Biomimetic Decarboxylation of Carboxylic Acids with PhI（OAc）2 Catalyzed by Manganese Porphyrin [Mn（TPP）OAc]

Manganese（Ⅲ） meso-tetraphenylporphyrin acetate [Mn（TPP）OAc] served as an effective catalyst for the oxidative decarboxylation of carboxylic acids with （diacetoxyiodo）benzene [PhI（OAc）2] in CH2CI2-H2O（95：5, volume ratio）. The aryl substituted acetic acids are more reactive than the less electron rich linear carboxylic acids in the presence of catalyst Mn（TPP）OAc. In the former case, the formation of carbonyl products was complete within just a few minutes with 〉97% selectivities, and no further oxidation of the produced aldehydes was achieved under these catalytic conditions. This method provides a benign procedure owing to the utilization of low toxic（diacetoxyiodo） benzene, biologically relevant manganese porphyrins, and carboxylic acids.     

Hydrogen peroxide oxidation of mustard-model sulfides catalyzed by iron and manganese tetraarylporphyrines. Oxygen transfer to sulfides versus H(2)O(2) dismutation and catalyst breakdown.

Fe(III)- and Mn(III)-meso-tetraarylporphyrin catalysis of H(2)O(2) oxidation of dibenzyl and phenyl-2-chloroethyl sulfides, 1, is investigated in ethanol with the aim of designing catalytic systems for mustard decontamination. The sulfide conversion, the sulfoxide and sulfone yields, the oxygen transfer from H(2)O(2) to the sulfide, and the catalyst stability depend markedly on the metal, on the substituents of its ligand, and on the presence or the absence of a cocatalyst, imidazole or ammonium acetate. With Fe, sulfones, the only oxidation products, are readily obtained whatever the ligand (TPP, F(20)TPP, or TDCPP) and the cocatalyst; the oxygen transfer is fairly good, up to 95% when the catalyst concentration is small ([1]/[Cat] = 420); the catalyst breakdown is insignificant only in the absence of any cocatalyst. With Mn, the sulfide conversion is achieved completely when the ligand is TDCPP or TSO(3)PP, but not F(20)TPP or TPP; a mixture of sulfoxide, 2, and sulfone, 3, is always obtained with [2]/[3] = 3.5-0.85 depending on the ligand and the cocatalyst (electron withdrawing substituents favor 3 and NH(4)OAc, 2). The catalyst stability is very good, but the oxygen transfer is poor whatever the ligand and the cocatalyst. These results are discussed in terms of a scheme in which sulfide oxygenation, H(2)O(2) dismutation, and oxidative ligand breaking compete. It is shown that the efficiency of the oxygen transfer is related not only to the rate constant of the dismutation route but also to the concentration of the active metal-oxo intermediate, most likely a perferryl or permanganyl species, i.e., to the rate of its formation.     

Oxygenation of saturated and unsaturated hydrocarbons with sodium periodate catalyzed by manganese(III) tetra-arylporphyrins, to study the axial ligation of imidazole

Competitive oxygenation of cyclooctene and tetralin with sodium periodate catalyzed by Mn^(III)(TPP)OAc, TPP = meso-tetraphenylporphyrin; Mn^(III) (TNP)OAc, TNP =meso-tetrakis(1-naphthyl) porphyrin; Mn^(III) (TMP)OAc, TMP =meso-tetrakis(2,4,6-trimethyl-phenyl)porphyrin; Mn^(III) (TDCPP)OAc, TDCPP =meso-tetrakis(2,6-dichlorophenyl) porphyrin, and Mn^(III) (TPNMe₂-TFPP)OAc, TPNMe₂-TFPP =meso-tetrakis(para-NMe₂-tetrafluorophenyl)porphyrin, was carried out in the presence or absence of imidazole. This study showed that, in the absence of imidazole, selectivity for epoxide formation was high with electron-rich catalysts such as Mn(TPP)OAc, Mn(TNP)OAc and Mn(TMP)OAc, but low with electron-deficient catalysts such as Mn(TDCPP)OAc and Mn(TPNMe₂-TFPP)OAc. Presumably, not only the axial ligation of imidazole to the four-coordinate Mn(III)-center, but also the steric and electronic influences of aryl-substituents on the porphyrin periphery affect the selectivity of the catalytic oxidation reaction.     

Zn(OAc)2 catalyzed microwave irradiated synthesis of substituted thieno[2,3-d]pyrimidin-4(3H)-one

Different Lewis acids were screened to catalyze the reaction of 2-amino-thiophene-3-carboxylate, orthoformate and aryl amine to form 2-substituted thieno[2,3-d]pyrimidin-4(3H)-one. Zn(OAc)₂ was demonstrated to efficiently catalyze the reaction. 20 substituted thieno[2,3-d]pyrimidines were synthesized by adding 0.5% mol Zn(OAc)₂ as catalyst under microwave irradiation.     

Iodine(III)-mediated ethoxychlorination of enamides with iron(III) chloride

The combination of (diacetoxyiodo)benzene and iron(III) chloride in ethanol allows the efficient regioselective ethoxychlorination of a broad range of enamides. Mechanistic studies tend to rule out the involvement of free radical species and point towards the implication of a mixed [chloro(ethoxy)iodo]benzene intermediate.     

Addition of carboxyalkyl radicals to alkenes through a catalytic process,using a Mn(II)/Co(II)/O2 redox system

A novel strategy for production of mono- and dicarboxylic acids by the addition of carboxyalkyl radicals to alkenes and dienes, respectively, was successfully developed through a catalytic process with use of Mn(II)/Co(II)/O(2) system. Thus, a variety of carboxylic acids were prepared by the reaction of alkenes and dienes with acid anhydrides in the presence of a very small amount of Mn(OAc)(2) (0.5 mol %) and Co(OAc)(2) (0.1 mol %) under dilute dioxygen.     

Easy and Safe preparations of (diacetoxyiodo) arenes from iodoarenes, with urea-hydrogen peroxide adduct (UHP) as the oxidant and the fully interpreted (1)H- and (13)C-NMR spectra of the products

An easy and safe, though only moderately effective method is presented for preparing (diacetoxyiodo)arenes, ArI(OAc)2, from iodoarenes, ArI, using the commercially available and easily handled urea-hydrogen peroxide adduct (UHP) as the oxidant. The reactions take place in anhydrous AcOH/Ac2O/AcONa (a catalyst)mixtures, at 40 oC for 3.5 h to afford the purified ArI(OAc)2 in 37-78% yields. The fully interpreted (1)H- and (13)C-NMR spectra of the ArI(OAc)2 products are reported.     

Oxidation of 2-imidazolines to 2-imidazoles with sodium periodate catalyzed by polystyrene-bound manganese(III) porphyrin

In the present work, the dehydrogenation of 2-substituted imidazolines with sodium periodate in the presence of tetraphenylporphyrinatomanganese(III) chloride supported on polystyrene-bound imidazole, [Mn(TPP)Cl@PSI] is reported. A wide variety of 2-imidazolines were efficiently converted to their corresponding imidazoles by the [Mn(TPP)Cl@PSI]/NaIO₄ catalytic system in a 1:2 CH₃CN/H₂O mixture under agitation with magnetic stirring. Ultrasonic irradiation enhanced the catalytic activity of this catalyst in the oxidation of 2-imidazolines and this led to shorter reaction times and higher product yields. This catalyst could be reused several times without significant loss of its catalytic activity.     

Trimanganese complexes bearing bidentate nitrogen ligands as a highly efficient catalyst precursor in the epoxidation of alkenes

A series of trinuclear manganese complexes coordinated with neutral bidentate nitrogen ligands, [Mn3L2(OAc)6], were prepared from manganese acetate and the corresponding ligands. Using peracetic acid as the oxidant, the air- and moisture-stable manganese clusters exhibited excellent catalytic activity and selectivity in the epoxidation of olefins under mild conditions. The highest activity was observed with a trinuclear complex containing a 2-pyridylimino ligand, [Mn3(ppei)2(OAc)6] (ppei = 2-pyridinal-1-phenylethylimine). With this system, the substrate scope was extremely wide to include terminal and electron-deficient double bonds of both aliphatic and aromatic alkenes. The high activity was undiminished under the reaction conditions even directly using a mixture of the pyridylimino ligands and manganese acetates, making this process more convenient. It was also observed that analogous trinuclear complexes, such as [Mn3(bipy)2(OAc)6] and [Mn3(phen)2(OAc)6], displayed excellent activities. While radical intermediacy was inferred from the product distribution, kinetic data revealed that the epoxidation is roughly first-order in manganese cluster precursor and oxidant, respectively, and zero-order in olefin. These results led us to propose that the trinuclear complexes [Mn3L2(OAc)6] serve as catalyst precursors that dissociate into monomeric species with the formulation of [MnL2(OAc)2] under the reaction conditions.     

Phosphonation of arenes with dialkyl phosphites catalyzed by Mn(II)/Co(II)/O2 redox couple

[reaction: see text]. Arylphosphonates were first synthesized through a catalytic phosphonation of various arenes with dialkyl phosphites under the influence of an Mn(OAc)2/Co(OAc)2/O2 redox couple. For instance, the reaction of benzene with diethyl phosphite in the presence of Mn(OAc)2 (5 mol %) and Co(OAc)2 (1 mol %) under a mixed gas of O2 (0.5 atm) and N2 (0.5 atm) at 45 degrees C led to diethyl phenylphosphonate in 81% selectivity at 62% conversion. This is the first successful phosphonation of benzene with dialkyl phosphites through a catalytic radical process.     

Mn(III)/Cu(II)-mediated oxidative radical cyclization of alpha-(Methylthio)acetamides leading to erythrinanes

Treatment of N-[2-(3,4-dimethoxyphenyl)ethyl]-alpha-(methylthio)acetamide 3 with Mn(OAc)3 in the presence of Cu(OAc)2 gave tetrahydroindol-2-one 4, which then cyclized with Mn(OAc)3 to give 4-acetoxyerythrinane 5. A similar reaction of the 3,4-methylenedioxyphenyl congener 8 also gave tetrahydroindol-2-one 9, which, however, gave only a trace amount of the Mn(OAc)3-mediated cyclization product 11 and afforded the oxidation product 10. On the basis of these results, formation of 5 from 4 was thought to proceed via nucleophilic attack of the pyrrole ring on the cation-radical lX, generated by a single electron-transfer reaction of the acetoxy-substituted intermediate V. Treatment of compound 16 with Mn(OAc)3/Cu(OAc)2 gave no erythrinane derivative with recovery of the starting material, indicating that the presence of a methylthio group of 4 is essential for effecting the formation of erythrinane 5. On the other hand, treatment of 3 with Mn(OAc)3 using Cu(OTf)2 as an additive in place of Cu(OAc)2 gave another erythrinane 17. This method was applied to a formal synthesis of 3-demethoxyerythratidinone (20), a naturally occurring Erythrina alkaloid.     

Reaction of [60]fullerene with free radicals generated from active methylene compounds by manganese(III) acetate dihydrate

The reaction of [60]fullerene with dimethyl malonate and diethyl malonate in the presence of manganese(III) acetate dihydrate (Mn(OAc)3.2H2O) for 20 min afforded singly bonded [60]fullerene dimers 1a and 1b in a 1,4-addition pattern. When the reaction time was extended to 1 h, 1,4-bisadducts 2a and 2b were obtained. Unsymmetrical 1,4-adduct 5 and C2 symmetrical 1,16-bisadduct 6 were obtained when diethyl bromomalonate was used as the active methylene compound. Reaction of [60]fullerene with malononitrile and ethyl cyanoacetate with the aid of Mn(OAc)3.2H2O produced methanofullerenes 7 and 8. It is proposed that all these products were formed the addition of free radicals from the active methylene compounds generated by Mn(OAc)3.2H2O.     

A new class of single-molecule magnet: [Mn9O7(OAc)11(thme)(py)3(H2O)2] with an S = 17/2 ground state

The reaction of [Mn3O(OAc)6(py)3] with 1,1,1-tris(hydroxymethyl)ethane (H3thme) gives the Mn(IV)3Mn(III)4Mn(II)2 complex [Mn9O7(OAc)11(thme)(py)3(H2O)2], which has an S = 17/2 ground state and displays strong out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet.     

Mechanism of cis-dihydroxylation and epoxidation of alkenes by highly H(2)O(2) efficient dinuclear manganese catalysts

In the presence of carboxylic acids the complex [Mn(IV)2(micro-O)3(tmtacn)2]2+ (1, where tmtacn = N,N',N'-trimethyl-1,4,7-triazacyclononane) is shown to be highly efficient in catalyzing the oxidation of alkenes to the corresponding cis-diol and epoxide with H2O2 as terminal oxidant. The selectivity of the catalytic system with respect to (w.r.t.) either cis-dihydroxylation or epoxidation of alkenes is shown to be dependent on the carboxylic acid employed. High turnover numbers (t.o.n. > 2000) can be achieved especially w.r.t. cis-dihydroxylation for which the use of 2,6-dichlorobenzoic acid allows for the highest t.o.n. reported thus far for cis-dihydroxylation of alkenes catalyzed by a first-row transition metal and high efficiency w.r.t. the terminal oxidant (H2O2). The high activity and selectivity is due to the in situ formation of bis(micro-carboxylato)-bridged dinuclear manganese(III) complexes. Tuning of the activity of the catalyst by variation in the carboxylate ligands is dependent on both the electron-withdrawing nature of the ligand and on steric effects. By contrast, the cis-diol/epoxide selectivity is dominated by steric factors. The role of solvent, catalyst oxidation state, H2O, and carboxylic acid concentration and the nature of the carboxylic acid employed on both the activity and the selectivity of the catalysis are explored together with speciation analysis and isotope labeling studies. The results confirm that the complexes of the type [Mn2(micro-O)(micro-R-CO2)2(tmtacn)2]2+, which show remarkable redox and solvent-dependent coordination chemistry, are the resting state of the catalytic system and that they retain a dinuclear structure throughout the catalytic cycle. The mechanistic understanding obtained from these studies holds considerable implications for both homogeneous manganese oxidation catalysis and in understanding related biological systems such as dinuclear catalase and arginase enzymes.     

New valence-sandwich [Mn(II)4Mn(III)4Mn(II)4] aggregate showing single-molecule magnet behavior

The reaction of manganese(II) acetate, 1,1,1-tris(hydroxymethyl)methane (H3thme), and triethylamine in methanol leads to the formation of [Mn12O2(OMe)2(thme)4(OAc)10(H2O)4].2MeOH. The [Mn(III)4Mn(II)8] core consists of a central [Mn(III)4O6] rhombus sandwiched by two [Mn(II)4O7] fragments. Frequency-dependent ac susceptibility and hysteresis loops in the magnetization indicate single-molecule magnet behavior with a pure quantum-tunneling regime of relaxation below 0.2 K.     

Oxidative azacyclization of 1-monosubstituted thioureas in reaction with [bis(acyloxy)iodo]arenes to form 1,2,4-thiadiazole derivatives

For the first time, derivatives of 1,2,4-thiadiazoles have been obtained by the reaction of [bis(acyloxy)iodo]arenes with 1-monosubstituted thioureas. 1-Acetylthiourea is subject to intermolecular azacyclization to form 3,5-bis-(acetylamino)-1,2,4-thiadiazole in reaction with [bis(acyloxy)iodo]benzene. 1-Phenylthiourea forms 3,5-bis-(phenylamino)-1,2,4-thiadiazole in a single-stage reaction with (diacetoxyiodo)benzene. The reaction of 1-phenylthiourea with [bis(trifluoroacetoxy)iodo]benzene leads to the formation of 5-imino-4-phenyl-3-phenylamino-4H-1,2,4-thiadiazoline.     

Selenium-catalyzed regioselective cyclization of unsaturated carboxylic acids using hypervalent iodine oxidants

A new and convenient selenium-catalyzed regioselective cyclization of γ,δ-unsaturated carboxylic acids to the corresponding 3,6-dihydro-2H-pyran-2-ones is described. The cyclization products have been obtained in good to excellent yields using diphenyl diselenide as a catalyst and [bis(trifluoroacetoxy)iodo]benzene as a stoichiometric oxidant.     

Epoxidation of olefins catalyzed by manganese(III) porphyrin in a room temperature ionic liquid

The epoxidation of several alkenes catalyzed by (meso-tetrakis(pentafluorophenyl)porphinato) manganese(III) chloride (MnTFPPCl) was carried out in a 3:1 [bmim]PF₆ ionic liquid/CH₂Cl₂ mixed solvent. The conversion and the yield of epoxide are excellent. It was also found that [bis(acetoxy)iodo]benzene [PhI(OAc)₂] is a more efficient oxidant than PhIO. The catalyst in the ionic liquids can be recycled for several runs without substantial diminution in the catalytic activity.     

Manganese(III) acetate-mediated synthesis of biaryls under microwave irradiation

Manganese(III) acetate (Mn(OAc)₃)-mediated synthesis of biaryls and heterobiaryls starting from arylboronic acid was developed under microwave irradiation in high yields. Microwaves were also used for the synthesis of Mn(OAc)₃ from KMnO₄ and acetic acid. Additional irradiation of this in situ generated Mn(OAc)₃ with arylboronic acids, which in turn furnished the biaryls in high yields in a one pot reaction. This is superior from the point of view of yield, short reaction time, sensitive functional group toleration, and more environmentally friendly than the reported methods with a minimum amount of benzene and thiophene as a reagent but not as a solvent.     

Reaction of (diacetoxyiodo)benzene with excess of trifluoromethanesulfonic acid. A convenient route to para-phenylene type hypervalent iodine oligomers

Reaction of (diacetoxyiodo)benzene [PhI(OAc)₂] in trifluoromethanesulfonic acid (TfOH) resulted in oligomerization of PhI(OAc)₂. Quenching with NaBr gave the bromide salts of hypervalent iodine oligomers that were determined by thermolysis with KI to be a para phenylene type of oligomers. Neutralization of the reaction mixture of PhI(OAc)₂ and TfOH with aqueous NaHCO₃ yielded the triflate salts of iodine oligomers. Furthermore, quenching the reaction mixture with aromatic substrates afforded arylated iodine oligomers. These iodine oligomers were found to be 3-4 of the number average degree of polymerization (P_n) by GC analysis of the thermolysis products and ¹H NMR analysis. The major products, trimer and tetramer, were synthesized independently.