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show the reaction machinism where a hydroboration-oxidation reaction is carried out for the synthesis for 2-methyl-2-butene

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The hydroboration-oxidation reaction is a two-step process that can be used to convert alkenes into alcohols. Here, I'll outline the reaction mechanism for synthesizing 2-methyl-2-butene via hydroboration-oxidation. However, note that hydroboration-oxidation typically leads to alcohols, and directly synthesizing 2-methyl-2-butene usually involves other methods (such as elimination reactions after the formation of a more stable alcohol).

Instead, we might consider starting with an appropriate alkene and then going through the hydroboration-oxidation steps.

  1. Hydroboration Step:

    • Start with an alkene that has the correct substitution pattern (in this case, we will look into the possibility of obtaining an intermediate which can be transformed later).
    • The reagent used for hydroboration is usually BH₃ (Borane), which can complex with the alkene.
    • Mechanism: 
      CH3-CH=CH-CH3 + BH3 → CH3-CH(⁻)–B(⁴)–H3
    • The boron atom attaches to the less substituted carbon of the double bond due to steric and electronic factors (anti-Markovnikov addition).

  2. Oxidation Step:

    • After hydroboration, the organoborane intermediate is oxidized with hydrogen peroxide (H₂O₂) in the presence of a base (most commonly NaOH).
    • Mechanism: 
      CH3-CH(⁻)–B(⁴)–H3 + H2O2 + OH⁻ → CH3-CH(OH)–B(⁴)–O + BH4⁻   (intermediate)
    • The resulting boron compound will lead to the formation of the alcohol: 
      CH3-CH(OH)–CH2-CH3 + B(OH)4

  3. Formation of 2-Methyl-2-Butene:

    • To finally convert 2-methyl-2-butanol to 2-methyl-2-butene, a dehydration step is conducted. This usually involves heating with an acid catalyst or simply applying heat to eliminate water from the alcohol, giving the alkene.
    • Reaction: 
      CH3-C(OH)(CH3)-CH2-CH3 → CH3-C(CH3)=CH-CH3 + H2O

In summary, the pathway from an appropriate starting material to 2-methyl-2-butene would involve the steps of hydroboration (to add the boron atom to the less substituted side), oxidation (to convert the B-alkane to an alcohol), and finally dehydration to yield the alkene.

It's important to note that while hydroboration-oxidation typically produces alcohols, the transformation into 2-methyl-2-butene requires an additional elimination step, as summarized here.