Catalytic multicomponent cycloaddition assembling three different substances to form highly substituted bicyclo[4.2.0]octanes

A catalytic multicomponent (4+2)-(2+2) cascade cycloaddition process assembling three different substances has been developed. The process is able to rapidly provide a highly substituted bicyclo[4.2.0]octane skeleton from a 2-siloxydiene and two molecules of α,β-unsaturated carbonyl partners. The MCR process is accompanied by stereoselective formation of four carbon-carbon bonds and four stereogenic centers in a single operation.     

Reaction of N-methyl-5-tributylstannyl-4-fluoro-1H-pyrazole and its application to N-methyl-chromeno[2,3-d]pyrazol-9-one synthesis

N-Methylation by sequential treatment of 5-tributylstannyl-4-fluoro-1H-pyrazole 1 with LDA and iodomethane regioselectively afforded the compound 2a in high yield. The addition reaction of 5-lithiated-4-fluoro-1H-pyrazole generated from 2a with a wide range of electrophiles allowed a facile introduction of different substituents at position 5 in good yields. The adduct 3d was efficiently converted to N-methyl-chromeno[2,3-d]pyrazol-9-one 9 in 3 steps.     

Angular distributions of H-induced HD and D2 desorptions from the Si(100) surfaces

We measured angular distributions of HD and D2 molecules desorbed via the reactions H+DSi(100)-->HD [abstraction (ABS)] and H+DSi(100)-->D2 [adsorption-induced-desorption (AID)], respectively. It was found that the angular distribution of HD molecules desorbed along ABS is broader than that of D2 molecules desorbed along AID, i.e., the former could be fit with cos(2.0+/-0.2) theta, while the latter with cos(5.0+/-0.5) theta. This difference of the angular distributions between the two reaction paths suggests that their dynamic mechanisms are different. The observed cos2 theta distribution for the ABS reaction was reproduced by the classical trajectory calculations over the London-Eyring-Polanyi-Sato potential-energy surfaces. The simulation suggests that the HD desorption along the ABS path takes place along the direction of Si-D bonds, but the apparent angular distribution is comprised of multiple components reflecting the different orientations of D-occupied Si dimers in the (2 x 1) and (1 x 2) double domain structures.     

Catalytic (2 + 2)-cycloaddition reactions of silyl enol ethers. A convenient and stereoselective method for cyclobutane ring formation

An efficient catalytic (2 + 2)-cycloaddition reaction leading to the formation of cyclobutane rings has been devised. The process transforms silyl enol ethers and alpha,beta-unsaturated esters into polysubstituted cyclobutanes with a high degree of trans-stereoselectivity. Both the rate and stereoselectivity of the process can be controlled by the choice of the ester group and silyl substituents. The results of stereochemical studies show that the cycloaddition step in this reaction proceeds in a nonstereospecific manner and, thus, by a pathway involving sequential nucleophilic additions via a short-lived zwitterionic intermediate.     

Chlorinated alkaloids in Menispermum dauricum DC: root culture

Feeding experiments using (36)Cl showed that Menispermum dauricum root culture produces four alkaloids containing chlorine. They included the novel alkaloids dauricumine and dauricumidine as well as the known alkaloids acutumine and acutumidine. The structures of novel alkaloids were established by spectroscopic, crystallographic, and chemical methods. These four alkaloids were labeled with (36)Cl, isolated, and fed independently to root cultures. Mutual conversion between acutumine and acutumidine, and between dauricumine and dauricumidine by N-methylation and N-demethylation, was demonstrated. Moreover, dauricumine was converted to acutumine and acutumidine. Epimerization of acutumidine to dauricumidine or vice versa was not observed. These results suggest that dauricumine is the first chlorinated alkaloid formed in cultured M. dauricum roots. Skewed distribution of radioactivity derived from labeled dauricumine is proof that epimerization at C-1 proceeds at a lower rate than N-demethylation.     

Nuclear structure explored by β-delayed decay spectroscopy of spin-polarized radioactive nuclei at TRIUMF ISAC-1

Spin-polarized radioactive nuclear beams at TRIUMF enable a new spectroscopic method which efficiently assigns spins and parities of the daughter levels by taking advantage of the asymmetric β-decay of the polarized parent nucleus. This method was successfully applied to structure studies of ²⁹Mg and ³⁰Mg in connection with the physics of the “island of inversion”. In ²⁹Mg, two low-lying levels with intruder configuration were assigned. In ³⁰Mg, coexistence of spherical shape, prolate shape and γ-collectivity was strongly suggested.     

Substantially low desorption barriers in recombinative desorption of deuterium from a Si(1 0 0) surface

We have studied desorption kinetics of deuterium molecules from a Si(1 0 0) surface by means of temperature-programmed desorption (TPD) spectra and isothermal desorptions.Three desorption components, denoted as β_1,A,β_1,B, and C, can be distinguished in semi-logarithmic plots of the TPD spectra.Their peak positions and intensities are strongly affected by the surface preparation methods employed, either with or without annealing to control the initial D coverage .Peak C appears at the leading edge of the TPD peak.It accounts for only about 5% of the TPD peak at and it diminishes rapidly with decreasing , vanishing at .In contrast, together the β_1,A and β_1,B peaks account for the whole TPD peak at any less than 1.0 ML. The maximum of the β_1,A peak is nearly constant at around the maximum temperature of the TPD peak.On the other hand, the β_1,B peak appears on the high-temperature side of the TPD peak and it systematically shifts to higher temperatures with decreasing .These results imply that first- and second-order kinetics are operating for the β_1,A and β_1,B desorptions, respectively.Isothermal desorption experiments confirm the above predicted kinetics for a limited region, namely .From the results for the rate curve analysis, the desorption barriers are evaluated to be 1.6 ± 0.1 eV and 1.8 ± 0.1 eV for the β_1,A and β_1,B desorptions, respectively.These values are substantially lower than the widely accepted value of ∼2.5 eV. To reproduce the measured TPD spectra we take the Arrhenius-type rate equation containing the first- and second-order rate terms for the β_1,A and β_1,B desorptions.The TPD spectra measured for can be reasonably fit with the proposed rate equation when the values given above for E_d,A and E_d,B are used. For , however, the TPD curves are not fit with the same values; rather, the best-fit curves require values for E_d,A and E_d,B larger than those given above. Combining the present kinetics results with those obtained by STM along with the studies, the β_1,A and β_1,B peaks may be attributed to desorption along the 2H path, while peak C may be attributed to desorption along the 4H path. The atomistic desorption mechanism as well as the energy relationship between the desorption barrier and isosteric heat of adsorption are discussed.     

Partial synthesis of aromatic carotenoids,tedanin, agelaxanthin a,tethyatene, and renieratene

Aromatic carotenoids, tedanin, agelaxanthin A, and tethyatene were synthesized from 0- acetyl-6-citraurin derived from natural zeaxanthin, and tethyatene was further transformed into renieratene as the first example of aromatization of an alicyclic ring in carotenoids.     

Highly enantioselective homogeneous catalysis of chiral rare earth phosphates in the hetero-Diels-Alder reaction

Two types of novel rare earth (RE) complexes were synthesized and used as a chiral Lewis acid catalyst for the hetero-Diels-Alder reaction of carbonyl compounds with the Danishefsky's diene under homogeneous conditions. The Y[(R)-H₈-BNP]₃ (3-Y)-catalyzed reaction of aromatic aldehydes and the Yb[(R)-BNP]₃ (1-Yb)-catalyzed reaction of phenylglyoxylates afforded the corresponding cycloadducts with excellent optical purities (up to 99% ee) in high yields at room temperature. The successful recycling uses of the scandium catalyst (3-Sc) are also described.