Boron compounds order systems

In order to explain the chemistry of allylic metals, the reactions of allylic boron compounds [8,12-14] are covered in detail. The boron chemistry is divided into four parts simple enantioselectivity (addition of CH2=CHCH2-, creating one new stereocenter), simple diastereoselectivity of crotyl additions (relative configuration after CH3CH=CHCH2- addition, where neither reagent is chiral), single asymmetric induction with chiral allyl boron compounds (one and two new stereocenters), and double asymmetric induction (both reactants chiral, one and two new stereocenters). Then follows a brief discussion of other allyl metal systems. 

Borazarophenanthrene was the first representative of a new class of heteroaromatic compounds containing boron atoms in six-membered aromatic rings.4 These compounds are of a different order of stability from previously known types of organoboron compounds, being chemically similar to normal aromatics, and their discovery has opened up a new field of aromatic chemistry. The procedure indicated here has been used to prepare a large number of related aromatic systems. 

All criteria of reactivity work well for even AH s, in which the it electrons are evenly distributed, owing to the fortuitous correlations that have been pointed out above. In order to get a real test of their empirical effectiveness, one should choose some compound in which the it electrons are very evenly distributed. Recently44 a whole new range of aromatic compounds have become available containing boron over twenty ring-systems of this kind have now been prepared. These compounds... 

The names borazole, boroxole and borthiole, respectively, for the three compounds in Examples 4, 5 and 6 have been abandoned long ago as they imply five-membered rings in the Hantzsch-Widman system. The names borazin(e), boroxin and borthiin indicate six-membered rings with unsaturation and only one boron atom and one other heteroatom (although the order of the element name stems is wrong) and are also not acceptable. 

In ternary systems of rare earths, cobalt and boron, quite a number of different ternary compounds are formed having a crystal structure related to the well-known CaCu5-type observed for RCo5 compounds. The sequence of structures obtained from GdCo5 by an ordered substitution of B atoms in some of the Co sites is shown in fig. 7. 

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