An efficient procedure for the preparation of (1S,3R)- and (1S,3S)-1-amino-3-(hydroxymethyl)cyclopentanes

Enantiomerically pure (1S,3S)- and (1S,3R)-1-amino-3-(hydroxymethyl)cyclopentanes have been efficiently synthesized from L-aspartic acid. The title compounds are isosteres of ribose and may be used to construct nucleoside analogs with important antiviral and antineoplastic activities as demonstrated by a concise total synthesis of (+)-4'-deoxycarbapentostatin nucleoside.     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The influence of the number of 3, 3, 3-trifluoropropyl(methyl)siloxane links (/) in the cyclotetrasiloxanes _mD_4-m, where D represents the dimethylsiloxane link and m=0–4, on the rearrangement of these compounds in acetone solution under the action of sodium siloxanolate has been studied. The rearrangement takes place with the formation of a linear polysiloxane the degradation of which yields, in addition to the initial ring, cyclosiloxanes with a different structure. The rate of rearrangement of _mD_4-m and of the formation of a linear polysiloxane rises with an increase in m from 0 to 3. The equilibrium concentration of the linear polysiloxane formed from _mD_4-m is inversely proportional to m. Results have been obtained on the kinetics of the formation of the cyclosiloxanes _mD_n, where m=0–5, n=0–5, and m+n=3–6, in the rearrangement of the rings D₃, ₂D₂, ₃D, and ₄. The reactivity of the siloxane links rises in the sequence (CH₃)₂Si-O-Si(CH₃)₂ < (CF₃CH₂CH₂)-(CH₃) Si-O-Si(CH₃)₂ <(CF₃CH₂CH₂) (CH₃)Si-O-Si(CH₃) (CH₂CH₂CF₃) . Because of the negative inductive effect transferred through the siloxane links, the 3, 3, 3-trifluoropropyl groups strongly activate the siloxane ring with respect to nucleophiiic reagents.For part I, see [3].     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The influence of the number of 3, 3, 3-trifluoropropyl(methyl)siloxane links (Φ/Φ) in the cyclotetrasiloxanes Φ_mD_4-m, where D represents the dimethylsiloxane link and m=0–4, on the rearrangement of these compounds in acetone solution under the action of sodium siloxanolate has been studied. The rearrangement takes place with the formation of a linear polysiloxane the degradation of which yields, in addition to the initial ring, cyclosiloxanes with a different structure. The rate of rearrangement of Φ_mD_4-m and of the formation of a linear polysiloxane rises with an increase in m from 0 to 3. The equilibrium concentration of the linear polysiloxane formed from Φ_mD_4-m is inversely proportional to m. Results have been obtained on the kinetics of the formation of the cyclosiloxanes Φ_mD_n, where m=0–5, n=0–5, and m+n=3–6, in the rearrangement of the rings ΦD₃, Φ₂D₂, Φ₃D, and Φ₄. The reactivity of the siloxane links rises in the sequence ～ (CH₃)₂Si-O-Si(CH₃)₂ ～<～ (CF₃CH₂CH₂)-(CH₃) Si-O-Si(CH₃)₂ ～<(CF₃CH₂CH₂) (CH₃)Si-O-Si(CH₃) (CH₂CH₂CF₃) ～. Because of the negative inductive effect transferred through the siloxane links, the 3, 3, 3-trifluoropropyl groups strongly activate the siloxane ring with respect to nucleophiiic reagents.     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The catalytic rearrangement of the cyclopentasiloxanes Φ_mD_5-m, where Φ represents a 3, 3, 3-trifluoropropyl(methyl)siloxane link and D a dimethylsiloxane link, and m=2–5 has been studied by the method described previously [1]. The rate of rearrangement and the rate of formation of a linear polysiloxane rise with an increase in m from 2 to 4. The equilibrium concentration of the linear polysiloxane formed from Φ_mD_5-m and from Φ_mD_4-m (m=0–4) [1] is inversely proportional to the molar fraction of Φ links in the ring and rises with an increase in the total concentration of siloxane links in solution. Results have been obtained on the kinetics of the formation of the cyclosiloxanes Φ_mD_n (where m=0–5, n=0–5, and m+n=3-6) during the rearrangement of the cyclopentasiloxanes Φ_mD_5-m. It has been established that at equilibrium a mixture of cyclosiloxanes Φ_mD_n containing practically constant ratios of tetramers, pentamers, and hexamers (m+n=4, 5, and 6) is obtained, regardless of the composition and structure of the initial cyclosiloxane and of the conditions of rearrangement (polymerization). The cyclopentasiloxanes Φ_mD_5-m are less active in the process of rearrangement than the cyclotetrasiloxanes Φ_mD_4-m. The activity of the cyclosiloxanes in rearrangement in the presence of a base rises in the sequence D₄?ΦD₃ ≈ Φ₂D₃<Φ₃D₂<Φ₄D < Φ₂D₂ < Φ₃D.     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The catalytic rearrangement of the cyclopentasiloxanes _mD_5-m, where represents a 3, 3, 3-trifluoropropyl(methyl)siloxane link and D a dimethylsiloxane link, and m=2–5 has been studied by the method described previously [1]. The rate of rearrangement and the rate of formation of a linear polysiloxane rise with an increase in m from 2 to 4. The equilibrium concentration of the linear polysiloxane formed from _mD_5-m and from _mD_4-m (m=0–4) [1] is inversely proportional to the molar fraction of links in the ring and rises with an increase in the total concentration of siloxane links in solution. Results have been obtained on the kinetics of the formation of the cyclosiloxanes _mD_n (where m=0–5, n=0–5, and m+n=3-6) during the rearrangement of the cyclopentasiloxanes _mD_5-m. It has been established that at equilibrium a mixture of cyclosiloxanes _mD_n containing practically constant ratios of tetramers, pentamers, and hexamers (m+n=4, 5, and 6) is obtained, regardless of the composition and structure of the initial cyclosiloxane and of the conditions of rearrangement (polymerization). The cyclopentasiloxanes _mD_5-m are less active in the process of rearrangement than the cyclotetrasiloxanes _mD_4-m. The activity of the cyclosiloxanes in rearrangement in the presence of a base rises in the sequence D₄D_{3 2}D₃<₃D₂<₄D < ₂D₂ < ₃D.For part II, see [1].     

Metastable ion study of organosilicon compounds. Part XIV-trimethylsilylacetic acid, (CH(3))(3)SiCH(2)COOH, and its methyl ester, (CH(3))(3)SiCH(2)COOCH(3)

The unimolecular metastable decompositions of trimethylsilylacetic acid, (CH(3))(3)SiCH(2)COOH (1), and its methyl ester, (CH(3))(3)SiCH(2)COOCH(3) (2), were investigated by mass-analyzed ion kinetic energy (MIKE) spectrometry in conjunction with thermochemical data. The abundance of the molecular ions of both compounds, generated by electron ionization, is extremely low. However, the abundance of the ions generated by the loss of (.)CH(3) and observed at m/z 117 and 131 is moderate. These fragment ions further decompose to form the most abundant m/z 75 and 89 ions, respectively, by the loss of CH(2)CO through a (CH(3))(2)Si group migration. The loss of CH(2)CO is also observed to occur from 2(+.) and its fragment ion at m/z 115 generated by the loss of (.)OCH(3). The former reaction is proposed to occur via an ion-radical complex.     

An efficient stereospecific preparation of (Z)-3-methylidene-selenophthalides and (z)-3-methylidenetellurophthalides

(Z)-3-Methylideneselenophthalides 5A and (Z)-3-methylidenetellurophthalides 5B were easily prepared by the regioselective and stereoselective reaction of 2-ethynylbenzoyl chlorides 3 with sodium hydroselenide and sodium hydrotelluride in good yields, respectively.     

Thermochemistry and dissociative photoionization of Si(CH3)4, BrSi(CH3)3, ISi(CH3)3, and Si2(CH3)6 studied by threshold photoelectron-photoion coincidence spectroscopy

Threshold photoelectron-photoion coincidence spectroscopy (TPEPICO) has been used to study the dissociation kinetics and thermochemistry of Me(4)Si, Me(6)Si(2), and Me(3)SiX, (X = Br, I) molecules. Accurate 0 K dissociative photoionization onsets for these species have been measured from the breakdown diagram and the ion time-of-flight distribution, both of them analyzed and simulated in terms of the statistical RRKM theory and DFT calculations. The average enthalpy of formation of trimethylsilyl ion, Delta fH(o)298K(Me(3)Si(+)) = 617.3 +/- 2.3 kJ/mol, has been determined from the measured onsets for methyl loss (10.243 +/- 0.010 eV) from Me(4)Si, and Br and I loss from Me(3)SiBr (10.624 +/- 0.010 eV) and Me(3)SiI (9.773 +/- 0.015 eV), respectively. The methyl loss onsets for the trimethyl halo silanes lead to Delta fH(o)298K(Me(2)SiBr(+)) = 590.3 +/- 4.4 kJ/mol and Delta fH(o)298K(Me(5)Si(2)(+)) = 487.6 +/- 6.2 kJ/mol. The dissociative photoionization of Me(3)SiSiMe(3) proceeds by a very slow Si-Si bond breaking step, whose rate constants were measured as a function of the ion internal energy. Extrapolation of this rate constant to the dissociation limit leads to the 0 K dissociation onset (9.670 +/- 0.030 eV). This onset, along with the previously determined trimethylsilyl ion energy, leads to an enthalpy of formation of the trimethylsilyl radical, Delta fH(o)298K(Me(3)Si(*)) = 14.0 +/- 6.6 kJ/mol. In combination with other experimental values, we propose a more accurate average value for Delta fH(o)298K(Me(3)Si(*)) of 14.8 +/- 2.0 kJ/mol. Finally, the bond dissociation enthalpies (DeltaH(298K)) Si-H, Si-C, Si-X (X=Cl, Br, I) and Si-Si are derived and discussed in this study.     

Hydrolytic reactions of guanosyl-(3',3')-uridine and guanosyl-(3',3')-(2',5'-di-O-methyluridine)

Hydrolytic reactions of guanosyl-(3',3')-uridine and guanosyl-(3',3')-(2',5'-di-O-methyluridine) have been followed by RP HPLC over a wide pH range at 363.2 K in order to elucidate the role of the 2'-hydroxyl group as a hydrogen-bond donor upon departure of the 3'-uridine moiety. Under neutral and basic conditions, guanosyl-(3',3')-uridine undergoes hydroxide ion-catalyzed cleavage (first order in [OH(-)]) of the P-O3' bonds, giving uridine and guanosine 2',3'-cyclic monophosphates, which are subsequently hydrolyzed to a mixture of 2'- and 3'-monophosphates. This bond rupture is 23 times as fast as the corresponding cleavage of the P-O3' bond of guanosyl-(3',3')-(2',5'-di-O-methyluridine) to yield 2',5'-O-dimethyluridine and guanosine 2',3'-cyclic phosphate. Under acidic conditions, where the reactivity differences are smaller, depurination and isomerization compete with the cleavage. The effect of Zn(2+) on the cleavage of the P-O3' bonds of guanosyl-(3',3')-uridine is modest: about 6-fold acceleration was observed at [Zn(2+)] = 5 mmol L(-)(1) and pH 5.6. With guanosyl-(3',3')-(2',5'-di-O-methyluridine) the rate-acceleration effect is greater: a 37-fold acceleration was observed. The mechanisms of the partial reactions, in particular the effects of the 2'-hydroxyl group on the departure of the 3'-linked nucleoside, are discussed.     

Tris(triphenylphosphaniminato)boran,B(NPPh3)3

Tris(triphenylphosphoraneiminato)borane, B(NPPh₃)₃ B(NPPh₃)₃ has been prepared by the reaction of BF₃ · OEt₂ with LiNPPh₃ in toluene/tetrahydrofuran. Moisture sensitive single crystals of B(NPPh₃)₃ · 0.5 C₇H₈ were obtained and characterized by NMR and IR spectroscopy as well as by a crystal structure determination. Space group P2₁/n, Z = 4, lattice dimensions at –70 °C; a = 2147.8(3), b = 978.5(2), c = 2423.8(2) pm, β = 114.11(1)°, R₁ = 0.070. The compound forms monomeric molecules with a planar BN₃ skeleton and BN bond lengths of 144.7 pm on average.     

Tris(tris(trimethylsilyl)silyl)gallium,Ga{Si(Si(CH3)3)3}3

The title compound has been prepared in good yield by the reaction of gallium trichloride with base‐free hypersilyl lithium (Li–Si(SiMe₃)₃, Me = CH₃) in a 1 : 3 molar ratio. Ga(Si(SiMe₃)₃)₃ is monomeric in solution and in the solid state. The compound has been characterized with NMR, IR and Raman techniques as well as by an X‐ray structure determination (planar GaSi₃‐skeleton, monoclinic space group P2₁/c, Z = 4, d(Ga–Si) = 249,8 ± 0,2 pm).     

An efficient, greener, and solvent-free one-pot multicomponent synthesis of 3-substituted quinazolin-4(3H)ones and thienopyrimidin-4(3H)ones

Herein, we report an efficient, greener, and solvent-free novel method for the synthesis of 3-substituted quinazolin-4(3H)ones and thienopyrimidin-4(3H)ones in a one-pot sequence using methyl anthranilate or 2-aminothiophene-3-carboxylate with N,N′-dimethyl formamide dimethyl acetal and various anilines. The driving force for this reaction is the removal of N,N′-dimethylamine by various anilines resulting in 3-substituted quinazolin-4(3H)ones and thienopyrimidin-4(3H)ones.     

Easy access to N,N-bis(but-3-enyl)-, N-allyl-N-(but-3-enyl)-, and N-(but-3-ynyl)-N-(but-3-enyl)-amines

N,N-Bis(but-3-enyl)amines 5a-i were prepared in overall 74% yield from 1-(triphenylphosphoroylideneaminoalkyl)benzotriazole using an aza-Wittig reaction with aldehydes followed by a double Grignard reaction with allylmagnesium bromide. Use of vinyl or 1-propynylmagnesium bromide and allylmagnesium bromide in a sequential fashion also formed the expected doubly unsaturated amines 9a,b and 12, respectively.     

Optical, Electrochemical, and Catalytic Properties of the Unsaturated Host Pd3(dppm)3(CO)2+ and Pd4(dppm)4(H)2+ 2 Clusters: An Overview

This paper presents an overview of the optical, photophysical, and photochemical properties including UV-visible and luminescence spectra in solution at 298 and 77 K, along with electrochemical, and catalytic behavior under reduction conditions (for both thermally and electrochemically assisted systems) of the tri- and tetranuclear Pd₃(dppm)₃(CO)²⁺ and Pd₄(dppm)₄(H)²⁺ ₂ clusters (dppm=bis(diphenylphosphino)methane). This review is also complemented with relevant information about their syntheses, molecular and electronic structures supported from computer modeling, EHMO and DFT calculations, and their host-guest behavior with anions and neutral molecules, in relation with their observed reactivity.     

An investigation of the catalytic systems Co(acac)2or3, C3H4, (iBu)3Al for the polymerization of propadiene

In the catalytic systems Co(acac)₂ or Co(acac)₃, C₃H₄, (iBu)₃Al, the active catalyst is formed via exchange of acac for iBu groups. From kinetic measurements it follows that Co(acac)₂ and Co(acac)₃ give the same catalyst with a polymerization rate constant k _p = 29 ± 3 min⁻¹ at relatively high Al/Co ratios (≥30). At low Al/Co ratios (≤0.05) a less active catalyst is formed with a polymerization rate constant k_p = 3.6 ± 0.4 min⁻¹, possibly due to the acac groups remaining in the catalytically active complex. The kinetic results show that the highly active cobalt catalyst is formed via an equilibrium with (iBu)₃Al which indicates that the active catalyst complex is bimetallic.     

二-(2,4,4-三甲基戊基)膦酸浸渍树脂分离Tb~(3 ),Dy~(3 ),Ho~(3 ),Er~(3 )的研究

研究了大孔网状树脂XAD 4 ,XAD 7,XAD 1 1 80对二 -( 2 ,4 ,4 三甲基戊基 )膦酸 (Cyanex 571 )浸渍树脂的吸附及制备方法 ,并对Cyanex571浸渍树脂分离稀土的性能进行了研究 ,发现在盐酸介质中Cyanex 571 /XAD 7具有最强的萃取能力 ,树脂中的萃取剂含量在 0 35～ 0 4 5g·g- 1时 ,其萃取性能最好。将上述浸渍树脂装入色层柱对稀土元素 (Tb3 ,Dy3 ,Ho3 ,Er3 )进行了分离 ,且降低负载量和流速分离效果更好。     

Azidotris(trifluoromethyl)germane, (CF(3))(3)GeN(3): Spectroscopic Characterization and Density Functional Computations

Azidotris(trifluoromethyl)germane, (CF(3))(3)GeN(3), was prepared from activated silver azide and iodotris(trifluoromethyl)germane in a neat reaction or in dichloromethane or toluene solution, respectively. (CF(3))(3)GeN(3) is a colorless, highly volatile liquid (mp ca. -85 degrees C) which was identified from MS data. The new compound was characterized by multinuclear solution NMR ((13)C, (14)N, (19)F) and gas-phase IR spectroscopy. The structure and the vibrational spectrum of (CF(3))(3)GeN(3) were computed employing density functional theory calculations (DFT) at the self-consistent level with the nonlocal exchange functional of Becke (B) and the nonlocal correlation functional of Lee, Yang, and Parr (B-LYP). The results of the DFT calculation and experimentally obtained vibrational spectra are in good agreement. The DFT computation at the correlated level (B-LYP) predicts the vibrational modes reasonably well, and no scaling was required.