Acetic Anhydride/Et3N/DMAP: An Effective Acetylating System for Hemiacetals

The selective and efficient acetylation of the hemiacetal hydroxyl in the equilibrium mixture between RCl2C(OAll)OH and AllOH/RCl2CHO was achieved using the acylating system Ac2O/Et3N/dimethylaminopyridine (DMAP). Keywords: AcetylationDMAPhaloaldehydehemiacetalUeno–Stork ACKNOWLEDGMENT We thank the Ministero della Istruzione, dell'Università e della Ricerca (MIUR), for financial assistance. Notes a 4 (0.875 mol), 5 (0.875 mol), Et3N (1.013 mol), AcCl (0.875 mol), CH2Cl2 (350 mL), T = −13 °C (2 h) → 0 °C (20 h). b Yields determined on isolated material. a 4 (0.2 mol), 5 (0.2 mol), Et3N (0.22 mol), Ac2O (0.2 mol), DMAP (0.02 mol), CH2Cl2 (70 mL), T = −13 °C (2 h) → 0 °C (20 h). b Yields determined on isolated material. c In parentheses, the yield observed when using AcCl (Table 1). d The reaction time at 0 °C is 46 h.