Mesoporous benzene-silica hybrid materials with a different degree of order in the wall structure: an IR comparative study

Recent joint IR and computational work (Onida et al. J. Phys. Chem B 2005) has allowed a detailed characterization of the isolated silanols at the surface of highly ordered benzene-silica hybrid material. In the present paper, a similar characterization is provided for a less ordered sample. The comparison permits the assignment of IR features to the interaction of silanols either with one another or with benzene rings of the structure. The extent of structural imperfections appears to be limited, for example, no more than pairs of interacting silanols are found, readily healed by thermal treatment. Evidence is also provided that probe molecules with simultaneous H-acceptor and H-donor properties (benzene, methylacetylene) may interact with both the acidic proton in silanols and the electronic cloud in the framework aromatic rings.     

Titanium(IV)-promoted Mukaiyama aldol-Prins cyclizations

[reaction: see text] A new version of the Mukaiyama aldol-Prins (MAP) cyclization has been developed. Unsaturated enol ethers such as 3 were found to couple with aldehydes in the presence of TiBr(4) to give 4-bromotetrahydropyran products. This cascade reaction sequence leads to the formation of two new carbon-carbon bonds, a ring, and three new stereogenic centers. We expect this reaction to be a powerful new tool in synthesis.     

Liquid-phase microextraction of tributyltin and triphenyltin coupled with gas chromatography-tandem mass spectrometry. Comparison between 4-fluorophenyl and ethyl derivatizations

This paper describes the liquid-phase microextraction (LPME) of tributyltin (TBT) and triphenyltin coupled with gas chromatography-tandem mass spectrometry. The 4-fluorophenylation and ethylation reactions were used for the derivatization of the organotins. For the two derivatizations, the LPME parameters such as organic solvent, stirring rate, temperature, extraction time and the other additional conditions were examined. Using pure water, the calibration curves, method detection limits (MDLs) and reproducibilities (RSDs) of the two derivatizations were compared under the respective optimized procedures. The 4-fluorophenyl derivatization, which showed a lower MDL (0.36 ng/l) and better reproducibility (RSD = 11% at 10 ng/l) for TBT, was applied to the analysis of seawater. The TBT was detected in the range from 1.1 to 2.0 ng/l in the seawater samples collected in Osaka Bay.     

Theoretical study on the electronic spectrum of TcO 4 −

Summary The theoretical electronic spectrum of TcO ₄ ^– calculated by the SAC(symmetry adapted cluster)/SAC-CI method is presented. The spectrum is in good agreement with the experimental one. The observed peaks are assigned and the existence of several absorptions in the energy region higher than that observed is predicted. The difference and the similarity between the electronic spectra of TcO ₄ ^– and MnO ₄ ^– are clarified. The spectral difference between TcO ₄ ^– and MnO ₄ ^– is due to a remarkably high energy shift of the 3¹T₂ state of TcO ₄ ^– .     

Preparation of 4'-substituted thymidines by substitution of the thymidine 5'-esters

tert-Butyl thymidylate 3 was prepared from thymidine 1 in six steps and 67% overall yield. When the lithium trianion of 3 (prepared by treatment of 3 with excess LDA and then excess tert-butyllithum) is reacted with electrophiles, trapping occurs stereoselectively from either the alpha- or beta-face depending on the electrophile (Scheme 1). Deuterioacetic acid in deuteriomethanol affords mainly the alpha-deuterated product (4a/4b = 2.4:1) while all other electrophiles, e.g., phenylselenenyl chloride, allyl bromide, and N-fluorobenzenesulfonimide (NFSI), give predominately (or completely) the products of attack from the beta-face (5bcd/4bcd = 3.7:1 to 100:0). The structures of the products were determined by coupling constant analysis of both the initial compounds and the diols 6bcd prepared by ester reduction and by formation of the acetonides 7bc. The methyl ester of the 3'-epimer of thymidylic acid 9 was also prepared from thymidine 1 in nine steps and 74% overall yield. When the lithium trianion of 9 (prepared by treatment of 9 with excess LDA and then excess tert-butyllithum) is reacted with electrophiles, trapping also occurs stereoselectively with attack on either the alpha- or beta-face depending on the electrophile (Scheme 2). Again, deuterioacetic acid in deuteriomethanol affords mainly the beta-deuterated product (11a/10a = 1.6:1) while all other electrophiles, e.g., phenylselenenyl chloride, methyl iodide, allyl bromide, and NFSI, gave predominately (or completely) the product of attack from the alpha-face (8.7:1 to 100: 0). Again, the structures of the products were determined by coupling constant analysis of both the initial compounds, and the diols 12b-e were prepared by reduction of the ester and by formation of the acetonides 13bcd. A rationale has been developed using molecular mechanics calculations to explain the diastereoselectivity that involves staggered axial attack on the sp(2) carbon opposite to the pseudoaxial alkoxy group in the most stable half-chair conformation of the enolates, as shown in Schemes 3-5.     

Catalytic addition of C-H bonds to multiple bonds with the aid of ruthenium complexes

Ruthenium complexes, e.g., RuH2(CO)(PPh3)3, have been found to catalyze the direct addition of ortho carbon-hydrogen bonds of aromatic ketones to olefins and acetylenes with high efficiency and selectivity. The C-H/olefin coupling reaction is applicable to not only C-H bonds in aromatic ketones but also to those in a,b-enones and aro-matic esters. Catalytic addition of ortho carbon-hydrogen bonds of aromatic imines to olefins is found to be catalyzed by Ru3(CO)12.     

Fragment interaction analysis based on local MP2

We have developed a fragment interaction analysis based on local MP2 (FILM) in the context of the fragment molecular orbital (FMO) scheme. The primary purpose of this work is to provide a tool for analyzing inter-fragment interaction associated with dispersion interactions in a large molecule such as protein and DNA. Our implementation of local MP2 (LMP2) is based on the algorithm developed by Pulay and Werner. A potential of FILM was demonstrated using the human immunodeficiency virus type 1 protease (HIV-1 PR) complexed with lopinavir (LPV). The total energy, binding affinity, and inter-fragment interaction energy (IFIE) by the FMO method using LMP2 were compared with those obtained by canonical MP2 and the site-specific information in dispersion interaction was obtained. It turned out that the FILM is a useful tool for analyzing the dispersion interaction between an amino acid residue and a specific site of a ligand.     

An efficient construction of bridged chiral tetracyclic indolidines, a core structure of asperparaline, via stereocontrolled catalytic Pauson-Khand reaction

A reaction of chiral enyne 22 derived from l-proline with a catalytic amount of cobalt (0) octacarbonyl in the presence of N-methylmorphorine N-oxide gave tricyclic enone 24 in 54% yield (73% based on consumed starting material). Treatment of enone 11 with aqueous methylamine followed by silica gel afforded bridged tetracyclic indolidine 1, a common structural motif of natural metabolites, an asperparaline series of compounds and also a potential intermediate for the synthesis of a paralytic alkaloid, asperparaline C (4), in 70% yield.     

Dichloroketene-induced cyclizations of vinyl sulfilimines: application of the method in the synthesis of (+/-)-desoxyeseroline

The reactions of several aryl-, furanyl-, and vinyl-substituted sulfilimines with dichloroketene proceeded at 25 degrees C to yield thioalkyl-substituted gamma-lactams. The overall process involves nucleophilic addition of the nitrogen atom of the sulfilimine onto the highly electrophilic dichloroketene to first generate a zwitterionic intermediate. A subsequent [3,3]-sigmatropic rearrangement is followed by intramolecular trapping of the Pummerer cation by the amido anion to furnish the observed gamma-lactam product. Incorporation of donor groups on the aromatic ring of the sulfonyl functionality had little effect when aryl-substituted sulfilimines were used but exhibited a major effect on the efficiency of the reaction with furanyl-substituted systems. The placement of an electron donor group (i.e., OMe) on the sulfonyl aryl group enhances the nucleophilicity of the amido anion contained within the sulfonium ion intermediate and facilitates the rate of the 3,3-sigmatropic rearrangement. Styryl-substituted sulfilimines cyclize in a stereospecific manner and produce a 3:2-mixture of gamma-lactams and the isomeric imino-lactone system. The heavily functionalized gamma-lactams are easily converted to a variety of nitrogen containing substrates. The vinyl sulfilimine cyclization method was applied to the total synthesis of the Calabar alkaloid (+/-)-desoxyeseroline.     

Total Synthesis of (±)-Hirsutene via Pd-Promoted Cycloalkenylation Reaction

Beginning with trans-2-methyl-4-cyclohexenecarboxylic acid (9), a total synthesis of linear triquinane sesquiterpene (±)-hirsutene (1) has been accomplished. An acid catalyzed intramolecular conjugate addition (7→6a) and a Pd²⁺-promoted highly stereocontrolled cyclization (5→4) were utilized for the key step of the sequence. Interestingly, some synthetic intermediates exhibited cytotoxicity.