Functional groups, versatility organoboranes

Another method for preparing functional Ziegler-Natta polymers is to use an organoborane mediated synthesis. This method has been extensively studied and reviewed by Chung . The success of this technique results from these factors (a) trialkyl boranes are Lewis acids, which are stable to Z-N catalysts, (b) they are soluble in Z-N (hydrocarbon) solvents, (c) they are remarkably versatile synthons for a variety of functional groups. In this case, borane functional alpha olefin monomers (31) are polymerized to polyboranes which can be hydrolyzed to a variety of functional groups. 

These versatile reactions, commonly referred to as Stille and Suzuki couplings, respectively, are performed with organostannanes or organoboranes as nucleophiles and are tolerant to most functional groups. Ketones are obtained if carbon monoxide is present in the Stille reaction. This gives the possibility to label an aromatic methyl ketone in two different positions by the use of either [ C] carbon monoxide or [ C] methyl iodide, as shown in O Fig. 41.22 (Andersson et al. 1995 Andersson and Langstrom 1995a, b). 

The Suzuki reaction is palladium-catalyzed coupling of organic halides or tri-flates with organoboranes under basic conditions. The organic halides and tri-flates react in the order of 1 > Br > OTf Cl. The reaction provides a highly versatile procedure for the construction of new carbon-carbon bond that tolerates many functional groups [1]. 

The versatility of organoboranes was explored during the early years of hydroboration chemistry. Conversions to several classes of functional groups, such as alcohols, amines, ketones, alkenes, acetylenes, dienes, enynes, etc. were achieved with ease. 

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