Highly efficient synthesis of aryl ketones by PEPPSI-palladium catalyzed acylative Suzuki coupling of amides with diarylborinic acids

An improved acylative cross-coupling of various N-methyl-N-tosyl amides with diarylborinic acids for synthesis of aryl ketones is developed. In most cases, aryl ketones could be obtained in excellent yields by using 1?mol% 2,6-diisopropylphenylimidazolylidene and 3-chloropyridine co-supported palladium chloride as catalyst in the presence of 3 equiv. K₂CO₃ as base in refluxing THF. The readily prepared and cost-effective substrates, N-methyl-N-tosylamides and diarylborinic acids, and the commercially available catalyst system promise a practical and efficient access to aryl ketones.     

New regiocontrolled syntheses of pyrrolopyrazinones and its application to the synthesis of peramine

Two novel regiocontrolled syntheses of pyrrolopyrazinones were developed. N-Methylpyrrole amide and 1-bromo-1-alkyne were annulated in the presence of a copper catalyst to give 3-substituted pyrrolopyrazinone in a regioselective manner. In contrast, heating N-methylpyrrole amide with the same haloalkyne in the presence of K₃PO₄ provided the haloaminal, which was transformed regioselectively into 4-substituted pyrrolopyrazinone. The former procedure was successfully applied to the synthesis of peramine, a natural product isolated from an endophytic fungus.     

The use of anhydrous CeCl3 as a catalyst for the synthesis of 3-sulfenyl indoles

Anhydrous CeCl₃ was successfully used as a catalyst for the synthesis of several 3-sulfenyl indoles in good to excellent yields through the reaction of indole with N-(alkylthio) and N-(arylthio)phthalimides in DMF.     

Asymmetric hydrogenation of N-alkyl and N-aryl ketimines using chiral cationic Ru(diamine) complexes as catalysts: the counteranion and solvent effects,and substrate scope

Asymmetric hydrogenation of N-alkyl and N-aryl ketimines catalyzed by chiral cationic η⁶-arene-(N-monosulfonylated diamine) Ru(II) complexes has been investigated. Strong counteranion and solvent effects on the enantioselectivity were observed. The ruthenium catalyst bearing non-coordinating BArF^? anion was found to be particularly effective for the hydrogenation of acyclic and exocyclic N-alkyl ketimines in the presence of (Boc)₂O in dichloromethane or even under solvent-free conditions, providing chiral amines with up to >99% ee and full conversions. Alternatively, the ruthenium catalyst bearing achiral phosphate anion together with corresponding phosphoric acid as the additive was also efficient for the hydrogenation of N-alkyl ketimines in the absence of (Boc)₂O with excellent enantioselectivities and full conversions. For N-aryl ketimines lower enantiomeric excesses were observed by using the ruthenium catalyst bearing BArF^? anion. This catalytic protocol thus provides a facile and practical access to optically active amines and has been successfully employed in the gram-scale synthesis of enantiomerically pure (+)-sertraline.     

Synthesis of N-aryl trifluoromethylarylketoimines by palladium-catalyzed Suzuki coupling reaction of N-aryltrifluoroacetimidoyl chlorides with aryl boronic acids

A highly efficient Suzuki reaction between N-aryltrifluoroacetimidoyl chlorides and aryl boronic acids using Pd(PPh₃)₄ as a catalyst has been developed. This route allows for selective synthesis of N-aryl trifluoromethylarylketoimines in high yields under mild reaction conditions.     

Synthesis of meso-tetraphenyl porphyrins via condensation of dipyrromethanes with N-tosyl imines

A new synthetic route for the synthesis of 5,10,15,20-tetraphenyl porphyrins has been developed based on the reaction of 5-substituted dipyrromethanes with N-tosyl imines in the presence of a metal triflate catalyst. meso-Substituted tetraphenyl porphyrins were synthesized in a two-step process. The first step of the method is the metal triflate-catalyzed condensation of 5-substituted dipyrromethanes with N-tosyl imines to form a porphyrinogen intermediate and the second step is the oxidation of the porphyrinogen to porphyrin. The method was applied to the synthesis of trans-A₂B₂-tetraarylporphyrins and the products were obtained with only a trace amount of one scrambling product. The synthesis of two important building blocks for porphyrin synthesis, mono and di-sulfonamide alkylated 5-substituted dipyrromethanes, was achieved by the addition of 5-substituted dipyrromethane to N-tosyl imine. The application of mono and di-sulfonamide alkylated 5-substituted dipyrromethanes in ‘2+2’ porphyrin formation reactions is presented.     

Lewis acid-catalyzed Friedel-Crafts/Michael cascade reaction of N,N-dialkyl-3-vinylanilines with N-tosylaziridines for the stereoselective synthesis of highly functionalized tetrahydroisoquinolines

A Lewis acid-catalyzed Friedel-Crafts/Michael cascade reaction between N-dialkyl-3-vinylanilines and N-tosylaziridines has been developed for the stereoselective synthesis of tetrahydroisoquinolines (THIQs). The reaction using Gd(OTf)₃ as the Lewis acid catalyst was tolerant to the various N-dialkyl-3-vinylaniline and N-tosylaziridine substrates and provided access to 28 new, highly functionalized THIQs in typically high yields with moderate- to- excellent diastereoselectivities.     

Nanocrystalline TiO2-HClO4:A novel,efficient and recyclable catalyst for the chemoselective N-Boc protection of amines under solvent-free conditions

Nanocrystalline TiO₂-HClO₄,as newly reported catalyst,has been used as an efficient and reusable catalyst for the chemoselective N-Boc protection of amines.The clean,mild acidity condition, quantitative yields of products,short reaction time and low reaction temperature are attractive features of this reaction.In practice,this method is a combination of a satisfactory synthesis and more significantly easy product isolation and purification.     

An improved Ullmann-Ukita-Buchwald-Li conditions for CuI-catalyzed coupling reaction of 2-pyridones with aryl halides

An effective CuI-trans-N,N′-dimethylcyclohexane-1,2-diamine (DMCDA)-K₂CO₃-catalyzed coupling reaction of 2-pyridones with aryl halides is described. Under our conditions, DMCDA was found to be an effective catalyst that facilitates the coupling reactions even in toluene, a common industrial solvent. In addition, 3-bromopyridine could also be coupled effectively under these conditions, indicating that the catalytic reactivity of this system is high. The reaction could be applied for polymer modification and iterative oligo-pyridone synthesis.     

UFU (‘Ullmann-Finkelstein-Ullmann’): a new multicomponent reaction

We developed conditions to carry out the first ‘one-pot’ Ullmann-Finkelstein-Ullmann multicomponent reaction reported. This reaction allows the one-pot synthesis of dissymmetrical para-disubstituted benzene scaffold from 1-bromo-4-iodobenzene and two N-nucleophiles. CuI/N,N′-dimethyl-cyclohexane-1,2-diamine was used as a catalyst/ligand couple, K₃PO₄ as a base and the reaction was performed in dioxane.     

Indole 3-alkylation/vinylation under catalysis of the guanidinium ionic liquids

Two ionic liquids, N,N,N,N-tetramethylguanidinium trifluoroacetate (TMGT) and the unprecedented N,N,N,N-tetramethylguanidinium triflate (TMGT_f), were used as catalyst solvents in condensations between indoles and arylaldehydes or 1,3-diketones providing a simple and efficient method for synthesis of bis(3-indolyl)methanes or casually 3-alkenylindoles due to stereoelectronic concerns of reactants. The ionic liquids are easily separated and reused for several times.     

Palladium-catalyzed selective N-(hetero)arylation or N,N′-di(hetero)arylation of 1-aminoindoles

The selective synthesis of N-(hetero)aryl-1-aminoindoles 3 from the corresponding N-aminoindoles and (hetero)aryl halides using a catalyst combination of Pd₂(dba)₃ associated to Josiphos is described. By switching to Xantphos as the ligand, the alternate catalytic system allows the coupling to proceed efficiently for the preparation of symmetrical and unsymmetrical N,N′-diaryl-1-aminoindole derivatives in good yields.     

An efficient catalytic method for the synthesis of 2,7-dialkyl-2,3a,5a,7,8a,10a-hexaazaperhydropyrenes

An efficient method for the synthesis of 2,7-dialkyl-2,3a,5a,7,8a,10a-hexaazaperhydropyrenes in high yields (up to 95%) via the intermolecular cyclization of 1,4,5,8-tetraazadecalin with N,N-bis(methoxymethyl)-N-alkylamines in the presence of SmCl₃·6H₂O as the catalyst has been developed.     

Lewis acid-catalyzed [3+3] cycloadditions of donor‒acceptor aziridines with N,N-dialkyl-3-vinylanilines via carbon-carbon bond cleavage

A Lewis acid-catalyzed [3 + 3] cycloaddition reaction of donor?acceptor aziridines with N,N-dialkyl-3-vinylanilines has been developed for the stereoselective synthesis of tetrahydroisoquinolines (THIQs). The reaction performed using Gd(OTf)₃ as the Lewis acid catalyst was tolerant to various N-tosylaziridine and N,N-dialkyl-3-vinylaniline substrates and provided access to highly functionalized THIQs in typically high yields with moderate-to-excellent diastereoselectivities.     

Dirhodium catalyzed intramolecular enantioselective C–H insertion reaction of N-cumyl-N-(2-p-anisylethyl)diazoacetamide: synthesis of (−)-Rolipram

Cumyl(2,2-dimethyl-benzyl) was used as an N-protecting group for intramolecular C–H insertion reaction of α-diazoacetamide. Excellent chemoselectivity (>98:2) in C–H insertion over the aromatic addition of N-cumyl-N-(2-p-anisylethyl)diazoacetamide was obtained with Rh₂[(4S)-MEOX)]₄ catalyst in moderate enantioselectivity (53% ee). The reaction was successfully applied in the synthesis of (−)-Rolipram in 15% total yield.     

Pd2dba3/P(i-BuNCH2CH2)3N: a highly efficient catalyst for the one-pot synthesis of trans-4-N,N-diarylaminostilbenes and N,N-diarylaminostyrenes

A Pd₂dba₃/P(i-BuNCH₂CH₂)₃N catalyzed one-pot synthesis of unsymmetrically substituted trans-4-N,N-diarylaminostilbenes and both symmetrically and unsymmetrically substituted N,N-diarylaminostyrene derivatives is reported. The procedure involves two or more palladium catalyzed sequential coupling reactions (an amination and an inter-molecular Heck reaction) in one-pot using the same catalyst system with two different aryl halides, including aryl chlorides and hetero aryl halides as the coupling partners.     

Intramolecular asymmetric C–H insertion of N-arylalkyl,N-bis(trimethylsilyl)methyldiazoamides mediated by chiral rhodium(II) catalysts. Synthesis of (R)-β-benzyl-γ-aminobutyric acid

The enantio- and site-selectivity of the intramolecular C–H insertion reactions of acyclic N-arylalkyl, N-bis(trimethylsilyl)methyl α-diazoacetamides, and α-carboalkoxy-α-diazoacetamides 1a–g, catalyzed by chiral Rh(II) carboxamidates and Rh(II) carboxylates were studied. In general, the reaction showed good to excellent chemoselectivity. Regioselectivity for most of the reactions was high, but was also found to be influenced by the structure of the diazo substrate and the chiral Rh(II) catalyst employed. The highest enantioselectivity for the reactions catalyzed by chiral Rh(II) carboxamidates was 69% and Rh₂(4R-MEOX)₄ was found to be the most effective. For the chiral Rh(II) carboxylate catalyzed reactions, the highest ee obtained was 75% and Rh₂(S-PTTL)₄ is the optimal catalyst. The method was applied toward the synthesis of a GABA analogue, (R)-β-benzyl-γ-aminobutyric acid.     

Co(acac)3/BMMImCl as a base-free catalyst system for clean syntheses of N,N′-disubstituted ureas from amines and CO2

A base-free catalyst system Co(acac)₃/BMMImCl was developed for the carbonylation of amines with CO₂. 45%\2-81% isolated yields for N,N-dialkylureas and 6%\2-23% isolated yields for N,N-diarylureas were obtained. The catalyst system was recovered and reused without significant loss in activity. In this catalyst system, the base catalyst and chemical dehydrant were efficiently avoided. Different reaction conditions were also discussed and a postulated mechanism was proposed.     

A Keggin heteropoly acid as an efficient catalyst for an expeditious, one-pot synthesis of 1-methyl-2-(hetero)arylbenzimidazoles

The Keggin heteropoly acid, silicotungstic acid, H₄SiW₁₂O₄₀, has been demonstrated to be highly efficient for an expeditious, one-pot synthesis of 1-methyl-2-(hetero)arylbenzimidazoles from N-methyl-1,2-phenylenediamine and (hetero)aryl aldehydes in ethyl acetate at room temperature. The catalyst works equally well for N-phenyl-1,2-phenylenediamine.     

Recyclable polyisobutylene-supported pyridyl N-oxide allylation catalysts

Polyisobutylene (PIB) is a useful soluble polymer support that facilitates catalyst recovery and recycling in liquid-liquid biphasic systems because the long polyisobutylene chain confers high phase selective solubility in the nonpolar phase of polar-nonpolar liquid-liquid biphasic systems on groups attached to the polymer’s terminus. This work shows that PIB-supports that are effective with metal catalysts can also facilitate synthesis and use of organocatalysts. This is demonstrated by the use of a PIB-supported pyridyl N-oxide to promote the allylation of several aromatic aldehydes with allyltrichlorosilane. These studies show that a PIB-supported pyridyl N-oxide is a very active recyclable catalyst that promotes the allylation of aromatic aldehydes in yields of up to 99% yield. These PIB-supported pyridyl N-oxide catalysts were recovered in the hexane phase of a hexane/90% EtOH-H₂O solvent system and were successfully recycled through 5 cycles with little effect on catalyst efficiency.