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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.
Regiospecific hydroboration with borane Hydroboration-oxidation of (E)-prop-1-en-1-ylbenzene Hydroboration-oxidation of 1-methyl-cyclohex-1-ene The net reaction is hydration. Because the addition of H-B to olefins is stereospecific, this oxidation reaction will be diastereoselective when the alkene is trisubstituted. [ 10 ]
One example is thexylborane (ThxBH 2), produced by the hydroboration of tetramethylethylene: [6] A chiral example is monoisopinocampheylborane. Although often written as IpcBH 2, it is a dimer [IpcBH 2] 2. It is obtained by hydroboration of (−)‐α‐pinene with borane dimethyl sulfide. [7] Dialkylboranes are also rare for small alkyl groups.
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]
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.
In the hydroboration reaction, diborane also reacts readily with alkenes to form trialkylboranes. This reaction pattern is rather general and the resulting alkyl borates can be readily derivatized, e.g. to alcohols. Although early work on hydroboration relied on diborane, it has been replaced by borane dimethylsulfide, which is more safely handled.
Simple protodeboronation scheme. Protodeboronation, or protodeborylation is a chemical reaction involving the protonolysis of a boronic acid (or other organoborane compound) in which a carbon-boron bond is broken and replaced with a carbon-hydrogen bond.
The complex is commercially available but can also be generated by the dissolution of diborane in THF. Alternatively, it can be prepared by the oxidation of sodium borohydride with iodine in THF. [2] The complex can reduce carboxylic acids to alcohols and is a common route for the reduction of amino acids to amino alcohols [3] (e.g. valinol).