The Chiral Glycine Enolate Derivative from 1-Benzoyl-2-(tert-butyl)-3-methyl-1,3-imidazolidin-4-one is Alkylated in the 5-Position with Relative Topicity lk. Preliminary Communication

An overall enantioselective substitution of the R-group of an α-hydroxy- or α-amino acid 1 [R? CH(XH)COOH] by another R-group is possible through heterocycles 2 obtained from 1 with pivaladehyde ( 1 → 7 ). The rac- and the (S)-(+)-heterocycles 8 (title compounds of type 5 ) are prepared from glycine and O-benzyl-(S)-serine, respectively. Their enolates (cf. 9 , type 6 ) are alkylated with iodomethane, iodobutane, 2-iodopropane, benzyl bromide, and acetone to give the trans-disubstituted imidazolidinones 10 with ≥ 95% diastereoselectivity. The configuration of the products is established by chemical correlation with alanine, phenylalanine, and valine.     

1H and 13C nuclear magnetic resonance study of (D3)-trishomocuban-4-ol and (D3)-trishomocubanone

The complete assignments of the ¹H and ¹³C NMR spectra for (D₃)-trishomocuban-4-ol (3) and (D₃)-trishomocubanone (4) are reported. The difference between the ¹H and ¹³C chemical shifts of 3 and 4 and those of the hydrocarbon (D₃)-trishomocubane, and the substituent effect of the hydroxy group, can be adequately explained by the unique stereochemistry of these compounds.     

Singuläre definition der äquivarianten Bredon homologie

Let G be a discrete group,o(G) the orbit category of G and M:o(G)a a covariant (contravariant) functor to abelian groups. We define a singular equivariant homology theory H_*(X;M) (resp. H^*(X;M)) which satisfies a dimension axiom, in the sense of Bredon (Lecture notes 34). It turns out, that all fundamental properties of these theories directly follow by naturality from the analogous theorems in the classical non equivariant case.     

1-aralkylated tetrahydro-2-benzazepines. Part II: Synthesis from 3-(3,4-dimethoxyphenyl)-propylamine

3-(3,4-Dimethoxyphenyl)-propylamine was N-acylated with aralkanecarboxylic acid chlorides. The resulting amides were subjected to Bischler-Napieralski ring closure to give the corresponding 1-aralkyl-dihydro-2-benzazepines. These were reduced to the title compounds.     

Mechanistic studies of the ethylene trimerization reaction with chromium-diphosphine catalysts: experimental evidence for a mechanism involving metallacyclic intermediates

A system for catalytic trimerization of ethylene utilizing CrCl3(THF)3 and a diphosphine ligand PNPOMe [= (o-MeO-C6H4)2PN(Me)P(o-MeO-C6H4)2] has been investigated. The coordination chemistry of chromium with PNPOMe has been explored, and (PNPOMe)CrCl3 and (PNPOMe)CrPh3 (3) have been synthesized by ether displacement from chromium(III) precursors. Salt metathesis of (PNPOMe)CrCl3 with o,o'-biphenyldiyl Grignard affords (PNPOMe)Cr(o,o'-biphenyldiyl)Br (4). Activation of 3 with H(Et2O)2B[C6H3(CF3)2]4 or 4 with NaB[C6H3(CF3)2]4 generates a catalytic system and trimerizes a 1:1 mixture of C2D4 and C2H4 to give isotopomers of 1-hexene without H/D scrambling (C6D12, C6D8H4, C6D4H8, and C6H12 in a 1:3:3:1 ratio). The lack of crossover supports a mechanism involving metallacyclic intermediates. The mechanism of the ethylene trimerization reaction has also been studied by the reaction of trans-, cis-, and gem-ethylene-d2 with 4 upon activation with NaB[C6H3(CF3)2]4.     

N-Heterocyclic Carbene Stabilized Dicarbondiphosphides: Strong Neutral Four-Membered Heterocyclic 6π-Electron Donors

In contrast to cyclic π-conjugated hydrocarbons, the coordination chemistry of inorganic heterocycles is less developed. Dicarbondiphosphides stabilized by N-heterocyclic carbenes (NHCs) NHC→C₂P₂←NHC ( 1 a , b ) (NHC=IPr or SIPr) contain a four-membered C₂P₂ ring with an aromatic 6π-electron configuration. These heterocycles coordinate to a variety of complex fragments with metals from groups 6, 9, and 10, namely [M⁰(CO)₃] (M=Cr, Mo), [Co^I(CO)₂]⁺, or [Ni^IIBr₂], through an η⁴-coordination mode, leading to complexes 2 a , b , 3 a , b , 5 a , b , and 6 a , b , respectively. These complexes were characterized by X-ray diffraction methods using single crystals, IR spectroscopy, and DFT calculations. In combination these methods indicate that 1 a , b behave as exceptionally strong 6π-electron donors.     

Bootstrap compression of a denseZ-pinch

Summary The process of radiation cooling of a denseZ-pinch compressed by an imploding cylindrical liner is discussed. It is pointed out that the radiation emitted by the pinch is capable of ablating hot plasma from the surface of the liner which can cause a supplementary compression of the pinch. If the radiation cooling is sufficiently intense, the pinch may collapse to a radius of the order of a few μm. Fusion output at such high densities can be considerable in spite of the pinch temperature being only a few keV.

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Riassunto Si discute il processo di raffreddamento per irraggiamento di un pinch-Z denso compresso da uno strato (liner) cilindrico implodente. Si fa notare che l'irraggiamento emesso dal pinch è capace di emettere un plasma caldo dalla superficie del „liner” e ciò può causare una compressione supplementare del pinch. Se il raffreddamento per irraggiamento è sufficientemente intenso, il pinch potrebbe collassare e raggiungere un raggio dell'ordine di pochi μm. L'energia di fusione generata a cosí alta densità può essere considerevole anche se la temperatura del pinch è soltanto di pochi keV.

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Рэзюме Обсуждается процесс радиационного охлаждения плотногоZ-пинча, сжатого за счета взрыва цилиндрического слоя. Отмечается, что излучение, испускаемое пинчем, способно удалить горячую плазму от поверхности слоя, что может вызвать дополнительное сжатие пинча. Если радиационное охлаждение достаточно интенсивное, то пинч может коллапсировать до радиуса порядка нескольких мкм. Выход синтеза при таких высоких плотностях может быть значительным, несмотря на то, что температура пинча составляет только несколько кеВ.

     

Theorie und Anwendungen des echten Kugelgetriebes

Summary A definition is given for a certain class of gears known as genuine spherical gears. The theoretical behaviour of these gears is analysed and formulae for calculating their efficiency are deduced. A large number of existing and possible applications for computing machines, servo systems and other purposes are described.