Chapter 25, Problem 31P

Interpretation Introduction

Interpretation:

The suitable reagents for the given transformations in the synthesis of Sabinene from $\text{6-methyl-2,5-heptanedione}$ are to be suggested.

Concept introduction:

The $\text{1,4}$ carbonyl compound having $\text{α-H}$ undergoes intramolecular aldol condensation in the presence of the base like hydroxides gives $\text{β-hydroxy}$ ketone which is on dehydration by heating forms cyclic $\text{α-β}$ unsaturated ketone.

The ketone on reduction with sodium borohydride forms secondary alcohol.

The conversion of alkene to cyclopropane is carried out by reacting the alkene with iodomethylzinc iodide $\left({\text{ICH}}_{\text{2}}\text{ZnI}\right)$ in diethyl ether.

Iodomethylzinc iodide $\left({\text{ICH}}_{\text{2}}\text{ZnI}\right)$ is the organozinc compound prepared by the reaction zinc-copper couple $\text{[Zn(Cu)]}$, with diiodomethane $\left({\text{CH}}_{\text{2}}{\text{I}}_{\text{2}}\right)$ in diethyl ether.

The potassium or sodium dichromate in presence of the strong acid forms chromic acid which is a good oxidizing agent, in hydrous medium oxidizes secondary alcohol to ketone.

The carbon-oxygen double bond can be replaced by carbon-carbon double bond with the help of Wittig reaction using an ylide methylenetriphenylphosphorane.