The catalytic activity of nickelacycles in the conjugate addition of arylboronates to α,β-unsaturated ketones was investigated. Nickelacycles afforded β-arylated ketones in moderate to high yields, whereas an analogous palladacycle did not catalyze the reaction. Studies on the time course of the reaction confirmed that the nickelacycles act as active species in the conjugate addition reaction.
17 CCDC 2268818, 2268817, and 2268816 contain the supplementary crystallographic data for compounds Ni1, Ni2, and Pd1, respectively. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures
181,3,3-Triphenylpropan-1-one (5a); Typical Procedure
A 15 mL vial equipped with a stirring bar was charged with 3a (104 mg, 0.50 mmol) and 4a (105 mg, 0.55 mmol) under air and transferred to a glovebox with a N2 atmosphere. Ni2 (11 mg, 25 μmol), t-BuONa (4.8 mg, 50 μmol), MeOH (32 mg, 1.0 mmol), and THF (5.0 mL) were added, and the vial was capped with a PTFE sealing screw cap and taken out of the glovebox. The mixture was then stirred for 15 h at 60 °C. The product was isolated by MPLC [Biotage Sfär Silica HC D High Capacity Duo (20 μm, 25 g), hexane–EtOAc (100:0 to 90:10)] to give a colorless solid; yield: 107 mg (0.37 mmol, 74%).
1H NMR (400 MHz, CDCl3): δ = 7.96 (d, J = 6.5 Hz, 2 H), 7.60–7.52 (m, 1 H), 7.45 (t, J = 7.6 Hz, 2 H), 7.35–7.26 (m, 8 H), 7.19 (dt, J = 9.2, 4.4 Hz, 2 H), 4.85 (t, J = 7.3 Hz, 1 H), 3.76 (d, J = 7.3 Hz, 2 H). 13C NMR (101 MHz, CDCl3): δ = 197.95, 144.09, 136.97, 133.06, 128.56, 128.52, 128.02, 127.80, 126.34, 45.84, 44.66. The spectra were consistent with the reported values.21
19 Coumarin was not viable under the standard conditions.
20 Although neither 3a nor MeOH appeared to show a reaction with Ni2, Ni2 was decomposed after silica gel column chromatography. See the Supporting Information for details.
21
Parveen N,
Saha R,
Sekar G.
Adv. Synth. Catal. 2017; 359: 3741
