Oxidative Cleavage of Silyl Ethers by an Oxoammonium Salt

^‡ These authors contributed equally

Abstract

A method for the oxidative cleavage of silyl ethers to their corresponding carbonyl species mediated by an oxoammonium salt is described. The resulting aldehydes and ketones are obtained under mild reaction conditions with no observed overoxidation. For robust substrates, heating to reflux temperatures significantly reduces the reaction time.

Key words

protecting groups - silicon - oxidation - oxoammonium salt - aldehydes - ketones

• References and Notes


Silyl protecting groups:
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Alternative oxidative deprotection strategies:
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• 14 Representative Procedure To a 100 mL round-bottom flask equipped with a stir bar was added the silyl ether 2c (1.95 g, 7.0 mmol, 1 equiv) and the oxoammonium salt 1 (2.10 g, 7.0 mmol, 1 equiv), followed by MeCN (35 mL, 0.2 M in the silyl ether). The solution was heated to 40 °C while stirring for 72 h. After this time, the crude mixture was diluted with Et₂O (200 mL) and deionized water (200 mL). The phases were separated, and the aqueous layer was extracted with Et₂O (3 × 50 mL). The combined organic layers were washed with deionized water (ca. 100 mL), brine (ca. 100 mL), and dried with Na₂SO₄. The solvent was removed in vacuo by rotary evaporation, and the resulting crude mixture was adhered to silica gel using 1.5 wt equiv of SiO₂ (relative to the theoretical yield). The dry-packed material was gently added atop a silica gel plug. The plug was washed with an excess of hexanes (ca. 5 column volumes). The desired product was eluted off the plug via a 95:5 by volume mixture of hexanes–EtOAc (3–4 column volumes). The solvent was removed in vacuo by rotary evaporation affording the pure aldehyde 3c (0.67 g, 59%) as a clear yellow liquid. ¹H NMR (400 MHz, CDCl₃): δ = 9.98 (s, 1 H), 7.88–7.77 (m, 2 H), 7.61–7.48 (m, 2 H), 1.36 (s, 9 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 192.05 (CH), 158.53 (C), 134.30 (C), 129.84 (CH), 126.13 (CH), 35.49 (C), 31.23 (CH₃) ppm.