Synthesis of Spiro Dihydrofurans and 1,8-Dioxo-xanthenes via DABCO Catalyzed Tandem Reaction of Aldehyde with Cyclohexane-1,3-dione and Dimedone

The 1,4-diazabicyclo[2.2.2]octane（DABCO） catalyzed reaction of cyclohexane-1,3-dione or dimedone with various aldehydes in acetonitrile resulted in the polysubstituted tetraketones, spiro dihydrofurans or 1,8-dioxo-xanthenes derivatives as main products respectively according to the structure of reactants and reaction conditions.

A straight synthesis of 2-(a-substituted N-tosylaminomethyl)-2,5-dihydrofurans by thereaction of N-sulfonylimines with arsonium 4-hydroxyl- cis -2-butenylides

On treatment of N-tosylimines (1) and 4-hydroxyl-cis-butenyl arsonium salt (5) with KOH in acetonitrile at room temperature, 2-(a-substituted N-tosylaminomethyl)-2,5-dihydrofurans (4) were obtained in moderate yields. The arsonium salt (5) acts formally as an equivalent of 2,5-dihydrofuran synon. A plausible mechanism was proposed for this new 5-membered cyclization reaction.

1,3-Dipolar Addition of Methyl α-Diazoacetoacetate to Enamines: A New Synthetic Route to 5-Amino-4,5-dihydrofurans

The reaction of methyl α-diazoacetoacetate with enamines catalyzed by dirhodium and copper complexes un-derwent formal 1,3-dipolar addition to give 5-amino-4,5-dihydrofurans in moderate yields. The reaction was sug-gested to proceed via a nucleophilic addition of enamines to metal-carbenes and a subsequent intramolecular cycli-zation of the resulting zwitterionic intermediates.

Ceric Ammonium Nitrate-mediated Oxidative Cycloaddition of 1,3-Dicarbonyls to β-Aryl-α, β-unsaturated Ketones

Regio and stereoselective synthesis of substituted dihydrofurans were accomplished by eeric ammonium nitrate mediated oxidative cycloaddition of 1,3-dicarbonyls to β-aryl-α,β-unsaturated ketones in moderate yields.

A new alkylene dihydrofuran glycoside with antioxidation activity from the root bark of Morus alba L.

A new alkylene dihydrofuran glycoside（1） was isolated from the root bark ofMorus alba L.,along with moracin M-3′-O-β-D-glucopyranoside （2）,and moracin M-6,3′-di-O-β-D-glucopyranoside（3）.Compound 1 was identified as 2-methylene-3-methoxy-2, 5-dihydrofuran-4-O-β-D-glucopyranoside on the basis of chemical and spectroscopic data including 1D and 2D NMR spectral analysis.In addition,the antioxidant activity of 1 was evaluated using the 1,1-diphenyl-2-picrylhydrazyl（DPPH） and 2,2′-azinobis- 3-ethylbenzothiazoline-6-sulphonic acid（ABTS） assay.The IC_（50） values were 2.49 and 0.45 mg/mL,respectively.

Pd-catalyzed sequential reaction for the synthesis of fused tricyclic compounds containing a dihydrofuran or isobenzofuranone unit

A novel Pd-catalyzed sequential reaction for the synthesis of fused tricyclic compounds with a dihydrofuran or isobenzofuranone unit was developed.

Ceric(Ⅳ)-mediated Oxidative Addition of 1,3-Dicarbonyl Compounds to MCPs:A Facile Access to Dihydrofuran Derivatives Incorporating Cyclopropyl Groups

Alkylidenecyclopropanes undergo ceric（Ⅳ） ammonium nitrate （CAN）-mediated addition reaction with 1,3-dicarbonyl compounds leading to dihydrofuran derivatives incorporating cyclopropyl groups in moderate yields.

Reaction of Arylnitroso Derivatives: Synthesis of Arylimino 2,5-Dihydrofuran and Arylamino Fulvenes Derivatives

Herein we report the reactivity of N-(2,4-dicyano-1,5-dimethyl-3-arylcyclopenta-2,4-dienyl)-2,2,2- trifluoroacetamides and N,N-dimethyl-4-nitrosoaniline which provide compounds derived from Ehrlich-Sachs condensation, dihydrofuran derivatives and fulvene derivatives by adjusting the reaction conditions.

Chiral nickel(Ⅱ) complex catalyzed asymmetric(3+2) cycloaddition ofα-diazo pyrazoleamides with 2-siloxy-1-alkenes

A highly efficient asymmetric(3 + 2) cycloaddition of α-diazo pyrazoleamides with silyl enol ethers was realized by employing a chiral N,N’-dioxide-Ni(II) complex catalyst. The process includes the formation of chiral nickel carbenoid intermediate and the following enantioselective cycloaddition reaction. The desired dihydrofuran O,O-acetal derivatives were obtained in good yields(up to 90%) with high enantioselectivity(up to 99% ee) under mild reaction conditions within short reaction time. On the basis of the determination of the catalyst structure, a possible transition state mode was proposed.

Formation, Isolation and Characterization of a New Ruthenium Complex in Reaction of Acetone Masked Terminal Alkynone with Transfer Hydrogenation Catalyst

Reaction of [1S,2S-(Ts-diphen)Ru(II)(p-cymene)] (1S,2S-Ts-diphen=1S,2S-N-tosyl-1,2-diphenylethylenedi- amine) and 2-hydroxy-2-methyl-non-3-yn-5-one under transfer hydrogenation condition gave a ruthenium complex bearing a 2,5-dihydrofuran moiety. The complex was characterized and a possible mechanism for the formation of the complex was proposed.

Efficient Synthesis of Spiro[furan-3,3＇-indoline] Derivatives via Reactions of Pyridinium Salts with Isatinylidene Acetoacetates

An efficient synthetic procedure for the functionalized spiro[furan-3,3＇-indoline] derivatives was successfully developed by domino reactions of N-phenacylpyridinium bromides or N-ethoxycarbonylmethylenepyridinium bro- mide with isatinylidene acetoacetate in the presence of triethylamine in ethanol at room temperature. The mecha- nism included sequential Michael addition of the in situ generated pyridinium ylide and intramolecular substitution of enolate.

Stereoselective Synthesis of Sulfonyl-substituted trans-2,3-Dihydrofuran Derivatives via Reaction of Arsonium Ylides with α,β-Unsaturated Ketones

Trans-2,3-dihydrofuran derivatives 3 or 4 substituted with a sulfonyl group were prepared with high chemoselectivity and good yields by [1＋4]-addition reaction of α,β-unsaturated ketones 1 with arsonium bromide 2 in CH2Cl2 in the presence of potassium carbonate at room temperature.The structures of the products were characterized by IR,MS,^1H NMR,elemental analysis and single crystal X-ray diffraction analysis.A mechanism for the formation of products was also proposed.

Highly Stereoselective Synthesis of trans-3-Aryl-4-carbethoxy-2,3-dihydro-2-fur-2＇-oyl-5-methylfurans

Multi-substituted dihydrofurans are valuable intermediates for the synthesis of natural products and pharmaceuticals. Considerable attention has been focused on the development of efficient and regioselective methods for their preparation. Using K2CO3 as a base, with the reaction of fur-2-oylmethyltriphenylarsonium bromide 1 and ethyl 2-acetyl-3-arylacrylate 2 in tetrahydrofuran at room temperature, we found an efficient protocol was achieved to synthesize trans-3-aryl-4-carbethoxy-2,3-dihydro-2-fur-2＇-oyl-5-methylfurans 3 in good yield with high stereoselectivity. The structure of compound 3 was confirmed by IR, ^1H NMR, MS and HRMS. The mechanism for the formation of 3 was proposed.

First Synthesis of (+)-2,14-Deoxyalatol from -Santonin

A novel and general approach for synthesis of the multi-oxygenated dihydrofuran sesquiterpenes has been de-veloped starting from santonin. The key steps involve: the strategic acid-catalyzed double-bond shifting affording 4, the novel base-promoted epoxide rearrangement of 5 generating two key functionals (the C5-OH and the D7,11 dou-ble bond), and the stereoselective cyclization of tetrahydrofuran ring without pre-controlling the stereochemistry of C-7. As an example of this approach, synthesis of (+)-2,14-deoxyalatol was described in detail.