Electronic states of radical cations of all-trans oligo[methyl(phenyl)silane]

The electronic states of radical cations of oligo[methyl(phenyl)silane] (OMPSi⁺) with all trans form (n = 2-8, where n is number of monomer unit of OMPSi) have been investigated by means of density functional theory (DFT) calculation to shed light on the mechanism of hole-transport in oligosilanes with phenyl group in the side chain. For the shorter oligomers (n < 3), the hole (unpaired electron) was widely distributed equivalently in both the Si main and side chains (55% for the Si main chain and 45% for the side chain). The distribution of hole on the chains was largely changed as a function of chain lengths (n). Ratios of the hole distribution on the main and side chains became almost constant at n = 7-8: 70% of spin density was distributed on the Si-main chain and 30% on the side-chain, which is much different from that of oligo(dimethyl)silane (the spin density on the methyl side chain was less than 3% of spin density). From these results, it was concluded that the hole in OMPSi⁺ can transfer by the mechanism for both intermolecular and the intrachain hole-transfer processes.     

Chiral induction controlled by aggregation of organometallics: trifluoromethylated aminoalcohols for chiral ligands in Et2Zn alkylation of benzaldehyde

Chiral induction in the reaction of Et2Zn with PhCHO by fluorinated chiral amino alcohols was correlated to the extent of aggregation of Et2Zn species, which was estimated by manometric study.     

Facile synthesis of N-alkyl-N'-arylimidazolium salts via addition of imidazoles to arynes

[reaction: see text] A novel synthetic approach to N-alkyl-N'-arylimidazolium salts has been developed on the basis of addition of imidazoles to arynes. A variety of N-alkyl-N'-arylimidazolium salts can be synthesized straightforwardly in modest to good yields. Furthermore, utility of the resulting imidazolium salts has been demonstrated by the palladium-catalyzed Suzuki-Miyaura coupling of aryl chlorides.     

Synthesis of polyphosphonates containing pendant chloromethyl groups by the polyaddition of bis(oxetane)s with phosphonic dichlorides

The polyaddition of 4,4′‐bis[(3‐ethyl‐3‐oxetanyl)methoxy]biphenyl (4,4′‐BEOBP) and phenylphosphonic dichloride (PPDC) with quaternary onium salts as catalysts proceeded under mild reaction conditions to afford a polymer containing phosphorous atoms in its main chain. A polyphosphonate with a high number‐average molecular weight (10,300) was obtained by the reaction of 4,4′‐BEOBP and PPDC in the presence of tetraphenylphosphonium chloride (TPPC) in o‐dichlorobenzene at 130 °C for 24 h. The structure of the resulting polymer was confirmed with IR, ¹H NMR, and ³¹P NMR spectroscopy. Furthermore, it was proved that the polyaddition of certain bis(oxetane)s with phosphonic dichlorides proceeded smoothly to give corresponding polyphosphonates with TPPC as the catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3835–3846, 2002     

Separation of single-stranded oligonucleotides on polyvinyl alcohol gel column

Summary Separation mechanisms for single-stranded oligodeoxyribo-or oligoribonucleic acid fragments were explored on an Asahipak polyvinyl alcohol gel column (GS-320) by use of sequential isomers of such molecules. Substrates having different base numbers were found to be separated by size-exclusion chromatography while those having the same numbers with different base sequences were isolated by use of the reversed-phase mode. By using those dual modes, a limit for the separation of the samples was found to arise because one mode shifted the peaks of the substrates in the sense opposite to the shift resulting from the other mode and it was found that when substrates had less than nine bases, the solutes eluted separately.     

The effect of aryl substituents on arylcarbene reactivity

Substituted (p-MeO, p-Me, H, p-Cl, p-Br, m-Br, m-MeO, 3,4-Cl₂, p-CO₂Me, m-CN and p-CN) monophenylcarbenes are generated in a binary mixture of substrates (methanol, cis-4-methyl-2-pentene and cyclohexane) and the relative rate of O—H insertion into methanol to stereospecific cyclopropanation of the olefin to C—H insertion into cyclohexane are calculated from the ratios of products and substrates. It is found (i) that the reactivities of the substrates decrease in the order of methanol, olefin and cyclohexane and (ii) that electron-donating substituents generally lead to reaction with the more reactive substrates while the reaction with the less reactive substrates is favoured in the case of electron-withdrawing substituents. These results are interpreted in terms of the change in the electrophilicity of the singlet arylcarbene by the substituents rather than the change in the singlet-triplet equilibrium.     

Asymmetric sulfoxidation and amine binding by H64D/V68A and H64D/V68S Mb: mechanistic insight into the chiral discrimination step

The H64D/V68A and H64D/V68S mutants of Myoglobin are found to oxidize thioanisole with high enantioselectivity and reactivity. These mutants are also capable of enantioselective binding of alpha-methylbenzylamine, which mimics an expected sulfoxidation intermediate. The kinetic study of the amine binding shows that the Fe-O bond cleavage in the intermediate may be the chiral discrimination step of the sulfoxidation.     

Total synthesis of (+)-muconin

(+)-Muconin (1), isolated from the leaves of Rollinia mucosa (Jacq.) Baill. (Annonaceae), is a sequential THF/THP-possessing acetogenin that exhibits potent and selective in vitro cytotoxicity toward pancreatic and breast tumor cell lines. In this study, a new route was established for obtaining (+)-muconin (1) starting with (-)-muricatacin (2), a compound recently synthesized via the novel alpha-C-H hydroxyalkylation and alpha'-C-H oxidation of tetrahydrofuran.     

A formal total synthesis of (+/-)-cephalotaxine using sequential N-acyliminium ion reactions

[reaction: see text] Novel synthesis of cephalotaxine 1 based on tertiary N-acyliminium ion chemistry starting from alkynylamide 2 was achieved. The key steps include the preparation of pyrroloisoquinoline 4 from alkynylamide 2, the ring expansion of pyrroloisoquinoline 4 to pyrrolobenzazepine 12, and the construction of cyclopentapyrrolobenzazepine ring system 6, all of which are derived from N-acyliminium ion intermediates.     

Catalytic reactions of oxetanes with protonic reagents and aprotic reagents leading to novel polymers

This paper reports new addition reactions of oxetanes with certain protonic reagents such as carboxylic acid, phenol, and thiol, and with certain aprotic reagents such as acyl chloride, thioester, phosphonyl dichloride, silyl chloride, and chloroformate using quaternary onium salts as catalysts. The kinetic study of the addition reactions of oxetanes was also investigated. These new addition reactions were applicable to the synthesis of new polymers. These polyaddition systems could also construct both polymer main chains and reactive side chains. The alternating copolymerization of oxetanes with carboxylic anhydride was performed. Furthermore, it was found that anionic ring‐opening polymerization of oxetanes containing hydroxy groups proceeded to afford the hyperbranched polymer (HBP) with an oxetanyl group and many hydroxy groups at the ends of the polymer chains. Alkali developable photofunctional HBPs were synthesized by the polyaddition of bis(oxetane)s or tris(oxetane)s, and their patterning properties were examined, too. The photo‐induced cationic polymerization of the polymers with pendant oxetanyl groups and the thermal curing reactions of polyfunctional oxetanes (oxetane resins) were also examined to give the crosslinking materials quantitatively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 709–726, 2007