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

Abstract

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:

• Acetylation
• DMAP
• haloaldehyde
• hemiacetal
• Ueno–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.