential of combining second-order calibration method with second-order analytical instrument for multi-residue analysis in honey samples.     

Synthesis of rhodamines from fluoresceins using Pd-catalyzed C-N cross-coupling

A unified, convenient, and efficient strategy for the preparation of rhodamines and N,N'-diacylated rhodamines has been developed. Fluorescein ditriflates were found to undergo palladium-catalyzed C-N cross-coupling with amines, amides, carbamates, and other nitrogen nucleophiles to provide direct access to known and novel rhodamine derivatives, including fluorescent dyes, quenchers, and latent fluorophores.