Journal of Chemical Research

This article gives an overview of synthetic approaches to the 2,3-dihydrobenzofuran ring system with an emphasis on recently developed methods. The synthetic approaches are classified according to the key bond(s) formed during the construction of the dihydrobenzofuran skeleton, and approaches of relevance to the synthesis of natural products are highlighted.

Eleven novel 1,3-bis{(6-aryl-1,2,4-triazolo[3,4-b][1,3,4]thiadiazol-3-yl)-methoxy}benzenes have been synthesised in high yields by the condensation of 5,5'-[1,3-phenylene-bis(oxymethylene)]bis(4-amino-3-mercapto-1,2,4-triazole) with substituted benzoic acids in the presence of phosphorus oxychloride under microwave irradiation. Compared with the conventional heating method, this method is facile, rapid and efficient. The structures of all new compounds were characterised by ¹H NMR, IR, MS and elemental analysis.

A simple procedure for the synthesis of 3-allyl-3-hydroxyoxindoles from isatins in PEG-400 using organoindium reagents generated in situ is described. A variety of isatins reactede with allyl bromides to give the target products with excellent yields in mild conditions.

A three-component and one-pot reaction between trimethyl phosphite and dimethyl acetylenedicarboxylate and ethyl 4-aryl-2,4-dioxobutanoates is described as a simple and efficient route for stereoselective synthesis of cyclobutene derivatives in high yields.

A green and highly efficient oxidation of alcohols in aqueous H₂O₂ using amphiphilic resin (PS-PEG-NH₂)-supported gold nanoparticles is described. The reaction proceeded with excellent yields and selectivities, in particular, for non-activated alcohols without base. The catalyst, in addition, could be readily recovered by simple work-up and reused several times without significant loss of its catalytic activity.

A convergent and efficient synthesis of anticoagulant rivaroxaban was developed using the cycloaddition of com-mercially available (R)-epichlorohydrin with 4-(morpholin-3-one)phenyl isocyanate catalysed by MgI₂ etherate as the key step, in 22% overall yield.

Novel nanotubes, composed of metallocene molecules, [(3-carboxypropyl)-ferrocene flat nanotubes], are reported. Scanning electron microscopy shows the nanotubes have lengths of 20–30 μm, and thicknesses of 0.2–3 μm. X-ray diffraction patterns indicate that they keep the original crystal structure. The optical properties of the products are characterised by FT-IR and UV spectrometry, and they display quantum size effects. A possible mechanism of formation is proposed.

A new pyridine-2-carboxylic acid complex, [Cu(2-PyCOOH)₂(H₂O)₂]Cl₂, has been prepared in situ through a hydrothermal reaction and its structure comprises discrete [Cu(2-PyCOOH)₂(H₂O)₂]²⁺ cations and chloride anions which are interlinked via hydrogen bonding interactions to give a 3-D supramolecular motif. Photoluminescent study shows that the complex exhibits an emission in the blue region. Theoretical studies reveal that the emission can be ascribed to metal-to-ligand charge transfer.

A series of amino oxazolinyl ligands were screened for palladium catalysed Heck reaction. These ligands work well as phosphine free system in aqueous, micellar medium, can be effectively recovered and reused for subsequent cycles.

Halomethylated iminolactones have been synthesised from alkyl isocyanides, acetylene dicarboxylic acid esters and halogenated acetophenones in solvent free microwave assisted multi-component reactions.

A series of novel 2-amino-5-thiazolecarboxamide derivatives have been designed and synthesised. All the compounds were evaluated for their antiproliferative activity against human leukaemia cancer HL 60 and K562 cell lines by standard MTT assay in vitro. Some of these compounds showed moderate cytotoxic potencies. Structure–activity relationships suggested that the piperazine moiety in the side chain of 2-amino-5-thiazolecarboxamide was associated with an increase in the cytotoxicity.

A convenient approach to the synthesis of haematoporphyrin ester-ethers from haemin under ultrasound irradiation has been developed. This method provides several advantages such as shorter reaction time, high yields and environmental friendliness.

The metal–organic framework, [Mn₂(H₄DDA)(phen)₂(H₂O)₅]·4.55H₂O (H₄DDA = 4,4'-diazenediyldiphthalic acid and phen=1,10-phenanthroline), has been synthesised and characterised by IR and single-crystal X-ray diffraction. The complex has a 2D layer structure, which extends into a 3D supramolecular framework via hydrogen bonds.

Several 2, 3-dimethoxy-5-methyl-1, 4-benzoquinones substituted at the C-6 position with alkoxy methyl groups were prepared by a reaction sequence starting from 2, 3, 4, 5-tetramethoxytoluene (alkoxy methyl) via a Blanc chloromethylation reaction, Williamson reaction and oxidation. The method provided a good yield of 2, 3-dimethoxy-5-methyl-1, 4-benzoquinones and is suitable for the synthesis of other benzoquinone analogues.

The title compound was prepared by a reaction sequence starting from 2, 3, 4, 5-tetramethoxytoluene via Blanc chloromethylation reaction, oxidation and alkylation. The described method provides a good yield of the heterocyclic-Coenzyme Q analogue and is suitable for the synthesis of other analogues.

The dinuclear Mn(II) complex [Mn₂(L)₂(bipy)₄]·(ClO₄)₂·3H₂O (HL = 2-benzothiazolylthioacetic acid; bipy = 2,2'-bipyridine) has been synthesised and characterised by single crystal X-ray diffraction, IR and elemental analysis. In the dimeric, cationic complex with a crystallographic centre of symmetry, two bipy molecules chelate each Mn atom. These two metal fragments are then bridged by two L groups in a syn–anti conformation with a Mn···Mn distance of 4.767 Å. The arrangement of these dimers allows the formation of tunnels that host the ClO₄^- anions and lattice water molecules through hydrogen bonds. Magnetic susceptibility measurement revealed antiferromagnetic coupling between the metal centres.