Silica Phosphoric Acid: An Efficient and Recyclable Catalyst for the Solvent-Free Synthesis of Acylals and Their Deprotection in MeOH

Abstract

Silica phosphoric acid was used as an efficient, mild, and recyclable solid catalyst for the synthesis of acylals from various structurally diverse aldehydes and acetic anhydride under solvent-free conditions. The acylation of aldehydes was highly chemoselective, and no ketone was acylated, which provided a method for the synthesis of acylals from aldehydes in the presence of ketones. Silica phosphoric acid–catalyzed deprotection of acylals to the corresponding aldehydes in MeOH has also been developed with excellent yield. The deprotection of the acylals of aromatic aldehydes took priority over those of aliphatic aldehydes.

Keywords:

• Acylal
• acylation
• silica phosphoric acid
• solvent-free

ACKNOWLEDGMENTS

The authors thank NNSF of China (No. 20972142), the State Key Laboratory of Bio-organic and Natural Products Chemistry, Chinese Academy of Sciences (CAS), the Natural Science Project of Henan Province (2009A150030, 082300420110), and the Innovation Fund of Zhengzhou University (2008CXSY147) for financial support.

Notes

^a The isolated yield.

^b All the products were characterized by ¹H NMR, IR, and mass spectroscopy.

^c 4.0 equivalents of Ac₂O.

^d Time in hours.

^e NR, no reaction.

^a The yields refer to the isolated pure products.