On the melting temperatures of 3,6-diamino-9H-carbazole and 3,6-dinitro-9H-carbazole

This article records the diversely reported melting temperatures of 3,6-diamino-9H-carbazole (DAC) and 3,6-dinitro-9H-carbazole (DNC), and reports a reinvestigation on their melting phenomena, and associated specific observations. A rationalization of these reports has been attempted on the basis of IR spectroscopic, X-ray diffraction, thermal response, solubility behavior, and differential scanning calorimetric data on DAC and DNC. The data indicate that an exothermic inter-molecular deaminative self-condensation involving N₉H and NH₂ sets in prior to melting of DAC, which obscures the actual melting process. An extrapolated onset melting temperature of 241.0 °C and a peak temperature of 296.5 °C at zero heating rate have been assigned for DAC from DSC measurements. A possible structure of the polymeric self-condensation product is also presented. For DNC, a peak melting temperature of 296.5 ± 1.8 °C, but no onset melting temperature could be assigned.     

Synthesis of 9-amino-, 9-aminomethyl-1,2,3,4-tetrahydro- and 1,2,3,4,5,6,7,8-octahydroacridine derivatives

This paper describes the synthesis of 9-amino-2- and 4-hydroxy- and 2,4-dihydroxy-1,2,3,4-tetrahydro-acridines 2 and of 9-aminomethyl-1,2,3,4-tetrahydro- and 1,2,3,4,5,6,7,8-octahydroacridines 3 starting from the corresponding 9-carboxamido derivatives. A new synthetical pathway to 9-amino-2-hydroxyacri-dine 9 is also reported.     

Synthesis and analysis of 1,2,3,4-tetrahydro-(9H)-pyrido[3,4-b]indole

The synthesis of 1,2,3,4-tetrahydro-(9H)-pyrido[3,4-b]indole derivatives was carried out in one pot, by condensation of tryptamin with cycloalkanones in the presence of a polyphosphate ester as the catalyst in moderate to low yields, the aldol condensation being the main products. Reaction of tryptamine and cyclic ketones was also carried out in two stage through the imine intermediate with protic catalysis giving the tetrahydro-β-carbolines 8–14 , in good yields. 2-Methyl derivatives 15–21 , of the tetrahydro-β-carbolines, were obtained in good yields, using methyl iodide in dimethyl sulphoxide-potassium carbonate.     

Stereoselective synthesis of isoindolinones and tert-butyl sulfoxides

A reaction of Grignard reagents with an optically pure N-sulfinylimine derived from methyl 2-formylbenzoate yields enantioenriched isoindolinones and tert-butyl sulfoxides. The products are formed by the addition of the nucleophile to N-sulfinylimine followed by cyclization to form N-tert-butylsulfinylisoindolinone, which readily undergoes substitution with a second equivalent of Grignard reagent. The reaction can be carried out in dichloromethane at room temperature or at elevated temperatures without any loss of stereoselectivity. The use of nucleophiles other than Grignard reagents has also been investigated.     

Stereoselective cycloaddition of 1-glucosyl-1,3-butadienes with tert-butyl 2H-azirine-3-carboxylate, glyoxylates and imines

Glucosyl dienes 1 have been reacted with the achiral 2H-azirine 4 and with glyoxylates, forming fused structures of type 5 and disaccharide-like compounds 7 with good to excellent selectivity. Glucosyl dienes 1 participated as dienophiles in reactions with Schiff bases derived from anilines forming isoquinolines 10 and 11. The diastereoselectivity of this reaction is poor.     

Tetrabutylammonium iodide catalyzed hydroxylation of naphthoquinone derivatives with tert-butyl hydroperoxide as an oxidant

We have developed an effective and environmentally benign procedure for the hydroxylation of naphthoquinone derivatives by using tetrabutylammonium iodide as a catalyst and tert-butyl hydroperoxide as an oxidant. This methodology provides a facile protocol for the synthesis of some new naphthoquinone-based hydroxylates in satisfactory yields and broad substrate scope. Based on this new protocol, the synthesis of the drug, parvaquone and lapachol, was achieved. Furthermore, based on the observations of control experiments and the results previously reported, we proposed a plausible mechanism for the hydroxylation of naphthoquinone derivatives.     

Gold-catalyzed cyclization of 1-alkynyl cyclopropyl tert-butyl carbonate to construct multifunctionalized vinyl cyclopropane derivatives

A convenient new method was developed to prepare two types of vinyl cyclopropane derivatives through gold-catalyzed cyclization of 1-alkynyl cyclopropyl tert-butyl carbonates 2. Different from the previous reported 5-exo-dig route, the 6-endo-dig addition is the preferred pathway to provide six-membered cyclized carbonates. Two factors, including stereoelectronic effect and steric effect might affect the regioselectivity. Therefore, low steric aliphatic substrates afforded only six-membered isomers. The synthetic utility of compound 3 was also explored to afford a series of β-carbonyl cyclopropanol derivatives.     

Formation of diindolylmethane derivatives from indole derivatives and schiff bases

Indoles react with aromatic aldehydes to form diindolylmethane derivatives.     

Benzyl and tert-butyl carbamate derivatives of 1,ω-amino acids as simple yet efficient gelators

We report the synthesis and a study of the gelation properties of a series of N-protected long-chain amino acids. Especially, benzyl and tert-butyl carbamate derivatives of 11-aminoundecanoic acid in their deprotonated form can gelate polar organic solvents and water at very low concentration (less than 5 mM). This is explained by the contribution of multiple forces—H-bond, van der Waals and ionic interactions—in the gel aggregate formation and stabilization, which is confirmed by the experimental data. Among the series of compounds investigated, only a dimer of 11-aminoundecanoic acid is capable of gelating toluene, which stems from the increased number of hydrogen bonding sites in the main aliphatic chain.     

TBHP/TBAI-mediated oxidation of thiophenols for the synthesis of tert-butyl arylsulfinates

A novel and efficient TBHP/TBAI-mediated oxidation of thiophenols is described. The reactions proceeded smoothly to give tert-butyl arylsulfinates in up to 82% yield with good functional group compatibility under mild conditions.     

Impact of amines as co-modifiers on the enantioseparation of various amino acid derivatives on a tert-butyl carbamoylated quinine-based chiral stationary phase

A tert-butyl carbamoylated quinine-based chiral stationary phase (CSP) for direct enantiomer separation of various natural and unnatural amino acid derivatives was studied. The influence of functional groups in the amino acid side chains upon the enantioseparation is discussed with the aim of realizing contributions to their overall chiral recognition. The effects of various amines as co-modifiers upon retention and overall enantioselectivity of amino acid derivatives in polar organic solvents was systematically investigated. In general, retention times decreased with increasing amine concentrations without a distinct alteration of enantioselectivity. All analytes were rapidly resolved on the CSP with the methanol-based mobile phase containing 87 mM acetic acid and 7 mM triethylamine.     

Controlled synthesis and fluorescent properties of poly(9-(4-vinylbenzyl)-9H-carbazole) via nitroxide-mediated living free-radical polymerization

The functional polymer containing carbazole unit, [(poly(9-(4-vinylbenzyl)-9H-carbazole) (PVBK)], was successfully prepared via nitroxide-mediated living free-radical polymerization of 9-(4-vinylbenzyl)-9H-carbazole (VBK). The controlled features of the polymerization were confirmed by the linear increase in the molecular weight with the monomer conversion while keeping the relative narrow molecular weight distribution (M_w/M_n ? 1.51), and successful chain extension with styrene. The resulting polymer absorbed light in the 305-355 nm range and exhibited fluorescent emission at 350 nm. The fluorescent intensity of the polymer was lower than that of monomer and was affected by the properties of the different solvents, which decreased in the following order: DMF > THF > CHCl₃ at the same concentration of carbazole units. The fluorescence intensity of the polymer was apparently influenced by chromophore concentration, and the maximum value was obtained when the carbazole unit concentration was around 8 × 10⁻⁵ mol/L. Moreover, it was shown that the strong fluorescence of PVBK can be quenched by methyl acrylate (MA).     

A facile synthesis of novel 9-substituted 2,3,4,9-tetrahydro-1H-xanthen-1-ones

A strategically new approach to 9-substituted 2,3,4,9-tetrahydro-1H-xanthen-1-ones is described. The protocol includes TMG promoted, conjugate addition of cyclohexane-1,3-diones to 3-(diethoxyphosphoryl)coumarins and a domino transesterification-cyclodehydration reaction of the adducts obtained. Modification of the tetrahydroxanthenone at position 9 is reported for the first time.     

Regioselective synthesis of 3,4,6,7-tetrahydro-3,3-dimethyl-9-phenyl-2H-xanthene-1,8(5H,9H)-diones through ascorbic acid catalyzed three-component domino reaction

An efficient, three-component domino reaction of dimedone 1, aromatic aldehydes (2a–o), and 1,3-cyclohexanedione 1a in the regio-selective synthesis of 3,3-dimethyl-9-phenyl-2H-xanthene-1,8(5H,9H)-diones (3a–o) is reported. The desired product, 3 is efficiently promoted by ascorbic acid as an organo catalyst.     

Synthesis and characterization of well-defined poly(tert-butyl acrylate) star polymers

Star polymers with different numbers and lengths of poly(tert-butyl acrylate) (PTBA) arms were obtained via atom transfer radical polymerization. Aliphatic alcohols with different number of hydroxyl groups varying from 3 to 6 and calix[4]arenes based on pyrogallol with 12 and 16 phenol groups were transformed to bromoester derivatives to prepare multifunctional ATRP initiators used as the cores of the stars. The star polymers were characterized by GPC with refractive index, multiangle laser light scattering and viscosimetric detectors. The molar masses of the stars reached 70,000 g/mol and the molar mass dispersities did not exceed 1.2. To elucidate the compact structure of the stars, their true molar masses were determined by GPC with triple detection (RI-MALLS-Visco) and compared with the apparent molar masses obtained from the calibration with linear poly(tert-butyl acrylate) standards. The intrinsic viscosities of the PTBA stars of the same molar mass decreased with the number of star arms but were always lower than the intrinsic viscosities of the analogue linear PTBA polymers. The values of the branching ratio g′ decreased with increasing number of arms indicating more compact structure of stars. The branching ratio g′ was correlated to the empirical predictions.     

A novel practical cleavage of tert-butyl esters and carbonates using fluorinated alcohols

Thermolytic cleavage of t-butyl esters and t-butyl carbonates was accomplished using TFE (2,2,2-trifluoroethanol) or HFIP (hexafluoroisopropanol) as solvent. Thus, a practical method to cleanly convert t-butyl esters and carbonates into the corresponding carboxylic acids, decarboxylated products, or alcohols in nearly quantitative yields was developed. The product is recovered by a simple solvent evaporation. The practicality of this methodology was demonstrated on alkyl, aryl, and heteroaromatic esters.     

Homo and block copolymers of tert-butyl methacrylate by atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) of tert-butyl methacrylate (tBMA) was investigated using cuprous bromide with different ligands, solvents, deactivators, etc. The polymerization in bulk and diphenyl ether solvent system performed using Cu(I)Br complexed with N, N, N′, N″, N″-pentamethyldiethylenetriamine (PMDETA) catalyst in conjunction with 2-bromopropionitrile as an initiator at room temperature showed a curvature in the first-order kinetic plot. The controlled polymerization in methanol solution resulted in slower rate of polymerization and lower molecular weights. Well-defined diblock copolymers of PSt-b-PtBMA synthesized by polystyrene bromo macroinitiator (PSt-Br) with Cu(I)Cl/PMDETA catalyst system yielded predetermined molecular weights and lower polydispersities. Otherwise, the Cu(I)Br/PMDETA catalytic system showed an inefficient polymerization of tert-butyl methacrylate with lower molecular weights and higher polydispersities. Subsequent hydrolysis of the homopolymer refluxed in dioxane with addition of HCl afforded well-defined poly(methacrylic acid).     

Alkaloids-catalyzed regio- and enantioselective allylic nucleophilic substitution of tert-butyl carbonate of the Morita-Baylis-Hillman products

The alkaloids-catalyzed regio- and enantioselective allylic nucleophilic substitution reactions of tert-butyl carbonate of the Morita-Baylis-Hillman products with pronucleophiles are reported. A number of pronucleophiles, such as nitrogen, oxygen, and active carbon pronucleophiles have been used in this facile reaction. In general, the reaction proceeded efficiently to give the substitution product in good yields with high regioselectivity and medium enantioselectivity.     

Solid-phase synthesis of 2,3,4,5-tetrahydro-1H-benzo[e][1,4]diazepine derivatives

We have developed an efficient solid-phase synthetic approach for the synthesis of 2,3,4,5-tetrahydro-1H-benzo[e][1,4]diazepine derivatives. The methodology is of value for high throughput synthesis of these potentially bioactive molecules.     

Reaction between tert-butyl isocyanide, dialkyl acetylenedicarboxylates, and aromatic carboxylic acids: an efficient method for the synthesis of dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives

Protonation of the reactive intermediates produced in the reaction between tert-butyl isocyanide and dialkyl acetylenedicarboxylates by aromatic carboxylic acids leads to vinylnitrilium cations, which undergo nucleophilic reaction with conjugate bases of the carboxylic acids to produce dialkyl (E)-2-[(benzoyloxy)(tert-butylimino)methyl]-2-butenedioates and this intermediate rearranges to the dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives.