2-(2-pyridyl-)ethyl esters A new carboxyl protecting group in peptide synthesis

2-(2-pyridyl-)ethyl esters are used as chemically inert, highly selective protecting groups that are removable under mild conditions via a two step procedure.     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. 53. Die Struktur des 1,3-Dimethyl-1,1,3,3-Tetraphenyldisilthians

Contributions to the Chemistry of Silicon-Sulphur Compounds. 53. Structure of 1,3-Dimethyl-1,1,3,3-tetraphenyldisilthiane 1,3-Dimethyl-1,1,3,3-tetraphenyldisilthiane was obtained by an insertion reaction of sulphur with Ph₂ MeSiH. The compound crystallizes triclinically (P1 ; a = 1166.7; b = 1231.1; c = 988.6 pm; α = 113.23; β = 90.34; γ = 112.43°; Z = 2). The X-ray structure analysis shows a bent configuration of the molecule with Si? S? Si = 108.7°. The results are discussed together with the structures of hexaphenyldisilthiane and dimethyltetraphenyldisiloxane.     

Acyl- und Alkylidenphosphane. XII [1]. Synthese und Eigenschaften des 2,2-Dimethylpropionylphosphans und einiger Derivate

Acyl and alkylidene phosphines. XII. Syntheses and properties of 2,2-dimethylpropionylphosphine and of some derivatives At ?25°C bis(trimethylsilyl)phosphine 1b and 2,2-dimethylpropionyl chloride form (2,2-dimethylpropionyl)trimethylsilylphosphine 2b . As this compound is thermally more stable than similar acyltrimethylsilylphosphines, it might be treated at ?55°C with methyllithium to form the correspondig lithium phosphide 2d ; after the addition of chlorotrimethylsilane [2,2-dimethyl-1-(trimethylsiloxy)propylidene]-trimethylsilylphosphine 3c is obtained. At +20°C 2b rearranges to the E and Z isomer of [2,2-dimethyl-1-(trimethylsiloxy)propylidene]phosphine 3b . The NMR data of E- 3b and Z- 3b differ mostly in the coupling constants. Kept in the diffuse daylight for several days 3b dimerizes to form 2,4-di(tert.butyl)-2,4-bis(trimethylsiloxy)-1,3-diphosphetane 10 . In solution 10 is unstable and decomposes again to a mixture of the E und Z isomer of 3b . Reacting 3b or 3c with alcoholes all trimethylsilyl groups are replaced by hydrogen atoms and unstable 2,2-dimethylpropionylphosphane 4b is formed. Lithium(2,2-dimethylpropionyl)phosphide 4d , synthesized at ?60°C from 4b and methyllithium, crystallizes with one molecule 1,2-dimethoxyethane per formula unit and is dimeric in benzene. As shown by the NMR data 4d has the structure of an alkylidene-phosphine with the lithium atom bound to oxygen. At ?50°C 4d and chlorotrimethylsilane react to form 3b .     

Off-shell NN annihilation studied in π+p interactions at 8 and 16 GeV/c

Interactions in which the baryon is emitted forwards in the c.m.s. are studied in 8 and 16 GeV/cπ⁺p collisions. These interactions are interpreted as representing baryon exchange. The properties of such off-shell $\text{N}$N annihilation events are studied. It is found that the multiplicity distribution of the multi-pion system as a function of the effective mass for events with |u_pp| < 1 GeV² is the same as for real $\text{N}\text{N}$ annihilations.     

Wasser, Abwasser

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Die Trennung von Isonicotins?urehydrazid und Natrium-4-aminosalicylat mit Hilfe eines Anionenaustauschers

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