Reaction of N-acetylimidazole with enamines

N-Acetylimidazole is a commonly used acylating reagent. When it is allowed to react with several typical enamines, amides are produced rather than the expected acylated enamines.     

Synthesis of new unsymmetric N,N′-dipyridylurea derivatives by selenium and selenium dioxide-catalyzed reductive carbonylation of substituted nitropyridines

Without using phosgene, a series of new unsymmetric N,N′-dipyridylurea derivatives have been synthesized in moderate to good yields by the one-pot reductive carbonylation of substituted nitropyridines. These reactions utilize selenium or selenium dioxide as the catalyst, aminopyridine derivatives as co-reagents, and carbon monoxide as the carbonyl source.     

Conjugate addition of nitroalkanes to N-substituted maleimides. Synthesis of 3-alkylsuccinimides and pyrrolidines

3-Alkylidenesuccinimides obtained by conjugate addition of nitroalkanes to N-substituted maleimides can be reduced to the corresponding 3-alkyl derivatives by catalytic hydrogenation. 3-Alkylsuccinimides can be further reduced using BH₃·Me₂S complex to afford 3-alkylpyrrolidines in good yield.     

Efficient synthesis of N-acylarenesulfenamides by acylation of arenesulfenamides

Acylation of arenesulfenamides proceeds efficiently by using either perfluorocarboxylic anhydrides or acid chlorides in the presence of pyridine as a base at low temperatures to give N-acylarenesulfenamides. Some N-alkylcarbonyl derivatives exist with imidic acid tautomers in an aprotic solvent.     

Indium-mediated regio- and diastereoselective reduction of norbornyl alpha-diketones

A novel, efficient, and regio- as well as diastereoselective conversion of non-enolizable bicyclic alpha-diketones into synthetically useful acyloins mediated by indium metal is described. The reduction is highly diastereoselective, leading exclusively to endo-acyloins (endo-hydroxyl groups) in excellent yields, and tolerates a variety of sensitive substituents, such as acetate, ester, and bridgehead halogens. The regioselectivity in the reductions of monosubstituted alpha-diketones varied from 70:30 to 100:0 for the two possible isomeric alcohols. The methodology is extended to the synthesis of highly functionalized cyclopentane carboxaldehydes, potential building blocks in organic syntheses, by cleavage of the acyloins by treating them with Pb(OAc)4 in MeOH/PhH. Allylindium additions to carboxaldehydes 22 have been found to be highly diastereoselective.     

Indium-mediated nucleophilic substitution reaction of β,γ-unsaturated α-methoxypiperidine derivative in water

Water as a solvent was found to accelerate the indium-mediated Barbier type allylation and benzylation of β,γ-unsaturated piperidinium ion which was generated from β,γ-unsaturated α-methoxy-N-methoxycarbonylpiperidine, while ring-opened allylated product was obtained in a case using β,γ-saturated α-methoxy-N-methoxycarbonylpiperidine. Other solvents than water resulted in low yield of the allylated and benzylated products, suggesting that water is essential to generate the piperidinium ion intermediate from β,γ-unsaturated α-methoxy-N-methoxycarbonylpiperidine.     

A convenient scalable one-pot conversion of esters and Weinreb amides to terminal alkynes

Esters and amides undergo reduction to the corresponding aldehydes using DIBAL-H followed by same pot conversion to terminal alkynes utilizing the Bestmann-Ohira reagent in good to excellent yields. Additionally chiral nonracemic substrates undergo this transformation with complete preservation of stereochemical integrity.     

Palladium nitrosoarene complexes in reductive carbonylation of nitroarenes

The reactions of carbon monoxide with the palladium nitrosoarene complexes Pd₂(-OCOR)₂(—CH₂C₆H₄NO)₂ (1, R = Me, CF₃, Bu^t, or Ph) and Pd₂(-OCOR)₂(PhNC₆H₄NO)₂ (2, R = Me, CF₃, Bu^t, or Ph) were studied. Complexes 1 contain the o-nitrosotoluene molecule metallated at the methyl group. In complexes 2, the phenyl-o-nitrosophenylamide ligand coordinated via two nitrogen atoms can be considered as a nitrosobenzene derivative bearing the NPh group in the ortho position of the Ph ring. It all cases, carbonylation of the complexes afforded the corresponding aryl isocyanates Ar—N=C=O or the products of their further transformations. The mechanism of reductive carbonylation of nitroarenes catalyzed by palladium compounds and the role of palladium nitrosoarene complexes as possible intermediates in this process are discussed.     

Reductive heterocyclizations via indium/iodine-promoted one-pot conversion of 2-nitroaryl aldehydes, ketones, and imines

2-Nitroaryl aldehydes, ketones, and imines were reductively cyclized to 2,1-benzisoxazoles with good yields in the presence of indium and iodine in MeOH. Under a similar condition, N-(2-nitrobenzylidene)anilines were produced mixtures of 2,1-benzisoxazoles and 3-anilino-2-phenyl-2H-indazoles.     

Double thioalkylation/arylation of nitroarenes with the reduction of nitro- to amino group

Some active bicyclic nitroarenes readily react with an excess of alkyl/arylthiols in the presence of DBU and bis-trimethylsilylacetamide (BSA) in DMF solution, to give dithioalkyl/aryl substituted anilines in moderate to good yields via displacement of ortho- and para-hydrogen atoms with simultaneous reduction of the nitro- to amino-group.     

Development of one-pot benzylic amination reactions of azine N-oxides

An efficient one-pot synthetic methodology has been developed for the benzylic amination reactions of methyl-substituted azine N-oxides that operate under mild conditions. The reaction was found to tolerate quinoline and isoquinoline N-oxides with electron donating and withdrawing substituents as the electrophilic reaction partners as well as a broad range of nucleophilic primary, secondary and aromatic amines, affording the benzylic amination products in up to 82% yield.     

Co/Cu bimetallic ZIF as New heterogeneous catalyst for reduction of nitroarenes and dyes

Nowadays one of the great challenges is to design new bimetallic catalysts with enhanced catalytic activity, selectivity and recycling properties. In this work, the preparation of new Co/Cu bimetallic Zeolitic Imidazolate Framework (Co-Cu/ZIF) as an efficient catalyst for the reduction of nitro compounds and organic dyes is described. Co-Cu/ZIF was characterized with different techniques such as SEM, TEM, XRD, XPS, TGA, FT-IR and UV–vis absorption indicating formation of entirely uniform cubic particles. Using this catalyst, structurally different aromatic nitro compounds were reduced efficiently to corresponding amines in excellent yields. Kinetic studies revealed that the reduction rates of nitrophenol isomers follow 3-NP > 4-NP > 2-NP order. The catalytic activity of Co-Cu/ZIF was further investigated in the reduction of organic dyes such as methyl orange (MO) and rhodamine B (RhB). This catalyst was recycled for at least ten runs in the reduction of 4-nitrophenol without a noticeable decrease in activity and reused catalyst was characterized.     

Bis-Lewis acids-catalyzed highly diastereoselective one-pot reductive dehydroxylation of chiral N,O-acetals

A one-pot and highly diastereoselective method for the reductive dehydroxylation of three classes of heterocyclic N,O-acetals with general structure 4 is reported. The method features a ‘two in one’ concept, namely, by synergetic action of two complementary Lewis acids (BF·OEt₂ and TiCl₄), the bicyclic or tricyclic oxazololactams 5 were formed in situ and reductively cleaved to give the corresponding lactams 6 in a high-yielding and highly diastereoselective manner.     

One pot conversion of azido arenes to N-arylacetamides and N-arylformamides: synthesis of 1,4-benzodiazepine-2,5-diones and fused [2,1-b]quinazolinones

Sodium iodide in acidic media has been employed for the synthesis of N-arylformamides and N-arylacetamides. The NaI/acetic acid reagent system has also been extended for the synthesis of 1,4-benzodiazepine-2,5-diones, pyrrolo[2,1-c][1,4]benzodiazepine-5,11-diones, and fused [2,1-b]quinazolinones.     

New chiral biscarboline N,N′-dioxide derivatives as catalyst in enantioselective reduction of ketoimines with trichlorosilane

New axial N,N′-dioxide secondary amide derived from l-tryptophan was synthesized and firstly employed in catalytic enantioselective reduction of ketoimines with trichlorosilane. It was found that 4f was an effective catalyst with excellent reactivity and good enantioselectivity. Possible mechanism for the catalytic procedure was tentatively proposed.     

Amide rotamers of N-acetyl-1,3-dimethyltetrahydroisoquinolines: synthesis, variable temperature NMR spectroscopy and molecular modelling

Mercury(II)-mediated ring closure of N-[1-(2-allyl-3-benzyloxy-4,6-dimethoxyphenyl)ethyl]acetamide 9 afforded N-acetyl-5-benzyloxy-6,8-dimethoxy-1,3-trans-dimethyl-1,2,3,4-tetrahydroisoquinoline 8. The product was shown to exist as a mixture of amide rotamers by NMR spectroscopy, since signals coalesced at higher temperatures. Variable temperature NMR spectroscopy and molecular modelling were used to investigate these rotamers and gave average values for the barrier of rotation in the range of 15-16 kcal mol⁻¹. 2-[2-[1-(Acetylamino)ethyl]-6-(benzyloxy)-3,5-dimethoxyphenyl]-1-methylethyl methanesulfonate 17 was also cyclized with sodium hydride to afford the same rotameric products with the same tetrahydroisoquinoline skeleton, but as a mixture of 1,3-trans- and cis-dimethyl isomers.     

Efficient synthesis of β-nitro amides by aminocarbonylation of ethoxycarbonyl-containing nitroalkenes with carbamoylsilane

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Nucleophilic aromatic substitution of hydrogen through lithiated phosphine borane complexes and N-phosphorylphosphazenes

Organophosphorus compounds containing nitroaryl and cyanoaryl groups have been prepared in good yield through nucleophilic aromatic substitution of hydrogen using α-lithiated phosphazenes and phosphine borane complexes as nucleophiles. In all cases, nearly exclusive replacement of the hydrogen in the para position with respect to the activating group has been observed.