Cobalt-Rhodium Heterobimetallic Nanoparticle-Catalyzed N-Alkylation of Amines with Alcohols to Secondary and Tertiary Amines.

Without the requirement for base or other additives, Co2Rh2/C can selectively catalyze both mono- and bis-N-alkylation through the coupling of simple alcohols with amines, yielding a range of secondary and tertiary amines in good to excellent isolated yields. The reaction can be applied to benzyl alcohol with optically active 1-phenylethan-1-amines, and secondary amines were isolated in quantitative yields with an excellent enantiomeric excess (ee > 94%). Selectivity is achieved by varying the reaction temperature and amount of catalyst used. This catalytic system has several advantages including eco-friendliness and a simple workup procedure. The catalyst can be successfully recovered and reused ten times without any significant loss of activity.

Rhodium-Catalyzed Synthesis of Imines and Esters from Benzyl Alcohols and Nitroarenes: Change in Catalyst Reactivity Depending on the Presence or Absence of the Phosphine Ligand.

The [Rh(COD)Cl]2/xantphos/Cs2CO3 system efficiently catalyzes the reductive N-alkylation of aryl nitro compounds with alcohols by a borrowing-hydrogen strategy to afford the corresponding imine products in good to excellent yields. In the absence of xantphos, the [Rh(COD)Cl]2/Cs2CO3 catalytic system behaves as an effective catalyst for the dehydrogenative coupling of alcohols to esters, with nitrobenzene as a hydrogen acceptor. The reactivity of the rhodium catalytic system can be easily manipulated to selectively afford the imine or ester.

Palladium(II)-Catalyzed Transformation of 3-Alkylbenzofurans to [2,3'-Bibenzofuran]-2'(3'H)-ones: Oxidative Dimerization of 3-Alkylbenzofurans.

An unprecedented oxidative dimerization by palladium catalysis has been developed using PhI(OPiv)2 as a by-standing oxidant. This provides a facile method for the synthesis of quaternary 2,3'-bibenzofuran-2'(3')-ones from readily accessible substrates. A plausible mechanism involving a Pd(II)-Pd(IV) catalytic cycle is proposed; a trace amount of water is required for subsequent oxidation.

Bimetallic Cobalt-Rhodium Nanoparticle-Catalyzed Reductive Amination of Aldehydes with Nitroarenes Under Atmospheric Hydrogen.

A cobalt-rhodium heterobimetallic nanoparticle (Co2Rh2/C)-catalyzed tandem reductive amination of aldehydes with nitroaromatics to sec-amines has been developed. The tandem reaction proceeds without any additives under mild conditions (1 atm H2 and 25 °C). This procedure can be scaled up to the gram scale, and the catalyst can be reused more than six times without loss of activity.

Phosphine-free palladium-catalyzed direct bisarylation of pyrroles with aryl iodides on water.

The Pd-catalyzed bisarylation of pyrroles with aryl iodides on water is described. The reaction proceeds under mild reaction conditions, i.e., relatively low temperature (40 °C) and phosphine-free.

Pd-catalyzed cycloisomerization of 4-aza-1,6-enynes to 3-aza-bicyclo[4.1.0]hept-2-enes.

A method for the synthesis of bicyclo[4.1.0]heptenes from 1,6-enynes through Pd-catalyzed cycloisomerization has been developed. N- and O-tethered 1,6-enynes were successfully transformed to their corresponding 3-aza- and 3-oxabicyclo[4.1.0]heptenes in reasonable-to-high yields using the catalysts [PdCl2(CH3CN)2]/P(OPh)3 or [Pd(maleimidate)2(PPh3)2] in toluene. The computational calculations using density functional theory indicate that [PdCl2{P(OPh)3}] in the oxidation state Pd(II) acts as the active catalyst species for the formation of 3-azabicyclo[4.1.0]heptenes through 6-endo-dig cyclization.

Ferrocenes with perfluorinated side chains and ferrocenophanes with fluorinated handles.

Trifluorovinyl groups are introduced onto the cyclopentadienyl ligands of ferrocene at the 1-, 1,1'-, and 1,2-positions by Negishi-type and Stille-type coupling reactions of trifluorovinylzinc chloride and tri-n-butyltrifluorovinyl stannane with several iodoferrocenes. Modification of the trifluorovinyl group by nucleophilic substitution and [2+2] cycloaddition make them versatile building blocks for synthetic transformations. 1,1'-Bis(trifluorovinyl) ferrocene reacts upon contact with silica or oxidizing agents and in the presence of a suitable nucleophile through a redox autocatalytic mechanism to afford ferrocenophanes with fluorinated handles. C(F)(H) and C(F)(OMe) moieties in α-positions allowed further modifications to be performed by nucleophilic substitution of the fluorine atoms. A series of ferrocenes with fluorinated side chains and ferrocenophanes with fluorinated handles were isolated and characterized. Several molecular structures were determined by single-crystal X-ray diffraction. The influence of the fluorine substituents on the redox properties of the iron center were studied by cyclic voltammetry.

Cytotoxic terpenoids from Juglans sinensis leaves and twigs.

Bioassay-guided fractionation of an 80% MeOH extract of Juglan sinensis leaves and twigs has resulted in the isolation of three new triterpenes (1-3) and two new sesquiterpenes (4-5) along with two known sesquiterpenes (6-7). The new compounds were determined to be 3ß, 11α, 19α, 24, 30-pentahydroxy-20ß, 28-epoxy-28ß-methoxy-ursane (1), 1α, 3ß-dihydroxy-olean-18-ene (2), 2α, 3α, 23-trihydroxy-urs-12-en-28-oic acid 28-O-ß-d-glucopyranoside (3), (4S, 5S, 7R, 8R, 14R)-8, 11-dihydroxy-2, 4-cyclo-eudesmane (4), 15-hydroxy-α-eudesmol-11-O-ß-d-glucopyranoside (5), by spectroscopic analysis. The cytotoxicity of compounds (1-7) against four cancer cell lines such as B16F10, Hep-2, MCF-7 and U87-MG was evaluated. Compounds 1, 2, 6 and 7 showed potent cytotoxicity against all of four cancer cell lines, respectively.

Rhodium(I)-catalyzed cycloisomerization of 1,6-enynes to bicyclo[4.1.0]heptenes.

Efficient rhodium(I)-catalyzed cyclopropanation reactions of nitrogen-tethered 1,6-enynes to azabicyclo[4.1.0]heptenes are reported. Moreover, rhodium(I)-catalyzed tandem cycloisomerization and carbonylative [3+3+1] cycloaddition reactions of a cyclopropylenyne have been observed.

Unsymmetric Ru(II) complexes with N-heterocyclic carbene and/or terpyridine ligands: synthesis, characterization, ground- and excited-state electronic structures and their application for DSSC sensitizers.

Three ruthenium(II) complexes with N-heterocyclic carbene (NHC) or NHC/2,2':6',2''-terpyridine (tpy) hybrid ligands, bis[2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine-4-carboxylic acid]ruthenium(II) (BCN), [2,6-bis(3-methylimidazolium-1-yl)pyridine-4-carboxylic acid](2,2';6'2''-terpyridine)ruthenium(II) (TCN), and [2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine](2,2';6'2''-terpyridine-4'-carboxylic acid)ruthenium(II) (CTN), have been synthesized and characterized by (1)H and (13)C NMR, high-resolution mass spectrometry, and elemental analysis. The molecular geometry of the TCN complex was determined by X-ray crystallography. Electronic absorption spectra of these complexes exhibit typical pi-pi* and metal-to-ligand charge transfer bands in the UV and visible regions, respectively. The lowest energy absorption maxima were 430, 448, and 463 nm with molar extinction coefficients of 28,100, 15,400, and 7400 M(-1)cm(-1) for BCN, TCN, and CTN, respectively. Voltammetric data suggest that energy levels of the highest occupied molecular orbitals (HOMOs) of the three complexes reside within a 10 meV window despite the varying degrees of electronic effect of the constituent ligands. The electronic structures of these complexes calculated via density functional theory (DFT) indicate that the three HOMOs and the three lowest unoccupied MOs (LUMOs) are metal and ligand centered in character, for the former and the latter, respectively. Time-dependent DFT (TD-DFT) calculation predicts that the lowest energy absorption bands of each complex are comprised of multiple one-electron excitations. TD-DFT calculation also suggests that the background of spectral red shift stems most likely from the stabilization of unoccupied MOs rather than the destabilization of occupied MOs. The overall efficiencies of the dye-sensitized solar cell systems of these complexes were found to be 0.48, 0.14, and 0.10% for BCN, TCN, and CTN, respectively, while that of a commercial bis(4,4'-dicarboxylato-2,2'-bipyridine)-bis(isothiocyanoto)ruthenium(II) (N719) system was 6.34%.

Au(I)-catalyzed cycloisomerization reaction of amide- or ester-tethered 1,6-enynes to bicyclo[3.2.0]hept-6-en-2-ones.

The cycloisomerization reaction of N-allyl-2-(2'-arylethyne-2-yl)amides or allylic 2-alkynoates in the presence of cationic triphenylphosphinegold(I) produced bicyclo[3.2.0]hept-6-en-2-ones under mild conditions. Computational investigations with a density functional theory (DFT) revealed that a stepwise 6-endo-dig cyclization of 1,6-enyne systems, followed by a skeletal rearrangement to form bicyclo[3.2.0]hept-6-en-2-one species represents the most probable reaction pathway. This can be further supported by employing N-(1',1'-dimethyl-1-propen-3-yl)-2-(1''-phenylethyne-2''-yl)amide as a substrate, which exclusively produced 4-phenyl-5-(prop-1-en-2-yl)-5,6-dihydropyridino-2(1H)-one unambiguously via 6-endo-dig cyclization. Theoretical calculations suggest both an aryl group at the terminal alkyne and a keto carbonyl at the C(5) position of the 1,6-enyne system play a complementary role for the reactivity.

N-heterocyclic carbene gold(I) catalyzed transformation of N-tethered 1,5-bisallenes to 6,7-dimethylene-3-azabicyclo[3.1.1]heptanes.

Tying up loose ends: The reaction of bisallenes tethered with N-(p-tolylsulfonamide) in the presence of a cationic gold N-heterocyclic carbene catalyst gave new cycloisomerization products, 6,7-dimethyleneazabicyclo[3.1.1]heptanes, in high yields (see scheme; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene).

Total synthesis of (-)-amphidinolide K.

Macrolide magic: An enyne cross-metathesis reaction of an alkynyl boronate with an alkene derivative as well as a radical cyclization reaction of a homopropargylic beta-alkoxyacrylate are the key transformations in the total synthesis of the cytotoxic macrolide (-)-amphidinolide K.

Palladium(0)-catalyzed decarboxylation of buta-2,3-dienyl 2'-alkynoates: approach to the synthesis of 2-alkynyl buta-1,3-dienes.

The Pd(PPh3)4-catalyzed decarboxylation of buta-2,3-dienyl 2'-alkynoates allows the rapid construction of 2-alkynyl buta-1,3-dienes. The carbon-carbon bond-forming reaction occurs at the central position of an allene moiety.

Cobalt/rhodium heterobimetallic nanoparticle-catalyzed carbonylative [2+2+1] cycloaddition of allenes and bisallenes to Pauson-Khand-type reaction products.

The first catalytic intra- and intermolecular [2+2+1] cocyclization reactions of allenes and carbon monoxide have been developed. In the Co(2)Rh(2) heterobimetallic nanoparticle-catalyzed carbonylative [2+2+1] cycloaddition of allenes and carbon monoxide, the allenes formally serve both as an excellent alkene- and alkyne-like moiety within a Pauson-Khand-type process.

Silver/NBS-Catalyzed Synthesis of α-Alkylated Aryl Ketones from Internal Alkynes and Benzyl Alcohols via Ether Intermediates.

The silver hexafluoroantimonate/ N-bromosuccinimide (NBS)-catalyzed synthesis of α-alkylated aryl ketones with a tertiary carbon center from internal alkynes and benzyl alcohols is reported. This reaction proceeds via the etherification of benzyl alcohols with an in situ generated benzyl bromide, formed by the reaction of benzyl alcohol with a catalytic amount of NBS and AgSbF6. Ag-catalyzed C-O cleavage of the ether leads to a tolyl radical, which undergoes addition to the alkyne, ultimately leading to the α-alkylated aryl ketone products.

Cobalt-rhodium heterobimetallic nanoparticle-catalyzed synthesis of alpha,beta-unsaturated amides from internal alkynes, amines, and carbon monoxide.

The first example of cobalt-rhodium heterobimetallic nanoparticle-catalyzed synthesis of alkenyl amides from alkynes, amines, and carbon monoxide is described.

Efficient chirality transfer in the SmI2-mediated cyclization of aldehydo beta-alkoxyvinyl sulfoxides: asymmetric synthesis of 3-hydroxyoxanes.

Stereoselective syntheses of 3-hydroxyoxanes were achieved via efficient chirality transfer in the SmI2-mediated cyclization reactions of aldehydo beta-alkoxyvinyl sulfoxides.

Transition-Metal-Free Poly(thiazolium) Iodide/1,8-Diazabicyclo[5.4.0]undec-7-ene/Phenazine-Catalyzed Esterification of Aldehydes with Alcohols.

Poly(3,4-dimethyl-5-vinylthiazolium) iodide was used as a polymer precatalyst in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and phenazine for the oxidative esterification of aldehydes with alcohols. Selective functionalization of OH groups was achieved in the presence of NH2 groups. The poly(thiazolium) iodide/DBU/phenazine system exhibited excellent catalytic activity and could be reused five times without loss of activity.

Rhodium-Catalyzed Intermolecular Carbonylative [2 + 2 + 1] Cycloaddition of Alkynes Using Alcohol as the Carbon Monoxide Source for the Formation of Cyclopentenones.

A highly regioselective rhodium-catalyzed intermolecular carbonylative [2 + 2 + 1] cycloaddition of alkynes using alcohol as a CO surrogate to access 4-methylene-2-cyclopenten-1-ones has been developed. In this transformation, the alcohol performs multiple roles, including generating the Rh-H intermediate, functioning as the CO source, and assisting in the isomerization of the alkyne. Alkynes can act as both the olefin and the alkyne partner in the cyclopentenone core.