Sulfilimines in organic syntheses: new entries into tetrahydro-1,2-benzothiazepine and 1,2-benzisothiazole systems

Novel ring transformations of thiochroman-4-ones and benzo[b]thiophen3(2H)-ones to tetrahydro-1,2-benzothiazepin-5-ones and 1,2-benzisothiazoles via sulfilimine intermediates are described.     

Formation and fragmentation of the [M + Na]+ ion of glycosides in fast atom bombardment mass spectrometry

Positive-ion fast atom bombardment (FAB) mass spectra of flavonol and steroid glycosides with sodium chloride added showed well known characteristic features; of the appearance of [M + Na]⁺ peaks, disappearance of [M + H]⁺ peaks and a significant decrease in the peak heights of fragment ions. Compared with the features in the FAB mass spectra of crown ethers with addition of salt, and above features suggest a complexation between Na⁺ and the glycosides in matrix solution. The B/E-constant linked scanning technique was used to obtain structural information of the [M + Na]⁺ ion of the glycosides. The B/E spectra gave the daughter-ion peaks, suggesting that coordination of Na⁺ with the biosides and triosides occurs at the sugar moiety, whereas the coordination with the monoglycosides occurs at the aglycone moiety, except for monoglycosides in which the aglycone moiety does not contain significant oxygen functional groups such as OH and CO.     

Total synthesis of (+/-)-8alpha-hydroxystreptazolone

[reaction: see text] The intramolecular Pauson-Khand reaction of 2-oxazolone derivatives with a suitable pentynyl appendage exclusively gave the corresponding 4-hydroxy-6-substituted-9-oxa-1-azatricyclo[6.2.1.0(5,11)]undec-5-en-7,10-diones. Based on this newly developed Pauson-Khand reaction of 2-oxazolone-alkyne derivatives, the first total synthesis of (+/-)-8alpha-hydroxystreptazolone was accomplished in a highly stereoselective manner.     

A facile method for the synthesis of 1,3-oxathiolan-2-ones by reaction of oxiranes, sulfur, and carbon monoxide

A new method for the synthesis of 1,3-oxathiolan-2-ones has been developed. When oxiranes were allowed to react with sulfur in the presence of a catalytic amount of sodium hydride under pressurized carbon monoxide, the three-component coupling of oxiranes, sulfur, and carbon monoxide smoothly proceeded to give the 1,3-oxathiolan-2-ones in moderate to good yields. The reaction proceeded with a high regioselectivity and stereospecificity. For the reaction of oxiranes possessing an aromatic ring, the yields of the 1,3-oxathiolan-2-ones were lower than that of the oxiranes possessing no aromatic ring due to the formation of alkenes and thiiranes as byproducts. However, the product yields were improved by the addition of a catalytic amount of selenium.     

Preparation of SnO2 Monolithic Gel by Sol-Gel Method

The effects of aging of a wet gel at room temperature and a use of a drying control chemical additive (DCCA) were investigated on the prevention of cracking of the gel during drying. N,N-Dimethylformamide (DMF) having low surface tension was used as a DCCA in this study. Before drying, the aged wet gel was immersed in DMF for several days to replace the pore liquid in the wet gel with DMF.The longer the aging and DMF immersing times became, a fewer cracks generated during drying. Especially, the immersion in DMF for over 8 days made it possible to obtain the SnO₂ gel monolith without cracking from the wet gel aged for short time (1 day). However, the wet gel aged for long time without immersing in DMF could not be dried without cracking. Therefore, the replacement of the pore liquid in the wet gel with DMF having low surface tension is thought to be more effective on avoiding a crack generation than aging. From a pore size distribution measurement by N₂ gas adsorption, it was found that the pore size and the breadth of the pore size distribution of the dried gel became larger and narrower respectively with increasing DMF immersing time. DMF is thought to be capable of forming strong hydrogen bonding to hydroxyl groups remaining on the surface of the wet gel and providing a shielding cage around the reactants (Sn–OH), thus further condensation reaction is probably suppressed. Consequently, a large pore distribution is developed in the gel, which reduces the magnitude of capillary stress induced during drying.     

Weber's force and Maxwell's equations

We explore the mathematical connection that exists between Weber's force and Maxwell's equations. The Weber force is shown to be compatible with Maxwell's equations when expressed in relative coordinates with the time dependence determined by the source motion.     

Comparability of data for natural radionuclides in marine sediment obtained by different analytical techniques

In the paper are presented results of potassium, uranium, thorium and radium measurements performed on the natural marine sediment sample SD-N-1/2 in the framework of the IAEA-organized worldwide intercomparison exercise. Analytical methods applied in this exercise were evaluated for performance and significance of the observed discrepancies are discussed in the light of statistical and operative criteria. Possible sources of error have been identified in alpha and gamma spectrometric measurements and suggestions are given about how to avoid them. Well characterized reference materials based on natural matrices have been shown helpful in achieving better data comparability in low level measurements of environmental radioactivity.     

Synthesis of hexahydropyrrolo[2,3-b]indole alkaloids based on the aza-Pauson-Khand-type reaction of alkynecarbodiimides

Upon treatment with 30 mol % of Co2(CO)(8) and 30 mol % of TMTU in toluene at 70 degrees C, benzene-bridged alkynecarbodiimides efficiently underwent a ring-closing reaction to give the pyrrolo[2,3-b]indol-2-ones in good yields. These conditions could nearly suppress the formation of the urea derivatives, which were consistently observed when 10 mol % of Co2(CO)(8) and 60 mol % of TMTU in benzene were used. The synthesis of the eight hexahydropyrrolo[2,3-b]indole alkaloids was accomplished from the resulting pyrrolo[2,3-b]indol-2-ones via the introduction of an angular substituent at the C(3a)-position by treatment with NaBH(4)/alkyl bromide as the crucial step.