Let's analyze the transformation: **Starting material:** Acetophenone (C₆H₅COCH₃) **Product:** 2-Phenylfuran-2(5H)-one (a γ-lactone fused with a benzene ring at the 2-position) This transformation is a classic example of the **intramolecular haloform-type reaction** known as the **α-halo ketone → furanone cyclization**. Here’s a stepwise synthesis and mechanism: --- ## **Step 1: α-Bromination of Acetophenone** **Reagents:** Br₂, AcOH (acetic acid) or Br₂, CCl₄ **Mechanism:** - The enol form of acetophenone reacts with bromine, leading to bromination at the α-position. **Product:** Phenacyl bromide (C₆H₅COCH₂Br) --- ## **Step 2: Nucleophilic Substitution with Base and Cyclization** **Reagents:** NaOH (aqueous), gentle heating **Mechanism:** 1. **Nucleophilic attack:** The base (OH⁻) abstracts a proton from the methyl group adjacent to the carbonyl, forming an enolate. 2. **Intramolecular cyclization:** The enolate oxygen attacks the α-bromo carbon, resulting in the formation of a five-membered ring (lactone) and loss of Br⁻. 3. **Protonation:** The newly formed alkoxide is protonated by water, generating the neutral lactone. --- ## **Detailed Mechanism** ### **Step 1: α-Bromination** ```markdown Br₂ C₆H₅COCH₃ ——→ C₆H₅COCH₂Br ``` ### **Step 2: Base-Induced Cyclization (Furanone formation)** ```markdown 1. NaOH (aq) C₆H₅COCH₂Br ———————→ γ-lactone (2-phenylfuran-2(5H)-one) ``` #### **Reaction mechanism:** 1. **Enolate Formation:** - OH⁻ abstracts a proton from the methylene group (–CH₂Br), generating an enolate. 2. **Intramolecular Nucleophilic Substitution:** - The enolate's oxygen attacks the carbon bearing Br, displacing Br⁻ and forming the 5-membered lactone ring. 3. **Protonation:** - The alkoxide formed is protonated by water, producing the neutral lactone. --- ### **Overall Reaction Scheme:** ```markdown Step 1: α-bromination C₆H₅COCH₃ + Br₂ → C₆H₅COCH₂Br + HBr Step 2: Cyclization C₆H₅COCH₂Br + NaOH → 2-Phenylfuran-2(5H)-one + NaBr + H₂O ``` --- ## **Summary Table:** | Step | Reagent(s) | Transformation | |----------------|-----------------|------------------------------------------| | 1. α-Bromination | Br₂, AcOH | Acetophenone → Phenacyl Bromide | | 2. Cyclization | NaOH (aq), heat | Phenacyl Bromide → 2-Phenylfuran-2(5H)-one | --- ## **Full Mechanism Illustration:** 1. **Enolization and Bromination** 2. **Enolate formation** 3. **Nucleophilic cyclization** 4. **Loss of Br⁻ and protonation** --- If you need the **detailed arrow-pushing mechanism**, let me know and I can sketch it out step-by-step!