Manganese(III)-mediated oxidative free-radical cyclisations of allenyl malonates

The regioselective synthesis of alkenylcyclanones by the oxidative radical cyclisation of malonyl radicals onto both allenes and an allylsilane is reported, along with the diastereoselective formation of [3.3.0]-bicyclic γ-lactones from two of these alkenylcyclanones. Furthermore, the cyclisation of 3-, 4- and 5-allenyl malonates on exposure to manganese(III) acetate under both oxidative and reductive termination conditions is reported.     

Manganese(III)-mediated phosphinoyl radical reactions for stereoselective synthesis of phosphinoylated tetrahydronaphthalenes

Reactions of diphenylphosphinoyl radicals with 5-aryl-2-pentenoates or β-phenylethylene styrenes generate trans-substituted tetrahydronaphthalenes through a cascade reaction sequence.     

Manganese(III)-mediated oxidative radical addition of malonates to 2-cyanoindoles

2-Cyanoindole and N-methyl-2-cyanoindole undergo manganese(III)-mediated radical addition with activated methylene and methine compounds. Products of the methylene addition underwent additional oxidation during the course of the reaction to furnish the corresponding acetoxy compounds. Several structures were confirmed by X-ray crystallography.     

Oxidative radical cyclisations for the synthesis of gamma-lactones

The use of manganese(III) acetate in combination with copper(II) triflate allows the synthesis of [3.3.0]-bicyclic gamma-lactones from 4-pentenylmalonates in excellent yields.     

Manganese(III)-mediated direct phosphonylation of arenes

Manganese (III)-promoted direct phosphonylation of mono- and disubstituted arenes with dialkylphosphite afforded regioselective dialkylphosphonates in good yields. The reactions can apply to arenes bearing electron-donating groups and electron-withdrawing groups such as ester and nitrile.     

One-pot synthesis of cyclophane-type macrocycles using manganese(III)-mediated oxidative radical cyclization

Cyclophane-type macrocyclic compounds from 21 to 56 members having two fused dihydrofuran rings were synthesized by the manganese(III)-mediated oxidation of terminal dienes with bis(3-oxobutanoate)s containing aromatics. The reaction detail, characterization and reaction pathways are described.     

Manganese(III) mediated radical cyclization. I. Factors affectingphenol and cyclopentanone synthesis

The oxidative radical cyclization of ω-unsaturated-β-dicarbonylcompounds to 2-substituted phenols and cyclopentanones has been achieved with manganese (III) acetate.     

Facile synthesis of functionalised spiroethers via radical cyclisations

Alcohols bearing suitable chains for radical initiation are smoothly condensed with cyclic β-diketones to afford systems which undergo radical cyclisation to give various spiroether products.     

Expedient synthesis of ialibinones A and B by manganese(III)-mediated oxidative free radical cyclisation

The tricyclic natural products ialibinone A and ialibinone B were prepared as a 41:59 mixture in four steps starting from phloroglucinol. The synthetic sequence involved (i) acylation of phloroglucinol under Friedel-Crafts conditions, (ii) double prenylation using phase-transfer methodology, (iii) dearomatising methylation, and (iv) oxidative free radical cyclisation using manganese(III) acetate.     

Efficient synthesis of (-)-gamma-lycorane alkaloid by two Bu3SnH-mediated radical cyclisations

An asymmetric induction using (S)-1-arylethylamine-based chiral auxiliary and two Bu(3)SnH-mediated radical cyclisations have been developed for a total synthesis of (-)-gamma-lycorane (1). The first cyclisation proceeded in 5-endo-trig manner with moderate diastereoselectivtiy to give (3aR,7aR)-octahydroindol-2-one 6b as the major product using alpha-iodo-N-(6-oxocyclohexen-1-yl)-N-[(S)-1-phenylethyl] acetamide (5b). In the second cyclisation, the radical precursor 8 was used as substrate to construct the optically active lycorane skeleton 15 which was reduced using LiAlH4 into (-)-gamma-lycorane (1).     

Highly (Z)-selective synthesis of beta-monosubstituted alpha,beta-unsaturated cyanides using the peterson reaction

[reaction: see text] The Peterson reaction between (t-BuO)Ph(2)SiCH(2)CN and various aldehydes furnishes the corresponding beta-monosubstituted alpha,beta-unsaturated cyanides with high Z selectivity (Z:E = 92:8 to >98:2).     

Manganese(III)-mediated intermolecular cyclization reactions of alkenes and active methylene compounds

The reactions of 1,1-diphenylethene, 1,1-bis(4-chlorophenyl)ethene, 1,1-bis(4-methylphenyl)ethene, and 1,1-bis(4-methoxyphenyl)ethene with 3,5-diacetyl-2,6-heptanedione in the presence of manganese(III) acetate in acetic acid at 80° yielded 4,6-diacetyl-8,8-diaryl-1,3-dimethyl-2,9-dioxabicyclo[4.3.0]non-3-enes (41-48%), 5-acetyl-2,2-diaryl-6-methyl-2,3-dihydrobenzo[b]furans (20–21%), 3-acetyl-5,5-diaryl-2-methyl-4,5-dihydrofurans (5–10%), and benzophenones (3–7%). Similarly, the reactions of 1,1-diarylethenes with dimethyl 2,4-diacetyl-1,5-pentanedioate or diethyl 2,4-diacetyl-1,5-pentanedioate gave the corresponding 4,6-bis(alkoxycarbonyl)-8,8-diaryl-1,3-dimethyl-2,9-dioxabicyclo[4.3.0]non-3-enes in moderate yields.     

Manganese(III)-mediated oxidative annulation of methylenecyclopropanes with 1,3-dicarbonyl compounds

[reactions: see text] Manganese(III)-mediated oxidative annulation of methylenecyclopropanes with 1,3-dicarbonyl compounds in acetic acid produces 4,5-dihydrofuran derivatives as [3+2] annulation products in moderate to good yields under mild conditions. The possible reaction mechanism is discussed on the basis of previous mechanistic investigation.     

Manganese(III)-mediated oxidative annulation of vinylidenecyclopropanes with 1,3-dicarbonyl compounds

Manganese(III)-mediated oxidative annulation of vinylidenecyclopropanes with 1,3-dicarbonyl compounds in acetonitrile/acetic acid produces the corresponding functionalized dihydrofuran derivatives in moderate to good yields under mild conditions. The substrate scope has been examined and a plausible reaction mechanism has been also proposed on the basis of experimental results and previous literature.     

Manganese(III)-based dioxapropellane synthesis using tricarbonyl compounds

The manganese(III)-induced oxidative cyclization of 3-(2-oxoethyl)piperidine-2,4-diones was conducted in the presence of 1,1-diarylethenes at reflux temperature to produce 3-aza-7,12-dioxatricyclo[4.3.3.0^1,6]dodec-8-en-2-ones, simply called azadioxa[4.3.3]propellanes, in excellent yields. A similar oxidation of 2-(2-oxoethyl)cycloalkane-1,3-diones gave the corresponding [4.3.3]-, [5.3.3]-, and [6.3.3]-propellanes. The oxidation of 3-oxopropyl-substituted cycloalkane-1,3-diones also afforded the corresponding propellanes along with the 3-oxopropyl-substituted bicyclic intermediates. The bicyclic intermediates were definitely converted into the corresponding propellanes in the presence of a Lewis acid. The structure determination and the reaction pathway were also described.     

Iron(III)-selective dendritic chelators

Two novel iron(III)-selective hexadentate chelator-terminated dendrimers have been synthesized in high yields. MALDI-TOF mass spectra demonstrate that both dendritic chelators bind iron(III) efficiently. Preliminary studies show that these molecules possess a high affinity for iron(III).     

Manganese(III) acetate-mediated alkylation of beta-keto esters and beta-keto amides: an enantio- and diastereo-selective approach to substituted pyrrolidinones

beta-Keto esters and beta-keto amides can be efficiently alkylated on reaction with enol ethers and manganese(III) acetate in the presence of copper(II) acetate. These intermolecular radical addition reactions can be used to construct quaternary carbon centres in excellent yield and this method has been utilised in a diastereoselective approach to substituted pyrrolidinones.     

Highly (Z)-selective hydrosilylation of terminal alkynes catalyzed by a diphosphinidenecyclobutene-coordinated ruthenium complex: application to the synthesis of (Z,Z)-bis(2-bromoethenyl)arenes

[reaction: see text] Complex 1 bearing a diphosphinidenecyclobutene ligand (DPCB-OMe) catalyzes highly stereoselective hydrosilylation of diethynylarenes with HSiMe2Ph to afford (Z,Z)-bis(2-silylethenyl)arenes. Treatment of the hydrosilylation products with N-bromosuccinimide causes bromodesilylation in a stereospecific manner, giving (Z,Z)-bis(2-bromoethenyl)arenes in high geometrical purity (>98%).