Synthesis of (s)-(-)-Benzyl-2-tert-butoxycarbonyl amino-4-iodobutyrate

The proteinogenic (-amino acids constitute an important section of the "chiral pool", being inexpensive in the L-form (but available if necessary as the D enantiomers), structurally varied and chemically versatile1, they are useful starting materials for chiral reagents, auxiliaries and ligands2. Any high-yielding transformation of an (-amino acids which proceeds without racemization is thus of potential importance, especially if it generates another reactive center and may be applied to the s…     

Barriers to racemization in C3-symmetric complexes containing the hydrotris(2-mercapto-1-ethylimidazolyl)borate (Tm(Et)) ligand

The tripodal ligands hydrotris(N-ethyl-2-mercaptoimidazol-1-yl)borate (NaTm(Et)) (1) and hydrotris(N-benzyl-2-mercaptoimidazol-1-yl)borate (NaTm(Bn)) (2), analogues of the hydrotris(N-methyl-2-mercaptoimidazol-1-yl)borate ligand (Tm) containing alternative nitrogen substituents, have been employed to examine the racemization of their C3-symmetric complexes with both four- and six-coordinate metals. The ligands react at room temperature with metal halides to provide C3-symmetric metal complexes. The syntheses of the four-coordinate complexes [Tm(Et)ZnCl] (3), [Tm(Et)CdBr] (4), [Tm(Et)HgCl] (5), [Tm(Et)CuPPh3] (6), [Tm(Et)AgPPh3] (7), and [Tm(Bn)ZnCl] (8) are reported. The six-coordinate complexes [Tm(Et)Ru(p-cymene)]Cl (9), [Tm(Et)Ru(p-cymene)]PF(6) (10), and [Tm(Et)Mn(CO)3] (11) were also synthesized. The X-ray crystal structures of 3, 4, 6, and 9 are reported. The diastereotopic nature of the ethyl and benzyl hydrogen atoms in the ligands allows the enantiomeric forms of these complexes to be distinguished by 1H NMR spectroscopy. Variable-temperature (VT) 1H NMR spectra have thus been used to investigate the energies of the racemization processes occurring in these chiral complexes. In solvents the activation energies to racemization for the four-coordinate complexes lay in the range of 53-77 kJ mol(-1). In non-donor solvents the energies are reduced and a dissociative mechanism is therefore implicated. No interconversion could be observed by VT NMR for the six-coordinate complexes in any solvent. To further explore the racemization mechanisms ab initio density functional theory calculations have been conducted on the ground- and transition-state structures of representative six-coordinate [Mn(I)] and four-coordinate [Zn(II)] complexes following a proposed nondissociative mechanism of racemization. The calculated energy barriers to racemization are 163 and 121 kJ mol(-1), respectively. It is concluded that the low-energy racemization of substitution-labile four-coordinate complexes occurs via a dissociative mechanism, while substitution-inert six-coordinate complexes experience a significantly higher barrier to racemization. Whether this is due to the operation of a dissociative mechanism with a higher activation barrier or to a nondissociative mechanism remains unknown.     

Synthesis and Solvatochromatic properties of 9-(4-Aminophenylethynyl)-10-(4-nitrophenylethynyl)anthracene

9-(4-Aminophenylethynyl)-10-(4-nitrophenylethynyl)anthracene (2) was synthesized in high yield by using a route involving sequential Sonogashira cross coupling reactions of 9-bromo-10-iodoanthracene with 4-nitrophenylacetylene and 4-aminophenylacetylene. Solvatochromism was observed in the absorption and fluorescence spectra of 2 in a variety of solvents. In less polar solvents, such as hexane and benzene, the fluorescence emission band of 2 appears in the green to orange region while this substance does not fluoresce in polar solvents, such as acetonitrile and DMF.     

Synthesis of sterically-hindered peptidomimetics using 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methyl-morpholinium chloride

Our study demonstrated that 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methyl-morpholinium chloride (DMTMM) is a versatile coupling reagent for the synthesis of sterically-hindered peptidomimetics. It is superior to HBTU/HOBt and CDMT in controlling racemization and N-arylation, respectively.     

3-(Diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT): a new coupling reagent with remarkable resistance to racemization

[formula: see text] The new crystalline phosphate reagent 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT) mediates amide bond formation with a remarkable resistance to racemization. Comparative racemization studies were carried out and DEPBT proved to be superior to typical phosphonium and uronium coupling reagents. DEPBT is easily prepared and is exceedingly stable with a shelf life of months at room temperature. The advantageous properties of DEPBT render it a useful and unique addition to the arsenal of coupling reagents.     

Synthesis of (R)-5-(2′-pentyl)barbituric acid derivatives of high optical purity

Natural (R)-(+)-pulegone ( 1 ) was converted to 3-methylhexanoic acid ( 4 ) by a sequence which precluded racemization. Conversion of this to malonic esters 8 , 5 , and 11 permitted the synthesis of pentobarbital ( 6 ) secobarbital ( 12 ), thiopental ( 9 ), thiamylal(10 ), and 5-(2′-pentyl)barbituric acid ( 7 ), all having the ( R )-configuration in the side chain.     

Synthesis and characterization of polyamides derived from (4-(4-(2, 6-diphenylpyridin-4yl)phenoxy)phenyl)-3, 5-diaminobezamide

New types of polyamides containing pendent triaryl pyridine groups were successfully synthesized by direct polycondensation of a symmetry diamine,（4-（4-（2,6-diphenylpyridin-4yl）phenoxy）phenyl）-3,5-diaminobezamide（DPDAB）, and various aromatic and aliphatic dicarboxylic diacids in NMP using triphenyl phosphate（TPP） and pyridine as catalyst. The diamine and all the prepared polyamides were fully characterized by using FT-IR,¹H-NMR,UV-Vis spectroscopy, fluorimetry and elemental analysis.The inherent viscosity of polyamides ranged from 0.45 dL/g to 0.68 dL/g.All the polymers exhibited solubility in common polar aprotic solvents such as NMP,DMAc,DMF,DMSO,pyridine,HMPA,and even in less polar solvents such as THF and m-cresol at room temperature.Thermal properties of polyamides were evaluated by means of DSC,DMTA and TGA.These polymers showed glass transition temperatures（T_g） in the range of 138-210℃. Their initial decomposition temperature（T_i） varied from 265℃to 310℃under N₂.The dilute solution（0.2 g/dL） of polyamides in DMF exhibited fluorescence emission withλ_max in the range of 470-550 nm.     

Stable helical polyguanidines: poly[N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]guanidines

Using chiral catalysts of (R)- and/or (S)-BINOL-Ti, the asymmetrical polymerization of achiral monomer, N-(1-anthryl)-N'-n-octadecylcarbodiimide, yielded soluble nonregioregular polyguanidines of Poly-R1 and Poly-S1. A racemization process occurred when the toluene solution of Poly-R1 was annealed at elevated temperatures (70-80 degrees C). Kinetic studies reveal this to be a slow process with an activation energy of ca. 36 kcal/mol. On the other hand, using titanium(IV) trifluoroethoxide catalyst, the polymerization of N-(1-anthryl)-N'-[(R)- and/or (S)-3,7-dimethyloctyl]carbodiimides afforded highly regioregular polyguanidines of Poly-R2 and Poly-S2. These polymers adopt stable helices in various solvents and elevated temperatures, whose kinetically controlled conformations and thermodynamically controlled conformations are essentially the same.     

Photophysical properties of izomeric N-chlorobenzyl substituted (E)-2' (3'-or 4')-hydroxy-4-stilbazolium chlorides in alcohols

Absorption and steady-state fluorescence spectra of nine N-p-(m- and o-) chlorobenzyl substituted (E)-2'-(3' and 4')-hydroxy-4-stilbazolium chlorides belonging to the hemicyanine class of compounds were studied in extra dry alcohols of different polarity. Derivatives with 2'-hydroxy or 4'-hydroxy substituent in the benzene moiety of stilbazol molecule displayed negative solvatochromizm. On the other hand, the excited state decay of compounds with a 3'-hydroxy group in the benzene moiety was dominated by non-radiative processes in protic solvents. Solutions of each of the compounds are yellow in extra dry solvents, red in solvents with small amount of water and yellow again if more water is added. The absorbance and steady-state fluorescence methods were used to explain the protonation/deprotonation processes for N-p-chlorobenzyl-(E)-4'-hydroxy-4-stilbazolium chloride and its zwitterionic or quinoid form in 2-propanol responsible for these phenomena.     

Preparation of Weinreb amides using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM)

Weinreb amides were successfully prepared from the corresponding carboxylic acids using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) in the solvents, methanol, isopropyl alcohol, and acetonitrile, which can solubilize DMT-MM. A variety of carboxylic acids were converted to the corresponding Weinreb amides in excellent yields by simply mixing with DMT-MM and N,O-dimethylhydroxylamine hydrochloride.     

New chromophores based on 2-(4-vinylchromen-2-ylidene)malononitrile and 2-(2-vinylchromen-4-ylidene)malononitrile

New derivatives of 2-(4-vinylchromen-2-ylidene)malononitrile and 2-(2-vinylchromen-4-ylidene)malononitrile were synthesized using the Knoevenagel reaction of 2-(4-methyl-chromen-2-ylidene)malononitrile and 2-(2-methylchromen-4-ylidene)malononitrile, respectively, with the participation of [1-(2-n-butoxyethyl)-2,2,4,7-tetramethyl-1,2,3,4-tetrahydroquinolin-6-yl)]-carbaldehyde. First hyperpolarizability (β) was calculated for the obtained compounds using the M05-2X functional and 6-31+G (d) basis. Optical properties and solvatochromism in solvents of different polarity (toluene, 1,4-dioxane, chlorobenzene, dichloromethane, DMF, and ethanol) were also investigated.

     

Solvatochromicity of 3-hydroxy-4-(1-(2,4-dihydroxyphenyl)-2-hydroxy-2,2-diphenylethylidene)cyclohexa-2,5-dienone for screening of solvents

The quinonic compound 3-hydroxy-4-(1-(2,4-dihydroxyphenyl)-2-hydroxy-2,2-diphenylethylidene)cyclohexa-2,5-dienone (I) is synthesised by the reaction of benzil with 1,3-dihydroxybenzene in basic medium. Solution of this compound shows visibly distinct colour differences in different solvents. From the different absorption maxima of the compound in visible spectra it can be used as an excellent analytical reagent to screen different solvents.     

Crystal Structure and Spectral Characters of 2-（4-Methylbenzoly）-3-（4-chlrolphenyl） -4-（1,2,4-triazole）-5-anilino-thiopene

1 INTRODUCTION The triazole derivatives were widely studied because they represent the largest group of modern fungicides and extensively used in both human and veterinary therapy and in agriculture[1～3]. For exam- ple, there are commercially available …     

含3-甲基苯基-2,3-二氮杂萘-1-酮结构聚醚酰胺的合成、表征与性能

合成了一种新型芳香二胺双-(4-氨基苯基)-4-(3-甲基-4-苯氧基)-2,3-二氮杂萘-1-酮(1)[2-(4-aminophenyl)-4-(3-methyl-4-phenoxy)-2,3-phthalazinone-1,DAMPP].采用Yamazaki体系,二胺(1)能与多种芳香二酸进行溶液亲核缩聚反应,制得一类新型聚芳醚酰胺,其特性粘度为0.40～0.60dL/g;以MS,FTIR和¹HNMR等分析手段研究了新型二胺单体及其聚合物的结构;利用DSC和TGA研究了聚合物的耐热性能,结果表明,新型聚芳酰胺具有高的玻璃化转变温度为598～620K,N2气气氛中10%热质量损失温度在673K以上.聚合物2a～2c的表面电阻系数为3.75×10¹⁴～9.87×10¹⁵Ω,体积电阻系数为1.39×10¹⁶～4.09×10¹⁶Ω·cm.聚合物在二甲基甲酰胺、1-甲基吡咯烷酮和间甲酚等极性有机溶剂中可溶解,并经浇注得到透明、韧性薄膜.     

Synthesis and properties of new pyridine-bridged poly(ether-imide)s based on 4-(4-trifluoromethylphenyl)-2,6-bis[4-(4-aminophenoxy)phenyl]pyridine

A novel pyridine-containing aromatic diamine monomer, 4-(4-trifluoromethylphenyl)-2,6-bis[4-(4-aminophenoxy)phenyl]pyridine (FAPP), was synthesized via the modified Chichibabin pyridine synthesis of 4-(4-nitrophenoxy)-acetophenone with 4-trifluoromethyl-benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step process. The resulting polyimides exhibited good solubility in aprotic amide solvents and m-cresol, such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and m-cresol, etc., which possessed the inherent viscosities of 0.76-0.91 dL/g. Strong and flexible poly(ether-imide) films were obtained, which showed excellent thermal properties with the glass transition temperatures of 268-353 °C, the temperature at 5% weight loss of 547-595 °C, and the residue at 700 °C of 65-74% in nitrogen, good mechanical properties with the tensile strengths of 87.6-104.2 MPa and elongations at breakage of 8.9-12.6%, and good optical transparency with the cut-off wavelengths of 357-380 nm, as well as low dielectric constants in the range of 2.49-3.04 at 1 MHz and low water uptake 0.43-0.69%. Furthermore, the resulted polyimides derived from FAPP were compared with non-fluorinated analogous polyimides and fluorinated analogous polyimides with trifluoromethyl groups in different positions, and the effects of substituents were also investigated and discussed.     

Enzyme-catalysed improved resolution of (RS)-4-cyano-4-(3,4-dimethoxyphenyl)-4-isopropyl-1-butanol

Resolutions of (RS)-4-cyano-4-(3,4-dimethoxyphenyl)-4-isopropyl-1-butanol 1 using various enzymes were performed. Among them, Pseudomonas fluorescens resolved it with moderate stereoselectivity (E=13) and reacted faster with the (S)-enantiomer. To optimize enzyme-catalysed reaction conditions for the resolution, the effect of solvents and additives was studied. In n-hexane:ethyl acetate (9:1), both reaction rate and selectivity were high. When pyridine, potassium carbonate and molecular sieves were used as additives, the enantiomeric excess of the (R)-enantiomer was 99, 99 and 98% at 52–60% conversion, respectively. However, in diisopropyl ether, the enantiomeric excess of unreacted alcohol (R)-1 was up to 99% at 70% conversion without additives.     

Preparation of 1-(4-nitrophenyl)-2-formylpyrrole from furfural

The products of the condensation of furfural with p-nitroaniline in an acidic medium in various solvents were investigated. It was established that the well-known method gives 1-(4-nitrophenyl)-2-formylpyrrole in no higher than 55% yield and 2,3-bis(4-nitrophenylamino)-2-formylpyrrole in 27% yield. A method based on a previously described method is recommended (the products are obtained in up to 72% yields).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1062–1066, August, 1981.     

Laser photolysis of 1-(4-nitrophenyl)-3-methylpyrazole and 1-ethyl-3-(4-nitrophenyl)-5-chloropyrazole

The spectral kinetic characteristics of the triplet states of 1-(4-nitrophenyl)-3-methylpyrazole (1) and 1-ethyl-3-(4-nitrophenyl)-5-chloropyrazole (2) were studied by the laser nanosecond photolysis technique in different solvents. The triplet lifetimes (τ_T) of molecules 1 and 2 were found to depend strongly on the solvent nature. An increase in τ_T by approximately two orders of magnitude on going from nonpolar and polar aprotic solvents (τ_T ≤ 15 ns) to aqueous-acetonitrile solutions (τ_T = 1100 ns for a volume acetonitrile to water ratio of 1 : 3) was analyzed, taking into account the influence of the medium on the relative contribution of the n,π*- and π,π*-configurations to the lowest triplet state. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1115–1119, May, 2005.     

Borohydride, azide, and chloride anions as terminal ligands on Fe/Mo/S clusters. Synthesis, structure and characterization of [(Cl4-cat)(PPr3) MoFe3S4(X)2]2(Bu4N)4 and [(Cl4-cat)(PPr3)MoFe3S4 (PPr3)(X)]2(Bu4N)2 (X = N3-, BH4-, Cl-) double-fused cubanes. NMR reactivity studies of [(Cl4-cat)(PPr3) MoFe3S4(BH4)2]2(Bu4N)4

Our explorations of the reactivity of Fe/Mo/S clusters of some relevance to the FeMoco nitrogenase have led to new double-fused cubane clusters with the Mo2Fe6S8 core as derivatives of the known (Cl4-cat)2Mo2Fe6S8(PPr3)6 (I) fused double cubane. The new clusters have been obtained by substitution reactions of the PPr3 ligands with Cl-, BH4-, and N3-. By careful control of the conditions of these reactions, the clusters [(Cl4-cat)(PPr3)MoFe3S4(BH4)2]2(Bu4N)4 (II), [(Cl4-cat)(PPr3)MoFe3S4(PPr3)(BH4)]2(Bu4N)2 (III), [(Cl4-cat)(PPr3)MoFe3S4(N3)2]2(Bu4N)4 (IV), [(Cl4-cat)(PPr3)MoFe3S4(PPr3)(N3)]2(Bu4N)2 (V), and [(Cl4-cat)(PPr3)MoFe3S4Cl2]2(Et4N)4 (VI) have been obtained and structurally characterized. A study of their electrochemistry shows that the reduction potentials for the derivatives of I are shifted to more positive values than those of I, suggesting a stabilization of the reduced clusters by the anionic ligands BH4- and N3-. Using 1H NMR spectroscopy, we have explored the lability of the BH4- ligand in II in coordinating solvents and its hydridic character, which is apparent in its reactivity toward proton sources such as MeOH or PhOH.     

Enzymatic resolution of trans-4-(4'-fluorophenyl)-3-hydroxymethylpiperidines, key intermediates in the synthesis of (-)-Paroxetine.

Two Candida antarctica lipases catalyze the enantioselective acylation of N-substituted trans-4-(4'-fluorophenyl)-3-hydroxymethylpiperidines in organic solvents. These two lipases show opposite stereochemical preference in these processes. Both enantiomers can be obtained in their optically pure forms. The (3S,4R) isomer, is an intermediate for the synthesis of (-)-Paroxetine.