A Mild and Efficient Method for the Chemoselective Synthesis of Acylals from Aldehydes and their Deprotections Catalysed by Ceric Ammonium Nitrate

Abstract

A mild and efficient method has been developed for the chemoselective synthesis of geminal diacetates (acylals) from aldehydes using acetic anhydride in the presence of a catalytic amount of ceric ammonium nitrate in excellent yield. Ketones are found to be unaffected under the reaction conditions. The deprotections of acylals by using water and ceric ammonium nitrate have also been achieved.

acylals - aldehydes - chemoselective - ceric ammonium nitrate

References

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<A NAME="RD14602ST-13">13</A>

General Procedure for Acylation: A solution of the aldehyde (1.13 mmol) in distilled acetic anhydride (2.26 mmol) was stirred with CAN (10 mol%) at r.t. under N₂. The progress of the reaction was monitored by TLC. After completion of the reaction, the mixture was quenched with sat. aq NaHCO₃ solution (4 mL) and was extracted with ether (3 × 25 mL). The combined organic layer was successively washed with sat. aq NaHCO₃ solution (3 × 10 mL), water (15 mL) and brine (20 mL) and then dried (Na₂SO₄). The solvent was removed under reduced pressure and the residue obtained that was column chromatographed over silica gel to obtain the pure acylal.

<A NAME="RD14602ST-14">14</A>

General Procedure for Deprotection: A mixture of the acylal (1.0 mmol), CAN (10 mol%), water (2 mL) in acetonitrile (2 mL) was stirred at 70 °C under N₂. The progress of the reaction was monitored by TLC. After completion of the reaction, the mixture was diluted with brine (10 mL), extractited with ether (3 × 20 mL). The combined ether extract was washed with sat. aq NaHCO₃ solution (3 × 10 mL) and dried (Na₂SO₄). Solvent was removed under reduced pressure and the residue obtained was column chromatographed over silica gel to obtain the pure aldehyde.

<A NAME="RD14602ST-15">15</A>

All the acylals prepared and the aldehydes obtained by the deprotection of the alylals were fully characterised by ¹H NMR and IR study and comparing the spectral data with those of authentic samples.