Novel Synthesis of α-Keto Esters and Amides by an sp³ C–H Oxidation of Nitromethyl Aryl Ketones Promoted by Ion-Supported (Diacetoxyiodo)benzene

Abstract

A simple and efficient method is described for the preparation of α-keto esters or amides from nitromethyl aryl ketones. In the presence of nucleophiles (alcohols or amines), the ion-supported (di­acetoxyiodo)benzene-promoted sp³ C–H oxidation of nitromethyl aryl ketones proceeded efficiently under mild conditions to give the corresponding α-keto esters and amides in moderate to good yields. This is the first reported use of (diacetoxyiodo)benzene in the synthesis of α-keto esters and amides. The reaction is ecofriendly and has the ­advantages of mild conditions, short reaction times, and a recyclable reagent.

Key words

keto esters - keto amides - diacetoxyiodobenzene - nitromethyl aryl ketones - oxidation

• References and Notes

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• 30 α-Keto Esters 3; General Procedure Nitromethyl aryl ketone 1 (0.5 mmol), [dibmim]⁺[BF₄]^–(1.5mmol), and the appropriate nucleophile (5 equiv) were dissolved in the appropriate solvent (8 mL), and the mixture was stirred and refluxed for 1 or 2 h. When the reaction was complete (TLC), hexane (40 mL) was added to precipitate ion-supported iodobenzene as a white solid that was collected by filtration and dried [yield: 0.50 g (86%)]. The filtrate was concentrated under vacuum, and the residue was purified by chromatography [silica gel, PE–EtOAc (20:1)]. Ethyl Oxo(phenyl)acetate (3a) Yellow oil; yield: 78 mg (88%); ¹H NMR (400 MHz, CDCl₃): δ = 1.43 (t, J = 7.2 Hz, 3 H), 4.46 (q, J = 7.2 Hz, 2 H), 7.50 (t, J = 8.0 Hz, 2 H), 7.63–7.67 (m, 1 H), 7.98–8.01 (m, 2 H). ¹³C NMR (100 MHz, CDCl₃): δ = 14.2, 62.3, 128.7, 129.8, 132.3, 134.7, 163.6, 186.1. ESI-HRMS: m/z [M + Na]⁺ calcd for C₁₀H₁₀NaO₃: 201.0522; found: 201.0250.