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Hydroboration–oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less-substituted carbon. The reaction thus provides a more stereospecific and complementary regiochemical alternative to other hydration reactions such as acid-catalyzed addition and the oxymercuration–reduction process.
Hydroboration of trisubstituted alkenes places boron on the less substituted carbon. [8] Hydroboration of 1,2-disubstituted alkenes, such as a cis or trans olefin, produces generally a mixture of the two organoboranes of comparable amounts, even if the steric properties of the substituents are very different. For such 1,2-disubstituted olefins ...
One example of an isolable (bulky) primary borane is thexylborane (ThxBH 2), produced by the hydroboration of tetramethylethylene: [6] A chiral example is monoisopinocampheylborane, obtained by hydroboration of (−)‐α‐pinene with borane dimethyl sulfide. Although often written as IpcBH 2, it is a dimer, [IpcBH 2] 2. [7]
9-Borabicyclo[3.3.1]nonane or 9-BBN is an organoborane compound. This colourless solid is used in organic chemistry as a hydroboration reagent.The compound exists as a hydride-bridged dimer, which easily cleaves in the presence of reducible substrates.
Disiamylborane is prepared by hydroboration of trimethylethylene with diborane. [1] The reaction stops at the secondary borane due to steric hindrance. Disiamylborane is relatively selective for terminal alkynes and alkenes vs internal alkynes and alkenes. Like most hydroboration, the addition proceeds in an anti-Markovnikov manner. [1]
Catalyzed hydroboration-oxidation of substituted alkenes can be rendered enantioselective. In 1990, Brown and co-workers achieved asymmetric hydroboration using an achiral catalyst and chiral borane sources derived from ephedrine and pseudoephedrine. In most cases, the regioselectivity was poor although the ee values can be close to 90%. [16]
Diisopinocampheylborane was originally prepared by hydroboration of excess α-pinene with borane, [2] but it is now more commonly generated from borane-methyl sulfide (BMS). [ 3 ] The compound can be isolated as a solid, but because it is quite sensitive to water and air, it is often generated in situ and used as a solution.
In organic chemistry, syn-and anti-addition are different ways in which substituent molecules can be added to an alkene (R 2 C=CR 2) or alkyne (RC≡CR).The concepts of syn and anti addition are used to characterize the different reactions of organic chemistry by reflecting the stereochemistry of the products in a reaction.