1. γ-Butyrolactone (7.7 mL, 0.1 mol) was added one time under stirring conditions to a mixed solution containing thionyl chloride (8 mL, 0.11 mol) and anhydrous zinc chloride (0.6 g, 4.4 mmol).
2. The reaction mixture was heated at 55 °C with continuous stirring for 12 hours.
3. Upon completion of the reaction, the reaction product was purified by fractional distillation at a pressure of 15-30 mmHg, and fractions with boiling points in the range of 110-125 °C were collected to afford the intermediate 4-chlorobutanoyl chloride (10.4 g, 74 mmol, 74% yield).
4. The resulting intermediate 4-chlorobutanoyl chloride was slowly (over 15 min) added dropwise to a mixed solution of pyridine (6 mL, 74 mmol) and tert-butanol (8.75 mL, 92 mmol) cooled to 0 °C. The solution was then added dropwise to a mixture of pyridine (6 mL, 74 mmol) and tert-butanol (8.75 mL, 92 mmol).
5. After the dropwise addition was completed, the reaction mixture was stirred at room temperature for 4 hours.
6. After completion of the reaction, the mixture was partitioned between water and ether, and the aqueous layer was acidified with concentrated sulfuric acid and extracted with ether (3 x 50 mL).
7. The organic layers were combined and washed sequentially with 1N HCl solution (3 x 100 mL), water (100 mL) and saturated NaCl solution (100 mL).
8. Collect the organic layer, dry with anhydrous Na2SO4, filter and remove the solvent in vacuum.
9. Purification by silica gel column chromatography using 100% dichloromethane as eluent (Rf = 0.9) gave the target product 9a as a clear oil in 25% yield (3.28 g, 18.35 mmol).
10. The structure of the product was confirmed by 1H NMR (CDCl3): δ 3.59 (t, 2H, CH2), 2.41 (t, 2H, CH2), 2.05 (t, 2H, CH2), 1.45 (s, 9H, CH3).
