Problematic boron derivatives

Palladium-mediated catalysis has only been exploited relatively recently in the synthesis of substituted PPV derivatives. The use of aryl dibromides as monomers is particularly useful as it allows the synthesis of PPVs substituted with alkyl rather than alkoxy sidechains. The Suzuki [53, 54], Heck [55], and Stille [56] reactions have been used in the synthesis of new PPV derivatives, but attaining high molecular weight PPV derivatives by these methodologies has proved problematic. A phenyl-subslilutcd PPV material PPPV 31 was synthesized by a Suzuki coupling (Scheme 1-10) of dibromoethene and fo/.v-boronic acid 30. Its absorption (2ni ix=385 nm) and emission (2max=475 nm) maxima were strongly... 

Dodecahydro-do50-dodecaborate anion [B,2H,2] , the isoelectronic and isostructural analog of carboranes, is a typical representative of anionic polyhedral boron hydrides. Sodium salts of the parent cZo o-dodecaborate and their derivatives have a good solubility in water, which is an important precondition of many medical applications. The sodium salt Na2[Bj2Hj2] was found to be practically nontoxic with the approximate lethal dose for rats >7.5 g/kg of body weight, which is roughly comparable with that of sodium chloride [12], However, functionalization of this purely inorganic system till recently was problematic due to the absence of a clear reaction center. There are two... 

The generation of cis-boron enolates from ketones with dialkylboron chlorides and hindered tertiary amines had been known for some time, from the work of Mukaiyama and Evans [13, 48, 87]. However, the synthesis of the corresponding trans-boron enolates remained problematic. Brown addressed this issue, reporting enolization conditions that provide access to either eno-late diastereomer [88]. The stereochemical outcome of ketone enolization was shown to be dependent both on the electronegative group on boron and on the nature of the alkyl substituents. In this regard, the combination of bulky boron ligands (cyclohexyl), a boron chloride derivative, and an unhindered base (EtjN) proved optimal for the stereoselective synthesis of trans-enolates (166) from a variety of ketones (Scheme 4.16). 

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