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Synlett 2005(14): 2195-2198  
DOI: 10.1055/s-2005-872257
LETTER
© Georg Thieme Verlag Stuttgart · New York

Cerium(IV) Ammonium Nitrate Catalysed Highly Chemoselective ­Deprotection of Ketals and THP Ethers in the Presence of Enol Triflates

Nuno Maulide, István E. Markó*
Université catholique de Louvain, Département de Chimie, Bâtiment Lavoisier, Place Louis Pasteur 1, 1348 Louvain-la-Neuve, Belgium
Fax: +32(10)472788; e-Mail: marko@chim.ucl.ac.be;
Further Information

Publication History

Received 6 April 2005
Publication Date:
29 July 2005 (online)

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Abstract

The chemoselective, catalytic deprotection of a variety of ketals, THP, and selected silyl ethers can be efficiently performed, in the presence of enol triflates, by the action of cerium(IV) ammonium nitrate (CAN).

Key words

cerium(IV) ammonium nitrate - catalysis - deprotection - ketals - enol triflates

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4

The successful Fe(III)-catalysed coupling of 2 with MeMgI was initially observed when an impure sample of 1, containing some ketone 2, was found to afford 3 and recovered substrate 1.

8

Readily prepared by deprotonation of the corresponding ketones with NaHMDS in THF, followed by capture with PhNTf2.

11

Typical Experimental Procedure - Deprotection of 12.
To a one-necked round-bottomed flask fitted with a reflux condenser and containing 100 mg (0.29 mmol, 1 equiv) of protected enol triflate 12 dissolved in 3 mL of MeCN and 3 mL of borate buffer (pH = 8.00), were added with stirring 5 mg (8.8 µmol, 0.03 equiv) of CAN. The resulting yellowish solution was then heated to 60 °C for 2 h, after which the mixture was diluted with H2O and repeatedly extracted with CH2Cl2. The combined organic layers were washed with brine, dried over MgSO4 and concentrated under reduced pressure. The crude ketone 12a was further purified by column chromatography (silica, PE-EtOAc 2:1) to afford 80 mg (94%) of a colourless oil. 1H NMR (300 MHz, CDCl3): δ = 1.50-1.60 (m, 2 H), 1.60-2.14 (m, 6 H), 2.20-2.50 (m, 4 H), 6.00 (t, J = 4.8 Hz, 1 H). 13C NMR (75 MHz, CDCl3): δ = 17.81, 18.90, 24.15, 32.06, 33.38, 37.78, 53.22, 106.37, 120.79, 148.15, 216.74. MS (APCI+, eV): m/z (%) = 299 (10) [M + H] + , 282 (30), 181 (40), 149 (100). IR (film): 3054, 2987, 2306, 1742, 1420 cm-1. HRMS (CI+, eV): m/z calcd for C11H14O4F3S [M + H]+: 299.0558; found: 299.0565.