Question

What is the final product of the reaction ?
$(C{H}_3{)}_{2}C=CHC{H}_{2}C{H}_3\underset{\left(ii\right)H_2{O}_2/O{H}^{-}}{\overset{\left(i\right)B{H}_{3}THF}{\to }}$ $\underset{PCC}{\overset{C{H}_{2}C{l}_2}{\to }}\underset{\left(ii\right)H_3{O}^{+}}{\overset{\left(i\right)C{H}_{3}MgBr}{\to }}$

• A. $2,3$-dimethyl-$3-$pentanol
• B. $2,4$-dimethyl-$3-$pentanol
• C. $2,3$-dimethyl-$2-$pentanol
• D. $2,2$-dimethyl-$3-$pentanol

Answer 1

Answer: (A)

$2,3$-dimethyl-$3-$pentanol

Step 1 - Hydroboration-oxidation transforms alkenes into alcohols. It performs the net addition of water across an alkene.

The reaction begins with the concerted syn addition of $B$ and $H$ across the double bond, with the boron adding to the less substituted carbon. In the second step, hydrogen peroxide and a base such as $O{H}^{-}$ are added. the $O{H}^{-}$ deprotonates the hydrogen peroxide which makes the conjugate base of hydrogen peroxide (a better nucleophile than $H_2{O}_2$ itself). The resulting $NaOH$ then attacks the boron.

Step 2- PCC is a milder version of chromic acid. Essentially, what it does is oxidize alcohols from primary alcohols to aldehydes and from secondary alcohols to ketones.

Step 3 - The Grignard reagent adds across the carbon-oxygen double bond and alcohol forms as a final product.