Catalytic arylation of carbon-carbon double bond followed by N- or O-cyclization

Under the catalytic action of palladium,o-hydroxy- oro-amino-substituted aryl iodides oxidatively add to palladium(0), insert strained or rigid olefins, and close the ring between the aliphatic carbon and theortho-functional group. This reaction occurs under mild conditions in the absence of phosphine ligands in a DMF solution and affords fused dihydrofurans or-pyrroles.     

Chemical repercussions of orbital interactions through bond and through space. Effect of remote substituents on the addition of nitrenes to bicyclic olefins

The reactivity of a series of bicyclic olefins with nitrenes is profoundly influenced by the nature of remote functional groups. There is a marked lack of reactivity for reactions with carboethoxynitrene as compared to phthalimidonitrene which is distinctly nucleophilic in character. An explanation for the reluctance to form aziridines is offered in terms of orbital interactions between the distant groups and the olefinic bond, making the latter remarkably electron deficient as evidenced by UV-photoelectron spectrosoopy. Because of the complexity of the spectra, identification of the Ip associated with the reactive π-centre was made by recourse to ab initio configuration interaction calculations for key members of the series.     

Iridium-Catalyzed Enantioselective Hydroarylation of Alkenes through C−H bond Activation: Experiment and Computation

A new catalytic enantioselective hydroarylation of unactivated olefins is developed that provides rapid access to functionalized chiral dihydrobenzofurans with good yields and excellent enantioselectivities. Simple aromatic ketones or amides act as a directing group allowing the regioselective reaction at the more hindered ortho position. Tertiary benzylic stereocenters are obtained directly under mild reaction conditions and with complete atom economy from readily available starting materials.     

Intermolecular cross-double-michael addition between nitro and carbonyl activated olefins as a new approach in C-C bond formation

A novel intermolecular cross-double-Michael addition between nitro and carbonyl activated olefins has been developed through Lewis base catalysis. The reaction took place with a large group of beta-alkyl nitroalkenes and alpha,beta-unsaturated ketone/esters, producing an allylic nitro compound in good to excellent yields.     

Pd-catalyzed aerobic oxidative coupling of anilides with olefins through regioselective C-H bond activation

Pd-catalyzed aerobic oxidative coupling of anilides with olefins was achieved through selective C-H bond activation. Compared to the previous studies, not only did we successfully use molecular oxygen to replace the chemical oxidant, but we also obtained improved yields for a number of substrates. The reaction tended to give high yields for electron-rich anilides and electron-deficient olefins, with a best yield up to 91%.     

Toluene as a novel carrier of xanthates—preparation,use and surrogate of S-tri- and di-chloromethyl xanthates

Toluene has been identified as a novel carrier of xanthates. Their corresponding fragmentative precursors proved to behave efficiently in radical group transfer reactions. As examples, unprecedented S-tri/di-chloromethyl xanthates could be prepared, isolated and further used in radical additions to olefins. Their precursors (de-aromatized toluene upon which is grafted, at one end, a tri/di-chloromethyl-group and, at the other end, a dithiocarbonyl group) can also be used directly in the transfer of both groups to olefins. The re-aromatizing loss of toluene by radical initiated fragmentation of the precursors brings thus new opportunities to the chemistry of xanthates, exemplified here in the intermolecular additions to olefins of new S-tri/di-chloromethyl xanthates.     

Relative olefin—metal bond strengths in some platinum (0) compounds. Part II1

Measurements are reported for the enthalpies of solution of:

where L is triphenylphosphine and the olefins used were cis- and trans-1,2-diphenyl-ethene. These enthalpies, when combined with other data, lead to the conclusion that the difference in the relative strengths of the platinum—olefin bonds (trans-1,2- diphenylethene&>;cis-1,2-diphenylethene&>;phenylethene) found previously arises mainly from electronic rather than from steric effects of the olefins in the complexes.     

Regioselective oxidation of internal olefins bearing neighboring oxygen functions by means of palladium catalysts. Preparation of β-alkoxy or acetoxy ketones from allyl and homoallyl ethers or esters

A new preparative method of β- and γ-alkoxy (acetoxy) ketones, which are important precursors of vinyl ketones and 1,4-diketones, respectively, is presented. With PdCl₂/CuCl/O₂ or PdCl₂/p-benzoquinone catalyst system, internal olefins bearing allylic alkoxy or acetoxy group underwent regioselective oxidation to form the corresponding β-alkoxy or β-acetoxy ketones. Similarly, γ-acetoxy ketones were obtained from homoallyl acetates having internal olefins with high regioselectivity.     

Clay-anchored non-heme iron-salen complex catalyzed cleavage of CC bond in aqueous medium

Clay-anchored iron[N,N′-ethylenebis(salicylideneaminato)] complex, synthesized by direct exchange, oxidizes various olefins and chalcones in aqueous acetonitrile using hydrogen peroxide as terminal oxidant. Aldehyde and its derivatives are obtained as oxidation products by the cleavage of CC double bond. In comparison with the catalysis by iron-salen complex in solution, the clay catalyzed pathway not only increases the rate of reaction significantly, but also provides selective oxidation toward the aldehyde. Some chalcones also give very good yield in water, compared to the solution and clay catalyzed pathways.     

Thermal stability and bond dissociation energy of fluorinated polymers: A critical evaluation

Intrinsic bond dissociation energies (BDEs) of selected fluorinated polymers are critically evaluated. Two distinctive approaches were followed. In the first one, according to Wu and Rodgers [E.-C. Wu, A.S. Rodgers, J. Am. Chem. Soc. 98 (1976) 6112-6115], starting from the gas-phase enthalpy of polymerization we obtained the polymer backbone BDE through appropriate thermodynamic cycles. Revised experimental results indicate that the CC BDEs of all the polymers taken into account fall within a limited energy interval, comparable to the average experimental uncertainty. Central to the second methodology adopted, is a model compound approach. Thanks to the large number of reliable thermodynamic data available in the scientific literature and to simple end-capping rules, C₂ molecules were chosen as suitable models for infinite linear polymers and alternating copolymers between ethylene and fluorinated olefins. For partially fluorinated polymers, like polyvinylidene fluoride (PVDF), alternating ethylene-tertrafluoroethylene (ETFE) and alternating ethylene-chlorotrifluoroethylene (ECTFE), the weight loss due to HF and HCl evolution during heating experiments was successfully related to the threshold energy E_o(HX) for 1,2-elimination from chemically activated hydrofluoro and hydrofluorochlorocarbons according to the modified Rice-Rampsberger-Kassel (RRKM) unimolecular theory.     

Regio- and stereoselective synthesis of (E)-1-bromo-2-iodoalkenes through iodobromination of internal alkynes

One-step synthesis of (E)-1-bromo-2-iodoalkenes from internal alkynes through IBr addition is described. The IBr was generated in situ from commercially available TMSBr and NIS. This simple protocol enables highly efficient regio- and stereoselective iodobromination of the triple bond on a gram scale in anti-mode, and provides a potentially diverse scaffold for preparation of differentially all-carbon tetrasubstituted olefins.     

A donor–acceptor complex enables the synthesis of E-olefins from alcohols,amines and carboxylic acids

Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor–acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.

A visible-light-induced defunctionalization strategy for the synthesis of olefins by using easily available alcohols, amines and carboxylic acids as starting materials is demonstrated.     

Synthesis of monohalocyclopropane derivatives from olefins by the reaction with trihalomethanes and copper

Fluoro-, chloro-, bromo-, and iodocyclopropane derivatives were obtained in 10–80% yields by the reaction of FCHI₂, ClCHI₂, BrCHI₂, and CHI₃, respectively, with Cu in the presence of olefins. The reaction was electrophilic, and proceeded stereospecifically, i.e., cis and trans olefins afforded cyclopropane derivatives whose configurations with respect to the substituents from original olefins were cis and trans, respectively. Since isomeric olefins were not detected in the reaction mixture which would be expected from the insertion of the corresponding free monohalocarbenes into C—H bonds, the reaction seemed to proceed via organocopper intermediates rather than free monohalocarbenes. With respect to the configuration of the halogen introduced by the new reaction, the cis or endo isomers were generally obtained predominantly over the corresponding trans or exo isomers.     

Preparation of silk fibroin-supported Pd(0) catalyst for chemoselective hydrogenation: reduction of palladium(II) acetate by methanol on the protein

The Pd/fibroin (Fib) was easily prepared by the auto-reduction of the silk-fibroin conjugated Pd(OAc)₂ using MeOH as a solvent and a reductant and exhibited good chemoselectivity in the hydrogenation of olefins and azides in the presence of aromatic carbonyls and/or halogens or an O-benzyl protective group.     

Synthesis of polyoxyethylene grafting nylon 6 and the selective separation of cyclohexane/cyclohexanone/cyclohexanol mixture through its membranes

A polymer membrane having polyoxyethylene grafting nylon 6 was prepared by reacting of nylon 6 and ethylene oxide. The chemical compositions of the polyoxyethylene grafting nylon 6 were determined by ¹H NMR. Degree of substitution for amide group, x, and degree of polymerization for polyoxyethylene, n, in bulk polymerization at 80°C for 4–9.5 h were evaluated: x = 0.32 ± 0.01–0.56 ± 0.02 and n = 2.8 ± 0.1–6.0 ± 0.3. The polyoxyethylene grafting nylon 6 membrane showed a selective separation of cyclohexanol from a cyclohexane/cyclohexanone/cyclohexanol mixture by a pervaporation technique. The FTIR and flux analyses verified that the selectivity for cyclohexanol was attributed to the hydrogen-bonding interaction between hydroxyl group in cyclohexanol and the hydroxyl group in polyoxyethylene grafting chain. The pervaporation and an adsorption experiment of cyclohexanol through the present membrane showed that hydroxyl group in graft chain acted as a carrier for cyclohexanol.     

Synthesis and olfactory properties of unnatural derivatives of lilac aldehydes

Lilac aldehydes are considered as principal olfactory molecules of lilac flowers. We have designed, prepared and evaluated two sets of their unnatural racemic analogues as pure diastereomers. While the synthesis of gem-dimethyl homologues starts from geranyl acetate, the preparation of methylene derivatives commences from linalyl acetate. The key Lewis and/or Brønsted acid catalysed cyclisation furnishes easily separable cis-/trans-tetrahydrofuranyl esters as common advanced intermediates. The subsequent functional group transformations lead to target aldehydes, alcohols, nitriles and olefins. Unlike the homologues possessing similar herbal scents, methylene derivatives exhibit woody and/or flowery odours. In the latter case, the sensory evaluation suggests the importance of relative stereochemistry and/or type of functional group on the odour character of respective compounds.     

Oxytelluration of olefins to (β-alkoxy- and β-hydroxy-alkyl)aryltellurium dihalides and their reactions with reducing agents and aqueous NaOH

Treatment of olefinic hydrocarbons with phenyltellurium tribromide or a mixture of diphenylditelluride and bromine in alcohol affords (β-alkoxyalkyl)phenyltellurium dibromides in fair to good yield (alkoxytelluration of olefins). Various aryltellurium trichlorides, diphenylditelluride/CuCl₂, and phenyltellurocyanate/CuCl₂ can be used for the preparation of (β-alkoxyalkyl)aryltellurium dichlorides. Similar reactions in aqueous tetrahydrofuran or aqueous t-butyl alcohol result in the formation of the corresponding β-hydroxy compound (hydroxytelluration of olefins). The reaction is trans stereospecific in the cases of cis-2-butene and cis- and trans-4-octenes and regiospecific in the cases of all terminal olefins examined (1-hexene, 1-octene, 1-decene, styrene, α-methylstyrene, 2-methyl-1-pentene, and isobutylene), tellurium species attacking the terminal carbon solely. The diorganyltellurium dihalide produced is reduced to the corresponding diorganyltelluride by reducing agents such as N₂H₄, Na₂S, Na₂S₂O₃, and NaHSO₄ in aqueous solution. Treatment of the diorganyltellurium dibromide with aqueous NaOH affords either an allylic ether (by telluroxide elimination) or a telluroxide depending on the structure of the telluroxide.     

Pyridinyl directed alkenylation with olefins via Rh(III)-catalyzed C-C bond cleavage of secondary arylmethanols

Novel C-C bond cleavage of secondary alcohols through Rh(III)-catalyzed β-carbon elimination directed by a pyridinyl group is reported. A five-membered rhodacycle is proposed as a key intermediate, which undergoes further alkenylation with various olefins. This novel transformation shows high efficiency along with excellent selectivity in mild conditions. A wide range of functionalities are compatible. This study offers a new strategy to carry out C-C bond activation.     

Platinum-catalyzed consecutive C-N bond formation-[1,3] shift of carbamoyl and ester groups

The reaction of ortho-alkynylphenylureas 1 having a carbamoyl group attached to the nitrogen atom proceeded in the presence of catalytic amounts of PtI₄, affording corresponding indole-3-carbamides 2 in moderate to high yields. In addition, the platinum-catalyzed cyclization of ortho-alkynylphenyl carbamates 3 afforded corresponding indole-3-carboxylates 4 in good yields. The present reaction proceeds through the intramolecular addition of carbon-nitrogen bonds to triple bonds, the so-called carboamination.     

Synthesis of novel 2-phenyl-5-substituted dihydropyrimidines using 2-phenyl-1,3-diaza-1,3-butadienes and electron-deficient olefins

A novel synthetic method for 2,5-disubstituted dihydropyrimidines was developed. The cyclization of 1,3-diaza-4-dimethylamino-1,3-butadienes having a N-protecting group (N-Boc, N-Cbz, N-n-C₄H₉, N-Bn or N-Ph) with electron-deficient olefins, such as α,β-unsaturated carbonyl compounds, phenyl vinyl sulfone, and acrylonitrile was studied in detail. The cyclization smoothly proceeded to afford 4-dimethylamino-1,4,5,6-tetrahydropyrimidines or 1,6-dihydropyrimidines in good yields. The isolated 4-dimethylamino-1,4,5,6-tetrahydropyrimidines were converted to 2,5-disubstituted-1,6-dihydropyrimidines through the β-elimination of the dimethylamino group. 2,5-Disubstituted-1,4(6)-dihydropyrimidines were obtained after removal of the N-Boc or N-Cbz group. Independent tautomers of the resulting dihydropyrimidines were observed.