Studies on Chiral Thiophosphoric Acids and Their Derivatives 15.The Asymmetric Cyclizations of L-prolinol with (Thio)phosphoro(-no)dichlorides

The cyclizations of L-(+)-prolinol 1 derived from L-proline with (thio)phosphoro(-no)dichlorides 2 give 1,2,3-azaphosphaoxabicyclo[3.3.0] 3 consisting of unequal amounts of diastereoisomers, eight pairs of which have been successfully separated by silica gel column chromatography or recrystallization.

Anodic Cyclizations, Seven-Membered Rings, and the Choice of Radical Cation vs.Radical Pathways

While many steps in an oxidative cyclization reaction can be important,it is the cyclization step itself that plays the central role.If this step does not proceed well,then optimization of the rest of the sequence is futile.We report here that the key to the cyclization is channeling the reaction down the correct pathway.Some reactions require the use of a radical pathway and some require the use of a radical cation pathway.An example of each is provided along with a strategy for accessing both pathways using a common intermediate.

Divergent asymmetric synthesis of azaarene-functionalized cyclic alcohols through stereocontrolled Beckwith-Enholm cyclizations

The first enantioselective Beckwith-Enholm cyclization reaction is reported herein.Under cooperative photoredox and chiral hydrogen-bonding catalysis mediated by visible light,cyclization of carbonyls with azaarene-based olefins as a new reaction system offers a general and divergent synthetic pathway to furnish a variety of highly valuable enantioenriched azaarenefunctionalized carbocyclic and heterocyclic alcohols,which bear adjacent 1,2-or nonadjacent 1,3-stereocentres on distinct cyclic frameworks,in high yields and enantio-and diastereoselectivities.The good compatibility of various azaarenes and carbonyls as well as the diversity of cyclic structures of the products underscores the generality of the catalysis platform.In addition to the ability to precisely introduce deuterium into molecules in an enantioselective manner,the considerable synthetic value of this method includes the excellent antioxidant stress potential of the products.In particular,molecule 29 was determined to be a promising lead compound for antioxidant stress drug design.

Au(Ⅰ)-Catalyzed 6-endo-dig Cyclizations of Aromatic 1,5-Enynes to 2-(Naphthalen-2-yl)anilines Leading to Divergent Syntheses of Benzo[α]carbazole, Benzo[c,h]cinnoline and Dibenzo[i]phenanthridine Derivatives

A gold(Ⅰ)-catalyzed 6-endo-dig cyclization of aromatic 1,5-enynes was developed to synthesize 2-(naphthalen-2-yl)anilines.The functional group tolerance of this cyclization was examined systematically and a possible mechanism was proposed.The derivatization of 2-(naphthalen-2-yl)aniline was carried out to facile access to benzo[α]carbazole,benzo[c,h]cinnoline and dibenzo[i]phenanthridine derivatives in a divergent way.

Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-Hexenyl and 4-Oxa-5-Hexenyl Radicals

The intramolecular cyclization of 5-hexenyl radicals continues to be an important synthetic method for the construction of five-membered rings. The synthetic utility arises from the high degree of regioselectivity to give predominantly cyclopentyl products in high yield under mild conditions. Recently we reported product cyclization studies on 4-oxa perturbed 5-hexenyl radical. In this paper, we report our results from a computational study (UB3LYP and UCCSD (T)) of the cyclization of a series of 5-hexenyl and 3-and 4-oxa-5-hexenyl radicals. Three highly conserved cyclization tran-sitions states (exo-chair, exo-boat and endo-chair) were located for 10 acyclic radicals. Activation energies were calcu-lated for the three modes of cyclization for each radical. Calculated values for the exo/endo cyclization ratios had a high level of agreement with experiment and predictions were offered for two cases that have not been experimentally tested. The increased percentage of exo-cyclization with 3-and 4-oxa substitution is the result of an increase in the energy dif-ference between the exo-and endo-chair transition states compared to the hydrocarbon systems. The decreased rate of cyclization of the 4-oxa compounds is primarily due to the stabilization of the initial acyclic radical by the vinyl ether linkage. The increase in the rate of cyclization with 3-methyl substitution is due to the increased conformational energy of the starting acyclic radical.

Synthesis of a highly hydrophobic cyclic decapeptide by solid-phase synthesis of linear peptide and cyclization in solution

A general method was described to synthesize a highly hydrophobic cyclic peptide,cyclo[LWLWLWLWLQ]where underlines indicate D-configuration of the amino acid,by a two-step solid-phase/solution synthesis strategy.The linear decapeptide was assembled by standard Boc chemistry on solid-phase and subsequently cyclized in solution with high efficiency and reproducibility. In subsequent purification by semi-preparative HPLC,50%(v/v) DMF/H_2O was employed as the solvent to overcome the difficulty of solubilization...

A Facile Synthesis of Squamosamide Cyclic Analogs

A series of novel cyclic derivatives have been synthesized by utilizing a nickel powder mediated radical cyclization as the key step. The structures of the new compounds were confirmed by 1H-NMR and MS.

Novel synthesis of a strained para-cyclophane derivative

A [P. Rajakumar, A.M.A. Rasheed, Tetrahedron 61（22） （2005） 5351] para-cyclophane derivative was synthesized via intramolecular esterification of a dipeptide surrogate containing asparagine to form tetrahydropyrimidinone ring. The structures of the product and intermediates were characterized by 1H NMR, 13C NMR and mass spectrum.

Unexpected Synthesis of 2,2'-[1-(4-Methoxyphenoxy)propane-2,2-diyl]bis(5-methoxy-3-methylbenzofuran)

A new bisbenzofuran analogue Ⅶ was achieved unexpectedly in one step procedure from 1-（4-methoxyphenoxy）acetone Ⅰ by using Amberlyst 15 resin as catalyst in excellent yield. The structure was elucidated by spectroscopy analysis including ^1H-NMR, ^13C-NMR, DEPT, ESI-MS, element analysis.

SYNTHESIS AND THERMAL PROPERTIES OF POLYBENZOXAZOLE FROM SOLUBLE PRECURSOR WITH HYDROXY-SUBSTITUTED POLYENAMINONITRILE

Aromatic polybenzoxazole (PBO) precursor, hydroxy-substituted polyenaminonitrile, was prepared by direct polycondensation of 1,4-bis(1-chloro-2,2-dicyanovinyl)benzene (CCB) and 4,6-diaminoresorcinol dihydrochloride (DAR) using pyridine and N,N-dimethylacetamide as condensing agent and solvent. The precursor has good solubility in polar aprotic solvent which is due to the strong dipolar nature of the main chain. The soluble precursor was subjected to thermal cyclization in an inert atmosphere to convert it into the corresponding PBO, which has its 5% weight loss temperature at The fully cyclized PBO were characterized by FT-IR and TGA. The introduction of 10% mol 1,3,5- benzenetricarboxylic chloride (BTC) into the main chain not only has little effect on the solubility of PBO precursor but also raises its 5% weight loss temperature to 552°C and char yield at 700°C for the cyclized PBO with BTC.

The Mechanism on Cyclization, Debenzylation and Oxidation of 1-[1-(Benzyloxy)-3-methylnaphthalen-4-yloxy]propan-2-one

1-[1-（Benzyloxy）-3-methylnaphthalen-4-yloxy]propan-2-one （la） took place a cyclization, debenzylation and oxidation to form 9-substitued benzo[de]chromene-7,8-dione （2a） and 5-benzyl-9-substitued benzo[de]chromene-7,8-dione （3a）. The mechanisms for these reactions were discussed.

Effect of Different Doses of Electron Beam Irradiation on the Structure of PAN Precursor Fibers and Resultant Stabilized Fibers

Different doses of electron beam was imposed on the polyacrylonitrile（PAN） precursor fibers before the fibers were stabilized. The effect of electron beam irradiation on the chemical structure, crystallite size of PAN precursor fibers and density, oxygen content, transverse section morphology of the stabilized fibers in the stabilization process were characterized by the use of fourier transform infrared spectroscopy（FTIR）, float- sink procedure, elemental analysis and scanning electron microscope（SEM）, respectively. The results showed that the extent of cyclization was increased and the crystallite size was decreased. We found that electron beam irradiation could accelerate the cyelization reaction and stabilization reaction in the stabilization process through density test and elemental analysis. We also found that the effect of 200 kGy electron beam irradiated fibers with the stabilization time of 75 min was better than that of the original stabilized fibers with 90 min. These results demonstrate that electron beam irradiation can shorten the stabilization time.

THERMO-CHEMICAL REACTIONS AND STRUCTURAL EVOLUTION OF ACRYLAMIDE-MODIFIED POLYACRYLONITRILE

Thermal properties of acrylonitrile （AN）-acrylamide （AM） copolymers for carbon fibers were studied by DSC and in situ FTIR techniques in nitrogen （N2） and air flows. The cyclization mechanism and stabilization behavior of polyacrylonitrile （PAN） were discussed. In N2 flow, it was found that AM had the ability to initiate and accelerate cyclization process, which was confirmed by the fact that the initiation of nitriles shifted to a lower temperature. Compared to AN homopolymer, the initiation temperature of cyclization was ahead 32 K by introducing 3.59 mol% AM into the copolymer. The exothermic reaction was relaxed due to the presence of two separated exothermic peaks. Accompanied by DSC, in situ FTIR and calculation of activation energy, the two peaks were proved to be caused by ionic cyclization and free radical cyclization, respectively, and the corresponding cyclization mechanism was proposed. With increasing in AM content, the ionic cyclization tends to be dominant and the total heat liberated first increases and then decreases. For AN homopolymer, the activation energy of cyclization is 179 kJ/mol. For AN-AM copolymer （containing 3.59 mol% AM）, the activation energy of ionic cyclization is 96 kJ/mol and that of free radical cyclization is 338 kJ/mol. In air flow, similar cyclization routes occur and the difference is the contribution of oxidation. The oxygen in environment has no remarkable effect on cyclization of AN homopolymer but retards the cyclization of AN-AM copolymers. For AN-AM copolymer with 3.59 mol% AM, the cyclization temperature is postponed 10℃ in air.

Stereoselective Functionalization at C-2 and C-3 of the Gibberellin via an Intramolecular Free Radical Cyclization Approach

Stereoselective functionalization at C-2 and C-3 of the gibberellin skeleton was achieved via an intramolecular free radical cyclization approach using a tethered C-19 halomethyl ester as the radical precursor.

A new member of the calix[4]crown family:Facile synthesis and characterization of a calix[4]crown-9 cone conformer

25,27-Dipropoxy-p-tert-butylcalix[4]crown-9 cone conformer 5 was readily synthesized via an intramolecular cyclization strategy in good yields. The structures of all the new compounds involved were confirmed by NMR, ESI-MS and elemental analyses. All of them were proved to be in the cone conformation.

Sol-Gel Distribution of Polycondensation Reaction

A theoretical approach to polycondensation reaction of Aa-Bb type Involving intramolecular cycllzatlon has been proposed by Tang Au-chin et al.. In this paper, the theoretical sol-gel distribution is tested by polycondensation of adipic acid with trimethylol propane in a sto-ichiometric ratio of 0. 8, and the effect of intramolecular cyclization is discussed in detail.

“Anti-Michael” and Michael Additions in the Reactions of 2-Arylmethyliden-1,3-Indandiones with 2-Aminothiophenol

A novel 2-indano[2,3b]-2-ferrocenyl- and 2-indano[2,3b]-2-(p-methoxy-phenyl)[1,5]benzo-2,5-dihydrothiazepine 5a,b (addition Michael/cyclization) (~30.32%), indano[2,3b]-2-ferrocenyl- and 2-(p-methoxyphenyl)[1,4] benzothiazine 4a,b (addition “anti-Michael”/cyclization) (~45.43%), respectively, were obtained by the condensation of 2-ferrocenyl-and 2-(p-methoxy-phenyl)methyliden-1,3-indandiones 1a,b with o-aminothiophenol 2 in the presence of AcOH and HCl. A new “anti-Michael” addition reaction of 1,4-bis-heteronucleophile 2 into 2-arylmethyliden-1,3-indandiones was reported. As a result of this reaction the product 1a,b was obtained. The structures of the resultant compounds were elucidated by IR, 1H and 13C NMR spectroscopy, mass spectrometry, elemental and X-ray diffraction analysis. The in vitro antitumor activity of the obtained products was researched using the following human cancer cell lines: glioblastoma (CNS U-251), prostatic adenocarcinoma (PC-3), chronic myelogenous leukemia (K562), colorectal adenocarcinoma (HCT-15), mammary adenocarcinoma (MCF-7), and small cell lung cancer (SKLU) and the sulforhodamine B (SRB) method. Among these new compounds some thiazine and thiazepine derivatives showed compelling in vitro antitumor effects on cell lines K-562, HCT-15, SKLU-1 and MCF-7.

Phase-Transfer-Catalyzed Intramolecular Hydroaryloxylation and Hydroamination of C≡C Triple Bonds: An Efficient Synthesis of Benzo[<i>b</i>]furan and 3-Methyleneisoindoline-1-one Derivatives

Phase-transfer-catalyzed intramolecular cyclization reaction of forming benzo[b]furan and 3-methyleneisoin- doline-1-one derivatives has been developed. The cyclization reaction of propargylic carbonates was also de- scribed under metal-free condition and the reaction was reported by Pd and Ni before. The reaction condi- tions and the scope of the process are examined. The catalysts are cheap and environmentally friendly and the substrates are readily available and the procedure is simple, rapid, and general. The development of C-O and C-N bond formation processes via an overall structural isomerization represents the most atom-eco- nomical approach.