Highly chemoselective reductive amination of carbonyl compounds promoted by InCl3/Et3SiH/MeOH system

A new strategy has been developed for reductive amination of aldehydes and ketones with the InCl3/Et3SiH/MeOH system, which is a nontoxic system with highly chemoselective and nonwater sensitive properties. The methodology can be applied to a variety of cyclic, acyclic, aromatic, and aliphatic amines. Functionalities including ester, hydroxyl, carboxylic acid, and olefin are found to be stable under our conditions. The reaction shows a first-order kinetics profile with respect to both InCl3 and Et3SiH. Spectroscopic techniques such as NMR and ESI-MS have been employed to probe the active and resulting species arising from InCl3 and Et3SiH in MeOH, which are important in deriving a mechanistic proposal. In the ESI-MS studies, we have first discovered the existence of stable methanol-coordinated indium(III) species which are presumably responsible for the gentle generation of indium hydride at room temperature. The solvent attribution was crucial in tuning the reactivity of [In-H] species, leading to the establishment of mild reaction conditions. The system is superior in flexible tuning of hydride reactivity, resulting in the system being highly chemoselective.     

Inter- and intramolecular isocarbon couplings of cobalt-complexed propargyl radicals: challenging the consensus

Intermolecular coupling reactions of Co₂(CO)₆-complexed, γ-ethyl propargyl radicals occurred with higher dl-diastereoselectivity than intramolecular cyclizations of isocarbon analogues (de_inter−de_intra≤52%). The observed phenomenon was interpreted in terms of a tandem action of two main determinants—sterics and CH/π coordination—with the latter being enabled by the methoxy groups located on the periphery of the aromatic nuclei (4-, 3,4-, 3,4,5-).     

Theoretical study and rate constants calculation for the reactions of SiH3 radical with SiH3CH3 and SiH2(CH3)2

The multiple‐channel reactions SiH₃ + SiH₃CH₃ → products and SiH₃ + SiH₂(CH₃)₂ → products are investigated by direct dynamics method. The minimum energy path (MEP) is calculated at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD method. The rate constants for individual reaction channels are calculated by the improved canonical variational transition state theory (ICVT) with small‐curvature tunneling (SCT) correction over the temperature range of 200–2400 K. The theoretical three‐parameter expression k₁(T) = 2.39 × 10⁻²³T^4.01exp(−2768.72/T) and k₂(T) = 9.67 × 10⁻²⁷T^4.92exp(−2165.15/T) (in unit of cm³ molecule⁻¹ s⁻¹) are given. Our calculations indicate that hydrogen abstraction channel from SiH group is the major channel because of the smaller barrier height among eight channels considered. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Diastereoselective synthesis of cyclopentanediols by InCl 3/Al mediated intramolecular pinacol coupling reaction in aqueous media

A "green" and practical intramolecular pinacol coupling reaction promoted by InCl 3/Al catalysts in aqueous media has been developed. Under mild conditions, a novel class of polysubstituted cyclopentane-1,2-diols have been obtained with excellent diastereoselectivity.     

Facile esterification promoted by the triphenylstibine oxide-phosphorus sulfide (Ph3SbO/P4S10) system

Various esters are conveniently prepared by direct esterification of the corresponding carboxylic acids with alcohols catalyzed by a triphenylstibine oxide–phosphorus(V) sulfide combined system (Ph₃SbO/P₄S₁₀) under mild conditions (25–80 °C).     

Oxidative intramolecular coupling of 2, 3-disubstituted phenyl acrylic acids and derivatives promoted by di-tert-butylperoxide

Polymethoxy-substituted phenanthrene-9-carboxylic acids or their methylate are key intermediates for the synthesis of tylophora alkaloids and their analogs. An intramolecular oxidative coupling reaction of unfunctionalized 2,3-disubstituted phenyl acrylic acids and derivatives promoted by di-tert-butylper- oxide gave above intermediates in high yields. The mild reaction conditions and easy purification procedures of this method provide a new approach for the synthesis of phenanthrenes.     

Inter- and intramolecular hydroacylation of alkenes employing a bifunctional catalyst system

Based on a conceptually innovative bifunctional P,N ligand, an efficient protocol for the rhodium-catalyzed inter- and intramolecular hydroacylation of alkenes has been developed.     

InCl3/I2-catalyzed cross-coupling of alkyl trimethylsilyl ethers and allylsilanes via an in situ derived combined Lewis acid of InCl3 and Me3SiI

Direct Csp3-Csp3 coupling of various aliphatic trimethylsilyl ethers and allylsilanes is effectively catalyzed by InCl3 and I2. The transformation is thought to involve an in situ-derived combined Lewis acid of InCl3 and Me3SiI. The reaction can be used for the construction of quaternary-quaternary and quaternary-tertiary carbon-carbon bonds. This system enabled a highly chemoselective coupling to be conducted with a trimethylsilyl ether including an aryl halide moiety. Furthermore, couplings were possible using an alkynyltrimethylsilane and a trimethylsilyl ketene acetal.     

Pyridinium N-2′-pyridylaminide: synthesis of 3-aryl-2-aminopyridines through an intramolecular radical process

Tris(trimethylsilyl)silane (TTMSS) and azobisisobutironitrile (AIBN) promote the intramolecular heteroarylation of arenesulfonamides with pyridyl radicals under thermal conditions. The arenesulfonamides are easily prepared from pyridinium N-2′-pyridylaminide. The heteroarylation process involves pyridyl radical cyclization and ipso substitution.     

Stereo-selective synthesis of cis-alkenes/halo-alkenes by reaction of diphenylmethane with ethynylbenzenes via sp C-H bond activation promoted by iron salts

A stereo-selective reaction for the synthesis of cis-alkenes/halo-alkenes from diphenylmethane and ethynylbenzenes was developed in the presence of iron(III) bromide or chloride. Alkenyl bromides/chlorides were obtained in comparatively good yields in chlorobenzene under mild reaction conditions.     

Homocoupling of aryl halides promoted by an NiCl2/bpy/Mg system in DMF

Homocoupling of aryl halides (2 ArX → Ar―Ar) promoted by NiCl₂/2,2′‐bipyridine (bpy)/Mg mixtures in DMF has been studied. Mixtures of NiCl₂, bpy and Mg in DMF promoted homocoupling of aryl halides such as phenyl bromide and p‐tolyl bromide to give the coupling products in good (e.g. approximately 60–75%) yields, and the homocoupling products were easily isolated from the reaction mixtures. Application of this homocoupling to dibromo‐aromatic compounds (Br–arylene–Br: 2,5‐dibromopyridine, 2,7‐dibromo‐9.9‐dioctylfluorene and 2,7‐dibromo‐9,10‐dioctyl‐9,10‐dihydrophenanthrene) gave the corresponding π‐conjugated polymers, –(arylene)_n–, in good yields. Organometallic processes for the homocoupling are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Isomerization of olefins catalysed by a CoCl2/Ph3P/NaBH4 system

The catalyst generated in situ using CoCl₂/Ph₃P/NaBH₄ in 1/3/1 ratio in THF at −10°C isomerizes 1-decene into predominantly cis-2-decene or trans-2-decene. Allyl benzene and safrole have been converted into the corresponding β-methylstyrenes. The catalyst also isomerizes cis,cis-1,5-cyclooctadiene to cis,cis-1,3-cyclooctadiene.     

Catalytic C-C bond cleavage and C-Si bond formation in the reaction of RCN with Et3SiH promoted by an iron complex

Catalytic C-C bond cleavage of acetonitrile and C-Si bond formation have been attained in the photoreaction of MeCN with Et3SiH in the presence of an iron complex, Cp(CO)2FeMe. This catalytic system can be applied for arylnitrile C-C bond cleavage.     

Free-radical version of the strecker synthesis of alpha-aminoamides promoted by aqueous H2O2/TiCl3/HCONH2 system

A new reaction of general synthetic interest representing the free-radical version of the Strecker synthesis to alpha-aminoamides is reported. A hydroxy radical, generated by Ti(III) one-electron reduction of H2O2, abstracts a H atom from the C-H bond of formamide, and the resulting carbamoyl radical adds to the C atom of aldimines formed in situ, leading to a one-pot synthesis of alpha-aminoamides. Several types of aldehydes can participate in this process.     

C-H bond activation and subsequent C-C bond formation promoted by osmium: 2-vinylpyridine-acetylene couplings

Complex OsH2Cl2(PiPr3)2 promotes the C-H activation of 2-vinylpyridine and subsequently couples the activated substrate with a second 2-vinylpyridine and two acetylene molecules. In the absence of 2-vinylpyridine, the activated substrate is coupled with an acetylene unit to afford a 2-butadienylpyridine derivative.     

Synthesis of amides from imines using Et3SiH/Zn system

A simple and efficient approach for the synthesis of amides by the reaction of imines and acyl chlorides in the presence of Et₃SiH/Zn system in THF at ambient temperature is reported. Mild reaction conditions, good yields of products, short reaction time and operational simplicity are the advantages of this procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Regiocontrolled intramolecular cyclizations of carboxylic acids to carbon-carbon triple bonds promoted by acid or base catalyst

We systematically investigated, for the first time, the relationship between regioselectivity and acid/base effects in the cyclization reactions between carboxylic acids and carbon-carbon triple bonds. We found novel acid- and base-promoted cyclizations to selectively give isocoumarin or pyran-2(2H)-one and phthalide or furan-2(5H)-one skeletons, respectively, and established a catalytic version of regioselective heterocyclic ring synthesis. Density functional theory calculations and application to a short route to thunberginol A were also described. [reaction: see text].