Recent topics in the desymmetrization of meso-diols

The desymmetrization of meso compounds is one of the most effective strategies for asymmetric synthesis. This digest focuses on recent progress in the desymmetrization of meso-diols and their derivatives. The topics discussed here include methods for the enzymatic acylation of meso-diols and the hydrolysis of meso-diesters, acylation, related reactions of meso-diols with organocatalysts and metal catalysts, the oxidation of meso-diols by enzymes, organocatalysts, and metal catalysts, and the desymmetrization of meso-dicarbamates with metal catalysts. The desymmetrization of meso-diols using tandem reactions is also discussed.     

Cu(Ⅱ)-catalyzed aerobic oxidative amidation of azoarenes with amides

A method for Cu(Ⅱ)-catalyzed dehydrogenative amidation of azoarene using air as the terminal oxidant was developed. Various amides, such as arylamides, alkylamides, lactams, and imides, are all effective amidation reagents and provide the desired products in moderate to excellent yields. Notably, good yields can also be obtained on a gram-scale with this amidation reaction.In this protocol of azoarene amidation, the catalyst(Cu(OAc)_2) and oxidant(air) are inexpensive and readily available, and the process is highly efficient and atom economical.     

Ruthenium(II)-catalyzed cyclization of azabenzonorbornadienes with alkynes

The ruthenium-catalyzed cyclization of azabenzonorbornadienes with alkynes leads to an unanticipated dihydrobenzoindole framework. Depending on the structure of the alkyne and the Ru catalyst, either a dihydrobenzoindole and/or a [2+2] cycloaddition product could be formed. Cp*Ru(COD)Cl was found to be an active catalyst for the cyclization of an azabenzonorbornadiene with a propargylic alcohol to produce the dihydrobenz[g]indole as a single regio and stereoisomer in good yield. For other alkynes, selective formation of the dihydrobenz[g]indole is possible by using a cationic Ru catalyst, [Cp*Ru(CH3CN)3]PF6.     

Intramolecular Pd(II)-catalyzed aerobic oxidative amination of alkenes: synthesis of six-membered N-heterocycles

Use of a base-free Pd(DMSO)(2)(TFA)(2) catalyst system enables the synthesis of six-membered nitrogen heterocycles via a Wacker-type aerobic oxidative cyclization of alkenes bearing tethered sulfonamides. Various heterocycles, including morpholines, piperidines, piperazines, and piperazinones, are accessible by this method.     

Ruthenium(II)-catalyzed homo-Diels-Alder reactions of disubstituted alkynes and norbornadiene

The homo-Diels-Alder (HDA) reaction of norbornadiene (NBD) and internal functionalized alkynes leading to 8,9-disubstituted deltacyclenes using readily available electron-rich phosphine-ruthenium(II) catalysts is described.     

Ruthenium(II)-catalyzed synthesis of 2-arylbenzimidazole and 2-arylbenzothiazole in water

Transition Metal Chemistry - Benzimidazoles/benzothiazoles are heterocyclic compounds which contain a five membered heteroatom and a benzene ring. They constitute a crucial structural unit of...     

Copper(I)-catalyzed asymmetric desymmetrization: synthesis of five-membered-ring compounds containing all-carbon quaternary stereocenters

A highly stereoselective catalytic alkylation sequence for the synthesis of highly functionalized and versatile five-membered-ring compounds bearing all-carbon quaternary stereocenters was developed. Enantioselective desymmetrization of achiral cyclopentene-1,3-diones was thus executed by chiral Cu-phosphoramidite catalysts. A variety of complicated cyclopentane derivatives can be synthesized with excellent stereoselectivities using a low catalyst loading in a one-pot operation.     

Synthesis of pyrrolidines via palladium(II)-catalyzed aerobic oxidative carboamination of butyl vinyl ether and styrenes with allyl tosylamides

[Structure: see text] Palladium(II) catalyzes the oxidative coupling of allyl tosylamides with butyl vinyl ether and various styrene derivatives to produce 2,4-substituted pyrrolidine products at room temperature. Molecular oxygen together with a copper(II) cocatalyst mediates reoxidation of the palladium catalyst. The reactions with styrene substrates can be performed in an open flask with ambient air as the source of O2. Several nontraditional cocatalysts, including catechol, cyclooctadiene, and methyl acrylate, have a beneficial effect on the reactions.     

Rhodium(III)-catalyzed oxidative mono- and di-olefination of isonicotinamides

[RhCp*Cl(2)](2) can catalyze the oxidative coupling of secondary isonicotinamides with activated olefins using Cu(OAc)(2) as an oxidant. The selectivity can be controlled by the solvent. In MeCN, the mono-olefination and two-fold oxidation reaction is the major pathway, while in THF this reaction gave mostly diolefination products. In both cases, the coupled products contain an exocyclic C=C bond.     

Metal(salen)-catalyzed oxidation of limonene in supercritical CO2

Summary The Mn(Salen)Cl and Ni(Salen)-catalyzed oxidation of limonene has been carried out. The catalytic cycle involved PhIO via a rebound mechanism. In all cases the use of organic solvents resulted in reasonable selectivities of oxidized products. The use of supercritical carbon dioxide (SCCO₂) led at least to comparable results in terms of conversions, but showed different selectivities. In ordinary solvents epoxidation appears to predominate over allylic oxidation. This tendency, in SCCO₂, appears only after 4 h of reaction. Shorter reaction times (2 h) appear to lead to opposite selectivity. These results showed the advantages of using SCCO₂ as solvent in these reactions. SCCO₂ is much more compatible with green technology than are organic solvents.     

Palladium(II)-catalyzed aerobic hydroalkoxylation of styrenes containing a phenol

An intermolecular Pd-catalyzed hydroalkoxylation of styrenes that contain a phenol is presented. The reaction can be performed on terminal, disubstituted, and trisubstituted olefins in a variety of alcoholic solvents. Initial mechanistic data suggest a mechanism that involves oxidation of the alcoholic solvent to provide a Pd-hydride that inserts into an olefin. This is followed by formation of a quinone methide and subsequent addition of an alcohol to yield the hydroalkoxylated product.     

Enantioselective Pd(II)-catalyzed aerobic oxidative amidation of alkenes and insights into the role of electronic asymmetry in pyridine-oxazoline ligands

Enantioselective intramolecular oxidative amidation of alkenes has been achieved using a (pyrox)Pd(II)(TFA)(2) catalyst (pyrox = pyridine-oxazoline, TFA = trifluoroacetate) and O(2) as the sole stoichiometric oxidant. The reactions proceed at room temperature in good-to-excellent yields (58-98%) and with high enantioselectivity (ee = 92-98%). Catalyst-controlled stereoselective cyclization reactions are demonstrated for a number of chiral substrates. DFT calculations suggest that the electronic asymmetry of the pyrox ligand synergizes with steric asymmetry to control the stereochemical outcome of the key amidopalladation step.     

Ruthenium(II)-catalyzed regio- and stereoselective hydroarylation of alkynes via directed C-H functionalization

The ruthenium-catalyzed hydroarylation of alkynes with benzamides proceeds regio- and stereoselectively through a directed C-H bond cleavage. Preliminary mechanistic investigations indicate that the reaction involves amide-directed ortho-metalation, carbometalation of alkyne, and protonolysis. Similarly, phenylazoles also add to alkynes regioselectively.     

Highly enantioselective (OC)Ru(salen)-catalyzed sulfimidation using N-alkoxycarbonyl azide as nitrene precursor

Enantioselective imidation of alkyl aryl sulfides with N-alkoxycarbonyl azide as a nitrene precursor was effected by using (OC)Ru(salen) complex 1 as catalyst. The steric and electronic nature of the N-alkoxycarbonyl group was found to strongly affect the enantioselectivity and the reaction rate, and high enantioselectivity (up to 99% ee) and good chemical yields were achieved by using 2,2,2-trichloro-1,1-dimethylethoxycarbonyl azide as the nitrene precursor at room temperature.     

Cu(I)-catalyzed oxidative cyclization of alkynyl oxiranes and oxetanes

In the presence of a Cu(I) catalyst and a pyridine oxide, alkynyl oxiranes and oxetanes can be converted into functionalized five- or six-membered α,β-unsaturated lactones or dihydrofuranaldehydes. This new oxidative cyclization is proposed to proceed via an unusual allenyloxypyridinium intermediate.     

两种新型salen金属络合物WO2(salen)和MoO2-(salen)的合成

新合成了两种过渡金属salen络合物WO2(salen)和MoO2(salen).通过和已经有的文献比较,发现这两种络合物的分子结构是少见的β-cis构型.