Question

Treatment of cyclohexene with ${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}{\mathbf{CHI}}_{\mathbf{2}}$and Zn(Cu) forms two stereoisomers of molecular formula ${\mathbf{C}}_{\mathbf{13}}{\mathbf{H}}_{\mathbf{16}}$. Draw their structures and explain why two compounds are formed.

Short answer

Answer

Step-by-step solution

Simmons-Smith reaction

The reaction of dihalocarbenes with the alkenes to form halogenated cyclopropanes is called the Simmons-Smith reaction.

Mechanism

The dihalocarbene reacts with the zinc-copper couple to form ${\mathbf{ICH}}_{\mathbf{2}}\mathbf{Znl}$, the Simmons–Smith reagent that is responsible for the transfer of the carbene $\left({\mathrm{CH}}_2\right)$group to the alkene in a stereoselective manner to form cyclopropane.

Products of the given reaction

In the cyclopropane ring, only the carbon attached to the phenyl ring is stereogenic. Hence, the different orientations of the phenyl ring on this carbon give two stereoisomers, i.e., diastereomers.

The structures of the two diastereomers thus formed are shown hereunder.