Carbon Bond-Forming Reactions of Organoboranes

Carbon-Carbon Bond-Forming Reactions of Organoboranes 

The electrophilic center is sometimes generated from the Lewis base by formation of the adduct. 

If the organoborane is heated with carbon monoxide to 100-125°C, all of the groups migrate and a tertiary alcohol is obtained after workup by oxidation. The presence of water 

CHAPTER 9 CARBON-CARBON BOND-FORMING REACTIONS OF COMPOUNDS OF BORON, SILICON, AND TIN 

Another useful reagent for introduction of the carbonyl carbon is dichloromethyl methyl ether. In the presence of a hindered alkoxide base, it is deprotonated and acts as a 

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Examples of these transformations are discussed in Chapter 9, where carbon-carbon bond-forming reactions of organoboranes are covered. 

Carbon-carbon bond forming reactions with organoboranes were developed during the 1970s. Several methods for the synthesis of ,Z-, and Z,Z-dienes, enynes, and diynes emerged during this period (6). An example of the synthesis of ,Z-diene is shown in Figure 16. 

Preparation.—Some of the syntheses of carbinols that were mentioned in earlier Reports and that use organoboranes in carbon-carbon bond-forming reactions (6,157 4, 139 2, 112, ere.) have been surveyed in a published lecture. - A route to some benzylic alcohols from the corresponding phenols that incorporates a Wittig rearrangement (Scheme 1) has been reported. ... 

This landmark discovery paved the way for the development of transition metal-catalyzed hydroboration. The conversion of an alkene into an organoborane intermediate has made this a valuable synthetic technique, particularly since the development of enantioselective variants.9,10 They serve as synthons for numerous functional groups11 and are often subjected to a consecutive carbon-oxygen, carbon-carbon, boron-carbon, boron-chlorine, or carbon-nitrogen24 bond-forming reaction (Scheme 3). 

While die above reactions represent only a small fraction of die reactions known for palladium, they form the basis of a powerful methodology for building carbon structures. Several variations have been developed which utilize certain types of reactants and give particular types of products. All diese variations, however, contain a common theme. In each case an electron-deficient reagent (e.g., a vinyl halide or aromatic triflate) reacts with an election-rich reagent (e.g., an alkene, an organoborane, or an organotin) witii the formation of a new carbon-carbon bond. In that sense diese reactions are related to die reactions between carbon nucleophiles and carbon electrophiles discussed previously in diis chapter. They are quite different, however, because diey proceed only in the presence of Pd(0). In fact they proceed only in die coordination sphere of Pd(0). The ability of Pd(0) to catalyze diese reactions is nearly unique We will now examine some of die more common processes. 

A useful transformation in synthesis is the reaction of an organoborane to form a carbon-carbon bond. One method to achieve this is by addition of carbon monoxide, followed by oxidation, which can be directed to give primary, secondary or tertiary alcohols, aldehydes or ketones under appropriate conditions. On heating, many... 

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