Oxidative Homocoupling of Diheteroaryl- or Diarylmanganese Reagents Generated via Directed Manganation Using TMP₂Mn

Abstract

We report an oxidative homocoupling of diheteroaryl or diarylmanganese reagents prepared by directed manganation using TMP₂Mn·2MgCl₂·4LiCl. The resulting diorganomanganese reagents can efficiently undergo an oxidative dimerization leading to the homocoupling products in good yields. Remarkably, a number of functional groups, as well as sensitive heterocycles are tolerated using this metalation–dimerization procedure.

Key words

homocoupling - manganese - metalation - dimerization - oxidation

• References and Notes

• 1 These authors contributed equally to this work.
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• 16 General Procedure for the Metalation and Homocoupling of (Hetero)arenes A dried and argon-flushed Schlenk tube is charged with the corresponding substrate (1.0 mmol, 1.0 equiv) and dissolved in THF (1.0 mL). TMP₂Mn·2MgCl₂·4LiCl (1.5 mL, 0.6 mmol, 0.6 equiv, 0.40 M solution in THF) is added dropwise at the given temperature and stirred until a reaction aliquot quenched with iodine in THF showed full consumption of the starting material. Then, the reaction mixture is cooled to the given temperature, and chloranil (1.0 mmol, 1.0 equiv) dissolved in THF (4.0 mL) is added dropwise. The reaction is stirred for 0.5 h and is then quenched with sat. aq NH₄Cl solution and extracted with CH₂Cl₂ (3 × 25 mL). The crude product is purified by column chromatography on silica to yield the corresponding title compound. Characterization of Typical Homocoupling Products 2,2′-Dichloro-[4,4′-bipyridine]-3,3′-dicarbonitrile (6a) White solid; yield 74%, 102 mg; mp 197–199 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.79 (d, J = 5.0 Hz, 2 H), 7.49 (d, J = 5.0 Hz, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 154.6, 153.0, 148.6, 122.2, 112.8, 109.5 ppm. FT-IR (ATR): ν = 2253, 1565, 1545, 1525, 1470, 1440, 1369, 1209, 1090, 904, 840, 807, 725, 690 cm^–1. HRMS (EI): m/z [M]⁺ calcd for C₁₂H₄Cl₂N₄: 273.9813; found: 273.9809. 3,3′,6,6′-Tetramethoxy-4,4′-bipyridazine (6f) Off-white solid; yield 67%, 95 mg; mp 230–232 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.02 (s, 2 H), 4.09 (s, 6 H), 4.04 (s, 6 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 161.9, 158.7, 126.5, 121.1, 55.0, 54.8 ppm. FT-IR (ATR): ν = 3020, 2999, 2958, 1690, 1679, 1608, 1569, 1526, 1469, 1452, 1390, 1363, 1341, 1264, 1244, 1206, 1183, 1176, 1130, 1109, 1008, 999, 907, 899, 887, 828, 768, 756, 712, 676, 662 cm^-1. HRMS (EI): m/z [M]⁺ calcd for C₁₂H₁₄N₄O₄: 278.1015; found: 278.1010. Diethyl 6,6′-Dicyano-[1,1′-biphenyl]-2,2′-dicarboxylate (8d) Yellowish solid; yield 87%, 153 mg; mp 180–182 °C. ¹H NMR (600 MHz, CDCl₃): δ = 8.38 (dd, J= 8.0, 1.3 Hz, 2 H), 7.93 (dd, J= 7.8, 1.3 Hz, 2 H), 7.66 (t, J= 7.9 Hz, 2 H), 4.11 (q, J = 7.1 Hz, 4 H), 1.08 (t, J = 7.2 Hz, 6 H) ppm. ¹³C NMR (150 MHz, CDCl₃): δ = 164.3, 143.4, 136.0, 134.7, 130.5, 129.1, 116.3, 114.3, 61.6, 13.7 ppm. FT-IR (ATR): ν = 2985, 2255, 2231, 1717, 1578, 1477, 1447, 1428, 1393, 1368, 1288, 1273, 1182, 1148, 1103, 1020, 905, 865, 829, 763, 727 cm^–1. HRMS (EI): m/z [M]⁺ calcd for C₂₀H₁₆N₂O₄: 348.1110; found: 348.1102.