Chapter 21, Problem 21.78P

Interpretation Introduction

(a)

Interpretation: An explanation for the use of ${\text{NaBH}}_{\text{4}}$ in ${\text{CH}}_{\text{3}}\text{OH}$ to reduce hemiacetal A into $\text{butane-1, 4-diol}\left({\text{OHCH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}\right)$ is to be stated.

Concept introduction: The hydride reduction or the nucleophilic addition of carbanions to carbonyl compounds (aldehyde/ketone), both involve two-step mechanism that is nucleophilic attack of hydride ion or carbanion followed by protonation.

Interpretation Introduction

(b)

Interpretation: The product formed from the treatment of A with ${\text{Ph}}_{\text{3}}\text{P}={\text{CHCH}}_{\text{2}}\text{CH}{\left({\text{CH}}_{\text{3}}\right)}_{\text{2}}$ is to be predicted.

Concept introduction: The Wittig reaction utilizes carbon nucleophile from the Wittig reagent to yield alkenes. When a hemiacetal is treated with a Wittig reagent, the $\text{C}-\text{OR}$ bond is cleaved, and the $\text{C}-\text{OH}$ bond is replaced by $\text{C}=\text{C}$, with by-product triphenylphosphine oxide $\left({\text{Ph}}_{\text{3}}\text{P}=\text{O}\right)$.

Interpretation Introduction

(c)

Interpretation: The structure of the isotretinoin, obtained from the reaction of X and Y is to be drawn.

Concept introduction: The Wittig reaction utilizes carbon nucleophile from the Wittig reagent to yield alkenes. When a carbonyl compound is treated with a Wittig reagent, the $\text{C}=\text{O}$ bond of carbonyl is replaced by $\text{C}=\text{C}$, with by-product triphenylphosphine oxide $\left({\text{Ph}}_{\text{3}}\text{P}=\text{O}\right)$.