Alkenylboranes cleavage

For some functionalized alkenylboranes, cleavage with methanol may be preferable to cleavage with a carboxylic acid. Relatively unhindered alkenyldialkylboranes, such as 9-alkenyl-9-BBNs, are readily cleaved by 1 equiv. of methanol under gentle heating. More hindered derivatives may require catalysis by 2,2-dimethylpropanoic acid, but these mild, almost neutral conditions may be beneficial for acid-labile functionalities. For example, methanolysis has been used for production of enol ethers e.g. equation 61). ... 

For regiodefined alkenylboranes, cleavage of the vinylic carbon-boron bond with deuterioacetic acid provides a simple, stereospecific preparation of deuterium-substituted alkenes. ... 

Protonolysis of alkenylboranes by carboxylic acids occurs readily. The stereochemistry of the alkenyl group is retained during the reaction and so hydroboration/protolytic cleavage of alkynes leads to cis alkenes. Deuterated... 

RB(0H)2 to RH) which is accelerated by the presence of bases, adjacent heteroatoms and orf/io-substituents. 2-Pyridyl-, 2,6-dimethoxy-, and 2-formyl ben-zeneboronic acids, and 1-trimethylsilyl-l-alkenylboranes are sensitive to such hydrolytic B-C bond cleavage 198,99]. 

Treatment of alkenylboranes with carboxylic acids at room temperature or, in the case of more hindered alkenylboranes, with hot propanoic acid results in the selective cleavage of the vinylic B-C bond with retention of configuration ... 

The cleavage of alkenylboranes may be carried out under non-acidic conditions by converting the alkenylborane into the ate complex with n-BuLi prior to hydrolysis with aqueous NaOH. " Also, alkenylboranes derived from internal alkynes may be protonated under neutral conditions using catalytic amounts of Pd(0Ac)2 in THF or acetoneor with aqueous silver ammonium nitrate [Ag(NH3)2 N03]. ... 

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