Übergangsmetall—methylen-komplexe: XLVIII. Addition und ringschluss bei reaktionen von α-ketodiazoalkanen mit metall—metall-doppelbindungen der metallcarbonyl-reihe: Aufbau metallacyclischer strukturen

The α-diazoketones 2a–h,k,l react with the dinuclear organorhodium complex 1 with elimination of dinitrogen and concomitant addition of their carbonyl-flanked carbene moieties upon the metal—metal double bond. The μ-alkylidene complexes 3f–h thus accessible, represent the final products; the trimethylsilyl derivative 3i was synthesized for comparison. By contrast, the derivatives 3a–e,l behave rather as IR-spectroscopically identified intermediates that, at room temperature, undergo rapid consecutive intramolecular cycloaddition reactions yielding the novel compounds 4a–e and 5l, respectively. Formation of 4a–e results from nucleophilic attack of the keto groups of the bridging ligands upon one of the metal carbonyl units. This type of cyclization process comprises the construction of a new oxygen—carbon bond. The metallacyclic structures thus obtained have been elucidated in the cases of 4c and 4e by means of single crystal X-ray diffraction techniques and no longer obey the structural criteria of type-3 μ-alkylidene complexes. An internal experiment concurrently carried out by use of the diazoalkane 2e furnished proof that the cyclization process occurred regiospecifically: only the more nucleophilic keto-oxygen atom is subject to ring closure, whereas the oxygen atom of the ester carbonyl group does not participate in this reaction. The bis(acyl)methylene derivatives 3f–h resist cyclization and retain their structures even at elevated temperatures (cf. boiling tetrahydrofuran). The carbocyclic diazo precursor 2k (diazodimedone) requires more drastic conditions (boiling benzene) for the reaction with compound 1 to occur; here, the cycloadduct 5k is formed following nitrogen elimination. According to a single crystal X-ray diffraction study, the ketocarbene fragment derived from 2k has been added across the dinuclear metalcarbonyl core, finally acting as a bridging structural unit. In contrast to the cycloadducts 4a–e, a new carbon—carbon bond is formed during the synthesis of 5k. The dimetallacycle 5l results from a two-step cyclo-elimination between the bisdiazoalkane 2l and the organorhodium compound 1.     

A new solution of Schmutzer's projective relativistic cosmology

Schmutzer's cosmological model on the basis of his projective unified field theory leads to a system of differential equations equivalent to a set of highly complicated Abel differential equations [1, 2]. This paper is concerned with the properties of this coupled system of differential equations. The main results of this paper are as follows, (i) We have found the explicit general solution of the cosmological equations for the case=±5/2,= ±1. (ii) The procedure of solving the general case arbitrary=0 is easily within this formalism, (iii) After having found the solution with arbitrary,=±1, one gets the corresponding solution= -, =±1. (iv) In general the coupled system of differential equations describing Schmutzer's cosmological model is equivalent to a single generalized Emden differential equation and it is identical to Emden's differential equation for special values of the parameter.     

Zur Kenntnis von BiBr und BiBr1,167

On BiBr and BiBr_1,167 Preparation and crystal structures of BiBr_1,167 and BiBr are describe as well as their phase relationships. BiBr_1,167 is isotypic with the familiar BiCl_1,167, the structures comprising the cluster Bi with the same Bi? Bi distances and deviations from trigonal symmetry. A simple electrostatic attraction-repulsion calculation with respect to the stability of the particular cluster configuration is given. The structure of BiBr consists of infinite onedimensional chains [Bi₄Br₄] as the structure of BiI. These compounds are structurally classified as special stacking variants of a common motif.     

Über die Wanderung der Carboxylatgruppe bei der Benzilsäureumlagerung. 26. Mitteilung über Reduktone und Tricarbonylverbindungen

The benzilic acid rearrangement of ethyl α,β-dioxo-butyrate was studied by NMR.-and UV.-techniques. In weak alkaline media (pH < 10) the ester group is hydrolyzed first, then the carboxylate group migrates to form methyltartronate. The migration of the carboxylate group was proved by radioactive labeling. At higher pH-values (pH > 11,5) the intakt ester group migrates, with ester hydrolysis occuring as a second step.     

Hexacyanoferrate-based composite ion-sensitive electrodes for voltammetry

Composite electrodes made of graphite, paraffin and metal hexacyanoferrates exhibit a voltammetric response of the hexacyanoferrate ions, the potential of which depends linearly on the logarithm of concentration of alkali and alkaline-earth metal ions. This behaviour has been observed on account of the fact that the electrochemical reaction is accompanied by an exchange of these ions between the solution and the zeolitic lattice of the hexacyanoferrates for charge compensation. The voltammetric determination of the formal potential of these electrodes in a solution allows the quantitative analysis of the ions which are exchanged between the metal hexacyanoferrates and the aqueous solutions. Iron(III), copper(II), silver(I), nickel(II) and cadmium(II) hexacyanoferrates have been studied for the determination of H(+), Li(+), Na(+), K(+), Rb(+), Cs(+), NH(+)(4), Mg(2+), Ca(2+) and Ba(2+). In some cases, the selectivity constants are as low as 3.10(-4), or even so small that their exact value is inaccessible. Electrodes made of iron (III), copper (II), silver (I), nickel (II) and cadmium (II) hexacyanoferrates are most suitable for the determination of potassium ions. Electrodes with nickel (II) and cadmium (II) hexacyanoferrates are also suitable for the determination of caesium ions. The working range of the electrodes also depends on the conductivity of the solutions and can range from 10(-5) to 1 mol l(-1). Typical standard deviations of the potential measurements are 3 mV.     

Zur Herstellung von 1,2,3-Tricarbonylverbindungen aus 1,3-Dicarbonylverbindungen. 27. Mitteilung über Reduktone und Tricarbonylverbindungen [1]

The synthesis of 22 substituted tricarbonyl compounds is reported. They were obtained either by oxidation of β-dicarbonyl compounds with SeO₂ or nitrous oxides or by oxidation of the α-bromo-β-dicarbonyl compounds with DMSO. The procedures using SeO₂ or DMSO are more rapid and give in general better yields than other methods described in the literature.     

Intramolecular Pauson-Khand reactions of methylenecyclopropane and bicyclopropylidene derivatives as an approach to spiro(cyclopropanebicyclo[n.3.0]alkenones)

The trimethylsilyl-protected enynes 9a-c and 14a,b with alkynyl substituents on the three-membered ring or on the double bond of a methylenecyclopropane or a bicyclopropylidene moiety were prepared in two steps from the alcohols 6a-c and 12a,b, respectively, by conversion to the iodides and their coupling with lithium (trimethylsilyl)acetylide (8) in 38-73% overall yields. The bicyclopropylidene derivative 9d was synthesized in 49% yield directly from bicyclopropylidene (3) by lithiation followed by coupling with (5-iodopent-1-ynyl)trimethylsilane (11). Enynes 9b-d were protiodesilylated by treatment with K2CO3 in methanol to give the corresponding unprotected enynes 10b-d in 53, 74 and 94% yield, respectively. Enynes 17a-c with a carbonyl group adjacent to the acetylenic moiety were synthesized from oxo derivatives 15a-c by Wittig olefination followed by coupling with 8 in 47, 18 and 12% overall yield, respectively. Pauson-Khand reactions of the methylenecyclopropane derivatives with a substituent on the ring (9a,b and 10a) as well as on the double bond (14a,b and their in situ prepared protiodesilylated analogues) proceeded smoothly by stirring of the corresponding enyne with [Co2(CO)8] in dichloromethane at ambient temperature followed by treatment of the formed complexes with trimethylamine N-oxide under an oxygen atmosphere at -78 degrees C to give tricyclic or spirocyclopropanated bicyclic enones 18a,b, 19a, 20a,b, 21a,b in good yields. Alkynylbicyclopropylidene derivatives 9c,d and 10c,d formed the corresponding cobalt complexes at -78 to -20 degrees C. Treatment of the latter with N-methylmorpholine N-oxide under an argon atmosphere at -20 degrees C gave the spirocyclopropanated tricyclic enones 18c, 19c and 18d in 31-45% yields. The structure of 19c was proved by X-ray crystal structure analysis. The cyclization of enynones 17a-c in MeCN at 80 degrees C gave the spirocyclopropanated bicyclic diketones 22a-c in 38-65% yields. Intramolecular PKRs of the enynes 25a,d with a chiral auxiliary adjacent to the triple bond gave the corresponding products 26a,d in 70 and 79% yield, respectively, as 5:1 and 8:1 mixtures of diastereomers, respectively. Addition of lithium dimethylcuprate or higher order cuprates to the double bond of the former furnished bridgehead-substituted bicyclo[3.3.0]octanones 27a-c in 57-86% yields. Protiodesilylation of 27a followed by acetal cleavage gave the enantiomerically pure spirocyclopropanated bicyclo[3.3.0]octanedione (1R,5R)- 29a with [alpha]D(20)=-148 (c=1.0 in CHCl3) in 55% overall yield.     

Nucleophilic 1,2-Shifts of Alkoxycarbonyl and Carboxylate Groups in the Benzilic-Acid Type Rearrangement of α,β-Dioxobutyric Esters

tert-Butyl α,β-dioxobutyrate (hydrate; 1d ) undergoes, at medium or high pH, the benzilic-acid rearrangement with exclusive 1,2-shift of the COO(t-Bu) group; the same is true for the corresponding isopropyl ester 1c and ethyl ester 1b at high pH, whereas at lower pH, the overall picture of these reactions is complicated by concurrent hydrolysis of the ester, followed by a 1,2-shift of the COO ^? group. Consequently, the shift of these electron-attracting groups cannot be considered to be systematically disfavoured (compared, e.g., with alkyl-group shifts). Kinetic measurements of the rearrangement show for both esters (as well as for the analogous ethyl ester 1b , and also for ethyl 3-cyclopropyl-α,β-dioxopropionate ( 4 )) a characteristic rate profile: at relatively low pH, k is proportional to [HO^?], approaching saturation with increasing [HO^?] (interpreted as complete transformation of the substrate into the hydrate monoanion), which is followed at higher pH by another rate increase with k proportional to [HO^?] (probably due to the reaction of the hydrate dianion). The similarity of k values for 1b-d shows that in the shift of COOR steric hindrance caused by R is negligible.