Compound natural oligomeric

Conclusion As expected, the double cyclisation of bicyclo-phosphanes induces a strong ring constraint. The marked tendency of these compounds to oligomerization by rupture of the P-0 bond is certainly favoured because it minimizes this tension. The driving force of the addition reaction of X-H molecules is the great stability of the bicyjJjphosphorane structure. Depending upon the nature of X, the P tautomer forms of the last compounds could be observed or not. 

As natural products chemists detect and investigate more and more complex structures, additional limitations of current NMR spectroscopic approaches have become apparent. Examples for compound classes that pose great difficulty for NMR spectroscopists include compounds with ill-defined conformations, natural products that occur as large families of structurally similar compounds, or oligomeric compounds whose... 

The chemistry of these compounds reflects the unsaturated nature of the B—N triple bond. Polar compounds add to iminoboranes, provided the addition proceeds more rapidly than oligomerization of R SIR ( ). For example, for R = R = CH(CH3)2 or /-C H. ... 

Some six hundred structures of naturally occurring carbogenic molecules appe on the pages which follow, together with the name of each compound and references to the original literature of successful chemical synthesis. Thus, Part Three of this book is effectively a key to the literature of chemical synthesis as applied to the complex molecules of nature. The survey does not include oligomeric or polymeric structures, such as peptides, proteins, carbohydrates and polynucleotides, which fall outside the scope of this book because they can be assembled by repetitive procedures. 

There have been several efforts geared toward reducing the oligomeric nature of the group 2 metallocene compounds. Reduction of the nuclearity has been accomplished via the use of sterically demanding cyclopentadienides and intermolecular Lewis bases (38-40). Hanusa and Williams have used bidentate amines to coordinatively saturate... 

The N-2, N-4 bridging coordination mode has not (yet) been observed in Fe(II) spin crossover compounds, whereas the N-l, N-2 bridging mode has been confirmed by X-ray structure determinations of oligomeric and polymeric Fe(II) spin crossover materials. Depending on the nature of the substituted 1,2,4-triazole ligand and the presence of potentially coordinating an-... 

Peroxidases have been used very frequently during the last ten years as biocatalysts in asymmetric synthesis. The transformation of a broad spectrum of substrates by these enzymes leads to valuable compounds for the asymmetric synthesis of natural products and biologically active molecules. Peroxidases catalyze regioselective hydroxylation of phenols and halogenation of olefins. Furthermore, they catalyze the epoxidation of olefins and the sulfoxidation of alkyl aryl sulfides in high enantioselectivities, as well as the asymmetric reduction of racemic hydroperoxides. The less selective oxidative coupHng of various phenols and aromatic amines by peroxidases provides a convenient access to dimeric, oligomeric and polymeric products for industrial applications. 

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