Chapter 11, Problem 11PP

Interpretation Introduction

Interpretation: To identify reagents that can be used to achieve each of the following transformations.

Concept Introduction:

$2,3-\text{dimethyl}-\text{but}-1-\text{ene}$ is a substituted alkene that is subjected to a variety of reactions such as bromination, oxidation, hydroboration-oxidation, etc. These reactions require the appropriate reagents and reaction conditions for the correct formation of the desired product. The use of suitable reagents for these reactions is of utmost importance.

Answer to Problem 11PP

Explanation of Solution

$2,3-\text{dimethyl}-\text{but}-1-\text{ene}$ undergoes a variety of reactions, which have been explained below.

• Hydroboration-oxidation of alkenes by ${\text{BH}}_{\text{3}}{\text{·THF/H}}_{\text{2}}{\text{O}}_{\text{2}}\text{/NaOH}$ produces fewer substituted alcohols.
• Treatment with $\text{HBr/ROOR}$ gives a less substituted bromo product.
• Dihydroxylation of alkenes by $\text{cat}{\text{.OsO}}_{\text{4}}\text{/NMO}$ produces cis diols.
• Halohydrin formation occurs in presence of ${\text{Br}}_{\text{2}}{\text{/H}}_{\text{2}}\text{O}$ in “anti” stereochemistry only.
• Treatment of alkenes with bromine $\left({\text{Br}}_{\text{2}}\right)$ gives vicinal dibromides.
• When treated with aqueous acid like ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ , alkenes form alcohols. The proton provided by the acid combines with to form ${\text{H}}_{\text{3}}{\text{O}}^{+}$ and thus reacts to form a more stable carbocation intermediate.
• Tert-butoxide can be used to form the “less substituted” alkenes in elimination reactions (using ${\text{E}}_{\text{2}}$, specifically).
• Alkene hydrogenation is the syn-addition of hydrogen to an alkene, saturating the bond, giving alkane.

Conclusion

The mentioned reagents can be used to achieve each of the transformations shown above. The reactions are addition reactions most of the time.