Relay Compound Research Articles

Kinetic Investigations of New Viologen Derivatives for Water Photolysis. The First Relay Compound with Stable Radicals.

Kinetic Investigations of New Viologen Derivatives for Water Photolysis. The First Relay Compound with Stable Radicals.

Synthesis of (.+-.)-15-deoxybruceolide and conversion of (-)-15-deoxybruceolide into (-)-bruceantin: total synthesis of bruceantin

A total synthesis of bruceantin (1) using 15-deoxybruceolides 9 and 43 derived from naturally occurring brusatol as relay compounds was achieved

On the Synthesis and Electrochemical Properties of Some New Bipyridinium and Related Compounds

Abstract The synthesis of some new bipyridinium salts is described. Their behavior upon reduction is studied by cyclovoltammetry, coulometry and spectroscopically. Halfwave potentials range from -0.28 V to -0.59 V and ε values of the reduced viologens lie around 104 M-1cm -1 . In addition two relay compounds (4,4′-pyridine-2,4-diyl)-bis-(1-methylpyridinium methylsulfate), 4.4′,4″-(pyridine-2,4,6-triyl)-tris-(1-methylpyridiniumchloride) that are not viologens are described. These substances also form a colored radical upon reduction, but with exceptional stability to-wards oxidation with dioxygen. From coulometric measurements it is inferred that three electrons are transferred in one step. Spectral changes observed in the course of the electrochemical reduction are explained by dimer formation.

ChemInform Abstract: TETRAAZA‐MACROCYCLIC COBALT(II) AND NICKEL(II) COMPLEXES AS ELECTRON‐TRANSFER AGENTS IN THE PHOTO(ELECTRO)CHEMICAL AND ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE

AbstractDas Potential der Komplexe (I)‐(III), die Photoreduktion von CO2 einzuleiten, wird untersucht.

A relay approach to (+)-pleuromutilin. III. direct degradation of the natural product to the key diketone intermediate and its chemospecific functionalization

Pleuromutilin or tiamulin can be degraded to the important bicyclic relay compound (−)- 1 in only four steps. Various methods for achieving chemoselective functionalization of 1 are set in focus.

Tetraaza‐macrocyclic cobalt(II) and nickel(II) complexes as electron‐transfer agents in the photo(electro)chemical and electrochemical reduction of carbon dioxide

AbstractThe potential of a number of tetraaza‐macrocyclic complexes of cobalt and nickel to mediate the photoreduction of carbon dioxide has been studied. Carbon monoxide and hydrogen are the main products, which result from illumination of an aqueous solution containing Ru(2, 2′‐bipyridine)2+3 as sensitizer, ascorbic acid as sacrificial eletron donor and a tetraaza‐macrocyclic complex as relay. Their ratio strongly depends upon the relay compound used. The complexes can be used as electrocatalysts for CO2 reduction at a mercury electrode since they lower the overpotential for CO2 reduction showing turnover numbers/hour of approximately 3. A minimum potential is required to induce reaction of electrocatalysts and CO2 (and H2O).Finally, the redox properties of the macrocyclic metal complexes at p‐GaP and p‐GaAs photocathodes in acetonitrile are compared with those observed at Pt.

Zum Mechanismus der Photoreduktion von Wasser mit Ruthenium‐trisbipyrazil als Sensibilisator

On the Mechanism of the Photoreduction of Water with Ruthenium‐trisbipyrazil as SensitizerOxidative and reductive primary steps can be differentiated in using Ru(bipy) and Ru(bipz), respectively, as sensitizers in a photochemically induced, Pt‐catalyzed sacrificial water reduction. Experimental evidence for the reductive primary step and kinetic data are given for the electron transfer to methylviologen as relay compound.

Selektive Reaktionen an Cytochalasin D

AbstractIn connection with the total synthesis of cytochalasans the cleavage of the macrocyclic system of cytochalasin D (3) was studied in order to gain useful relay compounds. Selective scission of the double bond in 19‐position was achieved by controlled ozonolysis leading to compound 7 (Scheme 1). Treatment of 3 with OsO4 and subsequent acetylation gave the tetraacetoxy‐ and diacetoxy derivatives 8 and 9, respectively. Sharpless epoxidation of 3 yielded the mono‐, di‐ and the two epimeric triepoxides 10, 11, 12, and 13, respectively.Further studies concerned the isomerization of the 6(12)‐double bond to 6(7)‐double bond by an allylic rearrangement. Treatment of 3 with mesylchloride and triethylamine led to 12‐hydroxy‐, 12‐mesyloxy‐ and 12‐chlorozygosporin (14, 16, and 17, resp.) (see Scheme 2). Epoxidation of 14 gave a mixture of the two epimeric 6,7‐epoxides 21 and 23. Zn‐reduction of 18 (the corresponding bromide of 17) led to zygosporin G (20).In order to convert a carbocyclic cytochalasan into a macrocyclic derivative, 3 was converted to 32 (Scheme 2). Treatment of 32 with H2O2 in acetic acid/chloroform or with phenylselenylperacid/H2O2 yielded the enollactone 33.Finally, 17,18‐secocytochalasin D derivatives were prepared for the synthesis of unnatural analogs of macrolidic cytochalasans. The diol 26 was converted into the ketoaldehydes 38 and 40 and to the corresponding keto‐acids 43 and 44 (Scheme 3), which were reduced to the ω‐hydroxycarboxylic acids 45–48. Treatment of 47 with 2,2/‐dipyridyldisulfide/triphenylphosphine/xylene gave probably the lactone 50.

Synthetic studies on terpenic compounds—XI : Stereospecific total synthesis of portulal ,

A stereospecific total synthesis of portulal 1 has been accomplished starting from the Diels-Alder adduct 2 from chloromethylmaleic anhydride and 1-vinylcyclohexene. Firstly 2 was converted by an efficient sequence of reactions to perhydroazulenoid lactone 5, which possesses the correct relative configuration with respect to three chiral centers out of the four present in 1. The fourth chiral center at C-6 was introduced stereospecifically together with the one-carbon substituent at C-4 by the ring formation between C-4 and C-6, and its cleavage to give an exomethylene lactone 35. At this stage the stereochemical validity of the crucial intermediate 35 was confirmed by chemical correlation with the hydroxy lactone 37 which was derived from natural 1 through a systematic degradation. Then 35 was transformed to 37 and the synthesis continued further by using 37 as a relay compound to afford 1.

ChemInform Abstract: STUDIES ON THE SYNTHESIS OF CARDIOTONIC STEROIDS. II. SYNTHESIS OF 17β‐(3‐FURYL)‐5β,14β‐ANDROSTANE‐3β,14β‐DIOL

AbstractAusgehend vom Pregnenon (I) wird auf dem in den Formeln wiedergegebenen Weg das Androstandiol (VI) erhalten, das eine Sch1üsselsubstanz zur Herstellung von Digitoxigenin (VII) dargestellt.

A total synthesis of (±)-gibberellin A 12 via methyl (±)-7,16-dioxo-17-norkauran-19-oate

A formal total synthesis of (±)-gibberellin A 12 ( 1) was achieved by employing methyl (±)-7,16-dioxo-17-norkauran-19-oate ( 13) as a relay compound.

Studies on the synthesis of cardiotonic steroids. II. Synthesis of 17 beta-(-3-furyl)-5beta, 14beta-androstane-3beta, 14beta-diol.

17β-(3-Furyl)-5β, 14β-androstane-3β, 14β-diol, a promissing relay compound leading to digitoxigenin, was synthesized starting with 3β-acetoxy-5β-pregn-14-en-20-one.

Cyclization Reactions of 1,2-Bis(2-cyanophenyl)propionitriles. II. Synthesis of 5-amino-4,7-dimethoxy-11H-indeno-[1,2-c]isoquinolin-11-one

Abstract The structure of 5-amino-4,7-dimethoxy-11H-indeno-[1,2-c]isoquinolin-11-one (2) derived by the degradation of the “red pigment” has been confirmed by synthesis. 5,6-Dihydro-4,7-dimethoxy-11H-indeno[1,2-c]isoquinoline-5,11-dione (3) obtained from 2 was used as a relay compound. This was first converted into 2 by chlorination with phosphorus oxychloride and treatment with ammonia. Subsequently 3 was synthesized from 2-(2-carboxy-3-methoxyphenyl)-4-methoxyindane-1,3-dione (13) via 4,7-dimethoxy-11H-indeno[1,2-c]isocoumarin-11-one (12).

Terpenoids. Part XXIX. Chemical conversion of enmein into an important relay compound for its total synthesis

The conversion of enmein (1) into ent-3β,20-epoxy-3-methoxy-17-norkaurane-6α,16α-diol (2), an important relay compond in its total synthesis, is reported.

Terpenoids. Part XXVIII. Total synthesis of enmein

The total synthesis of enmein (1) is reported. The diol acetal, ent-3β,20-epoxy-3-methoxy-17-norkaurane-6α,16α-diol (3) was used as the important relay compound.

The Synthesis of Delphinine: A Stereoselective Total Synthesis of an Optically Active Advanced Relay Compound

A stereoselective total synthesis of the optically active delphinine degradation product 3b is described.

Total synthesis of enmein

A total synthesis of enmein (1) has been accomplished by a transformation of the previously synthesised relay compound (2).

Crystal and Molecular Structure of 2-Bromo-11-ethyl-5,9-dimethoxytetracyclo[5.4.1.14,12•18,11]tetradecan-3-one, C18H27BrO3

The molecular structure of 2-bromo-11-ethyl-5,9-dimethoxytetracyclo[5.4.1.14,12•18,11]tetradecan-3-one, C18H27BrO3, synthesized in an attempt to develop a method of conversion from an advanced relay compound to the alkaloid delphinine, has been determined by the heavy atom method. The compound crystallizes in the monoclinic system, space group P21/c, with unit cell dimensions a = 9.684(9), b = 13.481(15), c = 12.988(14) Å, β = 99.47(7)°, and four molecules in the unit cell. The atomic parameters were refined by block-diagonal least squares using anisotropic thermal parameters. The hydrogen atom positions were established but the parameters were not refined. The final agreement residual for 816 observed reflections is R = 0.044.The stereochemistry of the compound was found to be unsuitable for the delphinine synthesis.

The total synthesis of delphinine: a stereoselective synthesis of an advanced relay compound.

Die stereoselektive Totalsynthese eines Delphininabbauproduktes wird beschrieben. Dieses Produkt, das 5 Ringe und 5 Substituenten besitzt, ist von Delphinin aus leicht zuganglich und kann deshalb als Relais-Verbindung fur die Totalsynthese dieses Alkaloids dienen.