Preparation and Reactions of Polyfunctional Magnesium Arylcuprates Obtained by an Iodine-Copper Exchange

Abstract

The preparation of polyfunctional magnesium cuprates of type 1 can be achieved via an iodine-copper exchange reaction using the cyclic magnesium cuprate 3. A range of functional groups like an ester, halide (F, Br), nitrile or even a ketone can be tolerated. The new cuprates can be acylated and allylated in good yields leading to a range of polyfunctional products.

functionalized organometallics - cuprates - acylation - magnesium - iodine-copper exchange

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14

Typical Procedure: A dry and argon filled 25 mL flask, equipped with a magnetic stirrer and a septum, was charged with a solution of 1,5-bis(bromomagnesium)pentane (0.46 M/THF, 4.4 mL, 2.0 mmol) in THF (8 mL). The solution of CuCN·2LiCl in THF (1.0 M/THF, 2.0 mL, 2.0 mmol) was added dropwise at -78 °C. The resulting mixture was stirred for 30 min and ethyl 4-iodobenzoate 4a (552 mg, 2.0 mmol) was added at -78 °C. The resulting mixture was warmed to r.t. for 1 h and then benzoyl chloride (421 mg, 3.0 mmol) was added. After 30 min, the solution was quenched with sat. aq NH₄Cl solution and poured into H₂O (20 mL). The organic layer was separated and the aqueous phase was extracted with Et₂O (3 × 50 mL). The organic fractions were washed with brine (30 mL), dried over MgSO₄ and concentrated in vacuo. Purification by chromatography (SiO₂, n-pentane/Et₂O = 50:1) yielded 478 mg (94% yield) of 8b as a colorless oil. IR (film): 3402 (m, br), 2982 (m), 1720(vs), 1661 (vs), 1597 (m), 1579 (w), 1448 (m), 1405 (s), 1356 (s), 1369 (s), 1317 (s), 1275(vs), 1105(vs), 1020 (m), 939 (m), 927 (m), 851 (w), 769 (w), 715 (s), 698 (m), 657 (m)cm^-1. ¹H NMR (300 MHz, CDCl₃): δ = 8.07 (dd, J = 8.4 and 1.8 Hz, 2 H), 7.73 (m, 4 H), 7.53 (m, 1 H), 7.40 (t, J = 8.0 Hz, 2 H), 4.34 (q, J = 7.2 Hz, 2 H), 1.33 (t, J = 7.1 Hz, 3 H). ¹³C NMR (75 MHz, CDCl₃): δ = 195.0, 164.8, 140.2, 136.0, 132.6, 131.9, 129.1, 128.7, 128.4, 127.4, 126.2, 60.4, 13.3. MS (EI, 70 eV): m/z (%) = 254 (48) [M⁺], 226 (14), 209 (45), 181 (18), 177 (57), 152 (10), 149 (14), 130 (20), 118 (17), 104 (100). HRMS (EI): calcd for C₁₆H₁₄O₃ [M⁺]: 527.7580. Found: 527.7579.