Iminium carbonic acid derivative salts. XII . electrophilic reactions of 2-methylthio-4,5-dihydrothiazolium iodides, 5-methyl-2-methylthiothiazolium iodides and 2-methylthio-5,6-dihydro-1,3-thiazinium iodides. part III. With Vinylogous and Phenylogous Active Methylene Compounds

3-Benzyl-2-memyltmo-4,5-dmydrothiazolium iodide ( 1 ), 5-metlyl-2-methylthio-3-phenethylthiazolium iodide ( 4 ) and 3-methyl and 3-benzyl-2-methylthio-5,6-dihydro-1,3-thiazinium iodides 7a, b were reacted with the vinylogous doubly activated CH-acidic compounds 2a-d and the phenylogous doubly activated components 8, 11, 16, 19 and 21 to yield new types of S, N-heterocycles 3, 5, 6, 9, 10, 12, 13, 14, 15 with the partial structure of push-pull substituted butadienes and 17, 18, 20, 22, 23 and 24 with the character of push-pull substituted phenyl ketene S, N-acetals.     

Model studies of colloidal silica precipitation using biosilica extracts from<Emphasis Type="Italic"> Equisetum telmateia</Emphasis>

Structural materials containing silicon are produced in single celled organisms through to higher plants and animals. Hydrated amorphous silica is a colloidal mineral of infinite functionality that is formed into structures with microscopic and macroscopic form. Proteins and proteoglycans are suggested to play a critical role in the catalysis of silica polycondensation and in structure direction during the formation of these magnificent structures. This article extends knowledge on the effect of protein containing biosilica extracts from Equisetum telmateia on the kinetics of silica formation and structure regulation. Utilising potassium silicon catecholate as the source of soluble silicon, bioextracts obtained from plant silica by dissolution of the siliceous phase with aqueous HF following extensive acid digestion of the plant cell wall were found to modify the kinetic rate constants for the formation of small silicic acid oligomers under circumneutral pH conditions and to modify the solubility of silicic acid in solution. Addition of the bioextracts at ca. 1 wt% to the reaction medium reduced the sizes and range of sizes of the fundamental silica particles formed and led to the formation of crystalline polymorphs of silica under conditions of ca. neutral pH, room temperature and in the absence of multiply charged cations, conditions assumed to be relevant to the biological mineralization environment. The ability of biological organisms to regulate the formation of silica structures with prevention of crystallinity is discussed as are the implications of this study in terms of the generation of new materials with specific form and function for industrial application.     

Highly enantiomerically enriched alpha-haloalkyl Grignard reagents

alpha-Chloro- and alpha-bromoalkyl Grignard reagents 11 and 30 with > 97% ee (enantiomeric excess) were generated by a sulfoxide/magnesium exchange reaction from the enantiomerically and diastereomerically pure sulfoxides 25 and 27. The resulting alpha-haloalkyl Grignard reagents are configurationally stable at -78 degrees C. Racemization sets in at or above -60 degrees C, especially when the solution contains bromide ions. In the absence of halide ions, the configurational stability extends up to -20 degrees C, when chemical decomposition commences.     

Pentazol‐Derivate und daraus entstehende Azide: [O3S—p‐C6H4—N5]— und [O3S—p‐C6H4—N3]— als Kalium‐Kronenether‐Salze

Pentazole Derivates and Azides Formed from them: Potassium‐Crown‐Ether Salts of [O₃S—p‐C₆H₄—N₅]^— and [O₃S—p‐C₆H₄—N₃]^{— —}O₃S—p‐C₆H₄—N₂⁺ was reacted with sodium azide at —50 °C in methanol, yielding a mixture of 4‐pentazolylbenzenesulfonate and 4‐azidobenzenesulfonate (amount‐of‐substance ratio 27:73 according to NMR). By addition of KOH in methanol at —50 °C a mixture of the potassium salts K[O₃S—p‐C₆H₄—N₅] and K[O₃S—p‐C₆H₄—N₃] was precipitated (ratio 60:40). A solution of this mixture along with 18‐crown‐6 in tetrahydrofurane yielded the crystalline pentazole derivate [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₅]·THF by addition of petrol ether at —70 °C. From the same solution upon evaporation and redissolution in THF/petrol ether the crystalline azide [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·THF was obtained. A solution of the latter in chloroform/toluene under air yielded [K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·1/3H₂O. According to their X‐ray crystal structure determinations [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₅]·THF and [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·THF have the same kind of crystal packing. Differences worth mentioning exist only for the atomic positions of the pentazole ring as compared to the azido group and for one THF molecule which is coordinated to the potassium ion; different orientations of the THF molecule take account for the different space requirements of the N₅ and the N₃ group. In [K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·1/3H₂O there exists one unit consisting of one [K‐18‐crown‐6]⁺ and one [O₃S‐C₆H₄—N₃]^— ion and another unit consisting of two [O₃S‐C₆H₄—N₃]^— ions joined via two [K‐18‐crown‐6]⁺ ions and one water molecule. The rate constants for the decomposition [O₃S‐C₆H₄—N₅]^— → [O₃S‐C₆H₄—N₃]^— + N₂ in methanol were determined at 0 °C and —20 °C.     

Die Kristallstrukturen von {Li3(12-Krone-4)2[HC(CN)2]3}, {Na(15-Krone-5)-[HC(CN)2]} und {Na[N(nBu)4][HC(CN)2]2 · THF}

The Crystal Structures of {Li₃(12-crown-4)₂[HC(CN)₂]₃}, {Na(15-crown-5)[HC(CN)₂]}, and {NaN(nBu)₄[HC(CN)₂]₂ · THF} The preparation and the crystal structures of the title compounds 1 — 3 are described. 1 forms a polymeric chain structure, in which one of the lithium ions is linked by Li…NCC(H)CN… bridges. The remaining lithium ions form (12-crown-4)Li[NCC(H)CN] units, which are coordinated by one of the nitrogen atoms of the dicyanomethanide ions with the lithium ions of the chain. 2 forms an ion pair, in which the sodium ion is coordinated by the five oxygen atoms of the crown ether molecule and by one nitrogen atom of the dicyanomethanide ion. 3 has a threedimensional network, in which the sodium ions are coordinated in a distorted tetrahedral manner by the nitrogen atoms of the dicyanomethanide ions. In the cavities of the network the tetrabutylammonium ions and the THF molecules are found.     

The first broad application of alkynyl sulfides as dienophiles in cobalt(I)-catalyzed Diels-Alder reactions

The cobalt(I)-catalyzed Diels-Alder reaction of nonactivated aryl alkynyl sulfides with acyclic 1,3-dienes generates dihydroaromatic vinyl sulfides under very mild reaction conditions, and these products can be oxidized with mild oxidants to the corresponding diaryl sulfides in good overall yields. The steric and electronic effects of substituents on the aryl, as well as on the alkynyl, moieties of the aryl alkynyl sulfide are discussed. While the cobalt catalyst system is quite efficient in converting alkynyl sulfides to the Diels-Alder adducts, the transformation of the corresponding aryl alkynyl sulfoxides and sulfones under similar mild reaction conditions gave only moderate yields of the desired adducts.     

The relation between ion pair structures and reactivities of lithium cuprates

From Li+ well-solvating solvents or complex ligands such as THF, [12]crown-4, amines etc., lithium cuprates R2CuLi(*LiX) crystallise in a solvent-separated ion pair (SSIP) structural type (e.g. 10). In contrast, solvents with little donor qualities for Li+ such as diethyl ether or dimethyl sulfide lead to solid-state structures of the contact ion pair (CIP) type (e.g. 11). 1H,6Li HOESY NMR investigations in solutions of R2CuLi(*LiX) (15, 16) are in agreement with these findings: in THF the SSIP 18 is strongly favoured in the equilibrium with the CIP 17, and in diethyl ether one observes essentially only the CIP 17. Salts LiX (X=CN, Cl, Br, I, SPh) have only a minor effect on the ion pair equilibrium. These structural investigations correspond perfectly with Bertz's logarithmic reactivity profiles (LRPs) of reactions of R2CuLi with enones in diethyl ether and THF: the faster reaction in diethyl ether is due to the predominance of the CIP 17 in this solvent, which is the reacting species; in THF only little CIP 17 is present in a fast equilibrium with the SSIP 18. A kinetic analysis of the LRPs quantifies these findings. Recent quantum-chemical studies are also in agreement with the CIP 17 being the reacting species. Thus a uniform picture of structure and reactivity of lithium cuprates emerges.     

Iminium carbonic acid derivative salts. VIII. Electrophilic reactions of 2-methylthio-5,6-dihydro-1,3-thiazinium iodides, 2-methylthio-5,6-dihydrothiazolium iodides and 5-methyl-2-methylthiothiazolium iodides. Part II. With active methylene compounds

The title compounds 1a-c and 2 werre reacted with several doubly activated methylene components to yield the cyclic ketene S,N-acetals 3-10 .