Consider the following reaction sequence: Reagents: (i) BuLi (ii) 0.5 equivalent Br - CH ₂- CH ₂- Br (iii) Dil. H ₂ SO ₄ (iv) OH ^- / Identify the major product formed.

Step-by-step solution

The starting material is 2-ethyl-1,3-dithiane. Treatment with BuLi, a strong base, abstracts the acidic proton at the C2 position (between the two sulfur atoms), forming a dithiane carbanion. Reaction with 0.5 equivalents of 1,2-dibromoethane ( Br - CH ₂- CH ₂- Br ) leads to the alkylation of two dithiane anions. Each anion displaces a bromide ion, forming a bridged intermediate: 1,2-bis(2-ethyl-1,3-dithian-2-yl)ethane. Hydrolysis with dilute H ₂ SO ₄ deprotects the dithiane groups, converting them back to carbonyl