The first one-pot amidation of alkanes and cycloalkanes

Alkanes (or cycloalkanes) and CO in the presence of superelectrophilic systems CX₄·2AlBr₃ (X = Cl, Br) have been applied for the first time as equivalents of acylium salts in one-pot selective syntheses of amides from amines.     

Peroxide-mediated efficient addition of cycloalkanes to imines

A novel direct addition of cycloalkanes to imines mediated by peroxide was developed. The reaction tolerates a wide range of functionalities as well as aqueous conditions.     

On the behaviour of solutions of xenon in liquid cycloalkanes: Solubility of xenon in cyclopentane

The solubility of xenon in liquid cyclopentane has been studied experimentally and theoretically. Measurements of the solubility of xenon in liquid cyclopentane are reported as a function of temperature from 254.60 K to 313.66 K. The imprecision of the experimental data is less than 0.3%. The thermodynamic functions of solvation of xenon in cyclopentane, such as the standard Gibbs energy, enthalpy, entropy and heat capacity of solvation, have been calculated from the temperature dependence of Henry's law coefficients. The results provide further information about the differences between the xenon + cycloalkanes and the xenon + n-alkane interactions. In particular, interaction enthalpies between xenon and CH₂ groups in n-alkanes and cycloalkanes have been estimated and compared. Using a version of the soft-SAFT approach developed to model cyclic molecules, we were able to reproduce the experimental solubility for xenon in cyclopentane using simple Lorentz-Berthelot rules to describe the unlike interaction.     

Photomediated synthesis of β-alkylketones from cycloalkanes

β-Cycloalkylketones are prepared through a photomediated radical addition reaction onto enones starting from the corresponding alkanes (i.e., cyclopentane, -hexane, -heptane, -dodecane and adamantane). The alkyl radicals are generated via hydrogen abstraction by either an organic (benzophenone) or an inorganic (tetrabutylammonium decatungstate, TBADT) photomediator. Isolated yields vary in the range 30-80%. Benzophenone has to be considered as a reagent, since it is used in an equimolar amount with respect to enone and is completely consumed in the reaction. On the contrary, TBADT is shown to behave as a photocatalyst, which is active for at least 50 cycles. The potential of photomediated reactions for the generation of radicals from unusual precursors and the synthetic significance of this method are discussed.     

Evaluation of phenylorganotellurium compounds as radical precursors in dialkylzinc-mediated radical addition to CN double bonds

Diethylzinc-mediated radical addition to CN bonds was investigated in the presence of phenylorganotellurium compounds as radical precursors. As group transfer agents, secondary alkyl phenyl tellurides were shown to be about twice as reactive as the corresponding alkyl iodides towards ethyl radical. Their use was proven to be advantageous regarding both chemoselectivity and yield. The replacement of diethylzinc by dimethylzinc, offers no advantage in these reactions.     

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.     

α,β-Unsaturated diesters: radical acceptors in dialkylzinc-mediated tandem radical addition/aldol condensation. A straightforward synthesis of rac-nephrosteranic acid

The sequence involving conjugate radical addition/aldol condensation/lactonization is a high yielding route to di- and tri-substituted γ-lactones starting from fumaric or maleic diesters. The reactions are mediated with dialkylzincs. The domino process relies on the ability of dialkylzinc to transform α-alkoxycarbonylalkyl radicals into zinc enolates. Compared to diethylzinc, dimethylzinc enables the use of a wider range of alkyl radical precursors. In addition, dimethylzinc is a convenient source of methyl radical, which leads to a straightforward synthesis of methylated derivatives related to α-methyl-paraconic acids.     

Direct aminoalkylation of arenes and hetarenes via Ni-catalyzed Negishi cross-coupling reactions

A direct room-temperature Ni-catalyzed cross-coupling of aminoalkylzinc halides, readily available from the corresponding aminoalkyl chlorides via Grignard reagents, with aryl and hetaryl electrophiles, allows a convenient one-step preparation of aminoalkyl (het)arenes, bearing a basic tertiary nitrogen in the side chain, including piperidine and tropane derivatives. Such aminoalkylarene scaffolds are widely present in various biologically active molecules.     

New photo-responsive unit of biindenylidene with TEMPO radical substituents

Incorporation of organic radical TEMPO into photochromic biindenylidene system leads to the synthesis of a novel dual functional compound 4. Its photochromism, structure, magnetic properties as well as ESR spectroscopy were deliberately investigated. Remarkable changes of the ESR spectra were observed for 4 upon photoirradiation with different light sources. The intermolecular interactions were interpreted with regard to its crystal structure.     

Direct aminoalkylation of arenes, heteroarenes, and alkenes via Ni-catalyzed Negishi cross-coupling reactions

A room-temperature Ni-catalyzed cross-coupling of aryl, heteroaryl, and alkenyl electrophiles with aminoalkylzinc bromides, readily available from the corresponding aminoalkyl chlorides via Grignard reagents, was developed. The reaction allows a convenient one-step preparation of various aminoalkyl products, including piperidine and tropane derivatives. Such functionalized amine moieties are widely present in various biologically active molecules. Aryl, heteroaryl, and alkenyl iodides, bromides, chlorides and triflates are suitable electrophiles. A short total synthesis of two natural products, (±)-galipinine and (±)-cusparine, is also reported.     

Direct synthesis of imines by 9-azabicyclo-[3,3,1]nonan-N-oxyl/KOH-catalyzed aerobic oxidative coupling of alcohols and amines

A simple and efficient method for preparation of imines by the oxidative coupling of alcohols and amines using ABNO/KOH as the catalysts, and air as the economic and green oxidant was developed.     

Tris(trimethylsilyl)methane is not an effective mediator of radical reactions

The reductive dehalogenation of organohalides by tris(trimethylsilyl)methane has been re-investigated. Contrary to claims made in a recent publication (Tetrahedron Lett.2006, 47, 5163-5165), (TMS)₃CH does not reduce organohalides. In competition experiments between (TMS)₃CH and the poor chain mediator Et₃SiH, the latter performed the reduction. Computational investigations support these experimental findings and indicate that the C-H bond of (TMS)₃CH is too strong for this compound to serve as an effective mediator of radical reactions.     

Phosphonyl radical addition to enol ethers. The stereoselective synthesis of cyclic ethers

Addition of diethyl phosphite or diethyl thiophosphite to enol ethers, in the presence of a radical initiator, results in the regioselective synthesis of organophosphonate or phosphonothioate derivatives, respectively, under mild conditions. This method can be applied to the stereoselective formation of substituted tetrahydrofurans and tetrahydropyrans, on cyclisation of vinyl ethers bearing unsaturated side chains.     

Dearomatization of Biaryls through Polarity Mismatched Radical Spirocyclization

Dearomatization reactions involving radical cyclizations can facilitate the synthesis of complex polycyclic systems that find applications in medicinal chemistry and natural product synthesis. Here we employ redox-neutral photocatalysis to affect a radical spirocyclization that transforms biaryls into spirocyclic cyclohexadienones under mild reaction conditions. In a departure from previously reported methods, our work demonstrates the polarity mismatched addition of a nucleophilic radical to an electron rich arene, and allows the regioselective synthesis of 2,4- or 2,5-cyclohexadienones with broad functional group tolerance. By transforming biaryls into spirocycles, our methodology accesses underexplored three-dimensional chemical space, and provides an efficient means of creating quaternary spirocenters that we apply to the first synthesis of the cytotoxic plant metabolite denobilone A.     

Direct synthesis of protected diethyl 1,2-diaminoalkylphosphonates

An efficient, diastereoselective synthesis of 5-substituted (2-thioxo-imidazolidin-4-yl)phosphonic acid diethyl esters from metallated diethyl isothiocyanatomethylphosphonate and activated imines has been developed. The three-step transformation of imidazolidine-2-thione derivatives into 1,2-diaminoalkylphosphonic acids is also described.     

Microwave-enhanced ruthenium-catalysed atom transfer radical additions

The first monomode microwave-assisted atom transfer radical additions (ATRA) of carbon tetrachloride to various olefins were successfully performed, affording the adducts with almost quantitative yields in less than 10 min at 160 °C.     

Direct reductive amination of carbonyl compounds with primary/secondary amines using recyclable water-soluble Fe/EDTA complex as catalyst

Direct reductive amination of aliphatic, aromatic and heterocyclic carbonyl compounds with primary/secondary amines is reported with water-soluble Fe^II/EDTA complex as a catalyst using low-pressure molecular hydrogen in a biphasic media. The catalyst is highly selective, recyclable and is an excellent replacement for expensive noble metal catalysts or stoichiometric reducing agents.     

Direct oxidative synthesis of nitrones from aldehydes and primary anilines using graphite oxide and Oxone

One-pot condensation/oxidation of aldehydes and primary anilines into nitrones using graphite oxide (GO) and Oxone as the oxidant under very mild reaction conditions is described. The proposed method provides a direct oxidative synthesis of various nitrones in good to excellent yields under metal-free conditions in short reaction times.