Some 3-manifolds with 2-generated fundamental group

We describe a family of graph manifolds that have 2-generated fundamental group but do not admit a Heegaard splitting of genus 2. They are closely related to the examples provided by Boileau and Zieschang if these are considered as (non-proper) graph manifolds.Received: 14 August 2002     

Synthesen von Xyluron- und Riburonsäurederivaten

Zusammenfassung Durch acylierende Dehydratisierung von 1,2-Isopropyliden-d-xylo-und-d-ribo-pentodialdo-furanoseoxim bzw. aus Furanuronsäureestern und-amiden werden über eine Reihe von Zwischenstufen verschiedene 3-O-Acyl-pentofuranuronsäurenitrile synthetisiert und deren Reaktionen untersucht.

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Synthesis of xyluronic and riburonic acid derivatives

Various 3-O-acyl-pentofuranurononitrils were synthesized by acylating dehydration of 1,2-isopropylidene-d-xylo- andd-ribo-pentodialdo-furanose oximes, or pentofuranuronic acids via intermediates. Their reactions were investigated.

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Mit 1 Abbildung

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Aus den DissertationenH. W. Oberwalder (1970) undE. Wildschek (1967), Technische Hochschule in Graz.     

Novel unexpected examples of 5JHH long range couplings in carbohydrates.

⁵J_HH Couplings proceeding through a HCCCCH - fragment rather than a HCOCCH - path in certain L-idofuranose derivatives are described. The probable mechanism is discussed.     

The chemistry of cyclic enaminoketones. III. Synthesis of bi- and tricyclic enaminoketones from enamine esters and nitriles

The cyclization of enamines derived from β-aminoesters and β-aminonitriles into bi- and tricyclic enaminoketones ( 6,9,13 and 24 ) has been investigated. The enamines derived from aminonitriles cyclize smoothly with magnesium perchlorate in benzene or toluene, whereas the enamines derived from aminoesters cyclize spontaneously during their formation. The scope and limitation of this process is discussed.     

Ag+ labeling: a convenient new tool for the characterization of hydrogen-bonded supramolecular assemblies by MALDI-TOF mass spectrometry

Herein we describe our results on the characterization of a wide variety of different hydrogen-bonded assemblies by means of a novel matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique with Ag+ labeling. The labeling technique with Ag+ ions is extremely mild and provides a nondestructive way to generate charged assemblies that can be detected by mass spectrometry. Up to now more than 25 different single (1(3).2(3)), double (3(3).2(6)), and tetrarosettes (4(3).2(12)) have been successfully characterized by the use of this method. The success of the method entirely depends on the presence of a suitable binding site for the Ag+ ion. A variety of functionalities has been identified that provide strong binding sites for Ag+, either acting in a cooperative way (pi-arene and pi-alkene donor functionalities) or individually (cyano and crown ether functionalities). The method works well for assemblies with molecular weights between 2,000 and 8,000 Da, and most likely far beyond this limit.     

Aminoalkoholester von Hydroxyboranen,IX Salicylamid-Bor-Mannichbasen als potentielle Antitumorwirkstoffe

A synthesis of new boron containingMannich bases of salicylamide by reaction of salicylamide, formaldehyde and boron-heterocycles is reported.

VIII. Mitteilung:Stump, R. K., Zimmerman jr., H. K., Schleppnik, A. A., Gutsche, C. D., Liebigs Ann. Chem.667, 18 (1963).     

Preparation of Functionalized Aryl,Heteroaryl, and Benzylic Potassium Organometallics Using Potassium Diisopropylamide in Continuous Flow

We report the preparation of lithium‐salt‐free KDA (potassium diisopropylamide; 0.6 m in hexane) complexed with TMEDA (N,N,N′,N′‐tetramethylethylenediamine) and its use for the flow‐metalation of (hetero)arenes between ?78 °C and 25 °C with reaction times between 0.2 s and 24 s and a combined flow rate of 10 mL min^?1 using a commercial flow setup. The resulting potassium organometallics react instantaneously with various electrophiles, such as ketones, aldehydes, alkyl and allylic halides, disulfides, Weinreb amides, and Me₃SiCl, affording functionalized (hetero)arenes in high yields. This flow procedure is successfully extended to the lateral metalation of methyl‐substituted arenes and heteroaromatics, resulting in the formation of various benzylic potassium organometallics. A metalation scale‐up was possible without further optimization.     

The Nielsen Method For Groups Acting on Trees

We use Nielsen methods to study generating sets of subgroupsof groups that act on simplicial trees and give several applications.In particular, we exhibit an explicit bound for the complexityof acylindrical splittings of a finitely generated group interms of its rank. This is applied to JSJ-splittings of word-hyperbolicgroups and 3-manifolds. As a last application we construct examplesof amalgamated products that show that there exists no non-trivialrank formula for amalgamated products. 2000 Mathematical Subject Classification: 20E06, 20E08, 57M27.     

Reaktionen derd-Glucuronsäure

Zusammenfassung Durch Acylierung. Methylierung und Benzylierung werden aus 1,2-Isopropyliden--d-glucofuranosidurono-6,3-lacton (I) selbst unter den verschiedensten Bedingungen ausschließlich die zu erwartenden 5-O-Acyl- bzw. 5-O-Alkylderivate von I erhalten. Die Dehydrierung von I ergibt 1,2-Isopropyliden--d-glucofuranosidurono-5-ulose-6,3-lacton (VI), welches keine Reduktionswirkung mehr zeigt und bei seiner Hydrierung I zurückbildet. Alle 5 möglichen Monomethyl-d-glucosen, die 3,6-Dimethyl-d-glucose, und die 5-Benzyl-d-glucofuranose, werden chromatographisch verglichen.

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Acylation, methylation and benzylation of 1,2-isopropylidene--d-glucofuranosidurono-6,3-lactone (I) invariably give the 5-Oacyl-or the 5-O-alkylderivatives to be expected, even under the most widely differing conditions. Dehydrogenation of I yields 1,2-isopropylidene--d-glucofuranosidurono-5-ulose-6,3-lactone (VI) which no longer has reducing properties and which on hydrogenation is reconverted to I. The 5 possible monomethyl-d-glucoses, 3,6-dimethyl-d-glucose and 5-benzyl-d-glucofuranose have been compared chromatographically.

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Frau Prof. Dr.Erika Cremer zum Geburtstag gewidmet.