Oxidative Chlorination of Activated Methylene Compounds with Sodium Chloride

Abstract

An operationally simple protocol for the direct chlorination of 1,3-dicarbonyls (and related compounds such as α-cyano ­ketones) is described. The procedure relies on mild conditions using IBX–SO₃K as the stoichiometric oxidizing agent and the ubiquitous sodium chloride. The presence of a phase-transfer catalyst is supportive to obtain good yields in a THF–water mixture.

Key words

hypervalent iodine - oxidations - chlorides - carbonyls - nitriles

• References and Notes


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• 15 General Procedure: The carbonyl substrate (1 equiv) was dissolved in a mixture of THF and aq 1 M NaCl solution (1:2, 0.3 M regarding substrate). Then, MeOc₃NCl (20 mol%) and IBX–SO₃K (3 equiv) were added and the suspension was heated to 50 °C for 24 h. After the suspension was cooled to r.t., the organic phase and the aqueous phase were separated. The aqueous phase was extracted with Et₂O (3 ×). The combined organic phase was washed with aq sat. NaHCO₃ solution and dried over Na₂SO₄. After concentration, the residue was purified by flash chromatography. Ethyl 1-Chloro-2-oxocyclohexanecarboxylate (ref. 6a): Following the general procedure, 4a was obtained from 2a (25.0 mg, 147 μmol) in 57% yield (17.2 mg, 84.0 μmol) as a colorless oil (flash chromatography with cyclohexane–Et₂O, 95:5); R_f 0.35 (cyclohexane–Et₂O, 9:1). ¹H NMR (400 MHz, CDCl₃): δ = 4.29 (qd, J = 7.1, 0.6 Hz, 2 H), 2.74–2.89 (m, 2 H), 2.39–2.46 (m, 1 H), 2.09–2.14 (m, 1 H), 1.81–2.00 (m, 3 H), 1.68–1.80 (m, 1 H), 1.31 (t, J = 7.1 Hz, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 199.8, 167.4, 73.6, 63.0, 39.8, 39.0, 26.8, 22.3, 14.0. HRMS (ESI): m/z [M + Na⁺] calcd for C₉H₁₃ClNaO₃ ⁺: 227.0445; found: 227.0451.