Synthesis of dendritic polyamide with protected amino functional groups in the periphery

A homologous series of first-to third-generation dendritic polyamides 2a, 3, and 5 with tris(aminoethyl) amine (TREA) as the core and the protected amino functional groups at the periphery were synthesized via active ester route from “Schlüter” type dendron 1a. Their structures were characterized by ¹H-NMR and mass spectra. Based on the efficient synthesis of the first generation dendrimer 2a (yield 75%), the synthesis of second-generation dendrimer 3 was found to be more efficient via the convergent method (yield 69%), while the mixed strategy was applied efficiently for the synthesis of the higher generation dendrimer 5 (yield 37%). The overall yield for the third generation dendrimer 5 from Schlüter dendron is 12%. __________ Translated from Huaxue Tongbao (Chemistry), 2005, 68(12) (in Chinese)     

Hydrothermal synthesis and intercalation behavior of a layered titanium phosphate Ti2(H2PO4)(HPO4)(PO4)2 · 0.5C6N2H16, with an extended γ-phase intercalated into organic amine

With a hydrothermal technique, a layered titanium phosphate with the formula Ti₂(H₂PO₄)(HPO₄)(PO₄)₂ · 0.5C₆N₂H₁₆ (denoted TP-J2) has been prepared by treating the Ti/H₃PO₄/H₂O/1-methylpiperazine system directly. The as-synthesized products were characterized by powder X-ray diffraction, CP-MAS solid-state ³¹P NMR spectroscopy, thermogravimetric and differential thermal analyses (TG-DTA). The structure was solved by single-crystal X-ray diffraction analysis and it presents an extended γ-phase intercalated with organic amine. Crystal data: triclinic, , a = 8.106 (2) Å, b = 8.197 (2) Å, c = 11.658 (2) Å.  = 78.32 (3)°, β = 80.85 (3)°, γ = 77.90 (3)°, Z = 2. Additionally, the intercalation behavior of TP-J2 with n-alkyl monoamine (n = 2, 3, 4, 6, 8, 10 and 12) was investigated. Owing to the strong brønsted base, N,N′-dimethylpiperazine, resides in the interlayer, it presented unusual features of TP-J2 in contrast with that of γ-Tip.     

Intramolecular Mannich reaction in the asymmetric synthesis of polysubstituted piperidines: concise synthesis of the dendrobate alkaloid (+)-241D and its C-4 epimer

[reaction: see text] The intramolecular Mannich reaction of delta-amino beta-keto esters with aldehydes and ketones is a new methodology for the synthesis of polysubstituted piperidines and is illustrated by the concise asymmetric synthesis of the dendrobate alkaloid (+)-241D and its C-4 epimer.     

Ring-closing metathesis of olefinic peptides: design, synthesis, and structural characterization of macrocyclic helical peptides

Heptapeptides containing residues with terminal olefin-derivatized side chains (3 and 4) have been treated with ruthenium alkylidene 1 and undergone facile ring-closing olefin metathesis (RCM) to give 21- and 23-membered macrocyclic peptides (5 and 6). The primary structures of peptides 3 and 4 were based upon a previously studied heptapeptide (2), which was shown to adopt a predominantly 3(10)-helical conformation in CDCl(3) solution and an alpha-helical conformation in the solid state. Circular dichroism, IR, and solution-phase (1)H NMR studies strongly suggested that acyclic precursors 3 and 4 and the fully saturated macrocyclic products 7 and 8 also adopted helical conformations in apolar organic solvents. Single-crystal X-ray diffraction of cyclic peptide 8 showed it to exist as a right-handed 3(10)-helix up to the fifth residue. Solution-phase NMR structures of both acyclic peptide 4 and cyclic peptide 8 in CD(2)Cl(2) indicated that the acyclic diene assumes a loosely 3(10)-helical conformation, which is considerably rigidified upon macrocyclization. The relative ease of introducing carbon-carbon bonds into peptide secondary structures by RCM and the predicted metabolic stability of these bonds renders olefin metathesis an exceptional methodology for the synthesis of rigidified peptide architectures.     

Conformational stabilities of 1,1-dicyclopropylethene determined from variable-temperature infrared spectra of xenon solutions and ab initio calculations

The infrared (3200-40 cm(-1)) spectra of gaseous and solid 1,1-dicyclopropylethene, (c-C3H5)2C=CH2, along with the Raman (3200-40 cm(-1)) spectra of liquid and solid phases, have been recorded. The major trans-gauche (C=C bond trans to one ring with the other ring rotated about 60 degrees from the C=C bond, trivial C(1) symmetry) and gauche-gauche (the two three-membered rings rotated oppositely about 60 degrees from the C=C bond, C2 symmetry) rotamers have been confidently identified in the fluid phases, but no definitive spectroscopic evidence was found for the gauche-gauche' form (the two three-membered rings rotated to the same side about 60 degrees from the C=C bond, Cs symmetry), which is calculated to be present in no more than 6% at ambient temperature. Variable-temperature (-55 to -100 degrees C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. Utilizing six different combinations of pairs of bands from the C1 and C2 conformers, the average enthalpy difference between these two has been determined to be 146 +/- 30 cm(-1) (1.75 +/- 0.36 kJ x mol(-1)), with the C1 form more stable. Given statistical weights of 2:1:1 respectively for the C1, C2, and Cs forms, it is estimated that there are 75 +/- 2% C(1) and 19 +/- 1% C2 conformers present at ambient temperature. By utilizing predicted frequencies, infrared intensities, Raman activities, and band envelopes from scaled MP2(full)/6-31G(d) ab initio calculations, a complete vibrational assignment is made for the C1 form and a number of fundamentals of the C2 conformer have been identified. The structural parameters, dipole moments, and conformational stabilities have been obtained from ab initio calculations at the level of Hartree-Fock (RHF), the perturbation method to second order with full electron correlation (MP2(full)), and hybrid density functional theory (DFT) by the B3LYP method with a variety of basis sets. The predicted conformational stabilities from the MP2 calculations with relatively large basis sets are consistent with the experimental results. Structural parameters are estimated from the MP2(full)/6-311+G(d,p) predictions which are compared to the previously reported electron diffraction parameters. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.     

N-甲基苯胺、二苯胺与质子受体相互作用的研究

测量了N-甲基苯胺、二苯胺与一些极性非质子溶剂（B）在CCl_4中的红外光谱，观察到这两种劳胺均与所研究的质子受体发生了氢键交叉缔合作用，并利用光谱数据计算了相应缔合物的形成常数和部分氢键能．结果表明，二苯胺是比N-甲基苯胺更强的质子供体，非质子溶剂的极性、空间效应和不同成键原子对交叉缔合物的稳定性均有一定的影响．还从分子结构对有关结果进行了讨论.     

Electrochemically Enabled Intramolecular Aminooxygenation of Alkynes via Amidyl Radical Cyclization

An electrochemical synthesis of oxazol‐2‐ones and imidazol‐2‐ones has been developed via 5‐exo‐dig cyclization of propargylic carbamates‐ and ureas‐derived amidyl radicals. The electrosynthesis relies on the dual function of 2,2,6,6‐tetramethylpiperidin‐ 1‐yl)oxyl (TEMPO) as a redox mediator for amidyl radical formation and an oxygen atom donor. The reactions are conducted under mild conditions using a simple setup and provide convenient access to functionalized oxazol‐2‐ones and imidazol‐2‐ones from readily available materials.