Mild method for the conversion of amides to thioamides

Aqueous ammonium sulfide was found to be an ideal substitute for hydrogen sulfide for the thiolysis of activated amides. High yields of the corresponding thioamides were obtained for a broad range of substrates, using two different procedures that are both operationally simple and inexpensive, as well as amenable to large-scale preparation. Preliminary results indicate that aqueous ammonium sulfide may also replace hydrogen sulfide in the synthesis of thionoesters from amides.     

One-step conversion to tertiary amines: InBr3/Et3SiH-mediated reductive deoxygenation of tertiary amides

We have developed a simple and practical procedure for a direct reductive conversion from a variety of tertiary amides to the corresponding tertiary amines using an InBr₃/Et₃SiH reducing system. This reducing system can be applied to the reduction of a secondary amide and provides a more efficient alternative to conventional methods that use aluminum and boron hydrides.     

Stereoselective synthesis of (Z)-enethiols and their derivatives: vinylic S(N)2 reaction of (E)-alkenyl(phenyl)-lambda3-iodanes with thioamides

[reaction: see text]. Exposure of (E)-beta-alkylvinyl(phenyl)-lambda3-iodanes to thioamides in dichloromethane at room temperature was found to result in a bimolecular nucleophilic substitution (S(N)2) at the vinylic carbon atom to give inverted (Z)-enethiols and/or (Z)-S-vinylthioimidonium salts. Vinylic S(N)2 reactions with thioureas are also discussed.     

Alkyl and aryllanthanum triflates: New reagents for the conversion of tertiary amides to ketones

Alkyl and aryllanthanum triflates 1 generated in situ from alkyl or aryllithium compounds and anhydrous lanthanum(III) triflate react with tertiary amides to provide, in excellent yield, the corresponding alkyl or aryl ketones.     

Diphenylphosphinodithioic acid: A reagent for the conversion of nitriles to thioamides

Diphenylphosphinodithioic acid is a reagent useful for a sequence effecting the hydrolysis of nitriles under mild conditions.     

Diisobutylaluminum borohydride: An efficient reagent for the reduction of tertiary amides to the corresponding amines under ambient conditions

A synthetically simple mixed metal hydride, diisobutylaluminum borohydride [(iBu)₂AlBH₄], is easily generated from a 1:1 mixture of borane-dimethylsulfide (BMS) and diisobutylaluminum hydride (DIBAL). The reduction of tertiary amides using (iBu)₂AlBH₄ is complete within five minutes under ambient conditions and the product tertiary amines were isolated in 70–99% yields by a simple acid-base extraction. This new methodology, reported herein, works well for reduction of tertiary aliphatic and aromatic amides as well as lactams to the corresponding amines and product isolation and purification does not require column chromatography.     

Synthesis of 2,4-disubstituted thiazoles from (Z)-(2-acetoxyvinyl)phenyl-lambda3-iodanes: nucleophilic substitution of alpha-lambda3-iodanyl ketones with thioureas and thioamides

In the presence of triethylamine, (Z)-(2-acetoxy-1-alkenyl)phenyl-lambda(3)-iodanes react with thioureas or thioamides in MeOH to give 2,4-disubstituted thiazoles directly in good yields. The reaction probably involves generation of highly reactive alpha-lambda(3)-iodanyl ketones through ester exchange of the beta-acetoxy group with liberation of methyl acetate, followed by nucleophilic substitutions with thioureas or thioamides.     

An efficient InCl3-catalyzed hydration of nitriles to amides: acetaldoxime as an effective water surrogate

An efficient InCl₃-catalyzed hydration protocol of nitriles to amides was developed. The reaction was carried out in toluene at refluxing temperature with the aid of acetaldoxime as an effective water surrogate to produce amides in high yields.     

Tetranitromethane as an efficient reagent for the conversion of epoxides into β-hydroxy nitrates

A convenient regioselective method for the preparation of β-hydroxy nitrates based on the ring opening reaction of epoxides by tetranitromethane in the presence of triethylamine is described. A series of substituted β-hydroxy nitrates were obtained in high yields under mild conditions.     

Chain-transfer-catalyst: strategy for construction of site-specific functional CO2-based polycarbonates

Site-specific functional polymers are generally synthesized from functionalized chain transfer agents(CTA)in the presence of catalysts.However,the poor solubility or chemical inertness of CTAs may make polymerizations uncontrollable.Now,this issue is addressed by proposing a strategy of designing chain-transfer-catalyst(CTC)that combines catalyst and CTA into one.The occurrence of catalytic effect naturally triggers the chain transfer process to give catalyst-labeled polymers with well-defined structures.As a proof-of-concept,cobalt(III)porphyrin catalysts with one,two and four hydroxyl groups act as efficient CTCs,giving the corresponding site-specific functional poly(propylene carbonate)s(PPC),diversifying the topology of polymers.Furthermore,porphyrin-capped PPCs with controllable Mn in the range of 1,000–16,800 g mol^-1were obtained by using monofunctional CTC(CTCOH).Moreover,different from traditional“catalyst+CTA”systems,a novel dynamic network transfer mechanism of CTCOH was proposed.This study provides a CTC strategy for the synthesis of site-specific functional polymers.     

Carbamoylimidazolium salts as diversification reagents: an application to the synthesis of tertiary amides from carboxylic acids

An efficient method for the preparation of tertiary amides from carbamoylimidazolium salts and carboxylic acids is described. The transformation occurs at room temperature and under relatively mild conditions. The carbamoylimidazolium salts are obtained from the reaction of secondary amines with N,N′-carbonyldiimidazole, followed by methylation with methyl iodide. The utility of this reaction was demonstrated in the formation of Weinreb amides and in a short synthesis of fused bicyclic amides. The introduction of this reaction now permits carbamoylimidazolium salts to be utilized in the formation of tertiary amides, ureas, carbamates and thiocarbamates under a single set of conditions.     

Nickel complexes from α-amino amides as efficient catalysts for the enantioselective Et2Zn addition to benzaldehyde

Ni²⁺ complexes derived from simple α-amino amides catalyze very efficiently the addition of Et₂Zn to benzaldehyde, giving (S)-1-phenylethanol as the major isomer in most cases (94% yield, 97% ee for R=Bn). The nature of the substituent on the amide nitrogen atom seems to play a key role in determining the asymmetric induction observed.     

Development and mechanistic investigation of a highly efficient iridium(V) silyl complex for the reduction of tertiary amides to amines

The cationic Ir(III) acetone complex (POCOP)Ir(H)(2)(acetone)(+) (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) was shown to catalyze the reduction of a variety of tertiary amides to amines using diethylsilane as reductant. Mechanistic studies established that a minor species generated in the reaction, the neutral silyl trihydride Ir(V) complex (POCOP)IrH(3)(SiEt(2)H), was the catalytically active species. High concentrations of this species could be conveniently generated by treatment of readily available (POCOP)IrHCl with tert-butoxide in the presence of Et(2)SiH(2) under H(2). Thus, using this mixture in the presence of a trialkylammonium salt, a wide array of tertiary amides, including extremely bulky substrates, are rapidly and quantitatively reduced to tertiary amines under mild conditions with low catalyst loading. A detailed mechanistic study has been carried out and intermediates identified. In brief, (POCOP)IrH(3)(SiEt(2)H) reduces the amide to the hemiaminal silyl ether that, in the presence of a trialkylammonium salt, is ionized to the iminium ion, which is then reduced to the tertiary amine by Et(2)SiH(2). Good functional group compatibility is demonstrated, and a high catalyst stability has provided turnover numbers as high as 10,000.     

Photoelectrochemical conversion of toluene to methylcyclohexane as an organic hydride by Cu2ZnSnS4-based photoelectrode assemblies

Direct photoelectrochemical conversion of toluene (TL) to methylcyclohexane (MC) with water has been examined as an organic hydride conversion using light irradiation. The production of MC from TL was observed on Pt/CdS/Cu(2)ZnSnS(4)/Mo photoelectrodes with anion-type ionomer membrane assemblies. A cathodic photocurrent was observed below 0.7 V vs RHE (V(RHE)) in 0.1 M Na(2)SO(4)/NaOH (pH 9.5) aqueous solution, and an apparent photocurrent density of 0.5 mA cm(-2) was obtained at 0 V(RHE) under the irradiation of a 300 W Xe lamp with a 420 nm cutoff filter. The yield of MC was measured by gas chromatography, and an 88% faradaic efficiency was estimated. This study suggests the possibility of direct energy conversion from solar energy to MC as an energy carrier of organic hydrides.     

Integration of Fe_2O_3-based photoanode and atomically dispersed cobalt cathode for efficient photoelectrochemical NH_3 synthesis

Realizing nitrogen reduction reaction(NRR) to synthesis NH_3 under mild conditions has gained extensive attention as a promising alternative way to the energy-and emission-intensive Haber-Bosch process.Among varieties of potential strategies,photoelectrochemical(PEC) NRR exhibits many advantages including utilization of solar energy,water(H_2O) as the hydrogen source and ambient operation conditions.Herein,we have designed a solar-driven PEC-NRR system integrating high-efficiency Fe_2O_3-based photoanode and atomically dispersed cobalt(Co) cathode for ambient NH_3 synthesis.Using such solar-driven PEC-NRR system,high-efficiency Fe_2O_3-based photoanode is responsible for H_2O/OH oxidatio n,and meanwhile the generated photoelectrons transfer to the single-atom Co cathode for the N_2 reduction to NH_3.As a result,this system can afford an NH_3 yield rate of 1021.5 μg mgco~(-1) h~(-1) and a faradic efficiency of 11.9% at an applied potential bias of 1.2 V(versus reversible hydrogen electrode) on photoanode in 0.2 mol/L NaOH electrolyte under simulated sunlight irradiation.     

Norbornadiene as an efficient hydrogen scavenger for the palladium-catalyzed conversion of hydrosilanes to alkoxysilanes

A palladium-catalyzed mild and efficient method for the alcoholysis of hydrosilanes containing a C=C bond in the presence of norbornadiene (NBD) is reported. The highly strained NBD acts as a hydrogen scavenger, which abstracts the hydrogen produced during the process, protecting the C=C bond from being hydrogenated.     

P-doped g-C3N4 as an efficient photocatalyst for CO2 conversion into value-added materials: a joint experimental and theoretical study

The photocatalytic yield of g-C₃N₄ for CO₂ reduction was modified by phosphorus doping. Possible reaction pathways for CO₂ reduction on the P-doped g-C₃N₄ (PCN) surface were investigated by density function theory calculations for the first time. The experimental results showed that P doping increases the carriers' lifetime, which improves the production of CH₄ through the increase in the driving force of the electrons. The partial density of states of the PCN showed that the valence band maximum and conduction band minimum are composed of p_x, p_y, and, s orbitals of the N atoms and p_z states of carbon, nitrogen, and phosphorus, respectively. Mechanism studies confirm that formic acid, formaldehyde, methanol, and methane are the most probable products. Methane, having positive adsorption energy, can be easily desorbed from the PCN surface, and the Gibbs activation energy of the final step is 1.98 eV. The formation of H₂COOH is the rate-determining step.     

Unprecedented direct oxygen atom transfer from hypervalent oxido-lambda(3)-iodanes to alpha,beta-unsaturated carbonyl compounds: synthesis of alpha,beta-epoxy carbonyl compounds

Tetra-n-butylammonium oxido-lambda(3)-iodane, prepared from 1-hydroxy-1,2-benziodoxol-3(1H)-one by reaction with tetra-n-butylammonium fluoride, directly undergoes oxygen atom transfer to alpha,beta-unsaturated carbonyl compounds, yielding epoxides.     

Bromamine-T/RuCl3 as an efficient system for the oxidation of tertiary amines to N-oxides

A variety of tertiary amines were efficiently and selectively oxidized to the corresponding N-oxides by bromamine-T using ruthenium trichloride as catalyst in alkaline (pH 8.4) acetonitrile/water (1:1) at 80 °C.     

An efficient strategy for the modification of α-cyclodextrin: direct conversion of one or two adjacent 6-OHs to phthalimides

α-Cyclodextrin was reacted with phthalimide under modified Mitsunobu conditions to give the 6^A-deoxy-6^A-phthalimido-α-cyclodextrin in 41% yield. This reaction also worked well in the modification of two methylene carbons, giving the 6^A,6^B-, 6^A,6^C- and 6^A,6^D-diphthalimido-α-cyclodextrins in 22, 9.5 and 4.6% isolated yields, respectively. All the phthalimido species can be quantitatively converted to the corresponding amino cyclodextrins by hydrazinolysis.