Synthesis of Organoboranes

The most widely used route to organoboranes is hydroboration, which was discussed in Section 4.9.1. Hydroboration provides access to both alkyl- and alkenylboranes. Aryl-, 

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

These reactions occur by oxidative addition at copper, followed by decomposition of the Cu(III) intermediate. 

Two successive reactions with different organocuprates can convert thexylborane to an unsymmetrical trialkylborane.  

and allyl derivatives of boron can be prepared directly from the corresponding halides, BF3, and magnesium metal. This process presumably involves in situ generation of a Grignard reagent, which then displaces fluoride from boron.  

Borane, BH3, is an avid electron pair acceptor because only a sextet of valence electrons is present at boron in the monomeric molecule. The pure material exists as a dimer. In aprotic solvents which act as electron pair donors such as ethers, tertiary amines, and sulfides, diborane forms stable Lewis acid-Lewis base 

Diborane can be generated in situ from sodium borohydride and boron trifluoride. Solutions in tetrahydrofuran are commercially available. An alternative commercially available reagent is the borane-dimethyl sulfide complex  

It is more amenable to storage over extended periods than diborane and exhibits comparable reactivity toward alkenes. 

Organic Synthesis via Boranes, John Wiley and Sons, New York (1975). 

CHAPTER 4 ELECTROPHILIC ADDITIONS TO CARBON-CARBON MULTIPLE BONDS 

The most widely used route to organoboranes is hydroboration, introduced in Section 4.5.1, which provides access to both alkyl- and alkenylboranes. Aryl-, methyl-, allylic, and benzylboranes cannot be prepared by hydroboration, and the most general route to these organoboranes is by reaction of an organometallic compound with a halo- or alkoxyboron derivative.1 

Alkoxy groups can be displaced from boron by alkyl- or aryllithium reagents. The reaction of diisopropoxy boranes with an organolithium reagent, for example, provides good yields of unsymmetrically disubstituted isopropoxyboranes.3 

Organoboranes can also be made using organocopper reagents. One route to methyl and aryl derivatives is by reaction of a dialkylborane, such as 9-BBN, with a cuprate reagent.4 

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In the following, the concept of micro modular process engineering is introduced together with the backbone interface developed in order to realize this modular approach. The integration of sensors and an electronic bus system is also described, and the physical characterization of the backbone is discussed within a case study of the enantioselective synthesis of organoboranes. Within the second case study, the sulfonation of toluene with gaseous sulfur tri oxide, the backbone system together with the micro structured devices used is finally assessed based on its application to chemical synthesis. 

Transmetallation reactions represent an important method for the synthesis of organoboranes. Organometallic... 

Haloboration Reactions. The haloboration of carbon-carbon triple bonds provides another entry point for the synthesis of organoboranes. A wide variety of haloboranes including BBrs, 9-BBN-Br, and 9-BBN-l has been found to react with terminal alkynes to produce (Z)-2-halo-l-aIkenylboranes. The reaction occurs in a stereo-, regio-, and chemoselective fashion specifically with terminal alkynes and has been used to synthesize numerous substituted olefins and related compounds. Diboration reactions of alkynes with B2CI4 are also well known. However, more convenient transition-metal-catalyzed procedures with the less reactive aUcoxy substituted diboranes B2(OR)4 have recently been developed. 

The in situ synthesis of organoboranes via reaction of alkyl halides with magnesium in the presence of diborane can also be used to prepare coupled products (equations 20 and 21). Oxidation of the reaction mixture with alkaline silver nitrate leads to good yields of dimeric products. The reaction is successful for primary and secondary halides. A related reaction is the coupling of secondary alkyl halides in the presence of catalytic quantities of thallium salts. This procedure fails for primary alkyl halides and gives modest yields for secondary alkyl halides (equation 22). 

E Jakle, Advances in the synthesis of organoborane polymers for optical, electronic, and sensory apphcations. Chemical Reviews, 2010. 110(7) p. 3985-4022. 

F. Sato, S. Haga, and M. Sato. Synthesis of organoboranes via organoaluminums. A convenient route to trialkenylboranes from non-conjugated diolefins. Chem. Letters, 1978, 999. 

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