1. 1 Zinc atom comes in and inserts itself between Carbon and Bromine

.

2. Another Zine atom comes in and inserts itself between the other Carbom-Bromine bond.

3. Titanium tetrachloride comes in and displaces one of the ZnBr groups.

4. Now the remaining ZnBr group on thecompleted reagent comes in and attacks the aldehide on molecule 41.

5. Lastly the molecule unergoes an intramolecular reaction to remove BrZnO and Titanium (III) chloride to form a carbon double bond.