Synthesis of polysubstituted pyrroles from sulfinimines (N-sulfinyl imines)

Polysubstituted 2-carboxylate and 2-phosphonate pyrroles are prepared by aromatization of the corresponding 3-oxo 2-carboxylate and 2-phosphonate NH-pyrrolidines using air. Reaction of electrophiles with 3-oxo pyrrolidine dianions readily introduces substituents, regioselectively at C-4 in these pyrrolidines.     

An organocatalytic synthesis of N-sulfonyl imines using chloramine-T in aqueous medium

N-Sulfonyl imines have been synthesized in good to excellent yields from aldehydes and chloramine-T using proline as an organocatalyst in aqueous medium at ambient temperature. The protocol is applicable to a wide range of aldehydes, especially enals exhibit remarkable efficiency in the reaction. The reaction presumably occurs via iminium activation and opens new avenues for the synthesis of N-sulfonyl imines under environmentally benign and mild conditions.     

Ruthenium-catalysed asymmetric transfer hydrogenation of N-(tert-butanesulfinyl)imines

The ruthenium complex prepared from [RuCl₂(p-cymene)]₂ and (1S,2R)-1-amino-2-indanol is a very efficient catalyst for the asymmetric transfer hydrogenation of (R)-N-(tert-butanesulfinyl)ketimines in isopropanol. By carefully removing all possible moisture from the reaction medium, chiral primary amines with very high optical purities (up to >99% ee) can be easily prepared in excellent yields by the diastereoselective reduction of the imines followed by removal of the sulfinyl group under mild acidic conditions. Reaction times of 1-4 h were needed to complete the reduction reactions when they were performed at 40 °C.     

Chiral N-phosphonyl imine chemistry: asymmetric 1,2-additions of allylmagnesium bromides

Chiral N-phosphonyl homoallylic amines were synthesized by the reaction of allylmagnesium bromide with chiral N-phosphonyl imines. The C₂-symmetric chiral N-phosphonyl group was optimized for this reaction. Excellent yields and good diastereoselectivities were obtained for eight examples.     

Enantioselective radical addition reactions to imines using binaphthol-derived chiral N-triflyl phosphoramides

Binaphthol-derived chiral phosphoric acid catalysts were applied to enantioselective radical addition reactions of imines and provided chiral amines with good enantioselectivities (73-84% ee). Furthermore, the enantioselectivities were not affected by either electronic properties of phenyl imines or radical precursors.     

Trifluoromethyl-containing N-acylmethylenequinone imines as novel highly electrophilic agents

The strategy of searching for highly electrophilic agents in a class of chemically inert compounds - methylenequinone imines - was developed and successfully performed. The first representative of such electrophiles - N-acyl-α-methoxycarbonyl-α-trifluoromethyl-p-methylenequinone imine 6 - was synthesized. Its reactions with N-, O- and C-nucleophiles were investigated that gave various derivatives of α-trifluoromethyl-α-amino(oxy) acids as well as ß,ß,ß-trifluoropropionic acids. 3-Chloro-3-trifluoro-1,3-dihydroindol-2-ones were first obtained and their reactions with nucleophiles were studied with 1-aza-3-trifluoroindene-2-ones being formed as intermediates.     

Carbon-carbon bond formations at the benzylic positions of N-benzylxanthone imines and N-benzyldi-1-naphthyl ketone imine

Two N-benzyl imines are designed to allow for carbon-carbon bond formations at the aminated benzylic positions. Direct benzylic arylation reactions of N-benzylxanthone imine with aryl chlorides proceed under palladium catalysis in the presence of cesium hydroxide, yielding the corresponding benzhydrylamine derivatives. Alkylation reactions of N-benzyldi-1-naphthyl ketone imine with alkyl halides in the presence of potassium tert-butoxide afford the corresponding 1-phenylalkylamines in high yields. Conjugate addition of N-benzyldi-1-naphthyl ketone imine is also described.     

Chiral N-phosphonyl imine chemistry: new reagents and their applications for asymmetric reactions

Novel chiral N-phosphonyl imines 2 have been designed and synthesized using chiral N-phosphoramide 1. These N-phosphonyl imines have been successfully utilized for asymmetric aza-Darzens reaction and asymmetric aza-Henry reaction. The C₂-symmetric chiral auxiliary tolerates oxidation, is not sensitive to racemization and can be recycled for large scale synthesis.     

Development of an N-sulfinyl prolinamide for the asymmetric aldol reaction

A new class of organocatalysts is reported that incorporates an N-sulfinyl amide in place of the carboxylic acid of proline to serve as a hydrogen bond donor, chiral directing group, and solubilizing element. The successful application of this type of catalyst to the asymmetric aldol reaction of acetone and aryl aldehydes, for which proline performs poorly, is also described.     

Efficient iodine catalyzed chemoselective synthesis of aminals—an access to N,N-acetals by the addition of lactams to N-acyl imines

A highly efficient protocol has been developed for the synthesis of aminals from γ-butyrolactam and benzaldehyde using iodine as Lewis acid catalyst. The attack of γ-butyrolactam nucleophile to intermediate N-acyliminium ion was more favorable, when aryl aldehyde bears the electron donating group (EDG). Iodine plays a key role in these reaction transformations. This current mild protocol is environmentally benign and cost-effective method for the synthesis of industrially and pharmaceutically useful scaffolds.     

A mild and efficient aza-Diels-Alder reaction of N-benzhydryl imines with trans-1-methoxy-2-methyl-3-trimethylsiloxybuta-1,3-diene catalyzed by Yb(OTf)3

The aza-Diels-Alder reaction of trans-1-methoxy-2-methyl-3-trimethylsiloxybuta-1,3-diene with N-benzhydryl imines in the presence of Yb(OTf)₃ in toluene at room temperature gave the corresponding 2,5-disubstituted 2,3-dihydro-4-pyridones in high yields. This reaction can also be carried out with diene, aldehydes, and amine in a three-component one-pot reaction manner in moderate to high yields under solvent-free conditions. The relationship between Lewis acids and activity, solvents and catalyst loading were studied. Some investigation towards the reaction mechanism was discussed.     

Regioselective addition of pyrrole to N-tosyl imines in the presence of Cu(OTf)2

The Cu(OTf)₂ catalysed reaction of pyrrole with N-tosyl imines gives pyrrole sulfonamides in high yields. The addition reaction takes place regioselectively at C(2) of the pyrrole. The procedure is simple and does not require anhydrous conditions.     

Synthesis of N,N-dialkylaminobenzonitriles and halo-(N,N-dialkyl)benzamidines by reaction of halobenzonitriles with lithium amides

3- and 4-N,N-Dialkylaminobenzonitriles and 4-chloro-(N,N-dialkyl)benzamidines were isolated by reacting 4-chlorobenzonitrile with hindered lithium amides under thermodynamic (0 °C) and kinetic control conditions (−78 °C), respectively. As previously reported, a benzyne mechanism seems to be confirmed since N,N-dialkylaminobenzonitriles are formed. Only benzamidines were isolated in fair to high yields at both 0 °C and −78 °C with non-hindered lithium amides. Exploitation and mechanistic rationale of the reaction of different halobenzonitriles are also reported.     

Simple pyridylmethylamines: efficient and robust N,N-ligands for Suzuki-Miyaura coupling reactions

A series of pyridylmethylamines have been synthesized in one step from commercially available starting material and identified as effective ligands for Pd-catalyzed carbon-carbon bond formation through Suzuki-Miyaura coupling reaction. The N,N-pyridylmethylamine-Pd catalytic systems appeared as an interesting and robust compromise between catalytic efficiency, substrate compatibility, and practical aspects.     

N,N′,N″-Tri-Boc-guanidine (TBG): a common starting material for both N-alkyl guanidines and amidinoureas

In this Letter, we describe the unexpected reaction pattern of N,N′N″-tri-Boc-guanidine (TBG) with amines at room temperature and under reflux conditions affording N-substituted guanidines and amidinoureas, potentially important compounds with extensive applications in medicinal chemistry. This investigation shows that TBG is an excellent, readily available common starting material for the synthesis of various N-alkyl guanidines as well as N-alkyl-N′-substituted amidinoureas by simply manipulating the reaction conditions.     

N,N′-Diisopropyl- and N,N′-dicyclohexylthiourea cadmium(II) complexes as precursors for the synthesis of CdS nanoparticles

Crystals of the cadmium(II) complexes of N,N-diisopropylthiourea and N,N-dicyclohexylthiourea were obtained and their X-ray single crystal structures determined. These complexes are air-stable, easy to prepare and inexpensive and decompose cleanly to give good quality crystalline CdS. The nanoparticles of CdS thus obtained showed quantum confinement effects in their optical spectra, with close to band-edge emission in luminescence experiments. The broad diffraction patterns observed are typical of nanodimensional particles. The variation of concentration of precursor-to-HDA ratio change the isolated materials from spheres to rod-shaped. TEM images showed agglomerates of needle-like plate of particles.     

Efficient preparation of (Z)-alkenyl derivatives from (Z)-vinyl (N,N-diisopropyl)carbamate via Ni-catalysed coupling reactions

A (Z)-vinyl (N,N-diisopropyl)carbamate treated with Grignard reagents, under Wenkert Nickel-catalysed conditions, gave access to several substituted (Z)-alkenyl derivatives. These Nickel-catalysed reactions, carried out with vinyl-, phenyl-, p-methoxyphenyl-, trimethylsilylmethylmagnesium bromide and benzylmagnesium chloride, led to the corresponding (Z)-alkenyl derivatives in good yields and high stereoselectivities.     

Phosphine-mediated annulation of N-protected imines with DEAD

In the presence of triphenylphosphine, the reactions of N-protected imines or their precursors with DEAD proceeded smoothly to give the corresponding functionalized 1H-1,2,4-triazole-1,4(5H)-dicarboxylate derivatives in good to high yields under mild conditions. A plausible mechanism has been proposed on the basis of the control experiments.     

Sulfonamide synthesis using N-hydroxybenzotriazole sulfonate: an alternative to pentafluorophenyl (PFP) and trichlorophenyl (TCP) esters of sulfonic acids

The N-hydroxybenzotriazole (HOBt) sulfonate esters undergo amidation under ambient conditions in the presence of di-isopropylethyl amine. This method can be applied to varieties of amines including sterically hindered amino acid esters in less time with reasonably good yields.HOBt ester of sulfonic acids can be a replacement for pentafluorophenyl and trichlorophenyl ester as well as chloride moiety of sulfonyl chloride for amidation.     

Structure of N,C,N-chelated organotin(IV) fluorides

The set of starting tri-, di- and monoorganotin(IV) halides containing N,C,N-chelating ligand (L^NCN = {1,3-[(CH₃)₂NCH₂]₂C₆H₃}⁻) has been prepared (1-5) and two compounds structurally characterized ([L^NCNPh₂Sn]⁺I₃⁻ (1c), L^NCNSnBr₃ (5)) in the solid state. These compounds were reacted with KF with 18-crown-6, NH₄F or L^CNnBu₂SnF to give derivatives containing fluorine atom(s). Triorganotin(IV) fluorides L^NCNMe₂SnF (2a) and L^NCNnBu₂SnF (3a) revealed monomeric structural arrangement with covalent Sn-F bond both in the coordinating and non-coordinating solvents, except the behaviour of 3a that was ionized in the methanol solution at low temperature. The products of fluorination of L^NCNSnPhCl₂ (4) and 5 were described by NMR in solution as the ionic hypervalent fluorostannates or the oligomeric species reacting with chloroform, methanol or moisture to zwitterionic monomeric stannate L^NCN(H)⁺SnF₄⁻ (5c), which was confirmed by XRD analysis in the solid state.