Question

Draw a stepwise mechanism for the following reaction.

Short answer

Answer

Mechanism

Step-by-step solution

Substrates of the Simmons-Smith reaction

The substrates of the Simmons-Smith reaction include a dihalocarbene and an alkene.

Mechanism of the Simmons-Smith reaction

The dihalocarbene reacts with the zinc-copper couple to form the Simmons-Smith reagent, i.e., ${\mathbf{XCH}}_{\mathbf{2}}\mathbf{ZnX}$, which transfers the CH₂ group to the alkene. Both C=C carbons join the CH₂ group to form a cyclopropane.

Mechanism of the given reaction

The Zn-Cu couple reacts with the carbon-containing two bromide groups and forms on the dihalo center of the ring. The Simmons-Smith reagent thus attacks the double bond in the ring to form a cyclopropane ring.

The mechanism of the given reaction is shown below.

Mechanism