Catalytic photocarboxylation of 1,1-diphenylethylene with N,N,N′,N′-tetramethylbenzidine and carbon dioxide

Photocarboxylation of 1,1-diphenylethylene with N,N,N′,N′-tetramethylbenzidine (TMB) in MeCN under bubbling of CO₂ proceeded with high catalytic efficiency, giving 3,3-diphenylacrylic acid (DPA) and 3-hydroxy-3,3-diphenylpropionic acid (20). The turnover number (TON=(DPA+20)/TMB) reached 17. Similarly, 1-phenyl-1-cyclohexene yielded cis-2-acetamido-2-phenylcyclohexanecarboxylic acid with TON 5.9. As compared with related N,N-dimethylaniline derivatives, TMB is more resistant to photodecomposition, has the much larger absorbance in the S₀→S₁ transition, and has the lower quenching efficiency by CO₂. Probably these factors are partly responsible for the high TON observed for TMB.     

Acyclic tertiary diamines and 1,4,7,10-tetraazacyclododecane with fluorine-containing β-diketones: Leading to low melting ionic adducts

N,N,N′,N′-Tetramethylmethanediamine (1a), N,N,N′,N′-tetramethylethanediamine (1b), N,N,N′,N′-tetramethyl-1,3-propanediamine (1c), and N,N,N′,N′-tetramethyl-1,6-hexanediamine (1d) were reacted at 25 °C with 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2a), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (2b), 2-thenoyltrifluoroacetone (2c), and 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (2d) to form the ionic adducts 3-18. 1,4,7,10-Tetraazacyclododecane (1e) reacted at 25 °C with β-diketones (2a-d) and 1,1,1-trifluoro-2,4-pentanedione (2e) to give ionic solids 19-23 in good yields. Some of the products are liquid at 25 °C and are thermally stable over long liquid ranges as determined by thermal gravimetric analyses. Single-crystal X-ray structure determinations show that compounds 9 and 21 crystallize in the monoclinic space groups P2(1)/c and P2(1)/n, respectively. All the new compounds were characterized by ¹H, ¹⁹F and ¹³C NMR, electrospray MS and/or elemental analyses.     

Dibutylphosphate (DBP) mediated synthesis of cyclic N,N′-disubstituted urea derivatives from amino esters: a comparative study

The N,N′-disubstituted urea derivatives such as amino acid hydantoins and dihydrouracil derivatives were prepared starting from natural and unnatural amino acid esters using dibutylphosphate (DBP). During the attempted synthesis of N-heterocycles with larger than six-membered rings containing the N,N′-disubstituted urea functionalities, three unexpected products namely squamolone, N-methyl pyrrolidine-2-one, and diketopiperazine were isolated.     

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.     

Influence of N,N,N′,N′-tetraalkyl terephthalamide on isothermal crystallization kinetics and morphology evolution of polypropylene

The influence of N,N,N′,N′-tetraalkyl terephthalamide (TATA) on the isothermal crystallization kinetics of polypropylene (PP) was studied using differential scanning calorimetry (DSC). It was found that TATA shows a heterogeneous nucleation effect and leads to the formation of β-PP. TATA can not only shorten the crystallization time but also heighten the crystallization temperature of PP. The crystallization rate constant of PP containing TATA is larger than that of pure PP. The evolution of crystalline morphology of PP was investigated on a polarized optical microscopy (POM) equipped with a hot stage and the results showed that the introduction of TATA into PP can quicken the crystallization of PP, which is consistent with DSC results. TATA also leads to a substantial decrease in the spherulite size of PP and the boundaries of spherulites are hardly distinguished.     

Synthesis and characterization of a tetraruthenium butterfly cluster containing a quadruply-bridging ligand derived from an N,N′-dipyrid-2-ylurea

The tetraruthenium cluster complex [Ru₄(μ₄-κ⁴-dmpu)(CO)₁₀], H₂dmpu = N,N′-bis(6-methylpyrid-2-yl)urea, has been prepared by treating [Ru₃(CO)₁₂] with H₂dmpu in toluene at reflux temperature. An X-ray diffraction study has determined that this cluster has a butterfly metallic skeleton hold up by a doubly-deprotonated N,N′-bis(6-methylpyrid-2-yl)urea ligand (dmpu). This ligand has the pyridine N atoms attached to the wing-tip Ru atoms and the amido N atoms spanning Ru-Ru wing-edges, in such a way that the cluster has C₂ symmetry. The donor atoms of doubly-deprotonated N,N′-dipyrid-2-ylureas seem to be appropriately arranged to hold butterfly tetranuclear clusters.     

A convenient, large-scale synthesis of 4′-carboxamido N-Boc-2′,6′-dimethyl-l-phenylalanines

A large-scale synthesis of a series of 4′-carboxamido N-Boc-2′,6′-dimethyl-l-phenylalanines is described. This method features mild reaction conditions and high chemical yields from commercially available N-Boc-2′,6′-dimethyl-l-tyrosine methyl ester.     

N,N,N,N-Tetramethyl-1,3-propanediamine as the catalyst of choice for the Baylis-Hillman reaction of cycloalkenone: rate acceleration by stabilizing the zwitterionic intermediate via the ion-dipole interaction

N,N,N^′,N^′-Tetramethyl-1,3-propanediamine (TMPDA) can be used as an efficient catalyst for the Baylis-Hillman reaction of cycloalkenones. The increased reaction rate was thought be derived from the stabilizing effect of the zwitterionic intermediate via the ion-dipole interaction.     

A concise synthesis of asymmetrical N,N′-disubstituted guanidines

We present a new and concise method for the preparation of asymmetrical N,N′-disubstituted guanidines starting from thiourea via the reaction of N-Boc-protected N′-alkyl/aryl substituted thioureas with an amine in the presence of mercury(II) chloride and triethylamine.     

DFT study of the reaction sites of N,N′-substituted p-phenylenediamine antioxidants

The geometry of N,N′-diphenyl-p-phenylenediamine (DPPD), N-phenyl-N′-(1′-methylbenzyl)-p-phenylenediamine (SPPD), N-phenyl-N′-(1,3-dimethyl-butyl)-p-phenylenediamine (6PPD), N-phenyl-N′-isopropyl-p-phenylenediamine (IPPD), and N-(1-methyl-1-phenylethyl)-N′-phenyl-p-phenylenediamine (CPPD) as well as of their dehydrogenation products has been optimized at B3LYP/6-31G^∗ level of theory. Our results support the idea of formation of stable ketimine Ph-NC structures (instead of quinonediimine structures) during consecutive dehydrogenation of SPPD, 6PPD, and IPPD antioxidants despite the formation of tertiary carbon-centered radicals in the first dehydrogenation step is energetically preferred for SPPD only.     

N,N′-Dioxide-scandium(III) complex catalyzed highly enantioselective Friedel-Crafts alkylation of indole to alkylidene malonates

A highly efficient enantioselective Friedel-Crafts alkylation of indoles with alkylidene malonates has been developed using chiral N,N′-dioxide L4-scandium(III) complex as the catalyst, giving the corresponding products in high yields with excellent enantioselectivities (up to 99% yield and 95% ee). The product 3a was facilely converted into several interesting compounds, such as tryptamines, indolepropionic acids and β-carbolines. It is noteworthy that the seven-membered β-carboline-like compound has been synthesized for the first time. Based on the crystal structure of the chiral N,N′-dioxide L10-scandium(III) complex, the proposed transition state and possible catalytic cycle were presented to elucidate the reaction mechanism.     

Copper(I) catalysis: Synthesis of N,N′-diarylated and N-aryl,N′-formylated chiral C2-symmetric diamines

Chiral N,N′-diaryl C₂-symmetric diamines and N-aryl,N′-formyl-trans-(1R,2R)-diaminocyclohexane are readily accessed by copper catalyzed N,N′-diarylation and N-aryl,N′-formylation of trans-(1R,2R)-diaminocyclohexane with aryl bromides. N,N′-diarylation using (R)-1,1′-binaphthyl-2,2′-diamine and iodobenzene gave the corresponding (R)-N,N′-diphenyl-1,1′-binaphthyl-2,2′-diamine derivative in 83% yield.     

Efficient synthesis of 5′-O(N)-carbamyl and -polycarbamyl nucleosides

A simple and efficient method for the preparation of 5′-O(N)-carbamyl and 5′-O(N)-polycarbamyl nucleoside derivatives is reported. The method consisted of treatment of 2′,3′-O-protected purine (Ado, Ino) or pyrimidine nucleosides (Thd, Urd) with trichloroacetylisocyanate, followed by cleavage of the trichloroacetyl moiety by silica-gel promoted methanolysis during column chromatography. Iterative application of this method gave mono, di, and tricarbamyl derivatives in good to excellent yields (ave = 80%).     

Synthesis of fluorinated imines and carbodiimides from azides via aza-Wittig reaction

The Staudinger reaction of fluoroalkylazides were studied. A series of N-fluoroalkylimines were synthesized via aza-Wittig reaction of N-fluoroalkyliminophosphoranes. The N,N′-difluoroalkylated carbodiimide was also synthesized via the reaction of N-fluoroalkyliminophosphoranes with carbon dioxide or carbon disulfide.     

Synthesis,spectral characterization of the zinc(II) mixed-ligand complexes of N(4)-allyl thiosemicarbazones and N,N,N′,N′-tetramethylethylenediamine,and crystal structure of the novel [ZnL2(tmen)] compound

Mixed-ligand zinc complexes with N,N,N′,N′-tetramethylethylenediamine (tmen) and R-salicylaldehyde N(4)-allyl thiosemicarbazones (R: 3-OCH₃ (L₁), 5-Br(L₂)), [ZnL_1,2(tmen)], were synthesized and the complexes were characterized by elemental analysis, atomic absorption spectrometer, magnetic susceptibility, molar conductivity, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectra and IR, UV–Vis, ¹H NMR and ¹⁵N spectroscopies. Crystal of [ZnL₂(tmen)] have a slightly distorted square pyramid involving O, N, S atoms of thiosemicarbazone and one N atom of tmen in basal plane and the other N atom of tmen in apex of the pyramid. The non-coordinated allyl group is disordered.     

Helicity of N,N′-diaryl-trans-1,2-diaminocyclohexane derivatives. Implications for molecular helicity manipulations

Derivatives of trans-1,2-diaminocyclohexane (DACH), useful as chiral ligands, scaffolds and building blocks, differ in their conformation. The conformation of N,N′-diaryl-DACH derivatives was studied by the semiempirical and DFT computational methods and by exciton-coupled circular dichroism. It was found that, contrary to M-helical N,N′-diimine, N,N′-diimide and N,N′-diamide derivatives, the aromatic residues in N,N′-diphenyl derivatives are oriented to form a P-helix for the (R,R)-DACH absolute configuration. The helicity of the bis-aryl system is modified in the case of 1-naphthyl or 2-naphthyl derivatives. Further switching of helicity has been demonstrated by either protonation or mono-N-acetylation of N,N′-diaryl DACH derivatives.     

Chiral N,N′-dioxide-Yb(III) complexes catalyzed enantioselective hydrophosphonylation of aldehydes

Chiral N,N′-dioxide-Ytterbium(III) complexes promoted the asymmetric addition of diethyl phosphate to aldehydes, giving the corresponding products with good yields and enantioselectivities. The addition of pyridine favored both reactivity and enantioselectivity. A possible catalytic cycle was proposed to explain the mechanism of the asymmetric hydrophosphonylation of aldehydes.     

Chemical and electrochemical procedures for the synthesis of diisopropyltetrahydroquinoxalinedione derivatives

Diisopropyltetrahydroquinoxalinedione derivatives are synthesized from the reaction of various catechols with N,N′-diisopropylethylenediamine. Both chemical and electrochemical methods give the same products. While the chemical synthesis is faster, the electrochemical synthesis provides higher yields.     

Further studies of tetrakis(N,N′-dialkylbenzamidinato)diruthenium(III) chloro and alkynyl compounds: molecular engineering of metallayne monomers

Three diruthenium(III) compounds Ru₂(L)₄Cl₂, where L is mMeODMBA (N,N′-dimethyl-3-methoxybenzamidinate, 1a), DiMeODMBA (N,N′-dimethyl-3,5-dimethoxy benzamidinate, 1b), or DEBA (N,N′-diethylbenzamidinate, 1c), were prepared from the reactions between Ru₂(OAc)₄Cl and respective HL under reflux conditions. Metathesis reactions between 1 and LiC₂Y resulted in bis-alkynyl derivatives Ru₂(L)₄(C₂Y)₂ [Y=Ph (2), SiMe₃ (3), SiⁱPr₃ (4) and C₂SiMe₃ (5)]. The parent compounds 1 are paramagnetic (S=1), while bis-alkynyl derivatives 2-5 are diamagnetic and display well-solved ¹H- and ¹³C-NMR spectra. Molecular structures of compounds 1b, 1c, 2c, 3c and 4b were established through single crystal X-ray diffraction studies, which revealed RuRu bond lengths of ca. 2.32 Å for parent compounds 1 and 2.45 Å for bis-alkynyl derivatives. Cyclic voltammograms of all compounds feature three one-electron couples: an oxidation and two reductions, while the reversibility of observed couples depends on the nature of axial ligands.     

On the dehydrogenation of N,N′-substituted p-phenylenediamine antioxidants. I. N-Phenyl-N′-isopropyl-p-phenylenediamine (IPPD)

Using B3LYP/6-31G^∗ treatment, the optimal geometries, electronic structures and IR spectra of N-phenyl-N′-isopropyl-p-phenylenediamine antioxidant (IPPD) and its doubly dehydrogenated oxidation products have been obtained. Experimental IR spectra of IPPD sample heated in air at 140 °C correspond to the doubly dehydrogenated IPPD structure with the Phenyl-NC double bond and not to its N,N′-dehydrogenated quinonediimine-type counterpart as supposed in the literature. This finding supports the idea of preferential dehydrogenation at N-bonded tertiary carbon atom in comparison with the amine nitrogen bonded to two phenyl rings.