The chemistry of binuclear palladium(II) and platinum(II) complexes

Multiple stereoselectivity and its application in organic synthesis

The catalytic hydrogenation of the LOHC compound dibenzyltoluene (H0-DBT) was investigated by 1H NMR spectroscopy in order to elucidate the reaction pathway of its charging process with hydrogen in the context of future hydrogen storage applications. Five different reaction pathways during H0-DBT hydrogenation were considered including middle-ring preference (middle-side-side, MSS), side-middle-side order of hydrogenation (SMS), side-ring preference (SSM), simultaneous hydrogenation of all three rings without intermediate formation and statistical hydrogenation without any ring preference. Detailed analysis of the 1H NMR spectra of the H0-DBT hydrogenation over time revealed that the reaction proceeds with a very high preference for the SSM order at temperatures between 120 °C and 200 °C and 50 bar in the presence of a Ru/Al2O3-catalyst. HPLC analysis supported this interpretation by confirming an accumulation of H12-DBT species prior to full hydrogenation to H18-DBT with middle ring hydrogenation as the final step.

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Hydrogenation of the liquid organic hydrogen carrier compound dibenzyltoluene – reaction pathway determination by 1H NMR spectroscopy

Strobilurins from fungi are the inspiration for the creation of the β-methoxyacrylate class of agricultural fungicides However, molecular details of the biosynthesis of strobilurins have remained cryptic Here we report the sequence of genomes of two fungi that produce strobilurins and show that each contains a biosynthetic gene cluster, which encodes a highly reducing polyketide synthase with very unusual C-terminal hydrolase and methyltransferase domains Expression of stpks1 in Aspergillus oryzae leads to the production of prestrobilurin A when the fermentation is supplemented with a benzoyl coenzyme A (CoA) analogue This enables the discovery of a previously unobserved route to benzoyl CoA Reconstruction of the gene cluster in A oryzae leads to the formation of prestrobilurin A, and addition of the gene str9 encoding an FAD-dependent oxygenase leads to the key oxidative rearrangement responsible for the creation of the β-methoxyacrylate toxophore Finally, two methyltransferases are required to complete the synthesis

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Strobilurin biosynthesis in Basidiomycete fungi

In recent years there has been what could be described as a renaissance in the redistribution reaction, and the growing interest in the chemistry of the metalloids has been partially responsible for this renewed interest. The generality and potential synthetic utility of this reaction in the chemistry of silicon, germanium, tin, boron, and phosphorus has necessitated a better understanding of this type of chemical transformation. With the advancement of modern computation and instrumental analytical techniques, this need is slowly being realized. Of the above mentioned elements, the chemistry of silicon has probably been the most intensely studied during recent years and, thus, it is not surprising that the chemistry of silicon provides the most comprehensive picture of the redistribution reaction. The redistribution reaction has been the subject of recent reviews by Moedritzer'\" and by Lockhart3 which cover quite comprehensively the general application of this reaction to silicon chemistry. In this current brief review, we shall confine our attention to the simplest form of this reaction; namely, that involving the redistribution of monodentate ligands about a central silicon atom.

Redistribution reactions in the chemistry of silicon

Known synthetic precursors of strobilurins A and X, i.e., methyl (3Z,5E)-6-aryl-3-methylhexa-3,5-dienoates (aryl is phenyl, 4-methoxyphenyl), were synthesized by highly stereospecific reactions from 2-(2-tert-butyldimethylsilyloxyethyl)- and 2-[2-(4-methoxybenzyloxy)-ethyl]-5-arylpenta-2E,4E-dien-1-ols. These dienols were efficiently dehydroxylated to (1E,3Z)-4-methyl-6-(4-methoxybenzyloxy)hexa-1,3-dienylarenes with their subsequent demethoxyben-zylation to (3Z,5E)-6-aryl-3-methylhexa-3,5-dien-1-ols. The latter through the step of corresponding aryldienals and aryldienoic acids were transformed to the target methyl (3Z,5E)-6-aryl-3-methylhexa-3,5-dienoates, which completes a formal synthesis of strobilurins A and X. Configuration of the C=C bonds of the conjugated aryldiene system is preserved in the considered transformations by 95–97%.

Formal synthesis of strobilurins A and X

When PdCl2 is reduced by hydrogen in the presence of S-(-)-α-phenylethylamine in chloroform, zero-valent complexes of Pd with S-(-)-α-phenylethylamine are formed. These are enantioselective catalysts for the reductive aminolysis of the azlactones of dehydroacyl-aminoacids.

Asymmetric aminoacid synthesis by catalytic reduction of azlactones of substituted acylaminoacrylic acids Communication 17. Reaction of PdCl2 with S-(-)-α-phenylmethylamine under reducing conditions

1.

With the aid of infrared spectra the structure of the fundamental structural unit was established for catalyticpolycondensation products obtained from α,ω-bistrimethylsilylalkanes and also for polymers obtained by the thermal polymerization of 1,1-dimethylsilacyclobutane and the catalytic polymerization of 1,1-dimethylsilacyclopentane.




2.

Under the action of aluminum halides, p-bis(trimethylsilylmethyl)benzene and p-bistrimethylsilylbenzene react with liberation of tetramethylsilane and formation of sila-hydrocarbon condensation products. The latter contain alternations of silicon atoms and p-phenylenedimethylene or p-phenylene fragments in the chain.

Organosilicon compounds having hydrocarbon bridges between silicon atoms

Quantum-chemical calculations of model systems, namely, benzaldehyde and its 1 : 1 and 1 : 2 complexes with AlCl3, were carried out by the MNDO method. In the 1 : 2 complex, a bridging Al-Cl-Al bond occurs. Apparently, this complex is stabilized through the Coulomb interaction between the positively charged C atom of the carbonyl group and the AlCl3 fragment, which carries an excessive negative charge and which is not involved in donor-acceptor bonding with the carbonyl O atom. The IR spectra of the 1 : 1 and 1 : 2 complexes of benzophenone with AlBr3 were recorded, and the differences in the low-frequency regions of these spectra, which are indicative of the presence of the Br2Al-Br-AlBr3 fragment in the 1 : 2 complex, are discussed.

Quantum-chemical and spectroscopic studies of structures of 1 : 2 complexes of carbonyl compounds with aluminum halides

1.

Some 4- and 5-hydroxyketones were synthesized by the free-radical addition of alcohols toα,β-unsaturated ketones.




2.

According to the data of the IR spectra, the 4-hydroxyketones exist in both the open and cyclic (hemiacetal) forms. The amount of the open form increases with increase in the steric hindrance in the cyclization step. The 5-hydroxyketones exist only in the open form.

E. D. Lubuzh

Papers

Formal synthesis of strobilurins A and X

Asymmetric aminoacid synthesis by catalytic reduction of azlactones of substituted acylaminoacrylic acids Communication 17. Reaction of PdCl2 with S-(-)-α-phenylmethylamine under reducing conditions

Organosilicon compounds having hydrocarbon bridges between silicon atoms

Quantum-chemical and spectroscopic studies of structures of 1 : 2 complexes of carbonyl compounds with aluminum halides

Free-radical addition of alcohols toα, β-unsaturated ketones and tautomerism of formed 4-hydroxyketones