Three-Component Chlorophosphinoylation of Alkenes via Anodically Coupled Electrolysis

Published as part of the Cluster Electrochemical Synthesis and Catalysis

Abstract

We report the development of an electrocatalytic protocol for the chlorophosphinoylation of simple alkenes. Driven by electricity and mediated by a Mn catalyst, the heterodifunctionalization reaction takes place with high efficiency and regioselectivity. Cyclic voltammetry data are consistent with a mechanistic scenario based on anodically coupled electrolysis in which the generation of two distinct radical intermediates occur simultaneously on the anode and are both mediated by the Mn catalyst.

Key words

electrochemistry - electrocatalysis - anodically coupled electrolysis - alkene difunctionalization - radical addition - chlorination - phosphine oxide

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• 10 Chlorophosphinoylation; General ProcedureAn oven-dried, 10 mL two-neck glass tube was equipped with a magnetic stir bar, a rubber septum, a Teflon cap fitted with electrical feedthroughs, a carbon felt anode (1.0 × 0.5 cm²) (connected to the electrical feedthrough via a 9 cm in length, 2 mm in diameter graphite rod), and a platinum foil cathode (0.5 × 1.0 cm²). To this reaction vessel, bipy (1.9 mg, 0.012 mmol, 6 mol%), Mn(OTf)₂ (3.6 mg, 0.01 mmol, 5 mol%), phosphorous source (0.2 mmol, 1.0 equiv), and lithium chloride (17.0 mg, 0.4 mmol, 2.0 equiv) were added. The cell was sealed, 3 mL of electrolyte solution (0.10 M LiClO₄ in acetonitrile) was added, and the mixture was flushed with nitrogen gas for 5 min, followed by the addition, via syringe, of a mixture of olefin substrate (0.2 mmol, 1.0 equiv), 0.5 mL of electrolyte solution, and acetic acid (0.40 mL). A nitrogen-filled balloon was connected through the septum to sustain a nitrogen atmosphere. Electrolysis was initiated at a constant cell voltage of 2.3 V at 22 °C. The reaction was stopped after 3.0 F charge was passed. The entire reaction mixture was then transferred to a short silica gel column (7–10 cm in length, ca. 10 g) and flushed through with 100 mL of a 1:1 mixture of hexanes and acetone to eliminate the inorganic salts, and the product solution was concentrated in vacuo. The residue was subjected to flash column chromatography on silica gel (eluted with hexanes/ethyl acetate) to yield the pure product. See the Supporting Information for full details and graphical guide.Representative Product Characterization; 3-Chloro-2-(diphenylphosphoryl)-3-methylbutyl Benzoate (16)Yield: 54.9 mg (65%); white solid; IR (film): 2982, 1972, 1719, 1438, 1273, 1182, 1114, 1100, 1072, 1026, 704, 524 cm^–1; ¹H NMR (500 MHz, CDCl₃): δ = 8.00 (dd, J = 8.3, 1.4 Hz, 4 H), 7.80–7.70 (m, 2 H), 7.63–7.51 (m, 4 H), 7.45 (t, J = 7.8 Hz, 2 H), 7.30 (td, J = 7.3, 1.4 Hz, 1 H), 7.25–7.19 (m, 2 H), 4.90 (ddd, J = 21.8, 12.2, 3.4 Hz, 1 H), 4.64–4.35 (m, 1 H), 3.35 (dt, J = 10.3, 3.7 Hz, 1 H), 2.02 (s, 3 H), 1.68 (s, 3 H); ¹³C NMR (126 MHz, CDCl₃): δ = 165.69, 134.79 (d, J = 97 Hz), 133.24, 132.42 (d, J = 98 Hz), 132.00 (d, J = 2.8 Hz), 131.79 (d, J = 2.8 Hz), 130.87 (d, J = 8.9 Hz), 130.69 (d, J = 8.7 Hz), 129.99, 129.55, 129.08 (d, J = 10 Hz), 128.59 (d, J = 11 Hz), 128.51, 74.30, 74.27, 62.79, 62.77, 50.50 (d, J = 62 Hz), 35.20, 31.12; ³¹P NMR (202 MHz, CDCl₃): δ = 27.38; HRMS (DART): m/z [M + H]⁺ calcd for C₂₄H₂₅ClO₃P⁺: 427.1224; found: 427.1222 .
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