(2,7-Disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) as bidentate organoaluminum Lewis acids: elucidation and synthetic Utility of the double electrophilic activation phenomenon

A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction. The structure of the bidentate Lewis acid 2 was unambiguously determined by single-crystal X-ray diffraction analysis of 2g possessing a bulky 3,5-di-tert-butylphenyl substituent, revealing the rigid dimeric assembly in the solid state. The double electrophilic activation of carbonyl substrate by 2a has been supported by low-temperature 13C NMR analysis as well as theoretical study using the Gaussian 98 program. Moreover, unique stereoselectivity has been observed in the 2a-promoted Mukaiyama Michael addition, and highly chemoselective functionalization of carbonyl compounds in the presence of their acetal counterparts has been realized using 2a. Finally, the effectiveness of 2a for the activation of ether functionality has been demonstrated in the Claisen rearrangement of allyl vinyl ethers.     

Observation of a liquid-gas-type transition in the pyrochlore spin ice compound Dy2Ti2O7 in a magnetic field

Low temperature magnetization measurements on the pyrochlore spin ice compound Dy2Ti2O7 reveal that the ice-rule breaking spin flip, appearing at H approximately 0.9 T applied parallel to the [111] direction, turns into a novel first-order transition for T<0.36 K which is most probably of a liquid-gas type. T-linear variation of the critical field observed down to 0.03 K suggests the unusual situation that the entropy release across the transition remains finite [approximately 0.5 (J/K) x mol-Dy] as T-->0, in accordance with a breaking of the macroscopic degeneracy in the intermediate "kagomé ice" state.     

Palladium-catalyzed intramolecular coupling between aryl iodides and allyl moieties via thermal and microwave-assisted conditions

Palladium-catalyzed intramolecular cross-coupling reactions between aryl iodides and allyl moieties were successfully demonstrated in the presence of palladium catalyst, tri-o-tolylphosphine, a tertiary amine, and water. Several kinds of trans-2,4-disubstituted 1,2,3,4-tetrahydroquinolines were synthesized in 73-88% yields with excellent diastereoselectivities. This method was further applied to a large variety of substrates to form five-, six-, and seven-membered carbo- and heterocycles in good yields, regardless of the ring-containing atom, via microwave-assisted conditions.     

Grafting of methyl methacrylate and its derivatives onto blood

The grafting of vinyl monomers by tri-n-butylborane to blood has been investigated. The infrared spectra indicated that the monomers were grafted onto blood components. The grafting seems to occur onto blood proteins, mainly onto hemoglobin. The presence of water was essential to the grafting. The hydrolysis of the graft suggests that basic amino acids in the blood proteins, such as lysine and histidine, play an important role in the grafting.     

Copper(II)–acid catalyzed cyclopropanation of 1,3-dienamides by electrophilic activation of α-aryl diazoesters

Copper(II)–acid catalyzed cyclopropanation of electron-rich alkenes, such as 1,3-dienamides, with α-aryl diazoesters are described. The reaction could be performed without rare metal catalysts, excess substrate, or the need for the slow addition of the diazoesters.     

New synthetic routes to optically active alpha-quaternary alpha-aryl amino acid derivatives via the diastereoselective Stevens and Sommelet-Hauser rearrangements

The Stevens rearrangement of N-allylic alpha-aryl amino acid-derived ammonium salts and the Sommelet-Hauser rearrangement of N-benzylic alpha-alkyl amino acid-derived ammonium salts are shown to proceed with remarkably high levels of diastereoselectivity. The methods presented in this work provide new routes to optically active alpha-quaternary alpha-aryl amino acid derivatives.     

Ultrafast vibrational dynamics of SCN(-) and N3(-) in polar solvents studied by nonlinear infrared spectroscopy

In this paper, we report on our investigation into the vibrational dynamics of the antisymmetric stretching modes of SCN(-) and N(3)(-) in several polar solvents. We used an infrared (IR) pump-probe method to study orientational relaxation processes. In two aprotic solvents (N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO)), the anisotropy decay shows a bimodal feature, whereas in other solvents the anisotropy decay can be fitted well by a single exponential function. We consider that the relative contribution of fast-decaying components is smaller in the other solvents than in DMF and DMSO. We discuss the possible origins of the different anisotropy decay behavior in different solvents. From the three-pulse IR photon echo measurements for SCN(-) and N(3)(-), we found that the time-correlation functions (TCFs) of vibrational frequency fluctuations decay on two different time scales, one of which is less than 100 fs and the other is approximately 3-6 ps. In aprotic solvents, the fast-decaying components of the TCFs on a <100 fs time scale play an important role in the vibrational frequency fluctuation, although the contribution of collective solvent reorganization in aprotic solvents was clearly observed to have small amplitudes. On the other hand, we found that the amplitude of components that decay in a few picoseconds and/or the constant offset of the TCF in protic solvents is relatively large compared with that in aprotic solvents. With the formation and dissociation of hydrogen bonds between ion solute and solvent molecules, the spectra of different solvated species are exchanged with each other and merged into one band. We considered that this exchange may be an origin of slow-decaying components of the TCFs and that the decay of the TCFs corresponds to the time scales of the exchange for protic solvents such as formamide. The mechanism of vibrational frequency fluctuations for the antisymmetric stretching modes of SCN(-) and N(3)(-) is discussed in terms of the difference between protic and aprotic solvents.     

Elution of residual ions with etching of heavy ion-injected polyimide

The experiment was carried out to estimate the amount of residual ions after the etching of polyimide irradiated by heavy ions, where etching resulted in a channel of measurable depth in the polyimide. None of the analytical techniques presents each ion separately in etched polyimide containing heavy ions. Activation analysis was used for the irradiated polyimide to see how the injected ions were eluted into the solution by etching. When the irradiated polyimide was etched for only a little longer than the time needed to dissolve a selected range of incident ions, the bulk began subsequently to dissolve. The residual radioactivity in polyimide was found to fall below the limit of detection when the depth of the etched channel appeared 10% deeper than the expected value.